What are the object priorities set to? If playfield is higher than players,
it will cover up the players.
-Chris
On Fri, 2 Mar 2001, Tempest wrote:
> Ok here's my code. It's pieced together from several other code snippets
> I've found in the archives. It use to display some multi-colored stripes on
> the screen but I disabled those for the time being by clearing the Playfield
> registers.
>
> What it should do is display my stupid ship graphic on scanline 92 and
> recognize the joystick input (that part works), but I'm getting nothing but
> a blank screen. Maybe I shouldn't write zero's to the Playfield registers?
> If someone can fill me in on what stupid mistake I'm making I'd appreciate
> it.
>
> Tempest
>
>
> ;***************************************
> ;* Galactic Tactic *
> ;* Ver. 0.01 *
> ;***************************************
>
>
> processor 6502
> include vcs.h
>
>
> org $F000
>
>
> ;*****************************************************
> ;* Equates *
> ;*****************************************************
>
> Scanctrl equ $91
>
>
> ;*****************************************************
> ;* Clear Memory *
> ;*****************************************************
>
> Start
>
> SEI ; Disable interrupts, if there are any.
> CLD ; Clear BCD math bit.
> LDX #$FF
> TXS ; Set stack to top of RAM.
>
> LDA #0 ;Zero everything except VSYNC.
> B1 STA 0,X
> DEX
> BNE B1
>
>
> JSR GameInit
>
>
> ;******************************************************
> ; Main Loop *
> ;******************************************************
>
> MainLoop
> JSR VerticalBlank ;Execute the vertical blank.
> JSR CheckSwitches ;Check console switches.
> JSR GameCalc ;Do calculations during Vblank
> JSR DrawScreen ;Draw the screen
> JSR OverScan ;Do more calculations during overscan
> JMP MainLoop ;Continue forever.
>
>
> ;******************************************************
> ; Verticle Blanking *
> ;******************************************************
>
> VerticalBlank
>
> LDA #2 ;VBLANK was set at the beginning of overscan.
> STA WSYNC
> STA WSYNC
> STA WSYNC
> STA VSYNC ;Begin vertical sync.
> STA WSYNC ;First line of VSYNC
> STA WSYNC ;Second line of VSYNC.
>
> LDA #44 ;Set timer to activate during the last line of VBLANK.
> STA TIM64T
>
> LDA #0 ;Now we can end the VSYNC period.
> STA WSYNC ;Third line of VSYNC.
> STA VSYNC ;Writing zero to VSYNC ends vertical sync period.
> RTS
>
>
> ;******************************************************
> ; Check Switches *
> ;******************************************************
>
> CheckSwitches
>
> LDA #0 ;Clear collision latches
> STA CXCLR ;In a real game, we'd probably check the collision
> ;registers before clearing them.
> RTS
>
>
> ;******************************************************
> ; Game Calculations *
> ;******************************************************
>
> GameCalc
>
> LDA #0
> STA COLUBK ;Background will be black.
>
> LDA #$80
> BIT SWCHA
> BEQ Right
> LSR
> BIT SWCHA
> BEQ Left
> LSR
> BIT SWCHA
> BEQ Down
> LSR
> BIT SWCHA
> BEQ Up
> JMP NoStick
>
>
> Right
> JMP NoStick
>
> Left
> JMP NoStick
>
> Down
> JMP NoStick
>
> Up
> JMP NoStick
>
> NoStick
>
> LDA #$00 ;Pixels: 00000000
> STA PF0
> STA PF2 ;Store alternating bit pattern to the playfield registers
> ASL ;Because PF1 displays in the opposite bit order from PF0
> STA PF1
> LDA #1
> STA CTRLPF ;Let's reflect the playfield just cause we feel like it =)
> STA RESP0
> RTS
>
>
> ;******************************************************
> ; Draw Screen *
> ;******************************************************
>
> DrawScreen
>
> LDA INTIM
> BNE DrawScreen ;Loops until the timer is done - that means we're
> ;somewhere in the last line of vertical blank.
> STA WSYNC ;End the current scanline - the last line of VBLANK.
> STA VBLANK ;End the VBLANK period. The TIA will display stuff
> ;starting with the next scanline. We do have 23 cycles
> ;of horizontal blank before it displays anything.
>
> LDY #192 ;We're going to use Y to count scanlines.
>
>
> ScanLoop
>
> STY COLUPF ;Keep changing the playfield color every line
> STA WSYNC ;Wait for end of scanline
> DEY
> TYA
> CMP #$91
> BEQ DrawSprite
> BNE ScanLoop ;Count scanlines.
> RTS
>
>
> DrawSprite
>
> LDX #07
> cont STA WSYNC
> LDA Sprite,X
> STA GRP0
> DEX
> BNE cont
> RTS
>
>
> ;******************************************************
> ; Overscan *
> ;******************************************************
>
> OverScan ;We've got 30 scanlines to kill.
> LDX #30 ;In a real game, we'd probably be doing calculations here,
>
> KillLines ;possibly using the timer again to tell us when overscan
> STA WSYNC ;is done instead of counting the scanlines.
> DEX
> BNE KillLines
> RTS
>
> GameInit ;Usually called to start a new game.. we're not using it yet.
> RTS
>
> Sprite
> .byte %00000000
> .byte %00011000
> .byte %00011000
> .byte %10011001
> .byte %10100101
> .byte %11000011
> .byte %00000000
>
>
> org $FFFC
> .word Start
> .word Start
>
>
>
> -
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>
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