mminer-apple2/src/apple2/screen.inc

1118 lines
38 KiB
PHP

;-----------------------------------------------------------------------------
; screen.inc
; Part of manic miner, the zx spectrum game, made for Apple II
;
; Stefan Wessels, 2020
; This is free and unencumbered software released into the public domain.
;-----------------------------------------------------------------------------
.segment "CODE"
;-----------------------------------------------------------------------------
; Swap visible HGR pages and update currPageH to the back page hi byte
.proc screenSwap
lda backPage
beq :+
bit HISCR
jmp valueSwap
:
bit LOWSCR
valueSwap:
lda backPage ; pretend flip the screen
eor #1
sta backPage
lda #$60 ; pretend flip the screen Hi value so all drawing
eor currPageH ; happens on the front screen
sta currPageH
rts
.endproc
;-----------------------------------------------------------------------------
; x 0 cleats top (play area minus 8 pixel row), x non-0 clears whole screen
.proc screenClear
lda #$00
ldy backPage
beq page1
jmp page2
page1:
cpx #0
bne :+
jmp p1p2
:
ldx #39
p1l1:
.repeat $48, Row
sta $100 * (>HGRPage1 + (Row + $78) & $07 << 2 | (Row + $78) & $30 >> 4) | (Row + $78) & $08 << 4 | (Row + $78) & $C0 >> 1 | (Row + $78) & $C0 >> 3, x
.endrepeat
dex
bmi p1p2
jmp p1l1
p1p2:
ldx #39
p1l2:
.repeat $78, Row
sta $100 * (>HGRPage1 + Row & $07 << 2 | Row & $30 >> 4) | Row & $08 << 4 | Row & $C0 >> 1 | Row & $C0 >> 3, x
.endrepeat
dex
bmi done0
jmp p1l2
done0:
rts
page2:
cpx #0
bne :+
jmp p2p2
:
ldx #39
p2l1:
.repeat $48, Row
sta $100 * (>HGRPage2 + (Row + $78) & $07 << 2 | (Row + $78) & $30 >> 4) | (Row + $78) & $08 << 4 | (Row + $78) & $C0 >> 1 | (Row + $78) & $C0 >> 3, x
.endrepeat
dex
bmi p2p2
jmp p2l1
p2p2:
ldx #39
p2l2:
.repeat $78, Row
sta $100 * (>HGRPage2 + Row & $07 << 2 | Row & $30 >> 4) | Row & $08 << 4 | Row & $C0 >> 1 | Row & $C0 >> 3, x
.endrepeat
dex
bmi done1
jmp p2l2
done1:
rts
.endproc
;-----------------------------------------------------------------------------
.proc screenDrawLevelName
clc
lda #20 ; screen is 20 "characters" wide
adc leftEdge ; but maybe is offset from the left
asl ; mult by 2 for columns
tay ; put into y
dey ; but 0 based so 0-39 or whatever (not 1-40)
ldx #39 ; screen index is 0-39
lda currPageH
cmp #$20
bne page2
:
lda levelNameGfx0 + $0000, y ; load the cache
sta $2050, x ; store to the screen (the hi byte is updated)
lda levelNameGfx0 + $0040, y ; but the lo byte ($50) is correct for row 16 (0 based)
sta $2450, x
lda levelNameGfx0 + $0080, y ; the cache is linear so each line is $40 from previous
sta $2850, x
lda levelNameGfx0 + $00C0, y
sta $2C50, x
lda levelNameGfx0 + $0100, y
sta $3050, x
lda levelNameGfx0 + $0140, y
sta $3450, x
lda levelNameGfx0 + $0180, y
sta $3850, x
lda levelNameGfx0 + $01C0, y
sta $3C50, x
dey ; previous cache byte
dex ; previous screen byte
bpl :- ; keep going till all 40 columns copied
rts
page2:
lda levelNameGfx0 + $0000, y ; load the cache
sta $4050, x ; store to the screen (the hi byte is updated)
lda levelNameGfx0 + $0040, y ; but the lo byte ($50) is correct for row 16 (0 based)
sta $4450, x
lda levelNameGfx0 + $0080, y
sta $4850, x
lda levelNameGfx0 + $00C0, y
sta $4C50, x
lda levelNameGfx0 + $0100, y
sta $5050, x
lda levelNameGfx0 + $0140, y
sta $5450, x
lda levelNameGfx0 + $0180, y
sta $5850, x
lda levelNameGfx0 + $01C0, y
