Graphics Programming Black Book (Special Edition)

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Assembly Source File | 1997-06-18 | 18.4 KB | 396 lines

; *** Listing 20.4 *** ; ; Contains 3 C-callable routines: GenerateEOctant, DrawVOctant, and ; DrawHOctant. See individual routines for comments. ; ; Assembled with TASM 4.0. Link with L20-2.C and L20-3.C. ; Checked by Jim Mischel 11/30/94. ; ISVGA equ 0 ;set to 1 to use VGA write mode 3 ; keep synchronized with Listing 3 .model small .code ;******************************************************************** ; Generates an octant of the specified ellipse, placing the results in ; PixList, with a 0 in PixList meaning draw pixel & move only along ; major axis, and a 1 in PixList meaning draw pixel & move along both ; axes. ; C near-callable as: ; int GenerateEOctant(unsigned char *PixList, long MinorAdjust, ; long Threshold, long MajorSquared, long MinorSquared); ; ; Return value = PixelCount (# of points) ; ; Passed parameters: ; GenerateOctantParms struc dw ? ;pushed BP dw ? ;return address pushed by call PixList dw ? ;pointer to list to store draw control data in MinorAdjust dd ? ;initially MajorAxis**2 * 2 * MinorAxis, used ; to adjust threshold after minor axis move Threshold dd ? ;initially MajorAxis**2 / 4 + MajorAxis**2 * ; MinorAxis, used to determine when to advance ; along the minor axis MajorSquared dd ? ;MajorAxis**2 MinorSquared dd ? ;MinorAxis**2 GenerateOctantParms ends ; ; Local variables (offsets relative to BP in stack frame): ; PixelCount equ -2 ;running major axis coordinate ; relative to center MajorAdjust equ -6 ;used to adjust threshold after major ; axis move MajorSquaredTimes2 equ -10 ;MajorSquared * 2 MinorSquaredTimes2 equ -14 ;MinorSquared * 2 ; public _GenerateEOctant _GenerateEOctant proc near push bp ;preserve caller's stack frame mov bp,sp ;point to our stack frame add sp,MinorSquaredTimes2 ;allocate room for local vars push si ;preserve C register variables push di ;Initialize local variables. mov word ptr [bp+PixelCount],0 ;initialize count of pixels ; to zero mov ax,word ptr [bp+MajorSquared] ;set MajorSquaredTimes2 shl ax,1 ;lower word times 2 mov word ptr [bp+MajorSquaredTimes2],ax mov ax,word ptr [bp+MajorSquared+2] rcl ax,1 ;upper word times 2 mov word ptr [bp+MajorSquaredTimes2+2],ax mov ax,word ptr [bp+MinorSquared] ;set MinorSquaredTimes2 shl ax,1 ;lower word times 2 mov word ptr [bp+MinorSquaredTimes2],ax mov ax,word ptr [bp+MinorSquared+2] rcl ax,1 ;upper word times 2 mov word ptr [bp+MinorSquaredTimes2+2],ax ;Set up registers for loop. mov di,[PixList+bp] ;point DI to PixList ; Set MajorAdjust to 0. sub cx,cx mov si,cx ;SI:CX = MajorAdjust mov bx,word ptr [bp+Threshold] ;DX:BX = threshold mov dx,word ptr [bp+Threshold+2] ; At this point: ; DX:BX = threshold ; SI:CX = MajorAdjust ; DI = PixList pointer GenLoop: ; Advance the threshold by MajorAdjust + MinorAxis**2. add bx,cx adc dx,si add bx,word ptr [bp+MinorSquared] adc dx,word ptr [bp+MinorSquared+2] ; If the threshold has passed 0, then the minor coordinate has ; advanced more than halfway to the next pixel and it's time to ; advance the minor coordinate by 1 and set the next threshold ; accordingly. mov byte ptr [di],0 ;assume we won't move along the ; minor axis js MoveMajor ;and, in fact, we won't move minor ; Minor