This article contains the following executables: RAHNER.EXE SPRITE.EXE
Rahner is an independent consultant living near Sacramento, Calif. He can be reached by phone at 916-722-1939 or through CompuServe at 71450,757.
"The distinction between a toy and a game is that the game has a goal; therefore, life is not a game, it is a toy." -- GOK
As a child, I could not differentiate between Bugs Bunny and Walter Cronkite. This is not to say that the man America most trusted had dental problems, but that the child did not have the experience to see the cartoon for what it was -- a stream of individually drawn pictures. Skilled professional help was required to deal with the trauma caused by the revealed truth. Even after the psychological defects were converted to scars, I had to wait until I could create two-dimensional life for myself.
The Time Has Come
Animation is achieved by showing a series of incrementally changing images. Depending on the duration of time that a single image is shown and the time it takes to switch to the next image increment, the viewer's visual persistence smooths out the image's transition. Anyone with a compiler and a graphics library can put a series of images on a computer display. But in order to create smooth, non-flickering, real-time animation, a fair amount of thought is necessary.
To support reasonable animation, the algorithm must conform to the following rules:
Coordinate Movement -- The routines must allow individual objects to be moved around on the screen and placed on any pixel boundary.
Independent Motion -- Each object in the image should be able to show a chain of sequences independent of its coordinate movement.
Smooth Transitions -- The transition between image frames should have no intermediate stages. This means that the viewer should see only complete images, not images that are half the first image and half the second image. These half-and-half images are perceived as a flicker and are distracting.
Regular Transitions -- All image transitions should occur at regular intervals. If this does not happen, the sequence will appear to jerk as if shown on an old projector.
Sprites -- If an object has a hole, any objects that are behind it should show through. Poorly done animation will not allow the viewer to see through a gap in an object.
Realistic Objects -- There is a difference between what is shown on the screen and what is perceived by the observer. Up to a point, jagged lines will be smoothed, imperfect colors accepted, and stairstep corners rounded. This point, the point of realism, is subjective and entirely dependent on the target audience. Below this point, other unrelated flaws can be magnified; above this point, the overall perception of the product is enhanced.
The elements of this list are all mutable by targeted hardware limitations. Accurate shading may be difficult on an AT-class machine. Absolute realism for anything but the simplest geometric shapes is impossible on CGA or EGA. The finished product's design constraints may adjust the significance of one element over the others. These are Rahner rules -- they may be burnt, bent, or beatified.
Zippy Tries His Hand at CGA Animation
When I first saw reasonable animated images on a CGA adapter, I was intrigued. It was a simple CGA sprite demo -- several helicopters flying aimlessly around the display. Because the demo allowed the helicopters to start only on a byte boundary (four pixels per byte) and did not allow them to exit smoothly from the side of the screen, I decided to try my hand at writing the ultimate animation driver for CGA.
After a lazy Sunday's work, the driver was finished. Given CGA's limitations (four colors and 320 x 200 resolution), ultimate is probably too strong a word. It was about the same as tying the ultimate shoelace or throwing the ultimate dirt clod. Anticlimactic would be the correct word for polite company.
Because the initial attempt was an unplanned, seat-of-the-pants, I've-got-Fritos-diet-Coke-and-plenty-of-time effort, my trial and error path would best illustrate some animation rudiments.
The first attempt was to whip a series of changing pictures past the monitor. This involved copying virtual screens, which I had prearranged, onto the CGA video RAM. This had the interesting effect of flickering the screen with seemingly random images caught in a blizzard.
The flicker and snowstorm were due to not waiting for the vertical retrace before displaying the next image. What is vertical retrace? A good question, because it is important later. The CRT monitor etches its pictures in the orbitals of fluorescent compounds with a single beam of electrons. This beam sweeps horizontally back and forth across the screen. In either direction -- back or forth -- the beam has to turn off, otherwise it looks funny. The off direction is called the horizontal retrace. The beam winds its way down the screen in this back and forth manner. When it reaches the bottom, it turns off and returns to the top of the screen: This off time is called the "vertical retrace." On the standard EGA setup, this vertical retrace occurs 60 times a second.
The standard CGA adapter has a bit that indicates when the horizontal refresh is occurring and another to show when the vertical refresh is occurring. It was a simple task to change the program so that it waited for the vertical retrace before blasting out the next virtual screen. -- I saw a series of pictures endlessly circling, but without snow or flicker.
Next I noticed that most of the screen was stationary and only a small fraction of the image moved at any one time. In fact, most of the things that did move were sets of pixels that did not reposition themselves with respect to one another, only with respect to the rest of the picture. After much deliberation (and lunch), I named these sets "sprites." Later I found that these sets had been noticed by others before and they had used my name for them. Rather than risking a protracted legal battle, I swallowed my pride and have allowed the others to take the credit.
The basic concept behind the sprite is simple. Cut a rectangular section out of the screen and store it. Then take the set of pixels that comprise the sprite and replace the cutout section with them.
Armed with my "new" creation, I reduced the series of virtual screens to a simple background and a few sprites. The background was displayed first, then the sprites were moved into position before the finish of the vertical retrace. Now I had the same cinematograph that I had before, but the program was more efficient and the storage requirements were reduced. Before I got bored with this endless video cycle, I noticed that when my sprites went in front of something, the background was completely covered, even in places that I should have been able to see through.
This meant another change. Instead of just storing the background, I masked off the solid areas of the sprite body. Instead of replacing the cutout, I ORed the sprite onto the masked background, then replaced the cutout around the finished product. This allowed me to have "holes" in the sprites, for increased realism.
With the inclusion of holes in the sprites, I had my ultimate CGA sprite routine. All the little fishes were swimming around in my video aquarium without the need for food. I was satisfied and went to bed.
You may be asking, "What does this have to do with EGA?" You may be getting sleepy and ready to close the magazine. You may just be hunting for good prices on software. Well, to the shopping sportsman, there are no good prices in this article; to the somnolent peruser, good night; and to the inquisitor in the back with his hand up, Everything!
The EGA and I
In its 640 x 350-pixel color graphics mode, an EGA adapter with 256K of RAM is set up as four planes of 28,000 bytes each. It also has two pages, one that is being viewed on the monitor and one that is in the ether. Both pages can be addressed directly by the CPU. The first page starts at memory address A000:0000h and the second page starts at A000:8000h. Each byte of EGA memory represents eight pixels with the most significant bit (MSB) being shown as the leftmost pixel. A byte or bit of any combination of the planes may be addressed depending on how the EGA registers have been set.
Superficially, there seemed to be little difference between a sprite driver for the CGA and EGA adapters. It seemed to be just another block of RAM that I needed to jam out bytes. Following that line of thought, the first code translation from CGA was conceptually simple. The sprites were placed on the visual page, a plane at a time. When I looked at the result for the first time, I found myself almost back to square one. No matter how efficiently I wrote the driver, there was a constant flicker. I ran to the bookstore, hoping for a tome of enlightenment. My hope was dashed by a limited selection. But a quick reread of the IBM EGA Technical Reference manual provided me with the answers: The EGA adapter can generate an interrupt and the visual page can be switched during the vertical retrace.