sta $5C50, x
dey ; previous cache byte
dex ; previous screen byte
bpl page2 ; keep going till all 40 columns copied
rts
.endproc
;-----------------------------------------------------------------------------
.proc screenDrawAirFrame
lda currPageH ; see if this is to page 1 or 2
cmp #$20
bne page2
ldx #28 ; draw the long green lines that outline the bar
:
lda #%00101010 ; green left
sta $20DA, x
sta $24DA, x
sta $38DA, x
sta $3CDA, x
lda #%01010101 ; green right
sta $20DB, x
sta $24DB, x
sta $38DB, x
sta $3CDB, x
dex ; step back in 2's for left/right
dex
bpl :-
ldx #31 ; draw the even longer white bar that counts down
lda #%01111111 ; white left & right
:
sta $28D7, x
sta $2CD7, x
sta $30D7, x
sta $34D7, x
dex ; in 1's since left/right is the same $7f
bpl :-
rts
page2: ; the same as page 1, just diff buffer
ldx #28
:
lda #%0101010
sta $40DA, x
sta $44DA, x
sta $58DA, x
sta $5CDA, x
lda #%01010101
sta $40DB, x
sta $44DB, x
sta $58DB, x
sta $5CDB, x
dex
dex
bpl :-
ldx #31
lda #%01111111 ; white left & right
:
sta $48D7, x
sta $4CD7, x
sta $50D7, x
sta $54D7, x
dex
bpl :-
rts
.endproc
;-----------------------------------------------------------------------------
.proc screenDrawAirRemaining
lda airTipGfx ; the "graphic" to use
ldx airCols ; where to draw the tip of the graph
cpx #3 ; last few cols are against orange
bpl :+
ora #$80 ; in the last few cols so make green orange
:
ldy currPageH ; which page
cpy #$20
bne page2
sta $28D7, x ; write the tip into page 1
sta $2CD7, x
sta $30D7, x
sta $34D7, x
rts
page2:
sta $48D7, x ; write the tip into page 2
sta $4CD7, x
sta $50D7, x
sta $54D7, x
rts
.endproc
;-----------------------------------------------------------------------------
.proc screenDrawLevel
tileReadL = srcPtrL ; tile to draw's data
tileReadH = srcPtrH
scrnPtrL = dstPtrL ; location in screen buffer to draw to
scrnPtrH = dstPtrH
rows = sizeL ; rows to draw (15 -> 0)
cols = sizeH ; cols to draw (20 + leftEdge -> leftEdge)
willyYRowEnd = tmpBot + 0 ; row where willy overlaps ends (+1)
willyXPosStart = tmpBot + 1 ; col where willy overlaps start
willyXPosEnd = tmpBot + 2 ; row where willy overlaps ends (+1)
rowStartL = tmpBot + 3 ; current screen draw row start
rowStartH = tmpBot + 4
height = tmpBot + 5 ; normally 8 except for collapsing platforms
lda #0
sta tilesRendered
lda willyYPos ; see if willy is across 2 or 3 rows
and #7
beq :+
lda #3
bne :++
:
lda #2
:
clc
adc willyYRow ; and set up the end row (+1)
sta willyYRowEnd
lda willyXPos ; calculate the cols that willy overlaps
sec
sbc leftEdge
sta willyXPosStart
clc
adc #2
sta willyXPosEnd
clc ; in demo-mode, the prev didn't make sense and carry is set
lda leftEdge ; col where to start drawing (right, bottom)
adc #<(levelLayout + (PLAY_ROWS - 1) * PLAY_COLS)
sta colLoop + 1
lda #>(levelLayout + (PLAY_ROWS - 1) * PLAY_COLS)
sta colLoop + 2 ; levelLayout aligned so carry always clear
lda #PLAY_ROWS - 1 ; zero based rows to process
sta rows ; draw rows bottom up
rowLoop:
clc
ldy rows ; rows are 8 lines high
lda mult8, y
tay
lda rowL, y ; put the row in screen space
sta rowStartL ; and save in a temp place
lda rowH, y
adc currPageH
sta rowStartH
ldx #VISIBLE_COLS - 1 ; draw 20 columns (0 based)
colLoop:
lda PLACEHOLDER, x ; get the tile from the unpacked level
bne :+ ; if non-zero process that tile
