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This commit is contained in:
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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24
39-05.md
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@ -5,7 +5,7 @@
**LISTING 39.4 L39-4.ASM**
; Scan converts an edge from (X1,Y1) to (X2,Y2), not including the
; point at (X2,Y2). If SkipFirst == 1, the point at (X1,Y1) isn’t
; point at (X2,Y2). If SkipFirst == 1, the point at (X1,Y1) isn't
; drawn; if SkipFirst == 0, it is. For each scan line, the pixel
; closest to the scanned edge without being to the left of the scanned
; edge is chosen. Uses an all-integer approach for speed & precision.
@ -46,10 +46,10 @@
public _ScanEdge
align 2
_ScanEdge proc
push bp ;preserve caller’s stack frame
push bp ;preserve caller's stack frame
mov bp,sp ;point to our stack frame
sub sp,LOCAL_SIZE ;allocate space for local variables
push si ;preserve caller’s register variables
push si ;preserve caller's register variables
push di
mov di,[bp+EdgePointPtr]
mov di,[di] ;point to the HLine array
@ -64,11 +64,11 @@
jle ToScanEdgeExit ;guard against 0-length & horz edges
mov [bp+Height],bx ;Height = Y2 - Y1
sub cx,cx ;assume ErrorTerm starts at 0 (true if
; we’re moving right as we draw)
; we're moving right as we draw)
mov dx,1 ;assume AdvanceAmt = 1 (move right)
mov ax,[bp+X2]
sub ax,[bp+X1] ;DeltaX = X2 - X1
jz IsVertical ;it’s a vertical edge--special case it
jz IsVertical ;it's a vertical edge--special case it
jns SetAdvanceAmt ;DeltaX >= 0
mov cx,1 ;DeltaX < 0 (move left as we draw)
sub cx,bx ;ErrorTerm = -Height + 1
@ -78,10 +78,10 @@
mov [bp+AdvanceAmt],dx
; Figure out whether the edge is diagonal, X-major (more horizontal),
; or Y-major (more vertical) and handle appropriately.
cmp ax,bx ;if Width==Height, it’s a diagonal edge
jz IsDiagonal ;it’s a diagonal edge--special case
jb YMajor ;it’s a Y-major (more vertical) edge
;it’s an X-major (more horz) edge
cmp ax,bx ;if Width==Height, it's a diagonal edge
jz IsDiagonal ;it's a diagonal edge--special case
jb YMajor ;it's a Y-major (more vertical) edge
;it's an X-major (more horz) edge
sub dx,dx ;prepare DX:AX (Width) for division
div bx ;Width/Height
;DX = error term advance per scan line
@ -161,12 +161,12 @@
sub di,XEnd ;no, point back to the XStart field
UpdateHLinePtr:
mov bx,[bp+EdgePointPtr] ;point to pointer to HLine array
mov [bx],di ;update caller’s HLine array pointer
mov [bx],di ;update caller's HLine array pointer
ScanEdgeExit:
pop di ;restore caller’s register variables
pop di ;restore caller's register variables
pop si
mov sp,bp ;deallocate local variables
pop bp ;restore caller’s stack frame
pop bp ;restore caller's stack frame
ret
_ScanEdge endp
end