coordinate has advanced. ; Adjust the minor axis adjust value. mov ax,word ptr [bp+MajorSquaredTimes2] sub word ptr [bp+MinorAdjust],ax mov ax,word ptr [bp+MajorSquaredTimes2+2] sbb word ptr [bp+MinorAdjust+2],ax ; Adjust the threshold for the minor axis move sub bx,word ptr [bp+MinorAdjust] sbb dx,word ptr [bp+MinorAdjust+2] mov byte ptr [di],1 MoveMajor: inc di ; Count this point. inc word ptr [bp+PixelCount] ; Adjust the major adjust for the new point. add cx,word ptr [bp+MinorSquaredTimes2] adc si,word ptr [bp+MinorSquaredTimes2+2] ; Stop if the major axis has switched (the arc has passed the ; 45-degree point). cmp si,word ptr [bp+MinorAdjust+2] ja Done jb GenLoop cmp cx,word ptr [bp+MinorAdjust] jb GenLoop Done: mov ax,[bp+PixelCount] ;return # of points pop di ;restore C register variables pop si mov sp,bp ;deallocate local vars pop bp ;restore caller's stack frame ret _GenerateEOctant endp ;******************************************************************** ; Draws the arc for an octant in which Y is the major axis. (X,Y) is the ; starting point of the arc. HorizontalMoveDirection selects whether the ; arc advances to the left or right horizontally (0=left, 1=right). ; RowOffset contains the offset in bytes from one scan line to the next, ; controlling whether the arc is drawn up or down. DrawLength is the ; vertical length in pixels of the arc, and DrawList is a list ; containing 0 for each point if the next point is vertically aligned, ; and 1 if the next point is 1 pixel diagonally to the left or right. ; ; The Graphics Controller Index register must already point to the Bit ; Mask register. ; ; C near-callable as: ; void DrawVOctant(int X, int Y, int DrawLength, int RowOffset, ; int HorizontalMoveDirection, unsigned char *DrawList); ; DrawParms struc dw ? ;pushed BP dw ? ;return address X dw ? ;initial coordinates Y dw ? DrawLength dw ? ;vertical length RowOffset dw ? ;distance from one scan line to the next HorizontalMoveDirection dw ? ;1 to move right, 0 to move left DrawList dw ? ;pointer to list containing 1 to draw DrawParms ends ; diagonally, 0 to draw vertically for ; each point SCREEN_SEGMENT equ 0a000h ;display memory segment in mode 12h SCREEN_WIDTH_IN_BYTES equ 80 ;distance from one scan line to next GC_INDEX equ 3ceh ;GC Index register address ; public _DrawVOctant _DrawVOctant proc near push bp ;preserve caller's stack frame mov bp,sp ;point to our stack frame push si ;preserve C register variables push di ;Point ES:DI to the byte the initial pixel is in. mov ax,SCREEN_SEGMENT mov es,ax mov ax,SCREEN_WIDTH_IN_BYTES mul [bp+Y] ;Y*SCREEN_WIDTH_IN_BYTES mov di,[bp+X] ;X mov cx,di ;set X aside in CX shr di,1 shr di,1 shr di,1 ;X/8 add di,ax ;screen offset = Y*SCREEN_WIDTH_IN_BYTES+X/8 and cl,07h ;X modulo 8 if ISVGA ;---VGA--- mov ah,80h ;keep VGA bit mask in AH shr ah,cl ;initial bit mask = 80h shr (X modulo 8); cld ;for LODSB, used below else ;---EGA--- mov al,80h ;keep EGA bit mask in AL shr al,cl ;initial bit mask = 80h shr (X modulo 8); mov dx,GC_INDEX+1 ;point DX to GC Data reg/bit mask endif ;--------- mov si,[bp+DrawList] ;SI points to list to draw from sub bx,bx ;so we have the constant 0 in a reg mov cx,[bp+DrawLength] ;CX=# of pixels to draw jcxz VDrawDone ;skip this if no pixels to draw cmp [bp+HorizontalMoveDirection],0 ;draw right or left mov