jmp prevCol ; 0 (space) - skip to next tile to process
:
cmp #DATA_COLLAPSE ; see if the tile is a collapsing tile
bcc notCollapse ; the $70 could be $71->$77 for the collapsed state
cmp #DATA_KEY
bcc isCollapse ; if it's less than $80 it is a collapsing platform
beq notCollapseClc ; is it a key
cmp #DATA_DOOR ; if not a key, is it a door
bcc setupSwitch ; if < door then it's a switch
jmp prevCol ; door tile isn't a rendered tile, only a collision tile
isCollapse:
and #7 ; get the level of collapse
tay
lda collapseHeight, y ; see how many lines remain to draw
sta height
lda mult1024H, y ; and move the screen pointer down as well
sta scrnPtrH
lda #DATA_COLLAPSE ; and set up to draw the tile from the top (for fewer lines)
bne setupTile ; BRA
setupSwitch:
ldy #0 ; this code duplicated from notCollapse since setupTile is skipped
sty scrnPtrH ; not a collapsing tile so set the screen ptr to top
ldy #8 ; and set the height to 8 lines to draw
sty height
and #1 ; is this an on switch?
beq :+ ; no
lda #16 ; yes - the image is 16 bytes further (tile36)
:
adc #<tile35 ; add the offset of the switch image
sta tileReadL
lda #>tile35 ; and set the hi byte too
adc #0 ; turns out tile36 is in a different block (if I remove these 2 bytes ;)
sta tileReadH ; points at the tile data
bne :+ ; skip the portion where the tile pointer is setup
notCollapseClc:
clc
notCollapse:
ldy #0 ; not a collapsing tile so set the screen ptr to top
sty scrnPtrH
ldy #8 ; and set the height to 8 lines to draw
sty height
setupTile:
adc #<(tilesInstances - TILE_BYTES) ; Index 1 has it's bytes at + 0, so move start 1 tile back
sta tileReadL
lda #>(tilesInstances - TILE_BYTES) + 1 ; carry always set, so + 1
sta tileReadH ; points at the tile data
:
inc tilesRendered
txa ; get the col
asl ; * 2 for 2-byte wide tiles and clears carry
adc rowStartL ; add to screen row start to get tile screen dest
sta scrnPtrL
lda rowStartH
adc scrnPtrH ; add the hi offset for collapsed tiles
sta scrnPtrH
intersect:
lda rows ; see if willy intersects this row
cmp willyYRow
bcc noOverlap ; is willy below this row?
cmp willyYRowEnd
bcs noOverlapClc ; is willy's end above this row
txa ; rows intersect, now check the cols
cmp willyXPosStart
bcc noOverlap ; is col < willyStartCol
cmp willyXPosEnd
bcs noOverlapClc ; is col > willyEndCol (>= willyEnd + 1)
overlap: ; willy will be "under" these tiles, so "or" in the
ldy #0 ; tile to the screen. Since willy's bits are 11, willy
lda (tileReadL), y ; will "appear" as though he's in front of the tile
ora (scrnPtrL), y ; see noOverlap for code explanation
sta (scrnPtrL), y
ldy #1
lda (tileReadL), y
ora (scrnPtrL), y
sta (scrnPtrL), y
lda tileReadL
adc #2
sta tileReadL
lda scrnPtrH
adc #$04
sta scrnPtrH
dec height
bne overlap
beq prevCol
noOverlapClc:
clc
noOverlap: ; tile's don't intercept with willy so just write to screen
ldy #0 ; start with a byte at 0 offset (left)
lda (tileReadL), y ; read tile byte
sta (scrnPtrL), y ; write to screen
ldy #1 ; do the same for the right byte at offset 1
lda (tileReadL), y
sta (scrnPtrL), y
lda tileReadL ; advance the tile ptr by 2 for the 2 just written
adc #2
sta tileReadL
lda scrnPtrH ; advance the screen ptr to next row ($400)
adc #$04
sta scrnPtrH
dec height ; done one more row
bne noOverlap ; keep going till all rows done
prevCol:
dex ; go to col to the left
bmi :+ ; reached the end of the row?
