Replace invalid characters with HTML entities
— with — ’ with ’ + with + × with x ç with ç “ with “ ” with ” ‘ with ‘ • with • – with - µ with µ † with † Fix C++ θ with θ Yen symbol instead of times Fix broken apos Bullet again E-circumflex
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James Gregory
parent
9e52de9586
commit
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353 changed files with 5091 additions and 5091 deletions
68
39-05.html
68
39-05.html
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@ -40,7 +40,7 @@
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<!-- CODE //-->
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<PRE>
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; Scan converts an edge from (X1,Y1) to (X2,Y2), not including the
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; point at (X2,Y2). If SkipFirst == 1, the point at (X1,Y1) isn’t
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; point at (X2,Y2). If SkipFirst == 1, the point at (X1,Y1) isn’t
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; drawn; if SkipFirst == 0, it is. For each scan line, the pixel
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; closest to the scanned edge without being to the left of the scanned
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; edge is chosen. Uses an all-integer approach for speed & precision.
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@ -81,54 +81,54 @@ LOCAL_SIZE equ 4 ;total size of local variables
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public _ScanEdge
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align 2
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_ScanEdge proc
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push bp ;preserve caller’s stack frame
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push bp ;preserve caller’s stack frame
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mov bp,sp ;point to our stack frame
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sub sp,LOCAL_SIZE ;allocate space for local variables
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push si ;preserve caller’s register variables
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push si ;preserve caller’s register variables
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push di
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mov di,[bp+EdgePointPtr]
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mov di,[bp+EdgePointPtr]
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mov di,[di] ;point to the HLine array
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cmp [bp+SetXStart],1 ;set the XStart field of each HLine
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cmp [bp+SetXStart],1 ;set the XStart field of each HLine
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; struc?
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jz HLinePtrSet ;yes, DI points to the first XStart
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add di,XEnd ;no, point to the XEnd field of the
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; first HLine struc
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HLinePtrSet:
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mov bx,[bp+Y2]
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sub bx,[bp+Y1] ;edge height
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mov bx,[bp+Y2]
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sub bx,[bp+Y1] ;edge height
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jle ToScanEdgeExit ;guard against 0-length & horz edges
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mov [bp+Height],bx ;Height = Y2 - Y1
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mov [bp+Height],bx ;Height = Y2 - Y1
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sub cx,cx ;assume ErrorTerm starts at 0 (true if
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; we’re moving right as we draw)
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; we’re moving right as we draw)
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mov dx,1 ;assume AdvanceAmt = 1 (move right)
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mov ax,[bp+X2]
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sub ax,[bp+X1] ;DeltaX = X2 - X1
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jz IsVertical ;it’s a vertical edge--special case it
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mov ax,[bp+X2]
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sub ax,[bp+X1] ;DeltaX = X2 - X1
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jz IsVertical ;it’s a vertical edge--special case it
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jns SetAdvanceAmt ;DeltaX >= 0
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mov cx,1 ;DeltaX < 0 (move left as we draw)
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sub cx,bx ;ErrorTerm = -Height + 1
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sub cx,bx ;ErrorTerm = -Height + 1
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neg dx ;AdvanceAmt = -1 (move left)
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neg ax ;Width = abs(DeltaX)
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SetAdvanceAmt:
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mov [bp+AdvanceAmt],dx
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mov [bp+AdvanceAmt],dx
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; Figure out whether the edge is diagonal, X-major (more horizontal),
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; or Y-major (more vertical) and handle appropriately.
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cmp ax,bx ;if Width==Height, it’s a diagonal edge
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jz IsDiagonal ;it’s a diagonal edge--special case
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jb YMajor ;it’s a Y-major (more vertical) edge
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;it’s an X-major (more horz) edge
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cmp ax,bx ;if Width==Height, it’s a diagonal edge
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jz IsDiagonal ;it’s a diagonal edge--special case
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jb YMajor ;it’s a Y-major (more vertical) edge
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;it’s an X-major (more horz) edge
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sub dx,dx ;prepare DX:AX (Width) for division
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div bx ;Width/Height
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;DX = error term advance per scan line
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mov si,ax ;SI = minimum # of pixels to advance X
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; on each scan line
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test [bp+AdvanceAmt],8000h ;move left or right?