Writing a Bit Map to EGA Memory
The EGA adapter has a fair number of features. All the features and the way the board reacts to CPU memory manipulations are determined by the configuration registers. Most of the registers are set up in pairs. The first register accepts an index value that determines the functionality of the second register. The major register pairs that we need to concern ourselves with are the Sequencer registers and the Graphics 1 & 2 Address registers. Another register that is important for this discussion is Input Status Register One.
The Sequencer register is located at 3C4h with its index register at 3C5h. It has five indexed registers: Reset (0), Clocking Mode (1), Map Mask (2), Character Map Select (3), and Memory Mode (4). To access an indexed register, the index's number is output to the Sequencer register followed by the value for that index output to the index port. For example, if you want to place a 5 in the Clocking Mode index register, which is index number 1, the assembly code in Example 1 would do. Because all the register pairs are one right after the other, this code segment could be replaced by that in Example 2. This replacement is usually valid, except when slow ports cause timing difficulties.
Example 1: Sample code for writing bit map to EGA memory
MOV DX, 3C4h ; DX - > Sequencer register MOV AL, 1 ; AL = index 1, Clocking Mode OUT DX, AL INC DX ; DX - > Sequencer index port MOV AL, 5 ; AL = to put in Clocking Mode OUT DX, AL
Example 2: Replacing the code in Example 1
MOV DX, 3C4h ; DX - > Sequencer reg. pair MOV AX, 501h ; AL = index 1, AH = value 5 OUT DX, AX ; Puts AL out 3C4h, then ; AH out 3C5h
The important Sequencer index register, with respect to our driver, is the Map Mask Register (index 2). This register enables planes so that the CPU can write to them. Setting bit 0 enables plane 0, bit 1 enables plane 1, and so on. Because there are only four planes, the four MSBs are not used and are ignored. If you wanted to write the same information to multiple planes, multiple bits could be set. No easy assumptions can be made about the sprite data, so we can't really take advantage of this feature.
The Graphics 1 & 2 register set deals with colors, pixel masks, and the Boolean graphic operations the EGA can perform. This register is configured the same as the Sequencer register, with nine indexed registers: Set/Reset (0), Enable Set/Reset (1), Color Compare (2), Data Rotate (3), Read Map Select (4), Mode Register (5), Miscellaneous (6), Color Don't Care (7), and Bit Mask (8). The index registers of concern are the Data Rotate register and the Read Map Select register.
The Data Rotate register has two controls. Bits 0-2 represent the Rotate Count. The Rotate Count is a binary encoded number that represents the bit positions to shift any data written to a video plane. Because all our data will be unshifted at the hardware level, this value should be 0. Bits 3-4 represent the Function Select. The Function Select indicates which Boolean-type operation is desired for pixels written to display memory. Table 1 shows the available functions.
Table 1: Available functions
Value Description -------------------- 0 0 Written data is not modified 0 1 Written data is ANDed with latched data 1 0 Written data is ORed with latched data 1 1 Written data is XORed with latched data
To diverge for a moment, a definition for "latched data"is in order. No matter how it appears, the video memory on the EGA adapter is never directly connected to the PC bus. When the registers are set properly, the program addresses the video memory in exactly the same manner it would any other portion of main memory. The memory can be accessed as a byte or a word, but those accesses are processed through the EGA's circuitry. The circuitry performs some gyrations on the data, then passes it on. In order to properly swing the binary song, that gyrating EGA circuitry latches the byte or word in its internal read/write buffer. A read of EGA memory will put that byte of pixels in the latch, which can then be operated on by some future operation. Because each plane has a separate latch buffer, if all four planes have been enabled, 32 bits at a time can be latched (read), operated on, and then rewritten to EGA memory with a single 8086 instruction.
Give me an inch and I'll take a while, diverging on to the 8086 instructions. When dealing with this aspect of the EGA adapter, a close look at how some 8086 instructions actually work would be in order. Let's start with the instruction:
OR [DI], AL
When the 8086 sees this instruction, it loads the value pointed at by the register DI into the 8086 internal register, ORs the value in register AL onto that internal register, then writes the result back out to the location pointed to by DI. If DI happened to point to EGA memory, this would latch up a number of pixels, add in pixels, then write the latch data back out to video memory -- all in a single instruction. If an additional EGA function, such as a bit rotate, were added to the previous example, some interesting and possibly useful results could be achieved. I don't use this in my routine, but, by jingo, it's just too nifty to be ignored!
The last register of importance is Input Status Register One. It has a few informative bits, but we will be concerned with only the Vertical Retrace bit (3). As the name implies, this bit is set to 1 when the display is in a vertical retrace time. As I stated before, this was the time to write to the video memory with the CGA adapter. It has approximately the same value with the EGA adapter, but not exactly.
When Blazing Fast Is Not Fast Enough to Start a Fire
When I converted my CGA animation routines to work with the EGA, there was an unexpected problem. I found that no matter how fast I blasted my sprites out to video memory, the raster line (another name for that beam of electrons described earlier) would catch up to where I was writing pixels. When the raster caught up, the screen would flicker annoyingly. Having to deal with four planes and EGA's higher resolution just took too much time. I made my code the most efficient assembly routines I could. I made assumptions about the data I was displaying in order to cut corners. I got a 25-MHz 386 system. Nothing worked. I felt like a laundry soap commercial. I went back to the EGA Technical Reference manual.
Almost immediately the answer, written by the IBM ancients, made me question what I had been thinking about in the first place. The standard EGA has 256K of RAM -- enough for two pages of display memory. I could write to one page, wait for the next vertical retrace, then swap pages. I rewrote everything.
Planning ahead, I continued reading the Technical Reference manual. The EGA can generate an interrupt request 2. If the driver could just swap pages whenever the video went into vertical retrace, then I wouldn't have to waste time polling. I rewrote it, again.
Animation Structures
To become animated objects, sprites must have four basic degrees of freedom: Coordinate Motion, Self-relative Motion, Rotation, and Perceived Distance. Coordinate Motion is simply the movement from one point on the screen to another. Self-relative Motion is the movement that the sprite could make without moving to a new coordinate location. Rotation is rotation of the sprite around some center point in its body. Perceived Distance is basically sizing the sprite according to its apparent distance from the viewer.
The increment resolution of each degree of freedom is independent of the others. A sprite picture of a person may be pumping its arm up and down a pixel at a time and traversing the screen five pixels at time. Given a monitor/graphics adapter combination that refreshed the screen an infinite number of times, the smaller the movement increment, the more realistic its action would be. Because the standard EGA board refreshes the screen at 60 Hz (60 times a second), the movement increment should be judged relative to the apparent velocity of the sprite, the display resolution, and the level of the art. Because I can draw only crude stick figures, my resolution granularity can be boulder-size.
Two of the four degrees of freedom (Rotation and Perceived Distance) should not be a function of a sprite driver. A good, general-purpose rotation algorithm requires fairly heavy calculations. These calculations are burdensome enough to detract from the real-time nature of the animation driver. Although Perceived Distance does not need as much time from the CPU, it should be done at a higher level than the driver. Perceived Distance requires the sprite to be resized larger as it gets closer to the viewer and smaller as it gets farther away. As the size of the sprite approaches the minimum resolution of the monitor, details disappear. No algorithm can make perfect decisions about which features of an object are important to the visual integrity of that object.