jmp colLoop ; not yet end of row so go do this col
:
dec rows ; done another row
bmi done ; done all rows?
lda colLoop + 1 ; not yet - setp up a row in the unpacked tile area
sec
sbc #32
sta colLoop + 1
bcs :+
dec colLoop + 2
:
jmp rowLoop ; go do the next row's worth of tiles
done:
lda currLevel
cmp #LEVEL_Solar_Power_Generator ; Is this the solar room
bne :+ ; if not, move on
jmp screenSolarBeam ; solar room needs a solar beam
:
rts
.endproc
;-----------------------------------------------------------------------------
.proc screenDrawSprites
count = sizeL
ldx numSprites ; render the AI
dex ; ignore the door
stx count
:
jsr screenDrawSprite
dec count
ldx count
bpl :-
rts
.endproc
;-----------------------------------------------------------------------------
.proc screenDrawSprite
col = sizeH
lines = tmpBot + 0
lda #0
sta read + 1 ; in case of left clipping, reset read
lda #3
sta stripLen + 1 ; in case of right clipping, reset length
lda spriteXPos, x ; col in 0..31 range
sec
sbc leftEdge ; move by the left edge
bpl leftOK ; if ge 0 then no clipping left
cmp #$ff
beq lClip
drawOffScreen:
sta lines
lda spriteClass, x
bit CLASS_MOVE_Y
beq :+ ; if yes, ignore
jmp screenDrawOffscreenSprite ; an off-screen amoeba gets an indicator
:
rts
lClip:
lda #2
sta read + 1
lda #1
sta stripLen + 1
lda #0
bne rightOK ; BRA
leftOK:
cmp #19 ; clip on the right
bcc rightOK
beq rClip
bne drawOffScreen ; BRA
rClip:
lda #1
sta stripLen + 1
lda #19
rightOK:
asl ; multiply times 2
sta col ; screen column for where to start draw
lda spriteFrame, x
adc spriteFramesIdx, x
tay
lda mult64H, y ; and add the 64 * frame hi
adc #>spriteInstances ; add the hi offset
sta read + 2
lda mult64L, y
adc #<spriteInstances
bcc :+
inc read + 2
clc
:
adc read + 1
sta read + 1
lda spriteYPos, x ; get the y position of the sprite
tay
lda #16 ; sprites are 16 high
sta lines
loop:
lda col ; start with the column
adc rowL, y ; add the row start
sta write + 1
lda rowH, y
adc currPageH ; and the page
sta write + 2 ; write points at the line to copy 4 bytes to
stripLen:
ldx #3 ; copy offsets 0..3
read:
lda PLACEHOLDER, x ; get the bytes from src instance
write:
sta PLACEHOLDER, x ; put them on screen
dex
bpl read ; do all the bytes
dec lines ; one more line done
beq done
lda read + 1 ; not all done, advance read by 4 bytes
adc #4
sta read + 1
bcc :+
inc read + 2
clc
:
iny ; and go to next line
bne loop ; BRA
done:
rts
.endproc
;-----------------------------------------------------------------------------
; used where vertical sprites are off-screen. Sometimes it matters to gameplay
; that you know where a sprite is before you get on a conveyor
.proc screenDrawOffscreenSprite
distance = tmpBot + 0
color = tmpBot + 1
col = tmpBot + 2
lda distance
bmi leftSide ; if negative, off on the left
sbc #20 ; make 0 based distance
lsr ; half the distance
sta distance ; save that
lda spriteColor, x ; get the color of this amoeba
tay
lda masksRight, y ; and read the mask
sta color ; and save that
lda #39 ; want to draw in the far right column
sta col ; save that
bne drawBlock ; BRA
leftSide:
eor #$FE ; make distance positive 0+
lsr ; half the distance
sta distance ; save
lda spriteColor, x ; get the color index
tay
lda masksLeft, y ; get the actual color mask
sta color ; save it
lda #0 ; draw in the left most column
sta col ; and save that
drawBlock:
clc ; carry undetermined
lda spriteYPos, x ; get the sprite's position (at top)
adc #5 ; put more or less in the center
tay ; put the draw row in y
lda #5 ; start with a distance of 5
sec
sbc distance ; subtract the actual distance
clc ; make carry clear
tax ; but that distance as a height in X
:
lda col ; start with the column
