>I'm concerned at my draw code - am I generating an acceptable frame?
>Does the TV synch OK?
No.
>I'd really like some feedback. If you think its interesting, say so. If
>you think it sucks, tell me why. Positive response will encourage me to
>continue sharing source - otherwise I'll go native.
It might be interesting, but all it does is roll the picture on my TV.
>OBJPATTERN EQU OBJPOS + OBJSIZE
>OBJPATTERNB EQU OBJPATTERN + OBJSIZE
> ; WHOO BOY THERE'S GONNA BE SOME PROBLEMS WITH BIT SHIFTING
> ; TO MOVE THE OBJECT PATTERNS. PROBABLY BETTER TO THINK ABOUT
> ; ROM TABLES FOR THIS STUFF
Do you always program in all caps? Hard on the eyes :)
> ; TYPICAL FRAME CONSISTS OF 3 VERTICAL SYNC (VSYNC) LINES,
> ; 37 VERTICAL BLANK (VBLANK) LINES,
> ; 192 TV PICTURE LINES
> ; 30 OVERSCAN LINES
Correct.
> ; WE HAVE JUST 37 LINES (@2812 CYCLES) OF VBLANK, SO WE HAVE TO MAKE
> ; SURE THE SCREEN DRAW DOESN'T GET STOMPED ON. THE TIMER WILL TELL
> ; US IF WE'VE SCREWED UP. TIMER DONE JUST BEFORE THE LAST WSYNC TO
> ; GIVE MAXIMUM POSSIBLE CYCLE COUNT AVAILABILITY/ACCURACY
>
> LDA #43 ; WELLL... 43.89..
> STA TIM64T ; WE HAVE 37 LINES (= 2812 CYCLES)
> ; UH... LESS THE 3 FOR THE LINE BELOW
The cycle/line counts here need not be exact... an extra line one way or
the other won't stop the TV from syncing.
> ; THE KERNEL
> ; WE HAVE TO DRAW THE SCREEN TOO? SHEESH, WHAT IS THIS... A 2600?
> ; YEAH, THATS RIGHT... LINE BY LINE WE HAVE TO HOLD HANDS WITH THE
> ; TIA, PASSING IT DATA SO THAT IT DRAWS THE SCREEN FOR US. NICE.
> ; NOT! GOOD FOR NOSTALGIA, THOUGH. WHY, BACK IN MY DAY...
Enough editorializing... will you write the damn code already? :)
>DRAWSCREEN
>
> ; WAIT FOR VERTICAL BLANK PERIOD TO END
> ; TIMER COUNTS DOWN 1 EVERY 64 CYCLES, SO JUST WAIT FOR IT
> ; IF ITS OVER-TIME ALREADY, WE COULD BE IN TROUBLE, AS THE TIMER
> ; COUNTS UP WHEN IT REACHES 0. DON'T GO OVER-TIME!!
>
>ENDVB LDA INTIM
> BNE ENDVB
If you change that BNE to a BMI, and store a 42 to the timer in the first
place instead of a 43, you're in a little better shape if you do overflow.
The timer actually counts down to zero from whatever you write to it, then
continues past zero, so a BMI will pick it up even if you've gone a few
extra cycles.
> LDX #32
>PREDRAW STA WSYNC
> DEX
> BNE PREDRAW ; WELLL.... YEAH
> ; PUTS BLANK AREA AT TOP OF SCREEN
> ; NO DOCUMENTATION ON THIS ONE - ARBRITRARY?
Huh? You just drew 32 blank lines at the top of the visible screen. Was
that what you wanted?
> ;----
> ; CYCLE THRU DRAWING LINE BY LINE...
> ; TIME IS PRECIOUS HERE... THERE ARE JUST 228/3 CYCLES PER LINE
> ; AND THAT'S NOT COUNTING THE WSYNCH, SHOULD YOU BE WRITING THAT
> ; THERE ARE 68 CYCLES IN THE HBLANK PERIOD, WHICH STARTS AT THE
> ; CONCEPTUAL BEGINNING OF A LINE ON THIS MACHINE
No. There are 68 *pixels* in the Hblank period, which is 22.667 cycles.
> LDY #0
> LDX #0
>
>NEXLIN0 LDA #4
> STA Temp0
>
>NxtLine
>
> STA WSYNC ; WAIT FOR START OF HBLANK
>
> ; THERE ARE 68 CYCLES IN THE HBLANK PERIOD.
