Subject: [stella] Playfield Basics (newbie question) From: Rico <wrbs@xxxxxxxxxx> Date: Sun, 03 Nov 2002 20:51:59 -0400 |
Hello stella programmers: Just recently got started with atari 2600 programming, and I am learning a lot. Searching through the archives answers most of my questions. I am learning how to draw a playfield. I have read Nick's famous playfield example and tried different variations that have been posted on the list. I have written a small program which only purpose is to draw a rectangle repeatedly from the top to the bottom of the screen (without worrying about the reflected portion of the screen). I initialized the playflied registers to draw something like this: * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * When I run the code, the atari draws the rectangle omitting one of the long lines (leaving the rectangle 'open'). How can I fix this? Let me know what I am doing wrong. My guess I am not correctly counting which playfield line to draw. Thank you for you time. --Rico Dones Here is the code: ; Learning atari playfields ; ; Objective: Draw a rectangle many times ; using the playfield registers. ; processor 6502 include eckvcs.h org $F000 START SEI CLD LDX #$FF TXS LDA #0 CLEARMEM STA 0,X DEX BNE CLEARMEM LDA #$00 ; SET BACKGROUND BLACK STA COLUBK LDA #$1E ; SET PLAYFIELD YELLOW STA COLUPF MAINLOOP LDA #2 ; TURN ON VSYNC STA VSYNC STA WSYNC STA WSYNC STA WSYNC LDA #43 STA TIM64T LDA #0 ; TURN OFF VSYNC STA VSYNC VBLANKTIME LDA INTIM BNE VBLANKTIME LDX #7 ; Use X register to count ; eight playfield lines ; to draw. LDY #191 SCANLOOP STA WSYNC ; Accumulator is still 0 STA VBLANK LDA PFData0,X STA PF0 LDA PFData1,X STA PF1 LDA PFData2,X STA PF2 DEX ; Decrement X. BNE SKIPINITX ; If X != 0 then skip next line LDX #7 ; Repeat playfield drawing ; by setting X to decimal 7. SKIPINITX DEY BNE SCANLOOP LDX #30 OVERSCAN STA WSYNC DEX BNE OVERSCAN JMP MAINLOOP org $FF00 ; GRAPHICS DATA STARTS HERE ; Playfield graphic is supposed to look like this: ; ; * * * * * * * * * * * * * * * * ; * * ; * * ; * * ; * * ; * * ; * * ; * * * * * * * * * * * * * * * * ; PFData0 .byte $F0,$10,$10,$10,$10,$10,$10,$F0 PFData1 .byte $FF,$00,$00,$00,$00,$00,$00,$FF PFData2 .byte $FF,$A0,$A0,$A0,$A0,$A0,$A0,$FF ORG $FFFC .WORD START .WORD START ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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