adc rowL, y ; calculate the byte address for the row
sta write + 1
lda rowH, y
adc currPageH ; include the hires buffer
sta write + 2 ; and save that as a write destination
lda color ; do all in the same color
write:
sta PLACEHOLDER ; write the color to the column
iny ; next row
dex ; one less row to do
bpl :- ; and repeat for the height that indicates distance
done:
rts
.endproc
;-----------------------------------------------------------------------------
.proc screenDrawLives
allDone = tmpBot + 0
ldx lives ; how many lives to draw
dex ; make 0 based
stx sizeL ; store as in sizeL as how many to draw
bpl :+ ; only if there's at least 1 spare, draw
bmi maybeCheat
:
lda #0
sta allDone
lda livesFrame ; get the animation frame
lsr
lsr
tay
lda mult64L, y ; mult 64
clc
adc #<sprites ; and add the sprite (willy) offset
sta srcPtrL
lda mult64H, y
adc #>sprites
sta srcPtrH ; save as srcPtr
txa ; how many lives (0 based) into a for column offset calc
oloop:
asl ; mult * 4 to set them apart
asl
sta sizeH ; store the column in sizeH
lda #16 ; draw 16 lines
sta dstPtrL ; store the lines in dstPrkL
ldy #22 * 8 ; Draw the lives in row 19 (0 based)
lda srcPtrL ; copy the srcPtr to where to read from
sta read + 1
lda srcPtrH
sta read + 2
loop:
lda sizeH ; start with the column
adc rowL, y ; add the row start
sta write + 1
lda rowH, y
adc currPageH ; and the page
sta write + 2 ; "write" points at the line to copy 4 bytes to
ldx #3 ; copy offsets 0..3
read:
lda PLACEHOLDER, x ; get the willy bytes
write:
sta PLACEHOLDER, x ; put them on screen
dex
bpl read ; do all the bytes
dec dstPtrL ; one more line done
beq next ; all lines done, see if more lives to draw
lda read + 1 ; not all done, advance read by 4 bytes
adc #4
sta read + 1
bcc :+
inc read + 2
clc
:
iny ; and go to next line
bne loop ; BRA
next:
dec sizeL ; dec the count of lives to draw
lda sizeL ; get it in a to calc the column
bpl oloop ; and go do that if ge 0
lda allDone ; sentinel to stop looping when cheat active
beq maybeCheat ; if not set then check if cheat is active
done:
rts ; exit
maybeCheat:
lda cheatActive ; see if cheat mode is on
beq done ; if not then done
sta allDone ; set sentinel
ldx lives ; get the column to draw the boot
txa
asl ; mult * 4 to set them apart
asl
sta sizeH ; store the column in sizeH
lda #16 ; draw 16 lines
sta dstPtrL ; store the lines in dstPrkL
ldy #22 * 8 ; Draw the lives in row 19 (0 based)
lda #<sprite19dw ; copy the srcPtr to where to read from
sta read + 1
lda #>sprite19dw
sta read + 2
jmp loop
.endproc
;-----------------------------------------------------------------------------
.proc screenDrawWilly
count = sizeL
col = sizeH
lines = tmpBot + 0
willyByte = tmpBot + 1
collision = tmpBot + 2
lda #0
sta collision
lda willyXPos ; col in 0..31 range
sec
sbc leftEdge ; move by the left edge
asl ; multiply times 2
sta col ; screen column for where to start draw
lda willyFrame ; get the frame
tay ; index through y
lda mult64L, y ; get the frame * 64 lo
adc #<sprite00 ; add instance base address
sta willyRead + 1 ; save as the lo src ptr
lda #>sprite00 ; add the hi offset
adc mult64H, y ; and add the 64 * frame hi
sta willyRead + 2 ; willyRead now a pointer at the frame to show
lda willyYPos ; get the y position of the sprite
tay
lda #16 ; sprites are 16 high
sta lines
loop:
lda col ; start with the column
adc rowL, y ; add the row start
sta screenRead + 1
sta write + 1
lda rowH, y
adc currPageH ; and the page
sta screenRead + 2 ; write points at the line to copy 4 bytes to
sta write + 2 ; write points at the line to copy 4 bytes to
stripLen:
ldx #3 ; copy offsets 0..3
willyRead:
