Misc/abrash-black-book
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James Gregory 2013-12-30 18:34:31 +11:00
commit 18011c595a
352 changed files with 6040 additions and 6040 deletions
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18
50-03.md
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@ -5,7 +5,7 @@
**LISTING 50.1 L50-1.ASM**
; Draws all pixels in the list of horizontal lines passed in, in
; Mode X, the VGA’s undocumented 320x240 256-color mode. Clips to
; Mode X, the VGA's undocumented 320x240 256-color mode. Clips to
; the rectangle specified by (ClipMinX,ClipMinY),(ClipMaxX,ClipMaxY).
; Draws to the page specified by CurrentPageBase.
; C near-callable as:
@ -50,9 +50,9 @@
public _DrawHorizontalLineList
align 2
_DrawHorizontalLineList proc
push bp ;preserve caller’s stack frame
push bp ;preserve caller's stack frame
mov bp,sp ;point to our stack frame
push si ;preserve caller’s register variables
push si ;preserve caller's register variables
push di
cld ;make string instructions inc pointers
mov dx,SC_INDEX
@ -66,7 +66,7 @@
mov cx,[si+YStart] ;first scan line to draw
mov si,[si+Lngth] ;# of scan lines to draw
cmp si,0 ;are there any lines to draw?
jle ToFillDone ;no, so we’re done
jle ToFillDone ;no, so we're done
cmp cx,[_ClipMinY] ;clipped at top?
jge MinYNotClipped ;no
neg cx ;yes, discard however many lines are
@ -122,8 +122,8 @@
sub cx,dx
shr cx,1
shr cx,1 ;# of addresses across rectangle to fill - 1
jnz MasksSet ;there’s more than one byte to draw
and bh,bl ;there’s only one byte, so combine the left
jnz MasksSet ;there's more than one byte to draw
and bh,bl ;there's only one byte, so combine the left
; and right edge clip masks
MasksSet:
mov dx,SC_INDEX+1 ;already points to the Map Mask reg
@ -133,7 +133,7 @@
mov al,ah ;put color in AL
stosb ;draw the left edge
dec cx ;count off left edge byte
js FillLoopBottom ;that’s the only byte
js FillLoopBottom ;that's the only byte
jz DoRightEdge ;there are only two bytes
mov al,00fh ;middle addresses are drawn 4 pixels at a pop
out dx,al ;set the middle pixel mask to no clip
@ -154,9 +154,9 @@
dec si ;count down lines
jnz FillLoop
FillDone:
pop di ;restore caller’s register variables
pop di ;restore caller's register variables
pop si
pop bp ;restore caller’s stack frame
pop bp ;restore caller's stack frame
ret
_DrawHorizontalLineList endp
end