Self-relative Motion deals with the movement of each of the individual pixels of the sprite with respect to each other, but not straying outside the boundary of the sprite. To illustrate Self-relative Motion without any other component, I have included a sprite of a flame. Each of the pixel groups that represent small flamelets rises to the top of the fire. The pixel groups that represent the edges of the flame billow in the updraft caused by the heated air. In my routine, the effect of the motion is created by a linked list of sprite frames. In the example, each successive frame shows the flame in the next point of time (without regard to mathematical proofs, in animation there is a quantum of time). Because motion in most biological or mechanical systems is cyclical, I join the terminal points of this linked list into a sprite circle. Each sprite can proceed through a cycle of self-relative motions whose complexity is determined by the circumference of the sprite circle.
Coordinate Motion involves moving the sprite circle from one point to another on the screen at some regular velocity. The sprite velocity is determined by the number of pixels that the sprite circle will move divided by the number of times per second the visual image will be changed. Say we make a sprite representation of a five-meter-long car that is drawn 32 pixels in length. To move that car from the right side of the screen to the center at an apparent velocity of 20 km/hour, the sprite would have to move to the left 176 pixels per second if everything is kept to scale. If our visual page changes come at 20 per second, the sprite would have to be moved nine pixels to the left for every page change.
How the Routines Work
The sprite routines are broken down into two parts. The portion that deals with the EGA ports, memory and interrupt service is written in 8086 assembly language. Listing One (page 82) shows the EGA sprite drivers and Listing Two (page 88), the sprite circle handler. The higher-level sprite circle and list managers are written in Microsoft C. Listing Three (page 92), SPRITES. C, displays a sprite file on an EGA screen, and Listing Four (page 93) is the make file.
Some assumptions were made about the nature of the sprites and the background. The sprite driver is written for sprites of any dimension, but the driver is optimized for a sprite that is 32 bits across. In my application, it was assumed that the observer could pan or tilt the viewing perspective. Because the perspective can be changing in smooth real time, the background is not a set quantity -- it is being regenerated in every visual frame. Additionally, because the 8086 family drops at least eight clock ticks every time it makes a JMP or CALL, the code favors execution speed (that is, very few jumps, calls, or loops) over program size.
The basic algorithm is simple. Before any operations can be performed, the sprite driver needs to be installed using the function EGA_INSTALL( ). This preps the adapter, initializes some variables, and installs the interrupt vector. The first sprite of a sprite circle is inserted into the linked list of circles by calling the function INSERT_SPRITE (START_X, START_Y, END_X, END_Y, SPEED_X, SPEED_Y, DEPTH, SPRITE_CIRCLE); where START_X and START_Y are the starting X, Y coordinates of the sprite, END_X and END_Y are the ending X, Y coordinates of the sprite, SPEED_X and SPEED_Y are the amounts that the X and Y coordinates will change per visual frame, DEPTH is the perceived distance from the observer, and SPRITE_CIRCLE is a pointer to the first entry of the sprite circle. Additional sprites can be added to the circumference of a sprite circle with the function ADD_SPRITE. Once all the sprite circles have been figured out and inserted into the sprite list, call DO_SPRITE_LIST( )whenever it is appropriate. DO_SPRITE_LIST( ) figures out the new sprite positions and places them on the nonvisual page. When it has placed all the sprites, it sets the flag DO_PAGE_FLIP, clears DONE_PAGE_FLIP, and returns. The main program body is then free to do anything with the sprite structures. At some time in the future, the EGA's vertical interrupts and the interrupt service routine decides whether to swap pages or not. If it does swap the pages, it clears DO_PAGE_FLIP and sets DONE_PAGE_FLIP. Although the routines are not completely reentrant, they are fairly immune to interrupts; they can be called from other interrupt service routines such as the timer tick or a mouse driver.
With regard to visual timing, movies project 24 frames per second on the silver screen. To decrease the cost of animation, some cartoon manufacturers will keep the same picture on the screen for more than one frame. The interrupt service routine has a counter that can be used to allow it to skip any number of vertical retraces between page changes. If your CPU is slow or the main body of your program needs more time to do its work, altering the skip count has the effect of smoothing out the movement of the sprites. To counteract the slowing effect that increasing the skip count would have, you must increase the velocity of any coordinate motion proportionately.
Finishing Thoughts
So much can be written about real-time animation that a conclusion at any point leaves us feeling a lot was left out. The scope of this article does not allow me to explore all the avenues with the depth they deserve. Maybe you can use the routines that have been provided with this article as learning aids to go beyond what has been written. Animation is a form for the presentation of ideas. Seminars, product demonstrations, and computer modeling programs can all be enhanced by the addition of animation graphics. Of course, the most obvious use only enhances what I have always said: The only useful thing someone can do with a computer is play a game on it.
_REAL-TIME ANIMATION_ by Rahner James
[LISTING ONE]<a name="001f_0010">
.model small, c
.286 ; This directive can be used to optimize procedure entry
; but not much else. I avoided all non-8088 commands
comment \
EGA Sprite Drivers for C
Copyright (c) February 1989, Ryu Consulting, Inc.
(916) 722 - 1939 anytime
Written by Rahner James, CS
This is a full functioning sprite driver for EGA graphics
adaptors. The sprite are given to the routines as a linked list
of sprite structures. All the function are re-entrant and can be
part of a multi-tasking system. The sprite structures are intended
to reside in far memory. The sprite can exist on any pixel boundary.
These were intended to be called from some C program, but probably
can be modified for some other language. This must be assembled with
Microsoft MASM version 5.0 or later since I make use of local
variables, forward/backward jumps and models. Expect to get some
incorrect size warnings because MASM doesn't seem to recognize its own
"byte ptr" and "word ptr" operators when used with words and dwords.
\
; ****************************************************************************
; EQUATES
; ****************************************************************************
EOI equ 20h ; End Of Interrupt signal
EOI_PORT equ 20h ; Port to output the EOI
CRT_MODE equ 49h
EGA_ADDRESS equ 63h
EGA_PIXELS_WORD equ 16 ; Number of pixels per word
EGA_PIXELS_BYTE equ 8 ; Number of pixels per byte
NUMBER_OF_PLANES equ 4 ; Number of EGA color planes
EGA_RETRACE_STATUS equ 3dah ; EGA retrace status register
RETRACE_BIT equ 1 shl 3 ; Bit set to signal a vertical retrace
SEQUENCE_REG equ 3c4h ; Sequencer register
GRAPHICS_12 equ 3ceh ; Graphics 1 & 2 register
MAP_MASK_REG equ 2 ; Map mask Indexed register
DATA_ROTATE_REG equ 3 ; Data Rotate Indexed register
DATA_OR equ 1 shl 4 ; Set to OR data on the EGA
DATA_MOVE equ 0 ; Write data unmodified onto EGA
BOTTOM_LINE equ 200 ; Lowest pixel line to allow a sprite
RIGHT_SIDE equ 640 ; Right-most visual pixel allowed
; ****************************************************************************
; STRUCTURES
; ****************************************************************************
; All sprites are stored on disk using the same internal format.
