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Improved tunnel trimming

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The old method used a mix of black attributes and data masking to trim sprites at the screen edges, with every sprite trimmed separately.

The new method no longer uses attributes, so it's compatible with the colour version.  It also finds the extent of the trim block for all sprites, for more efficient clearing.
This commit is contained in:
Simon Owen
2012-01-08 01:44:59 +00:00
parent a7cfef97b2
commit eba439a3ba
1 changed files with 62 additions and 40 deletions
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102
pacemuzx.asm
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@ -1589,65 +1589,87 @@ ENDIF
; Trim sprites that overlap the maze edges, as the real hardware does automatically
; Here we trim partial bytes, as full blocks are hidden behind black on black attrs
;
do_trim: ld de,&5062 ; start of sprite data
ld b,&07 ; 7 sprites to check
do_trim: ld hl,&5062 ; sprite x for first sprite
ld de,&ff00 ; no trim yet
ld b,7 ; 7 sprites to check
trim_lp: ld a,(de) ; sprite x
inc e
cp &10 ; hidden sprite?
jr c,no_trim
trim_lp: ld a,(hl) ; sprite x
inc l
cp &10 ; hidden?
jr c,trim_next
cp &20 ; clipped at right edge?
jr c,may_trim
cp &f0 ; clipped at left edge?
jr nc,may_trim
no_trim: inc e
jr c,trim_next
may_trim: ld a,(hl) ; sprite y
cp &10 ; hidden?
jr c,trim_next
cp d ; compare min
jr nc,no_trim_min
ld d,a ; update min
no_trim_min: cp e ; compare max
jr c,trim_next
ld e,a ; update max
jr trim_next
trim_next: inc l ; skip sprite y
djnz trim_lp
ret
may_trim: ld a,(de) ; sprite y
cp &10 ; hidden sprite?
jr c,no_trim
ld a,e ; max
and a
jp z,page_rom ; zero means no trim
sub d ; subtract min to give block
add a,12 ; add sprite height to give span
ld b,a ; line count for trim
ld e,12 ; height of sprite
ld hl,&4f45 ; left of tunnel
cp &8c ; sprite y for tunnel?
jr z,trim_edge
ld e,24 ; height of 2 sprites
ld hl,&4d65 ; left of intermission row
trim_edge:
ld a,h
or ixh ; offset to current screen
ld l,e ; top line, due to mirrored y!
ld h,conv_y/256
ld l,(hl) ; convert y to Speccy line
ld h,scradtab/256
ld c,(hl) ; LSB of line start
inc h
ld a,(hl) ; MSB of line start
add a,ixh ; current screen offset
ld h,a
ld l,c
ld a,%00000100 ; +3 normal paging, R3/5/2/7
ld bc,&1ffd
out (c),a ; normal paging (screen)
call page_screen
ld b,e ; line count
ld de,&03fc ; masks for below
ld de,&0300 ; D=left mask, E=clear byte
trim_r_lp: ld c,l ; save line start LSB
trim_line_lp: ld a,(hl)
and d ; clear 6 pixels
ld (hl),a
ld c,l
ld a,l
add a,&15 ; advance to right edge
ld a,c
add a,4
ld l,a
ld (hl),e ; full byte to trim 6 pixels
inc l
ld a,(hl)
and e ; clear 2 pixels
and d ; trim 6 pixels at maze left
ld (hl),a
ld l,c ; restore left position
ld a,c
add a,26 ; right tunnel offset
ld l,a
ld a,(hl)
and &fc ; trim 2 pixels at maze right
ld (hl),a
inc l
ld (hl),e ; full byte
inc l
ld (hl),e ; full byte for final 2 pixels
ld l,c ; restore original LSB
inc h ; next line
ld a,h
and %00000111
call z,blockdown_hl
djnz trim_line_lp
ld a,%00000001 ; +3 special paging, banks 0/1/2/3
ld bc,&1ffd
out (c),a ; page ROM
ret
djnz trim_r_lp
jp page_rom
; Clear a sprite-sized hole, used for blank tiles in our fruit and lives display