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Added some comments

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alpine9000
2016-03-29 16:01:59 +11:00
parent a1106476d9
commit 17f2b81f87
1 changed files with 32 additions and 33 deletions
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024.simple_text/blittext.s
+32 -33
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@@ -11,30 +11,31 @@ DrawText8:
;; d0 - xpos
;; d1 - ypos
movem.l d0-d7/a0-a4,-(sp)
WaitBlitter
WaitBlitter
;; blitter config that is shared for every character
move.w #SCREEN_WIDTH_BYTES-BLIT_WIDTH_BYTES,BLTAMOD(a6) ; A modulo
if MASKED_FONT==1
move.w #BLIT_SRCA|BLIT_SRCB|BLIT_SRCC|BLIT_DEST|BLIT_LF_MINTERM,d6 ; BLTCON0 value (masked version)
move.w #SCREEN_WIDTH_BYTES-BLIT_WIDTH_BYTES,BLTAMOD(a6) ; A modulo (only used for masked version)
else
move.w #BLIT_SRCB|BLIT_SRCC|BLIT_DEST|BLIT_LF_MINTERM,d6 ; BLTCON0 value
endif
move.w #SCREEN_WIDTH_BYTES-BLIT_WIDTH_BYTES,BLTBMOD(a6) ; B modulo
move.w #SCREEN_WIDTH_BYTES-BLIT_WIDTH_BYTES,BLTCMOD(a6) ; C modulo
move.w #SCREEN_WIDTH_BYTES-BLIT_WIDTH_BYTES,BLTDMOD(a6) ; D modulo
mulu.w #SCREEN_WIDTH_BYTES*SCREEN_BIT_DEPTH,d1 ; ypos bytes
move.w #$0000,BLTALWM(a6) ; mask out extra word used for shifting
move.w #$ffff,BLTADAT(a6) ; preload source mask so only BLTA?WM mask is used
move.l a1,a3
move.l #font,a5
move.l #fontMask,d7
move.w #SCREEN_WIDTH_BYTES*SCREEN_BIT_DEPTH*FONT_HEIGHT,d3
if MASKED_FONT==1
move.w #BLIT_SRCA|BLIT_SRCB|BLIT_SRCC|BLIT_DEST|BLIT_LF_MINTERM,d6
else
move.w #BLIT_SRCB|BLIT_SRCC|BLIT_DEST|BLIT_LF_MINTERM,d6
endif
move.w #$0000,BLTALWM(a6) ; mask out extra word used for shifting
move.w #$ffff,BLTADAT(a6) ; preload source mask so only BLTA?WM mask is used
move.l a1,a3 ; character pointer
move.l #font,a5 ; font pointer
move.l #fontMask,d7 ; font mask pointer
move.w #SCREEN_WIDTH_BYTES*SCREEN_BIT_DEPTH*FONT_HEIGHT,d3 ; bytes per font line
.loop:
clr.l d2
move.b (a3)+,d2 ; get next character
cmp.b #0,d2 ; 0 terminates the string
beq .done
move.l a0,a4
move.l a0,a4 ; bitplane pointer
bsr DrawChar8 ; draw it
add.w #FONT_WIDTH,d0 ; increment the x position
bra .loop
@@ -44,16 +45,15 @@ DrawText8:
DrawChar8:
;; kills d2,d4,d5,a1,a2,a4
;; d0 - xpos
;; d1 - ypos bytes
;; d2 - char
;; d3 - bytes per font line
;; d6 - bplcon0 value
;; a4 - bitplane
;; a5 - #font
;; d7 - #fontMask
;; d0 - xpos
;; d1 - ypos bytes
;; d2* - char
;; d3 - bytes per font line
;; d6 - bltcon0 value
;; a4* - bitplane
;; a5 - #font
;; d7 - #fontMask
;; calculating the font offset will be simplier when we have a less weird font image
sub.w #'!',d2 ; index = char - '!'
move.w d2,d5
@@ -83,24 +83,23 @@ DrawChar8:
;; d1 - ypos bytes
;; d2.0 - odd character = 1, even character = 0
;; d3 - bytes per font line
;; d6 - bplcon0 value
;; d6 - bltcon0 value
;; a4 - display
;; a1 - object
;; a2 - mask
move.l d0,d4
move.l d0,d5
lsr.w #3,d4 ; d4 = XPOS_BYTES
move.l d0,d4 ; xpos
move.l d0,d5 ; xpos
lsr.w #3,d4 ; d4 = xpos bytes
WaitBlitter
btst #0,d2
beq .evenChar
btst #0,d2 ; check if odd or even char
beq .evenChar ;
.oddChar
subq #8,d5 ; offset the x position for the odd character
move.w #$00FF,BLTAFWM(a6) ; select the second (odd) character in the word
subq #1,a4
subq #1,a4 ; move the destination pointer left by one byte
bra .continue
.evenChar:
move.w #$FF00,BLTAFWM(a6) ; select the first character in the word
@@ -108,9 +107,9 @@ DrawChar8:
;; this shift will give us the bits to shift (bits 0-3) in bits (12-15) of d5
swap d5 ; d5 << 12
lsr.l #4,d5
lsr.l #4,d5 ;
move.w d5,BLTCON1(A6)
move.w d5,BLTCON1(A6) ; set the shift bits 12-15, bits 00-11 cleared
if MASKED_FONT==1
move.l a2,BLTAPTH(a6) ; mask bitplane