bp,[bp+RowOffset] ;BP=offset to next row jz VGoLeft ;draw from right to left VDrawRightLoop: ;draw from left to right if ISVGA ;---VGA--- and es:[di],ah ;AH becomes bit mask in write mode 3, ; set/reset provides color lodsb ;get next draw control byte and al,al ;move right? jz VAdvanceOneLineRight ;no move right ror ah,1 ;move right else ;---EGA--- out dx,al ;set the desired bit mask and es:[di],al ;data doesn't matter (set/reset provides ; color); just force read then write cmp [si],bl ;check draw control byte; move right? jz VAdvanceOneLineRight ;no move right ror al,1 ;move right endif ;--------- adc di,bx ;move one byte to the right if mask wrapped VAdvanceOneLineRight: ife ISVGA ;---EGA--- inc si ;advance draw control list pointer endif ;--------- add di,bp ;move to the next scan line up or down loop VDrawRightLoop ;do next pixel, if any jmp short VDrawDone ;done VGoLeft: ;draw from right to left VDrawLeftLoop: if ISVGA ;---VGA--- and es:[di],ah ;AH becomes bit mask in write mode 3 lodsb ;get next draw control byte and al,al ;move left? jz VAdvanceOneLineLeft ;no move left rol ah,1 ;move left else ;---EGA--- out dx,al ;set the desired bit mask and es:[di],al ;data doesn't matter; force read/write cmp [si],bl ;check draw control byte; move left? jz VAdvanceOneLineLeft ;no move left rol al,1 ;move left endif ;--------- sbb di,bx ;move one byte to the left if mask wrapped VAdvanceOneLineLeft: ife ISVGA ;---EGA--- inc si ;advance draw control list pointer endif ;--------- add di,bp ;move to the next scan line up or down loop VDrawLeftLoop ;do next pixel, if any VDrawDone: pop di ;restore C register variables pop si pop bp ret _DrawVOctant endp ;******************************************************************** ; Draws the arc for an octant in which X is the major axis. (X,Y) is the ; starting point of the arc. HorizontalMoveDirection selects whether the ; arc advances to the left or right horizontally (0=left, 1=right). ; RowOffset contains the offset in bytes from one scan line to the next, ; controlling whether the arc is drawn up or down. DrawLength is the ; horizontal length in pixels of the arc, and DrawList is a list ; containing 0 for each point if the next point is horizontally aligned, ; and 1 if the next point is 1 pixel above or below diagonally. ; ; Graphics Controller Index register must already point to the Bit Mask ; register. ; ; C near-callable as: ; void DrawHOctant(int X, int Y, int DrawLength, int RowOffset, ; int HorizontalMoveDirection, unsigned char *DrawList) ; ; Uses same parameter structure as DrawVOctant(). ; public _DrawHOctant _DrawHOctant proc near push bp ;preserve caller's stack frame mov bp,sp ;point to our stack frame push si ;preserve C register variables push di ;Point ES:DI to the byte the initial pixel is in. mov ax,SCREEN_SEGMENT mov es,ax mov ax,SCREEN_WIDTH_IN_BYTES mul [bp+Y] ;Y*SCREEN_WIDTH_IN_BYTES mov di,[bp+X] ;X mov cx,di ;set X aside in CX shr di,1 shr di,1 shr di,1 ;X/8 add di,ax ;screen offset = Y*SCREEN_WIDTH_IN_BYTES+X/8 and cl,07h ;X modulo 8 mov bh,80h shr bh,cl ;initial bit mask = 80h shr (X modulo 8); if ISVGA ;---VGA--- cld ;for LODSB, used below else ;---EGA--- mov dx,GC_INDEX+1 ;point DX to GC Data reg/bit mask endif ;--------- mov si,[bp+DrawList] ;SI points to list to draw from sub bl,bl ;so we have the constant 0 in a