; The first word is the width of the sprites in bytes and the second
; word is the height of the sprite in widths. Each byte represents
; one pixel's worth of information. Bit 7 of the byte is the intensity
; bit, 0=off. This allows for 128 colors, black will be 0 or 80h. The
; intensity bit set indicates an opaque black surface. All color
; translations are table driven.
internal_sprite_structure struc ; Storage structure used for sprites
int_width dw ? ; Width in bytes for the sprite
int_height dw ? ; Height in widths of the sprite
int_body db ? ; Start of the sprite's body
internal_sprite_structure ends
ega_sprite_structure struc ; Internal EGA sprite structure
e_animate_ptr dw 0,0 ; Far ptr to next sprite struct in animation seq.
e_width dw ? ; Width of the sprite in words
e_height dw ? ; Height of sprite in widths
e_body dw ? ; Beginning of body
;.word 0: mask, word 1: sprite
;.throughout the body. That way you can pull
;.the background up, mask it, OR the sprite,
;.then store the background
; The body is organized into four planes,
;.termed PLANE0 to PLANE3. Each represents a
;.different color in the EGA spectrum, except
;.PLANE0 which is the intensity bit.
ega_sprite_structure ends
style_structure struc
style_width dw ? ; Width of each style entry in bytes
style_height dw ? ; Height of each style entry in pixels
style_body db ? ; Start of the style entries
style_structure ends
; ****************************************************************************
; LOCAL DATA STORAGE for DS
; ****************************************************************************
.data
public do_page_flip, done_page_flip
even
do_page_flip db 0 ; Set to -1 when non-visual page is completed
done_page_flip db -1 ; Set to -1 right after page has been swapped
flip_turn db 4 ; # of interrupts before an EGA page flip
old_irq_mask db 0 ; Old IRQ mask
EGA_settings db 2bh,2bh,2bh,2bh,24h,24h,23h,2eh
db 0,0,0,0,0,24h,23h,2eh,2bh
even
ega_base_port dw ?
default_retrace label word
v_retrace_reg db 11h
v_retrace_value db ?
.code
; ****************************************************************************
; LOCAL DATA STORAGE for CS
; ****************************************************************************
even
ega_segment dw 0a800h ; EGA page memory segment being set up
old_vector dw 0,0 ; Old IRQ-2 vector (as Checkov would say wecter)
; EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
; EGA sprite related routines below this line
; void EGA_CONVERT( dest_ptr, source_ptr )
; Converts long storage format sprite into EGA structure sprite
; Given:
; dest_ptr far -> EGA sprite buffer ready to go
; source_ptr far -> disk sprite structure to convert
; Returns:
; EGA sprite buffer set up accordingly
ega_convert proc near uses di si ds, dest:dword, source:dword
local store_width:word, store_height:word
local source_width:word
local plane_size:word
cld
lds si, source ; DS:SI -> source sprite
les di, dest ; ES:DI -> CGA sprite buffer
mov es:[di], di ; Make the animate ptr point to itself
mov es:[di+2], es
add di, E_WIDTH
lodsw ; Get width in byte pixels
mov source_width, ax
add ax, EGA_PIXELS_WORD-1 ; Want to include those border pixels
mov cl, 4 ; Divide by sixteen to convert one byte
shr ax, cl ;.per pixel to 16 pixels/word for EGA
mov bx, ax ; Use this as our width count
stosw ; Store as words/pixels
lodsw ; Get height
mov store_height, ax
stosw ; Move height straight across
mul bx ; AX = Body size in mask/sprite entries
add ax, ax ; AX = body size in words
add ax, ax ; AX = plane size in bytes
mov plane_size, ax ; Save as our plane index
mov ax, ds ; Swap DS:SI and ES:DI
mov bx, es
mov ds, bx
mov es, ax
xchg di, si
sub si, 4 ; This is to prep for the next INC
next_row:
mov cx, source_width ; Get source row width
next_word:
add si, 4 ; SI -> next word in line
mov dx, -1 ; DX = the destination mask
xor ax, ax
mov [si], dx ; Set the mask word
mov [si+2], ax ; Clear the sprite word
mov bx, plane_size ; BX offset to next plane
mov [si+bx], dx ; Set the mask word
mov [si+bx+2], ax ; Clear the sprite word
add bx, plane_size ; BX offset to next plane
mov [si+bx], dx ; Set the mask word
mov [si+bx+2], ax ; Clear the sprite word
add bx, plane_size ; BX offset to next plane
mov [si+bx], dx ; Set the mask word
mov [si+bx+2], ax ; Clear the sprite word
mov dx, 1 shl 7 ; Start at MSB which is pixel LSB
next_pixel_byte:
jc next_word ; Only be set by pixel shift below
mov al, es:[di] ; Get the source pixel byte
inc di ; DI -> next source pixel byte
or al, al ; See if it's anything at all
jz end_pixel_byte ; Skip all the checks
xor [si], dx ; Reset the mask bit
test al, 1 shl 4 ; Check bit 7
jz @F ; Skip if nothing here
or [si+2], dx ; Place the sprite bit
@@: mov bx, plane_size ; BX -> plane 1 offset
xor [si+bx], dx ; Clear the mask bit
test al, 1 shl 7 ; Check bit 6
jz @F ; Skip if nothing here
or [si+bx+2], dx ; Place the sprite bit
@@: add bx, plane_size ; BX -> plane 2 offset
xor [si+bx], dx ; Clear the mask bit
test al, 1 shl 6 ; Check bit 5
jz @F ; Skip if nothing here
or [si+bx+2], dx ; Place the sprite bit
@@: add bx, plane_size ; BX -> plane 3 offset
xor [si+bx], dx ; Clear the mask bit
test al, 1 shl 5 ; Check bit 4
jz end_pixel_byte ; Skip if nothing here
or [si+bx+2], dx ; Place the sprite bit
end_pixel_byte:
shr dl, 1 ; Move pixel bit toward MS pixel bit
rcr dh, 1
loop next_pixel_byte ; Loop through the pixel bytes
dec store_height ; One less row
jnz next_row
ret
ega_convert endp
; EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
; ui EGA_CALCULATE( source_ptr )
; Calculates the amount of storage needed for an unconverted sprite
; Given:
