ftp.whtech.com

home *** CD-ROM | disk | FTP | other *** search

/ ftp.whtech.com / ftp.whtech.com.tar / ftp.whtech.com / Geneve / 9640news / CAT14 / SPRITS.ARK < prev next >

Wrap

Text File | 2006-10-19 | 14KB | 368 lines

? SPIRITED SPRITES by Mack Mc Cormick 74206,1522 This tutorial is intended for the advanced assembler programmer (beyond Molesworth). Apple pie and motherhood. We all know this but I've got to start someplace. Sprites may occupy screen positions independently of any character already present. Once set into motion, they can move independently of direct program control. You can magnify or make double size by changing VDP register 1. How can they be used? Up to 32 sprites on the screen at any one time. Can be used in GRAPHICS and MULTICOLOR modes. Also can be used in BIT MAP mode but not the automatic motion feature. Sprites cannot be used in the TEXT mode. There are three tables which contain all the information needed to use sprites: 1. SPRITE ATTRIBUTE TABLE a. Sprite Position b. Sprite Color 2. SPRITE DESCRIPTOR TABLE a. Sprite Pattern Identifier b. Specify magnified or double sized sprites. 3. SPRITE MOTION TABLE a. Define X and Y velocities of Sprites. DEFAULT LOCATIONS OF SPRITE TABLES --------------------------------------------------------- Table Table Begins at this VDP address --------------------------------------------------------- SPRITE ATTRIBUTE TABLE >0300 SPRITE DESCRIPTOR TABLE >0400 SPRITE MOTION TABLE >0780 --------------------------------------------------------- Sprites are numbered from 0 to 31. Here's how the screen is defined for Sprites: Columns are labeled starting from the left from 0 to 255 (>00 to >FF). Rows are numbered from top left, the first row is numbered 255 (>FF) followed by the numbers 0 to 190 (>0 to >BE). Each screen location defined in this manner is referred to as a pixel. A pixel is the smallest area of the screen you can turn on or off. Heres the way it looks: >00 >01 >02 >03... >FF >FF >00 P1 . . . >BE P2 Pixel 1 is in row >00 column >02. P2 is in row >BE column >FF. Here are the formulas to convert row and column locations to pixel locations: GRAPHIC TO PIXEL CONVERSIONS ---------------------------------------------------- GRAPHIC ROW TO PIXEL ROW GR*8-7=PR GRAPHIC COLUMN TO PIXEL COLUMN GC*8-7=PC PIXEL ROW TO GRAPHIC ROW INT[(PR+7)/8]=GR PIXEL COLUMN TO GRAPHIC COLUMN INT[(PC+7)/8]=GC ---------------------------------------------------- SPRITE ATTRIBUTE TABLE Begins at VDP >0300 by default. Contains the present position of sprites and their colors. Each sprite takes up four bytes in the table. The first byte is the row or Y position of the sprite. The second byte is the column or X position. The third byte references the pattern of the sprite as to where it is located in the Sprite Descriptor Table. The fourth byte is the early clock attribute and also codes for the color of the sprite. When the computer moves sprites it updates the information in the sprite attribute table. The more sprites it has to update the longer it takes to execute the program. To shorten this time place a value of >D0 as the Y location of the lowest numbered non-moving sprite. Always let the final unused sprite be undefined by specifying the Y location as >D0. The third byte references a pattern in the Pattern Descriptor Table. Can range from >00 to >FF. For example if the third byte contained >80 it would point to >0400 through >0407 in the Sprite Descriptor Table. The forth byte controls the early clock and color. The first four bits control the early clock. If the last bit (3) is reset to zero the early clock is off and the location of the sprite is said to be it's upper left hand corner. This means the sprite will fade in and out on the right hand side of the screen. If bit 3 is on the sprites location is shifted 32 pixels to the left. The sprite can then fade in and out from the left side of the