reg mov cx,[bp+DrawLength] ;CX=# of pixels to draw jcxz HDrawDone ;skip this if no pixels to draw if ISVGA ;---VGA--- sub ah,ah ;clear bit mask accumulator else ;---EGA--- sub al,al ;clear bit mask accumulator endif ;--------- cmp [bp+HorizontalMoveDirection],0 ;draw right or left mov bp,[bp+RowOffset] ;BP=offset to next row jz HGoLeft ;draw from right to left HDrawRightLoop: ;draw from left to right if ISVGA ;---VGA--- or ah,bh ;put this pixel in bit mask accumulator lodsb ;get next draw control byte and al,al ;move up/down? else ;---EGA--- or al,bh ;put this pixel in bit mask accumulator cmp [si],bl ;check draw control byte; move up/down? endif ;--------- jz HAdvanceOneLineRight ;no move up/down ;move up/down; first draw accumulated pixels if ISVGA ;---VGA--- and es:[di],ah ;AH becomes bit mask in write mode 3 sub ah,ah ;clear bit mask accumulator else ;---EGA--- out dx,al ;set the desired bit mask and es:[di],al ;data doesn't matter; force read/write sub al,al ;clear bit mask accumulator endif ;--------- add di,bp ;move to the next scan line up or down HAdvanceOneLineRight: ife ISVGA ;---EGA--- inc si ;advance draw control list pointer endif ;--------- ror bh,1 ;move to right; shift mask jnc HDrawLoopRightBottom ;didn't wrap to the next byte ;move to next byte; 1st draw accumulated pixels if ISVGA ;---VGA--- and es:[di],ah ;AH becomes bit mask in write mode 3 sub ah,ah ;clear bit mask accumulator else out dx,al ;set the desired bit mask and es:[di],al ;data doesn't matter; force read/write sub al,al ;clear bit mask accumulator endif ;--------- inc di ;move 1 byte to the right HDrawLoopRightBottom: loop HDrawRightLoop ;draw next pixel, if any jmp short HDrawDone ;done HGoLeft: ;draw from right to left HDrawLeftLoop: if ISVGA ;---VGA--- or ah,bh ;put this pixel in bit mask accumulator lodsb ;get next draw control byte and al,al ;move up/down? else ;---EGA--- or al,bh ;put this pixel in bit mask accumulator cmp [si],bl ;check draw control byte; move up/down? endif ;--------- jz HAdvanceOneLineLeft ;no move up/down ;move up/down; first draw accumulated pixels if ISVGA ;---VGA--- and es:[di],ah ;AH becomes bit mask in write mode 3 sub ah,ah ;clear bit mask accumulator else ;---EGA--- out dx,al ;set the desired bit mask and es:[di],al ;data doesn't matter; force read/write sub al,al ;clear bit mask accumulator endif ;--------- add di,bp ;move to the next scan line up or down HAdvanceOneLineLeft: ife ISVGA ;---EGA--- inc si ;advance draw control list pointer endif ;--------- rol bh,1 ;move to left; shift mask jnc HDrawLoopLeftBottom ;didn't wrap to next byte ;move to next byte; 1st draw accumulated pixels if ISVGA ;---VGA--- and es:[di],ah ;AH becomes bit mask in write mode 3 sub ah,ah ;clear bit mask accumulator else ;---EGA--- out dx,al ;set the desired bit mask and es:[di],al ;data doesn't matter; force read/write sub al,al ;clear bit mask accumulator endif ;--------- dec di ;move 1 byte to the left HDrawLoopLeftBottom: loop HDrawLeftLoop ;draw next pixel, if any HDrawDone: ;draw any remaining accumulated pixels if ISVGA ;---VGA--- and es:[di],ah ;AH becomes bit mask in write mode 3 else ;---EGA--- out dx,al ;set the desired bit mask and es:[di],al ;data doesn't matter; force read/write endif ;--------- pop di ;restore C register variables pop si pop bp ret _DrawHOctant endp end