> ; WE NEED TO HAVE EACH PF BYTE WRITTEN BEFORE THE SCAN REQUIRES IT
>
> LDA PLAYFIELD,X
> STA PF0
> LDA PLAYFIELD+1,X
> STA PF1
> LDA PLAYFIELD+2,X
> STA PF2
>
> NOP
> NOP
> NOP
> NOP
> NOP
>
> ; RIGHT PF
>
> LDA PLAYFIELD+3,X
> STA PF0
> LDA PLAYFIELD+4,X
> STA PF1
> LDA PLAYFIELD+5,X
> STA PF2
>
> NOP
> NOP
> NOP
> NOP
> NOP
> NOP
>
>
> ; LINE 2
>
> NOP
> NOP
> NOP
>
> ; LEFT PF
>
> LDA PLAYFIELD,X
> STA PF0
> LDA PLAYFIELD+1,X
> STA PF1
> LDA PLAYFIELD+2,X
> STA PF2
>
> NOP
> NOP
> NOP
> NOP
> NOP
>
> ; RIGHT PF
>
> LDA PLAYFIELD+3,X
> STA PF0
> LDA PLAYFIELD+4,X
> STA PF1
> LDA PLAYFIELD+5,X
> STA PF2
>
> INY
>
> DEC Temp0
> BNE NxtLine
>
> CLC
> TXA
> ADC #6
> TAX
>
> CMP #96
> BCC NEXLIN0
>
>
> ; MAKE SURE WE HAVE A 192 LINE DISPLAY
> ; PAL MUST HAVE AN EVEN # OR THE COLOURS SCREW UP?!
>
>
>FIN LDA #0
> STA WSYNC
> INY
> CPY #192
> BCC FIN
>
>
> LDA #D1
> STA VBLANK ; END OF SCREEN - ENTER BLANKING
>
> ; DISABLE ALL THINGS THAT COULD APPEAR ONSCREEN
>
> LDA #0
> STA PF0
> STA PF1
> STA PF1
> STA GRP0
> STA GRP1
> STA ENAM0
> STA ENAM1
> STA ENABL
>
> RTS
>
>;--------
>OVERSCAN
>
> ; AFTER THE SCREEN IS DRAWN, WE HAVE 30 LINES OF OVERSCAN
> ; THIS TIME SHOULD BE USED FOR GAME LOGIC
>
> LDX #30
>OVERLIN STA WSYNC
> DEX
> BNE OVERLIN
>
> RTS
>
>; In PF0 and PF2, the most significant bit (bit 7) is on the RIGHT
>; side. In PF1, the most significant bit is on the LEFT side. This
>; means that relative to PF0 and PF2, PF1 has a reversed bit order.
>; It's just really weird.
>;
>; PF0 | PF1 | PF2
>; 4 5 6 7|7 6 5 4 3 2 1 0|0 1 2 3 4 5 6 7
>
>
>;---------
>; DRAWOBJECTS
>
>DRAWOBJECTS
>
> ; PASS
> ; TOGGLE = FRAME NUMBER (1 OR 2)
>
> ; ROUTINE EITHER DRAWS OR UNDRAWS OBJECTS, DEPENDING ON REQUIRED
> ; PRESENCE IN FRAME BUFFER. OBJECTS USUALLY REMAIN DRAWN.
> ; OBJECT FLAG CAN OVERRIDE AND FORCE DRAW
>
> ; NOW WE NEED TO ADD THOSE "JUST-THIS-FRAME" COLOURS
> ; FRAME ACTION
> ; 0 ONLY SHOW COLOUR 1 AND COLOUR 3 OBJECTS
> ; IE: (UN)DRAW COLOUR 1
> ; 1 ONLY SHOW COLOUR 2 AND COLOUR 3 OBJECTS
> ; IE: (UN)DRAW COLOUR 2
>
> ; LOOP THROUGH OBJECTS, (UN)DRAWING ONLY TRANSIENT COLOURS
> ; OBJECT (UN)DRAW CAN BE FORCED (D7 OF OBJFLAGS)
>
> LDX #OBJSIZE-1
>
>FOROBJ LDY OBJPOS,X ; POSITION IN VIRTUAL SCREEN
> BMI NEXTOBJ ; NOT PRESENT
>
> ; COLOUR 0 IS "ON" ALL THE TIME
> ; COLOUR 1 IS ON DURING FRAME 1 ONLY
> ; COLOUR 2 IS ON DURING FRAME 2 ONLY
> ; COLOUR 3 IS ON DURING FRAME 1 AND 2
>
> LDA OBJFLAGS,X
> BMI FORCED
> EOR TOGGLE ; FRAME 1 OR 2
> AND #3
>
> ; NOW, F0 C0 -> 1
> ; F0 C1 -> 0
> ; F0 C2 -> 3
> ; F0 C3 -> 2
> ; AND, F1 C0 -> 2
> ; F1 C1 -> 3
> ; F1 C2 -> 0
> ; F1 C3 -> 1
>
> BNE NEXTOBJ ; NEAT!!