lda PLACEHOLDER, x ; get the bytes from src instance
sta willyByte
screenRead:
lda PLACEHOLDER, x
eor willyByte
write:
sta PLACEHOLDER, x ; put them on screen
and willyByte
cmp willyByte
beq :+
inc collision
:
dex
bpl willyRead ; do all the bytes
dec lines ; one more line done
beq done
clc
lda willyRead + 1 ; not all done, advance read by 4 bytes
adc #4
sta willyRead + 1
bcc :+
inc willyRead + 2
clc
:
iny ; and go to next line
bne loop ; BRA
done:
lda collision
beq :+
sec
rts
:
clc
rts
.endproc
;-----------------------------------------------------------------------------
; Mask the front screen with the color index passed in at tmpBot + 0 (colIdx)
.proc screenInvertVisibleScreen
colIdx = tmpBot + 0
rows = tmpBot + 1
hiresRows = tmpBot + 2
colL = tmpBot + 3
colR = tmpBot + 4
jsr screenSwap::valueSwap
ldx colIdx ; load the color mask based on the index
lda masksLeft, x
sta colL
lda masksRight, x
sta colR
lda #PLAY_ROWS ; init a counter for how many rows to do
sta rows
lda #0 ; init the index to the starting hires row for the same "text" row
sta hiresRows
clc
rowLoop:
ldy hiresRows ; init the pointer to the top line of the hires row
lda rowL, y
sta dstPtrL
lda currPageH
adc rowH, y
sta dstPtrH
ldy #2 * (VISIBLE_COLS - 1) ; start at column 38
colLoop:
ldx #8 ; 8 hires rows per text row
:
lda (dstPtrL), y ; get the left col/byte on screen
and #%01111111 ; ignore the msb
eor colL ; eor with the color
sta (dstPtrL), y ; write it back
iny ; go to the right col
lda (dstPtrL), y
and #%01111111
eor colR
sta (dstPtrL), y
dey ; back to left
dex ; one more hires row done
beq :+ ; all done?
lda dstPtrH ; not yet
adc #4 ; move hires row down by 1
sta dstPtrH
bne :- ; BRA to do all 8 hires rows
:
lda dstPtrH ; move the hires ptr back to the top row
sec ; for the text row being processed
sbc #7*4
sta dstPtrH
clc ; clear carry from last set
next:
dey ; move to the prev col right
dey ; and move to the prev col left
bpl colLoop ; and repeat for all columns ge 0
dec rows ; done a row
beq done ; stop when all rows done
lda hiresRows ; more to do so move the hires
clc ; starting row down by 8 to be at the
adc #8 ; start of the next "text" row
sta hiresRows
jmp rowLoop ; go back and do this row now
done:
jsr screenSwap::valueSwap ; put the screen buffer info back
rts ; all done
.endproc
;-----------------------------------------------------------------------------
.proc screenSolarBeam
worldPtrL = srcPtrL
worldPtrH = srcPtrH
screenPtrL = dstPtrL
screenPtrH = dstPtrH
column = sizeL
row = sizeH
screenCol = tmpBot + 0
direction = tmpBot + 1
collision = tmpBot + 2
isWilly = tmpBot + 3
lda #0 ; init some local variables to 0
sta row
sta direction
sta collision
sta isWilly
lda #23 ; column where solar beam starts
sta column
sta worldPtrL ; also the column in levelLayout (aligned in mem)
lda #>levelLayout ; make worldPtr point at the start of the beam
sta worldPtrH
while:
lda column ; start with the column
sec
sbc leftEdge ; and see if it's on screen
bmi beamLeft ; if c - le <= 0 then c is left of screen and done
sta screenCol ; save this
cmp #20 ; if c - le >= 20 then c is to right of screen
bcc onScreen ; c - l1 >= 0 and < 20 so visible
offScreen:
ldy #0 ; beam is to the right so may become visible
lda (worldPtrL), y ; see if beam hits a world tile
beq :+ ; if not, process beam
beamLeft:
jmp done
:
ldx numSprites ; need to see if beam hits a sprite (not door) to bend
checkLoop:
dex
bmi checkCollision ; checked all sprites
lda spriteXPos, x ; get the sprite x
cmp column ; compare to the beam x
beq matchX ; if it matches it's a hit
bcs checkLoop ; sprite is to the right of the beam
adc #1 ; right col of the sprite
cmp column ; is it in the beam?