; source_ptr far -> disk sprite structure to convert
; Returns:
; AX = number of bytes needed to store the converted sprite
ega_calculate proc near uses si ds, source:dword
lds si, source ; DS:SI -> disk sprite structure for calculation
mov ax, [si] ; Get the width in bytes
add ax, EGA_PIXELS_WORD-1 ; Round up to nearest word
shr ax, 4 ; AX = number of words for stoarge
add ax, ax ; AX = number of bytes storage
add ax, ax ; AX = number of globs in one row
add ax, ax ; AX = number of row/planes
add ax, ax
mul word ptr [si].int_height ; AX = bytes per row * number of rows
add ax, E_BODY ; AX = body size + header size
ret
ega_calculate endp
; EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
; void PUT_SPRITE( ui X, ui Y, ega_sprite_structure far *SPRITE_PTR )
; Maps a sprite list into the display video buffer
; Sprite is assumed to be 32-bits wide
; Given:
; X = X pixel location of sprite
; Y = Y pixel location of sprite
; SPRITE_PTR -> sprite structure to put on the screen
; Returns:
; The sprite is mapped onto the screen buffer
put_sprite proc uses di si, x:word, y:word, sprite_ptr:dword
local mask_msw:word ; OR'ed with the mask dword
local mask_lsw:word
local or_msw:word ; AND'ed with the sprite dword
local or_lsw:word
local start_di:word
local start_si:word
local sprite_plane_size:word
local number_of_rows:word
local shift:byte
local plane_number:byte
push ds
cmp y, 200 ; See if below 200
jc @F
short_done:
jmp done
@@: cmp x, 640
jnc short_done
cld
mov es, ega_segment
lds si, sprite_ptr ; DS:SI -> sprite to be driven
mov ax, 80 ; Calculate the offset
mul y
mov cx, x
mov di, cx
and cl, 7 ; CL = shift value
mov shift, cl
shr di, 3
add di, ax ; DI -> byte offset
mov start_di, di
mov ax, [si].e_height ; AX = height of the sprite in rows
mov number_of_rows, ax ; Save for later use
shl ax, 3 ; AX *= 8, to get size of 1 sprite plane
mov sprite_plane_size, ax
mov ax, number_of_rows ; Let's see if it goes too low
add ax, y
sub ax, BOTTOM_LINE
jbe @F ; Skip if it doesn't
sub number_of_rows, ax ; Update the number of rows
@@: add si, E_BODY ; SI -> start of sprite body
mov start_si, si
cmp x, 640-32 ; See if we are going to be right
ja short_mask ; Skip if no mask
cmp shift, 0
jnz shifted
mov bl, NUMBER_OF_PLANES
next_plane:
dec bl
mov dx, GRAPHICS_12 ; Talk to EGA control logic
mov al, 4
mov ah, bl
out dx, ax
mov dx, SEQUENCE_REG ; Set up the ports for writing as well
mov ax, 100h + MAP_MASK_REG
mov cl, bl
shl ah, cl
out dx, ax
mov cx, number_of_rows
@@: mov ax, es:[di] ; Get the background dword
mov dx, es:[di+2]
and ax, [si] ; Do the mask dword
and dx, [si+4]
or ax, [si+2] ; Bring on the sprite
or dx, [si+6]
mov es:[di], ax ; Replace with new graphic dword
mov es:[di+2], dx
add si, 8 ; Next row stuff
add di, 80
loop @B
mov di, start_di
mov si, start_si
add si, sprite_plane_size
mov start_si, si
or bl, bl
jnz next_plane
jmp done
short_mask:
jmp masked
shifted:
mov plane_number, NUMBER_OF_PLANES-1
mov cl, shift
mov bh, -1
shr bh, cl
next_shift_plane:
mov dx, GRAPHICS_12 ; Talk to EGA control logic
mov al, 4
mov ah, plane_number
out dx, ax
mov dx, SEQUENCE_REG ; Set up the ports for writing as well
mov ax, 100h + MAP_MASK_REG
mov cl, plane_number
shl ah, cl
out dx, ax
mov ch, byte ptr number_of_rows
mov cl, shift
@@: lodsw ; Get the sprite mask
xchg ah, al ; Switch them around
ror ax, cl
mov bl, ah ; Top CL bits are ones to mask 3rd byte
not bh ; BH = ~BH
and bl, bh
or ah, bh ; Now set the top ones of source byte
mov dx, es:[di] ; Get the first destination word
xchg ah, al ; Re-order the mask bytes
and dx, ax ; Mask it
lodsw ; Get the sprite
xchg ah, al
ror ax, cl
or dh, al ; OR DH w/ old AH
mov al, ah ; Save the upper bits
and ah, bh ; Mask off other bits
not bh ; BH = BH
and al, bh ; Cut out the rotunds
or dl, al ; OR least sig. bytes
mov es:[di], dx ; Save that first word, whew!
mov dl, ah ; DL = pushed up sprite bits
lodsw ; Get the next sprite mask
xchg ah, al ; Switch them around
ror ax, cl
mov dh, ah ; DH = MS shifted mask bits
and ah, bh ; Get rid of shifted bits
or ah, bl ; OR with shifted mask, previous byte
or dh, bh ; Add on the mask
xchg ah, al ; AH:AL back to normal
and es:[di+4], dh ; Easy way to get rid of DH
mov bl, dl ; BL = previous sprite bits
mov dx, es:[di+2] ; Get the destination word
and dx, ax ; Mask it
lodsw ; Get the sprite
xchg ah, al
ror ax, cl
or dh, al ; OR DH w/ old AH
mov al, ah ; Save the upper bits
not bh ; BH = ~BH
and ah, bh ; Mask off other bits
not bh ; BH = BH
and al, bh ; Cut out the rotunds
or al, bl
or dl, al ; OR least sig. bytes
mov es:[di+2], dx ; Save that first word, whew!
or es:[di+4], ah
add di, 80
dec ch
jnz @B
mov di, start_di
mov si, start_si
add si, sprite_plane_size
mov start_si, si
sub plane_number, 1
jc @F
jmp next_shift_plane
@@: jmp done
masked:
xor ax, ax ; Set up masks and ORs
mov mask_lsw, ax
mov mask_msw, ax
dec ax
mov or_lsw, ax
mov or_msw, ax
cmp x, 640-24 ; See if we have masked it already
jc @F ; Skip if we have
mov mask_msw, 0ff00h
mov or_msw, 0ffh
cmp x, 640-16
jc @F
mov mask_msw, -1 ; Make sure nothing gets masked
mov or_msw, 0
cmp x, 640-8 ; See if that's all
jc @F
mov mask_lsw, 0ff00h
mov or_lsw, 0ffh
@@: mov plane_number, NUMBER_OF_PLANES-1
next_mask_plane:
mov dx, GRAPHICS_12 ; Talk to EGA control logic
mov al, 4
mov ah, plane_number
out dx, ax
mov dx, SEQUENCE_REG ; Set up the ports for writing as well
mov ax, 100h + MAP_MASK_REG
mov cl, plane_number
shl ah, cl
out dx, ax
mov cx, number_of_rows
@@: mov ax, [si] ; Get the first mask
mov dx, [si+4] ; Get the second mask
or ax, mask_lsw
or dx, mask_msw
and ax, es:[di] ; Get the background dword
and dx, es:[di+2]
mov bx, or_lsw ; Get the OR lsw