>
>FORCED
>
> ; HAVE DETERMINED THAT DRAW/ERASE IS REQUIRED
>
> LDA OBJPATTERN,X
> EOR PLAYFIELD,Y
> STA PLAYFIELD,Y
>
> LDA OBJPATTERN,X
> EOR PLAYFIELD+6,Y
> STA PLAYFIELD+6,Y
>
> LDA OBJPATTERNB,X
> EOR PLAYFIELD+1,Y
> STA PLAYFIELD+1,Y
>
> LDA OBJPATTERNB,X
> EOR PLAYFIELD+7,Y
> STA PLAYFIELD+7,Y
>
>NEXTOBJ DEX
> BPL FOROBJ
>
> RTS
>
>
>; --------
>; INIT1CE
>
> ; ONE-TIME INITIALIZATION
> ; HAPPENS AT SYSTEM RESET, NO OTHER TIME
>
>INIT1CE
>
> LDA #D1
> STA VBLANK ; START WITH TIA DISABLED
>
> LDA #D1
> STA CTRLPF ; SCORE (COLOUR SEP)
>
>
> ; COPY THE PLAYFIELD FROM THE TABLE
>
> LDX #93
>
>PLAYFILLED
>
> LDA BITMAP,X
> STA PLAYFIELD,X
> LDA BITMAP+1,X
> STA PLAYFIELD+1,X
> LDA BITMAP+2,X
> STA PLAYFIELD+2,X
>
> TXA
> SEC
> SBC #3
> TAX
> BCS PLAYFILLED
>
>
>
> ; INIT OBJECTS TO NONE
>
> LDX #OBJSIZE-1
> LDA #$80 ; D7 = INACTIVE
>INITOBJ STA OBJPOS,X
> DEX
> BPL INITOBJ
>
>
> ; ADD A COUPLE OF TEST OBJECTS
>
> LDA #31
> STA OBJPOS
> LDA #1
> STA OBJFLAGS
> LDA #%11111111
> STA OBJPATTERN
> LDA #0
> STA OBJPATTERNB
>
> LDA #19
> STA OBJPOS+1
> LDA #2
> STA OBJFLAGS+1
> LDA #%11111111
> STA OBJPATTERN+1
> LDA #0
> STA OBJPATTERNB+1
>
>
> LDA #1
> STA TOGGLE ; CYCLES 1/2/1/2...
>
>
> ; JSR DRAWOBJECTS
>
> ; AT THIS STAGE WE HAVEN'T DRAWN COLOUR 3 OBJECTS
> ; THAT COMES LATER - GIVE IT TIME :)
>
> RTS
>
>
>BITMAP
>
> ; JUST TREAT THIS AS A 40X24 BITMAP
> ; THIS IS D0 OF 4 COLOUR PLAYFIELD
>
> ; PF0 <-- PF1 --> PF2 <-- PF0 <-- PF1 --> PF2 <--
> ; FLIP XXXX OK FLIP FLIP XXXX OK FLIP
> .BYTE %11110000,%11111111,%11111111,%11110000,%11111111,%11111111
> .BYTE %00010000,%10000000,%10000000,%00000000,%00000000,%10000000
> .BYTE %00010000,%10000000,%10000000,%10010000,%11001110,%10001110
> .BYTE %00010000,%11100000,%10000000,%10010000,%11001110,%10001110
> .BYTE %00010000,%11100000,%10000000,%10010000,%11001110,%10001110
> .BYTE %00010000,%11100000,%10000000,%10010000,%11001110,%10001110
> .BYTE %00010000,%00000000,%10000000,%00000000,%00000000,%10000000
> .BYTE %00010000,%00000000,%10000000,%00000000,%00000000,%10000000
> .BYTE %00010000,%00000000,%10000000,%00000000,%00000000,%10000000
> .BYTE %00010000,%00000000,%10000000,%00000000,%00000001,%10100010
> .BYTE %00010000,%00000000,%10000000,%00000000,%00000011,%10110111
> .BYTE %00010000,%00000000,%10000000,%00000000,%00000001,%10100010
> .BYTE %11010000,%00000000,%10000000,%00000000,%00000011,%10100111
> .BYTE %11010000,%00000000,%10000000,%00000000,%00000001,%10100010
> .BYTE %00010000,%00000000,%10000000,%00000000,%00000000,%10000000
> .BYTE %11110000,%11111111,%11111111,%11110000,%11111111,%11111111
> ; ^^^^ ^^^^
> ; UNUSED UNUSED
>
>
> ; COLOURS FOR 4-COLOUR SCREEN
> ; THESE COLOURS CORRESPOND TO EACH OF 2 FRAMES OF THE MULTIPLEXED
> ; DISPLAY. THERE ARE TWO BKCOLS AVAILABLE, AND TWO SIDES OF THE SCREEN
> ; THE 4 COLOURS ARE FROM COMBINATION OF THE TWO FRAME MULTIPLEX, AND
> ; THE COMBINATION DISPLAY ON THESE FRAMES. COLOURS ARE COMBINIATIONS
> ; HOPEFULLY THIS WON'T FLICKER TO BUGGERY ON THE REAL THING, LIKE IT
> ; DOES ON MY EMULATOR!
>
> ; FR.1 FR.2
>BKCOL .BYTE 100, 100
>PFCOL1 .BYTE 16, 196
>PFCOL2 .BYTE 22, 45
>
>
>;--------
>; SYSTEM VECTORS
>
> org $FFFC
> .WORD START ; NMI?
> .WORD START ; RESET VECTOR
>
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