screen. Bits 4-7 of byte four contain the color. Same as other VDP colors 0 to >F. Heres an example Sprite Attribute: Sprite 0 Sprite 1 SAL DATA >3356,>8001,>A828,>810F,>D0 -- Third Sprite Undefined / / / / Y X / color pattern SPRITE DESCRIPTOR TABLE Just like the pattern descriptor table for characters. Usually begins at >0400. Addresses >0400 through >0407 are defined as sprite pattern >80. You can also make sprites magnified or double sized by writing a value to the two least significant bits of VDP register 1. See page 340 of the E/A manual for the values. SPRITE MOTION TABLE Describes the X and Y velocities of each sprite. This table begins at >0780. Before a sprite can be placed into motion several conditions must be met. Your program must allow interrupts using LIMI 2 but before accessing VDP RAM you must disable interrupts with a LIMI 0. You must indicate how many sprites will be in motion by placing a value at CPU address >837A. For example if sprites 2, 5, and 7 are in motion you must place an >8 at address >837A which will allow motion of 0 through 7. A description of the motion must be placed in the Sprite Motion Table. Each sprite takes up four bytes in the table. The first byte is the Y velocity, the second byte is the X velocity. The third and fourth bytes are used by the interrupt routines, just be sure you leave space for them. The following are allowed as values for X and Y velocities: >00 to >FF. >00 to >7F are positive velocities (down for vertical motion and right for horizontal motion), and velocities >FF to >80 are two's compliment negative velocities (up for vertical motion and left for horizontal motion). A value of >01 will cause the sprite to move one pixel every 16 VDP interrupts. About once every 16/60 of a second. A thought: Have you ever seen a screen dump program that would dump sprites? It could be done by obtaining their location and pattern and converting to printer bit graphics. Program explanation: I will make the assumption that you understand basic assembler and therefore will only explain the advanced concepts. General: You will note right away that only 1/4 of the sprite initially appears on the screen until you press a key the second time to load VDP R1 with the value to use double sized sprites, and again to use double size and magnified sprites. This was intentional to show you what all four sizes look like. When using double size sprites the sprite generator looks at four consecutive patterns in memory to make up the sprite. START LWPI MYREG You'll note right away that I am using the CPU scratchpad RAM for my workspace. This is because this is the only RAM that is on a 16 bit data bus and therefore is twice as fast. Always try to place your workspace in this area when you can. LI R0,>0400 LI R1,HELI LI R2,32 Loads all four sprite patterns into the sprite descriptor table. LI R0,>0300 LI R1,SDATA LI R2,6 Loads the initial Y location, X location, the sprite number, early clock, and the color of the sprite in the sprite attribute table. Note the early clock byte is set so the sprites fades out from the right side of the screen. Experiment here with the early clock and color to observe the results. LI R0,>0780 LI R1,SPEED LI R2,4 Establishes the speed of the sprite as down and right. Remember the next two bytes must equal 0. LI R1,>0100 MOVB R1,@>837A Lets the VDP interrupt routine know you only want to move one sprite by placing he number 1 at >837A. The rest of the program scans the keyboard and alters VDP R1 to vary the size an magnification of the sprites. LIMI 2 enables interrupts. 