and bx, [si+2] ; Bring on the sprite
or ax, bx
mov bx, or_msw
and bx, [si+6]
or dx, bx
mov es:[di], ax ; Replace with new graphic dword
mov es:[di+2], dx
add si, 8 ; Next row stuff
add di, 80
loop @B
mov di, start_di
mov si, start_si
add si, sprite_plane_size
mov start_si, si
sub plane_number, 1
jnc next_mask_plane
jmp done
done: pop ds
ret
put_sprite endp
; EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
; void EGA_CLEAR_AREA( ui X1, ui Y1, ui X2, ui Y2 )
; Clears an area on the EGA display to black
; Given:
; X1,Y1 = X,Y pixel coordinates of the upper left corner
; X2,Y2 = X,Y pixel coordinates of the lower right corner
; Returns:
; Rectangular area from X1,Y1 to X2,Y2 (inclusive) cleared to black
public ega_clear_area
ega_clear_area proc uses ds si di, x1:word, y1:word, x2:word, y2:word
local height:word
local di_start:word
local word_columns:word
local di_offset:word
cld
cmp x1, 640 ; See if too far to the right
jc @F
mov x1, 0
@@: cmp x2, 640
jc @F
mov x2, 639
@@: mov ax, y2 ; Check out number of rows
sub ax, y1
jnc @F ; See if jerk put them in backwards
neg ax
@@: inc ax
mov bx, ax ; BX = number of rows
mov height, ax
mov ax, y1 ; Check our starting offset
mov cx, 80
mov di_offset, cx
mul cx
mov di, ax
mov ax, x1 ; See where we start
shr ax, 3
add di, ax
mov ax, x2
sub ax, x1
jnc @F
neg ax
@@: add ax, 16
shr ax, 4
jnz @F
jmp done
@@: mov word_columns, ax
add ax, ax
sub di_offset, ax
mov es, ega_segment
mov dx, SEQUENCE_REG ; Set up the ports for writing
mov ax, 0f00h+MAP_MASK_REG
out dx, ax
mov dx, di_offset
xor ax, ax
mov di_start, di
@@: mov cx, word_columns
rep stosw
add di, dx
dec bx
jnz @B
done: ret
ega_clear_area endp
; EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
; void EGA_INSTALL()
; Installs IRQ-2 vectors for EGA card
; Given:
; nothing
; Returns:
; -1 if neither EGA or VGA else
; EGA interrupt vector installed and enabled
public ega_install
ega_install proc
mov ax, 40h ; ES -> video BIOS data area
mov es, ax
mov dx, es:[EGA_ADDRESS] ; DX -> CRTC Address port
mov ega_base_port, dx ; Save the port address
mov ax, 1a00h ; Read display combination
int 10h
cmp al, 1ah ; See if EGA
jne ega_adaptor
cmp bl, 7 ; See if VGA
je vga_adaptor
cmp bl, 8
je vga_adaptor
error_out:
mov ax, -1
jmp short done
ega_adaptor:
mov al, es:[CRT_MODE] ; AL = video BIOS mode number
mov bx, offset EGA_settings
xlat
jmp short @F
vga_adaptor:
mov al, v_retrace_reg ; AL = Vertical retrace register
out dx, al
inc dx
in al, dx
@@: mov v_retrace_value, al
mov done_page_flip, -1
mov do_page_flip, 0
xor ax, ax ; ES -> base page
mov es, ax
mov bx, 0ah*4 ; Vector for IRQ 2
mov dx, cs
mov ax, offset ega_interrupt
cli
xchg es:[bx], ax
xchg es:[bx+2], dx
mov old_vector, ax
mov old_vector+2, dx
in al, 21h ; Get present mask
mov old_irq_mask, al
and al, 11111011b
out 21h, al
mov dx, ega_base_port
mov ax, default_retrace
and ah, 11001111b
out dx, ax
jmp short $+2
or ah, 00010000b
out dx, ax
sti
done: ret
ega_install endp
; EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
; void EGA_RIP_OUT()
; Undoes all the interrupt processing for the EGA
; Given:
; nothing
; Returns:
; EGA interrupt vector removed
public ega_rip_out
ega_rip_out proc uses es
mov ax, old_vector ; See if installed
or ax, old_vector+2
jz done ; Return if not installed
xor ax, ax ; ES -> base page
mov es, ax
mov bx, 0ah*4 ; Vector for IRQ 2
mov ax, old_vector
mov dx, old_vector+2
mov old_vector, 0
mov old_vector+2, 0
cli
mov es:[bx], ax
mov es:[bx+2], dx
in al, 21h
mov ah, old_irq_mask ; Restore old interrupt mask
and ah, 1 shl 2
and al, 11111011b
or al, ah
out 21h, al
mov dx, 3d4h
mov ax, 2b11h
out dx, ax
sti
done: ret
ega_rip_out endp
; EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
; void EGA_INTERRUPT( void )
; Handles all the interrupt processing for the EGA controller
; Given:
; This is run at every IRQ-2 spike (ie. vertical retrace)
; Returns:
; If FLIP_TURN is brought to zero, EGA visual pages are swapped
; If swap is made, DO_PAGE_FLIP set to 0, DONE_PAGE_FLIP set to -1
ega_interrupt proc far
push ax
push dx
push ds
mov ax, @DATA
mov ds, ax
mov dx, 3c2h ; DX -> I/O port for input status
in al, dx
test al, 1 shl 7
jnz @F ; Interrupt is ours
pushf
call dword ptr [old_vector]
jmp done
@@: mov dx, ega_base_port ; DX -> EGA/VGA register port
in al, dx
push ax
mov ax, default_retrace
and ah, 11101111b
out dx, ax
jmp short $+2
mov al, EOI
out EOI_PORT, al
jmp short $+2
sti
dec flip_turn
jnz @F
mov flip_turn, 4
cmp do_page_flip, 0 ; See if we need to do this
jz @F
mov al, 0ch ; Select register for page MSB
mov ah, byte ptr ega_segment+1
shl ah, 4
out dx, ax ; Output the most significant byte
xor ega_segment, 800h ; Swap the active page
jmp short $+2
mov do_page_flip, 0
mov done_page_flip, -1
@@: cli
mov ax, default_retrace
and ah, 11011111b
or ah, 00010000b
out dx, ax
jmp short $+2
pop ax
out dx, al
done: pop ds
pop dx
pop ax
iret
ega_interrupt endp
end
<a name="001f_0011"><a name="001f_0011">
<a name="001f_0012">
[LISTING TWO]<a name="001f_0012">
comment \
Sprite Circle Handler
Copyright (c) February 1989, Ryu Consulting, Inc.
(916) 722 - 1939 anytime
Written by Rahner James, CS
\
; ****************************************************************************
; EQUATES
; ****************************************************************************
MAX_SPRITES equ 50
; ****************************************************************************
; STRUCTURES
; ****************************************************************************
sprite_structure struc
animate_ptr dw 0,0
sprite_width dw 0 ; Width in words
sprite_height dw 0 ; Height in pixels
sprite_body db ?