bne checkLoop ; if not this sprite is out
matchX:
lda spriteYPos, x ; see if y also matches
cmp row ; test against beam height
beq matchy
bcs checkLoop ; sprite top is lower than beam
adc #16 ; prep to test bottom of sprite
cmp row ; against the beam
bcc checkLoop ; sprite bottom is above beam
matchy:
inc collision ; set the collision
bne checkCollision ; and exit the check since sprites don't overlap
onScreen:
lda willyYPos ; see if the beam intersects willy
adc #16 ; if willyY + 16 >= row and willyY <= row + 8
cmp row ; then willy intersects in Y
bcc drawBlock
clc
lda row
adc #8
cmp willyYPos
bcc drawBlock
lda column ; if col >= willyX and col < willyX + 3
cmp willyXPos ; then willy intersects in X also, so hitting willy
bcc drawBlock
lda willyXPos
clc
adc #2
cmp column
bcc drawBlock
sta isWilly ; set isWIlly to true when hitting willy
clc
drawBlock:
ldy row ; set up to draw
lda screenCol ; on screen
asl ; which is 2 bytes per column
adc rowL, y
sta screenPtrL
lda rowH, y
adc currPageH
sta screenPtrH
ldx #8 ; beam block is 8 rows high
ldy #0 ; y 0 and 1 for left and right
blockLoop:
lda (screenPtrL), y ; get what's on screen (sprite)
beq nocol ; if nothing just overwrite
inc collision ; hit a sprite
nocol:
ora #%10101010 ; orange left
sta (screenPtrL), y ; write to screen
iny ; go to right column
lda (screenPtrL), y ; repeat for right col
beq :+
inc collision
:
ora #%11010101
sta (screenPtrL), y
dey ; set y back to 0
dex ; done one more row
beq checkCollision ; if all rows done, then done with plot
lda screenPtrH ; move down a row by adding $0400
adc #$04
sta screenPtrH
bne blockLoop ; BRA
checkCollision:
lda isWilly ; was willy hit
beq chkDirChng ; if not, normal collision checks
lda #2 ; don't set airflow to less than 2 so both
cmp airFlow ; buffers get to draw
bcs :+
sta airFlow
:
lda #0 ; willy was hit so reset locals
sta isWilly
beq setCollision ; go move the beam
chkDirChng:
lda collision ; see if there was a collision
beq moveBeam ; if there wasn't move the beam
lda direction ; there was a sprite collision
eor #1 ; so change the direction of the beam
sta direction
lda #0
setCollision:
sta collision ; reset the collision counter
moveBeam:
lda direction ; get the beam direction
beq down ; 0 is down and 1 is left
left:
dec column ; move a world column left
lda worldPtrL ; and move the pointer as well
bne :+
dec worldPtrH
:
dec worldPtrL
jmp checkWorld ; see that the new location isn't a world tile
down:
clc
lda row ; move the row
adc #8 ; down by 8 (1 block height)
sta row
lda worldPtrL ; and move the world pointer as well
adc #32
sta worldPtrL
bcc checkWorld
inc worldPtrH
checkWorld:
lda (worldPtrL), y ; load a world location
bne done ; if occupied, beam dies
jmp while ; keep going till beam dies
done:
rts
.endproc