0 and 2 are the only values with any meaning on the TI-99. More on LIMI later. Just remember VDP interrupts must be disabled LIMI 0 before accessing VDP RAM. I recommend you read the chapter on Sprites in the Editor/Assembler manual Pages 338-348. Be glad to answer any questions. Until next time...Assembler Executing. **************************************** ** ** ** SPRITES AND TEXT FROM BIT MAP ** ** BY MACK MCCORMICK ** ** ENTRY POINT START ** ** WORKSPACE AT >8300 ** ** R0,R1,R2 - GEN VDP ** ** NO RESERVED REGISTERS ON EXIT ** ** ** **************************************** DEF START REF VSBW,VMBW,VSBR,VMBR,VWTR PDT EQU >0000 PATTERN DESCRIPTOR TABLE SVVDP1 EQU >83D4 SAVE LOC FOR VDP R1 SIT EQU >1800 SCREEN IMAGE TABLE CT EQU >2000 COLOR TABLE SATAB EQU >1B00 SPRITE ATTRIBUTE LIST SDTAB EQU >1C00 SPRITE DESCRIPTOR TABLE STATUS EQU >837C WS EQU >8300 MY WORKSPACE IN HIGH SPEED CPU RAM * DATA STATEMENTS * VDPREG DATA >02A0,>06FF,>0336,>030F VDP REGS BIT MAP MODE SPRITE DATA >0001,>0307,>0F0F,>3FFF,>3F0F,>0F07,>0301,0 SPRITE DESCRIPTOR DATA >F0E0,>E0C0,>8286,>FEFF,>FE86,>82C0,>E0E0,>F000 SALINT DATA >5080,>8005,>D000 CHRTAB BSS >2F8 STRING TEXT 'THIS IS THE TEXT TO BE DISPLAYED' EVEN * BEGIN CODE * START LWPI WS * SAVE THE CHAR SET FROM E/A LOADER * LI R0,>900 DASE ADDRESS E/A (START CHAR >20) NOTEA LI R1,CHRTAB READ THE CHAR SET INTO CHRTAB LI R2,>2F8 BLWP @VMBR * SET VDP REGS TO BIT MAP * CLR R0 VDP REG VALUE LI R1,VDPREG VDP REG POINTER LI R2,8 REGISTERS TO WRITE TO VDPL MOVB *R1+,@WS+1 MOV TO R0 LSB BLWP @VWTR AI R0,>0100 NEXT VDP REG DEC R2 JNE VDPL MOVB @VDPREG+1,@SVVDP1 BLANK DISABLED * YOU MUST SAVE A COPY OD VDP R1 AT >83D4 OR KEYSCAN WILL INTERFERE * FORMAT SCREEN >00->FF THREE TIMES * LI R0,SIT CLR R1 BEGIN WITH 0 LI R2,>300 LEN OF SIT THIRDS BLWP @VSBW INC R0 NEXT LOCATION AI R1,>0100 WILL WRAP AFTER >FF00 DEC R2 JNE THIRDS * CLEAR THE PATTERN AREA BLANK AND MAKE COLOR TABLE RED ON WHITE* BL @CLRVDP CLEAR PATTERN AREA DATA PDT,>1800,0 DATA FOR SUBROUTINE BL @CLRVDP RED ON WHITE COLOR AREA DATA CT,>1800,>9F9F * ENABLE THE SCREEN SO YOU CAN SEE * LI R0,>01E3 WRITE >E3 TO VDP REG 1 BLWP @VWTR DOUBLE/MAGNIFIED SPRITES SWPB R0 MOVB R0,@SVVDP1 SAVE THE VALUE * PUT THE TEXT ON THE SCREEN * BL @DISTEX SUBROUTINE TO PLACE TEXT ON THE SCREEN DATA >B00,STRING,32 * SET UP SPRITES * LI R0,SDTAB SPRITE DESCRIPTOR TABLE ADDRESS LI R1,SPRITE SPRITE CHARACTER DATA LI R2,32 DOUBLE SIZE SPRITE BLWP @VMBW LI R0,SATAB SPRITE ATTRIBUTE TABLE LI R1,SALINT INIT DATA FOR SPRITE ATTRIBUTE LIST LI R2,5 FIVE BYTES TO WRITE BLWP @VMBW >D0 REQUIRED TO DISABLE REMAINING SPRITES * THE SPRITE IS ON THE SCREEN. NOW TO MOVE IT. LOOP LI R0,SATAB+1 X POSITION OF THE SPRITE. Y AT SATAB BLWP @VSBR READ THE CURRENT X POSITION SRL R1,8 PUT VALUE IN RIGHT BYTE DEC R1 SUBTRACT 1 FROM THE X VALUE JNE MOVE IF X=0 THEN LI R1,>FF X=>FF MOVE SLA R1,8 MOVE TO MSBYTE BLWP @VSBW WRITE THE NEW X POSITION UP LI R2,800 DELAY TO SLOW DOWN THE SPEED OF THE SPRITE DELAY NOP WASTE TIME DEC R2 JNE DELAY JMP LOOP THIS IS WHERE YOU COULD PLACE THE REMAINING PROGRAM * THIS IS A CONTINUOUS LOOP NO PROVISION FOR EXITING GIVEN * ************************************** * * * SUBROUTINE TO FILL VDP WITH DATA * * RT IS R12 * * DATA PDT,>1800,>0000 * * (DEST,LEN,VALUE TO FILL) * * * ************************************** CLRVDP MOV *R11+,R0 DEST CLRLV MOV *R11+,R3 LEN CLRV MOV *R11+,R4 VALUE(S) CLR MOV R11,R12 SAVRTN SRL R3,1 DIVIDE BY 2 LI R2,2 BYTES OF DATA LI R1,WS+8 FROM R4 CLRVL BLWP @VMBW INCT R0 NEXT 2 LOCATIONS DEC R3 DONE? JNE CLRVL B *R12 RT ************************************* * * * DISPLAY TEXT SUBROUTINE * * (LOC,TEXT,LENGTH) * * >388,MMENU,9 * * * ************************************* DISTEX MOV *R11+,R0 LOCATION * LOC=((ROW-1)*256)+((COLUMN-1)*8) MOV *R11+,R3 ADDRESS OF TEXT TO WRITE MOV *R11+,R5 LENGTH OF TEXT STRING LI R2,8 8 BYTES IN A CHAR DESCRIPTION PUTDIS MOVB *R3+,R1 BYTE TO WRITE SRL R1,8 RIGHT JUSTIFY AI R1,-32 STRIP THE ASCII OFFSET SLA R1,3 MULTIPLY BY 8 FOR OFFSET AI R1,CHRTAB ADD THE BASE ADDRESS OF THE CHAR TABLE BLWP @VMBW PUT IT ON THE SCREEN AI R0,8 NEXT SCREEN LOCATION DEC R5 DECREMENT LENGTH COUNTER JNE PUTDIS ANY MORE TO WRITE? RT END Download complete. Turn off Capture File.