sprite_structure ends
struc
x dw 0
y dw 0
depth dw 0
pre_x dw 0
pre_y dw 0
dest_x dw 0
dest_y dw 0
adder_x dw 0
adder_y dw 0
sprite_ptr dw 0,0
next_node dw 0
sprite_node ends
.data
; ****************************************************************************
; DATA VARIABLES and EXTERNAL DEFINITIONS
; ****************************************************************************
extrn done_page_flip:byte, do_page_flip:byte
extrn min_x:word, min_y:word, max_y:word, max_x:word
first_sprite dw 0
public sprite_list
sprite_list sprite_node MAX_SPRITES dup(<>)
pre_max_x dw 639
pre_max_y dw 199
pre_min_x dw 0
pre_min_y dw 0
.code
; ****************************************************************************
; ROUTINES and EXTERNAL CODE DEFINITIONS
; ****************************************************************************
extrn do_background:near, put_sprite:near
; ****************************************************************************
; void DO_SPRITE_LIST( void )
; Sets up the sprites on the unviewed back page
; Given:
; A sprite list has been created and is stored in the array SPRITE_LIST
; Returns:
; If DONE_PAGE_FLIP is 0, no processing is done
; else all sprites in the sprite list are put on the non-visual page
; then DONE_PAGE_FLIP is set to 0 and DO_PAGE_FLIP is set to -1
do_sprite_list proc uses si
cmp done_page_flip, 0 ; See if we need to do this
jnz @F
jmp done
@@: call do_background
mov ax, pre_max_x
mov max_x, ax
mov ax, pre_max_y
mov max_y, ax
mov ax, pre_min_x
mov min_x, ax
mov ax, pre_min_y
mov min_y, ax
xor ax, ax ; Clear out some variables
mov pre_max_x, ax
mov pre_max_y, ax
dec ax
mov pre_min_x, ax
mov pre_min_y, ax
mov si, first_sprite ; SI -> sprite node to start with
next_sprite:
or si, si ; See if this is a NULL pointer
jnz @F
jmp almost_done
@@: mov ax, [si].x
mov [si].pre_x, ax
cmp [si].dest_x, ax ; See if we are already there
je no_add_x ; Skip if we are
mov cx, [si].dest_x ; Get our absolute value
sub cx, [si].x
jnc @F
neg cx
@@: add ax, [si].adder_x
mov [si].x, ax
sub ax, [si].dest_x
jnc @F
neg ax
@@: cmp cx, ax
jnc no_add_x
mov ax, [si].dest_x
mov [si].x, ax
no_add_x:
mov ax, [si].y
mov [si].pre_y, ax
cmp [si].dest_y, ax ; See if we are already there
je no_add_y ; Skip if we are
mov cx, [si].dest_y ; Get our absolute value
sub cx, [si].y
jnc @F
neg cx
@@: add ax, [si].adder_y
mov [si].y, ax
sub ax, [si].dest_y
jnc @F
neg ax
@@: cmp cx, ax
jnc no_add_y
mov ax, [si].dest_y
mov [si].y, ax
no_add_y:
cmp [si].y, 200 ; See if beyond bottom line
jnc pre_next_sprite
mov ax, [si].x ; See if we need to update some things
cmp ax, 640 ; See if beyond right column
jnc pre_next_sprite
cmp ax, pre_min_x ; See if pre_x < min_x
jnc @F ; Skip if not
mov pre_min_x, ax ; Update with new MIN_X
@@: mov ax, [si].y ; See if need to update min_y
cmp ax, pre_min_y
jnc @F
mov pre_min_y, ax
@@: les bx, dword ptr [si].sprite_ptr ; ES:BX -> sprite structure
mov ax, es:[bx].sprite_width
inc ax
if (@Cpu AND 2)
shl ax, 4 ; AX = AX * 16
else
rept 4
add ax, ax
endm
endif
add ax, [si].x
cmp pre_max_x, ax ; See if > max_x
jnc @F ; Jump if not
mov pre_max_x, ax ; Assume we are going to save it
@@: mov ax, es:[bx].sprite_height
add ax, [si].y
cmp pre_max_y, ax ; See if > max_x
jnc @F ; Jump if not
mov pre_max_y, ax ; Assume we are going to save it
@@: push es ; Set up for call to put_sprite()
push bx
push [si].y
push [si].x
call put_sprite
add sp, 4 ; Clear the stack
pop bx ; ES:BX -> sprite pointer
pop es
les bx, dword ptr es:[bx].animate_ptr
mov [si].sprite_ptr, bx
mov [si].sprite_ptr+2, es
pre_next_sprite:
mov si, [si].next_node ; SI -> next sprite node in line
jmp next_sprite
almost_done:
mov ax, pre_max_x
cmp ax, 640
jb @F
mov ax, 639
mov pre_max_x, ax
@@: cmp pre_min_x, ax
jb @F
dec ax
mov pre_min_x, ax
@@: mov ax, pre_max_y
cmp ax, 200
jb @F
mov ax, 199
mov pre_max_y, ax
@@: cmp pre_min_y, ax
jb @F
mov pre_min_y, ax
@@: mov done_page_flip, 0
mov do_page_flip, -1
done: ret
do_sprite_list endp
; ****************************************************************************
; void CLEAR_SPRITE_LIST( void )
; Zeros out the present sprite list
; Given:
; nothing
; Returns:
; FIRST_SPRITE and SPRITE_LIST array are zeroed
clear_sprite_list proc uses di
cld
mov di, offset sprite_list
mov ax, ds
mov es, ax
xor ax, ax
mov first_sprite, ax
mov cx, (MAX_SPRITES * (size sprite_node))/2
rep stosw
ret
clear_sprite_list endp
; ****************************************************************************
; int INSERT_SPRITE( ui X1,ui Y1, ui D_X,ui D_Y, ui PLUS_X,ui PLUS_Y,
; ui THE_DEPTH, sprite_structure far *SPRITE )
; Inserts the first sprite of a sprite circle into the linked list of circles
; Given:
; X1,Y1 = pixel location of the upper left corner of the sprite
; D_X,D_Y = pixel location of the destination of the sprite
; PLUS_X,PLUS_Y = pixels the sprite moves every page flip
; THE_DEPTH = apparent distance of the sprite from the viewer
; SPRITE -> sprite to insert
; Returns:
; If 0, sprite pointer was inserted in the array
; else !0 if there is no room
insert_sprite proc uses si, x1:word,y1:word, d_x:word,d_y:word,\
plus_x:word,plus_y:word, the_depth:word,\
sprite:dword
mov cx, MAX_SPRITES
mov bx, (offset sprite_list) - (size sprite_node)
@@: add bx, size sprite_node
mov ax, [bx].sprite_ptr ; See if this has been set yet
or ax, [bx].sprite_ptr+2
loopnz @B
jnz done_bad
les ax, sprite ; ES:AX -> sprite location
mov [bx].sprite_ptr, ax ; Save it
mov [bx].sprite_ptr+2, es
mov ax, x1 ; Set up the structure
mov [bx].x, ax
mov [bx].pre_x, ax
mov ax, y1
mov [bx].y, ax
mov [bx].pre_y, ax
mov ax, d_x
mov [bx].dest_x, ax
mov ax, d_y
mov [bx].dest_y, ax
mov ax, plus_x
mov [bx].adder_x, ax
mov ax, plus_y
mov [bx].adder_y, ax
mov ax, the_depth
mov [bx].depth, ax ; This is used in the following loop
mov dx, bx ; Save this s[rite entry for later
mov si, first_sprite ; SI -> sprite furthest from the viewer
mov bx, offset first_sprite ; BX -> previous sprite entry
mov cx, MAX_SPRITES
@@: or si, si ; See if it's a NULL ptr
jz @F ; Skip out if it is
cmp ax, [si].depth ; See if farther from observer
jnc @F
mov bx, si ; BX = this pointer
mov si, [si].next_node ; SI -> next sprite node in line
loop @B
done_bad:
mov ax, -1 ; Indicate we had a problem
jmp short done
@@: xchg si, dx ; SI -> sprite_list[i]
mov [si].next_node, dx
cmp bx, offset first_sprite
jne @F
mov [bx], si
jmp short done_good
@@: mov [bx].next_node, si
done_good:
xor ax, ax
done: ret
insert_sprite endp
; ****************************************************************************
; void ADD_SPRITE( sprite_structure far *DEST, far *SOURCE )
; Adds a self-relative sprite motion to the end of a sprite circle
; Given:
; DEST -> sprite circle header
; SOURCE -> sprite to add on
; Returns:
; SOURCE is added to the end of the sprite linked list and the
; circle ends are rejoined, may the circle be unbroken (ie Johnny Cash)
add_sprite proc uses si di ds, dest:dword, source:dword
lds si, dest
les di, source
next_sprite:
mov ax, [si].animate_ptr ; See if this is the end of the line
cmp ax, word ptr dest
jne @F
mov ax, [si].animate_ptr+2
cmp ax, word ptr dest+2
je got_the_end
@@: lds si, [si].animate_ptr
jmp next_sprite
got_the_end:
mov [si].animate_ptr, di
mov [si].animate_ptr+2, es
mov ax, word ptr dest
mov es:[di].animate_ptr, ax
mov ax, word ptr dest+2
mov es:[di].animate_ptr+2, ax
ret
add_sprite endp
end
<a name="001f_0013"><a name="001f_0013">
<a name="001f_0014">
[LISTING THREE]<a name="001f_0014">
/***************************************************************************
TITLE: SPRITES.C
Displays a sprite file on an EGA screen
Written by: Rahner James, CS
of Ryu Consulting, Inc.