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test [bp+AdvanceAmt],8000h ;move left or right?
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jz XMajorAdvanceAmtSet ;right, already set
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neg si ;left, negate the distance to advance
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; on each scan line
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XMajorAdvanceAmtSet: ;
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mov ax,[bp+X1] ;starting X coordinate
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cmp [bp+SkipFirst],1 ;skip the first point?
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mov ax,[bp+X1] ;starting X coordinate
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cmp [bp+SkipFirst],1 ;skip the first point?
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jz XMajorSkipEntry ;yes
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XMajorLoop:
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mov [di],ax ;store the current X value
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@ -138,8 +138,8 @@ XMajorSkipEntry:
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add cx,dx ;advance error term
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jle XMajorNoAdvance ;not time for X coord to advance one
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; extra
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add ax,[bp+AdvanceAmt] ;advance X coord one extra
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sub cx,[bp+Height] ;adjust error term back
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add ax,[bp+AdvanceAmt] ;advance X coord one extra
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sub cx,[bp+Height] ;adjust error term back
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XMajorNoAdvance:
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dec bx ;count off this scan line
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jnz XMajorLoop
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@ -149,8 +149,8 @@ ToScanEdgeExit:
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jmp ScanEdgeExit
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align2
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IsVertical:
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mov ax,[bp+X1] ;starting (and only) X coordinate
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sub bx,[bp+SkipFirst] ;loop count = Height - SkipFirst
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mov ax,[bp+X1] ;starting (and only) X coordinate
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sub bx,[bp+SkipFirst] ;loop count = Height - SkipFirst
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jz ScanEdgeExit ;no scan lines left after skipping 1st
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VerticalLoop:
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mov [di],ax ;store the current X value
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@ -160,8 +160,8 @@ VerticalLoop:
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jmp ScanEdgeDone
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align 2
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IsDiagonal:
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mov ax,[bp+X1] ;starting X coordinate
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cmp [bp+SkipFirst],1 ;skip the first point?
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mov ax,[bp+X1] ;starting X coordinate
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cmp [bp+SkipFirst],1 ;skip the first point?
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jz DiagonalSkipEntry ;yes
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DiagonalLoop:
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mov [di],ax ;store the current X value
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@ -174,8 +174,8 @@ DiagonalSkipEntry:
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align 2
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YMajor:
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pushbp ;preserve stack frame pointer
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mov si,[bp+X1] ;starting X coordinate
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cmp [bp+SkipFirst],1 ;skip the first point?
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mov si,[bp+X1] ;starting X coordinate
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cmp [bp+SkipFirst],1 ;skip the first point?
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mov bp,bx ;put Height in BP for error term calcs
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jz YMajorSkipEntry ;yes, skip the first point
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YMajorLoop:
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@ -191,17 +191,17 @@ YMajorNoAdvance:
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jnz YMajorLoop
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popbp ;restore stack frame pointer
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ScanEdgeDone:
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cmp [bp+SetXStart],1 ;were we working with XStart field?
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cmp [bp+SetXStart],1 ;were we working with XStart field?
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jz UpdateHLinePtr ;yes, DI points to the next XStart
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sub di,XEnd ;no, point back to the XStart field
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UpdateHLinePtr:
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mov bx,[bp+EdgePointPtr] ;point to pointer to HLine array
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mov [bx],di ;update caller’s HLine array pointer
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mov bx,[bp+EdgePointPtr] ;point to pointer to HLine array
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mov [bx],di ;update caller’s HLine array pointer
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ScanEdgeExit:
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pop di ;restore caller’s register variables
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pop di ;restore caller’s register variables
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pop si
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mov sp,bp ;deallocate local variables
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pop bp ;restore caller’s stack frame
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pop bp ;restore caller’s stack frame
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ret
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_ScanEdge endp
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end
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