***************************************************************************/
#include <stdio.h>
#include <dos.h>
#include <fcntl.h>
/***************************************************************************
VARIOUS DEFINITIONS
***************************************************************************/
#pragma pack(1)
typedef unsigned char uc;
typedef unsigned int ui;
typedef unsigned long ul;
/***************************************************************************
EXTERNAL DECLARATIONS
***************************************************************************/
extern void ega_convert();
extern ui ega_calculate( uc far * );
extern void ega_install();
extern void ega_clear_area( ui, ui, ui, ui );
/***************************************************************************
GLOBAL DATA
***************************************************************************/
ui min_x=0, min_y=0, max_x=639, max_y=199;
/***************************************************************************
long READ_ALL_FILE( uc *FILENAME, uc huge *BUFFER, ul BUFFER_SIZE )
Opens and reads an entire sprite file
Given:
FILENAME -> name of sprite file to read
BUFFER -> buffer to read the sprite file into
BUFFER_SIZE = number of bytes the buffer can hold
Returns:
File is opened, read and closed
Number of bytes read, if all went well
If error, returns -1
***************************************************************************/
long read_all_file( uc *filename, uc huge *buffer, ul buffer_size )
{
long rv = 0;
ui handle, dos_return, amount_read;
ui amount_to_read;
if ( _dos_open( filename, O_RDONLY, &handle ) )
return -1;
while ( buffer_size )
{
amount_to_read = buffer_size<60000L ? buffer_size : 60000L;
if ( _dos_read( handle, buffer+rv, amount_to_read, &amount_read ) )
{
rv = -1;
break;
}
rv += amount_read;
if ( amount_read < 60000 )
break;
buffer_size -= amount_read;
}
_dos_close( handle );
return rv;
}
/***************************************************************************
void DO_BACKGROUND( void )
Sets up the background for the sprite visual screen
Given:
nothing
Returns:
visual sprite screen erased
***************************************************************************/
void do_background( void )
{
ega_clear_area( min_x, min_y, max_x, max_y );
}
/***************************************************************************
uc SET_MODE( uc MODE_NUMBER )
Sets the video mode
Given:
Mode number to set video to
Returns:
Present video mode number
***************************************************************************/
uc set_mode( uc mode_number )
{
uc rv;
union REGS regs;
regs.h.ah = 15;
int86( 0x10, ®s, ®s );
rv = regs.h.al;
regs.h.ah = 0;
regs.h.al = mode_number;
int86( 0x10, ®s, ®s );
return rv;
}
/***************************************************************************
MAIN( int ARGC, uc *ARGV[] )
Allocates memory, reads in a sprite file, displays the sprites
until a key is pressed, frees up memory and interrupt vectors
Given:
ARGC = number of command line values, must be > 1
ARGV[1] -> file name of the sprite file to display
Returns:
0 if all went well, otherwise numbered according to error
***************************************************************************/
main( int argc, uc *argv[] )
{
ui i, x, y;
uc far *file_ptr, huge *sprite_start, huge *buffer_start;
uc huge *sprite_ptr[20];
uc old_mode;
ui memory_segment;
ul memory_size=0, file_size;
/* Check initial values and allocate memory for buffers */
if ( argc<2 )
{
printf( "\nNo file name has been given\n" );
exit( 1 );
}
if ( _dos_allocmem( -1, (ui *)&memory_size ) )
{
if ( _dos_allocmem( memory_size, &memory_segment ) )
{
printf( "\nMemory allocation error\n" );
exit( 2 );
}
}
else
{
memory_segment = memory_size;
memory_size = 0xffff;
}
memory_size <<= 4;
buffer_start = (uc huge *)((ul)memory_segment << 16L);
/* Read in the sprite file and then convert it to our intenal structure */
file_ptr = buffer_start;
if ( (file_size=read_all_file(argv[1],file_ptr,memory_size)) == -1 )
{
_dos_freemem( memory_segment );
printf( "\nGot error reading %s. Aborting.\n", argv[1] );
exit( 3 );
}
clear_sprite_list();
sprite_start = file_ptr + file_size;
for ( i=0 ; i<20 && file_size ; ++i )
{
ega_convert( sprite_ptr[i]=sprite_start, file_ptr );
x = ega_calculate( file_ptr );
sprite_start += x;
x = (ui)*file_ptr * (ui)*(file_ptr+2) + 4;
file_ptr += x;
if ( file_size > (ul)x )
file_size -= (ul)x;
else
file_size = 0;
}
/* Create linked list of sprite circles */
insert_sprite( 100,100, 100,100, 0,0, 7, sprite_ptr[0] );
for ( x=1 ; x<i ; ++x )
add_sprite( sprite_ptr[0], sprite_ptr[x] );
/* Setup the EGA screen mode and interrupt vector */
old_mode = set_mode( 0x10 );
ega_install();
/* Process the sprite list until someone taps a key */
while ( !kbhit() )
do_sprite_list();
/* Restore screen and allocated memory to original state */
ega_rip_out();
set_mode( old_mode );
_dos_freemem( memory_segment );
exit( 0 );
}
<a name="001f_0015"><a name="001f_0015">
<a name="001f_0016">
[LISTING FOUR]<a name="001f_0016">
sprite.obj: sprite.c
cl /c sprite.c
ega_drv.obj: ega_drv.asm
masm ega_drv;
gen_asm.obj: gen_asm.asm
masm gen_asm;
sprite.exe: sprite.obj ega_drv.obj gen_asm.obj
link sprite+gen_asm+ega_drv;
Example 1: Sample code for writing bit map to EGA memory
MOV DX, 3C4h ; DX -> Sequencer register
MOV AL, 1 ; AL = index 1, Clocking Mode
OUT DX, AL
INC DX ; DX -> Sequencer index port
MOV AL, 5 ; AL = to put in Clocking Mode
OUT DX, AL
Example 2: Replacing the code in Example 1
MOV DX, 3C4h ; DX -> Sequencer reg. pair
MOV AX, 501h ; AL = index 1, AH = value 5
OUT DX, AX ; Puts AL out 3C4h, then
; AH out 3C5h