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Assembly Source File | 1994-09-18 | 22.3 KB | 502 lines

; Draws all pixels in the specified column, with the pixel colors ; taken from the specified texture map. Uses approach of pre-stepping ; 1/2 pixel into the source image and rounding to the nearest source ; pixel at each step, so that texture maps will appear reasonably similar ; at all angles. This routine is specific to 320-pixel-wide planar ; (non-Chain4) 256-color modes, such as mode X, which is a planar ; (non-chain4) 256-color mode with a resolution of 320x240. ; ; SS must == DS so that the texture map can be accessed via SS:BP. ; ; C near-callable as: ; void ScanOutLine(EdgeScan * TopEdge, EdgeScan * BottomEdge); ; ; Tested with TASM 3.0. ; SC_INDEX equ 03c4h ;Sequence Controller Index MAP_MASK equ 02h ;index in SC of Map Mask register SCREEN_SEG equ 0a000h ;segment of display memory in mode X SCREEN_WIDTH equ 80 ;width of screen in bytes from one scan line ; to the next .model small .386 .data extrn _TexMapBits:word, _TexMapWidth:word, _DestX:word extrn _CurrentPageBase:word, _ClipMinX:word extrn _ClipMinY:word, _ClipMaxX:word, _ClipMaxY:word ; Describes the current location and stepping, in both the source and ; the destination, of an edge. Mirrors structure in DRAWTEXP.C. EdgeScan struc Direction dw ? ;through edge list; 1 for a right edge (forward ; through vertex list), -1 for a left edge (backward ; through vertex list) RemainingScans dw ? ;height left to scan out in dest CurrentEnd dw ? ;vertex # of end of current edge SourceX dd ? ;X location in source for this edge SourceY dd ? ;Y location in source for this edge SourceStepX dd ? ;X step in source for Y step in dest of 1 SourceStepY dd ? ;Y step in source for Y step in dest of 1 ;variables used for all-integer Bresenham's-type ; X stepping through the dest, needed for precise ; pixel placement to avoid gaps DestY dw ? ;current Y location in dest for this edge DestYIntStep dw ? ;whole part of dest Y step per column X step DestYDirection dw ? ;-1 or 1 to indicate which way Y steps (left/right) DestYErrTerm dw ? ;current error term for dest Y stepping DestYAdjUp dw ? ;amount to add to error term per scan line move DestYAdjDown dw ? ;amount to subtract from error term when the ; error term turns over EdgeScan ends Parms struc dw 2 dup(?) ;return address & pushed BP TopEdge dw ? ;pointer to EdgeScan structure for left edge BottomEdge dw ? ;pointer to EdgeScan structure for right edge Parms ends ;Offsets from BP in stack frame of local variables. lSourceX equ -4 ;current X coordinate in source image lSourceY equ -8 ;current Y coordinate in source image lSourceStepX equ -12 ;X step in source image for X dest step of 1 lSourceStepY equ -16 ;Y step in source image for X dest step of 1 lXAdvanceByOne equ -18 ;used to step source pointer 1 pixel ; incrementally in X lBaseAdvance equ -20 ;use to step source pointer minimum number of ; pixels incrementally in X+Y simultaneously lYAdvanceByOne equ -22 ;used to step source pointer 1 pixel ; incrementally in Y LOCAL_SIZE equ 22 ;total size of local variables .code extrn _FixedMul:near, _FixedDiv:near align 2 ToScanDone: jmp ScanDone public _ScanOutLine align 2 _ScanOutLine proc near 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 di ; Nothing to do if destination is fully Y clipped. mov di,[bp].BottomEdge mov si,[di].DestY cmp si,[_ClipMinY] jle short ToScanDone ;bottom edge is to left of clip rect, so done mov bx,[bp].TopEdge mov dx,[bx].DestY cmp dx,[_ClipMaxY] jge short ToScanDone ;top edge is to right of clip rect, so done sub si,dx ;destination fill height jle short ToScanDone ;null or negative full height, so done mov ax,word ptr [bx].SourceX ;initial source X coordinate mov word ptr [bp].lSourceX,ax mov ax,word ptr [bx].SourceX+2 mov word ptr [bp].lSourceX+2,ax mov ax,word ptr [bx].SourceY ;initial source Y coordinate mov word ptr [bp].lSourceY,ax mov ax,word ptr [bx].SourceY+2 mov word ptr [bp].lSourceY+2,ax ; Calculate source steps that correspond to each 1-pixel destination X step ; (across the destination scan line). push si ;push dest Y height, in fixedpoint form sub ax,ax push ax ;push 0 as fractional part of dest Y height mov ax,word ptr [di].SourceX sub ax,word ptr [bp].lSourceX ;low word of source X width mov dx,word ptr [di].SourceX+2 sbb dx,word ptr [bp].lSourceX+2 ;high word of source X width push dx ;push source X width, in fixedpoint form push ax call _FixedDiv ;scale source X width to dest Y height add sp,8 ;clear parameters from stack mov word ptr [bp].lSourceStepX,ax ;remember source X step for mov word ptr [bp].lSourceStepX+2,dx ; 1-pixel destination Y height mov cx,1 ;assume source X advances non-negative and dx,dx ;which way does source X advance? jns short SourceXNonNeg ;non-negative neg cx ;negative cmp ax,0 ;is the whole step exactly an integer? jz short SourceXNonNeg ;yes inc dx ;no, truncate to integer in the direction of ; 0, because otherwise we'll end up with a ; whole step of 1-too-large magnitude SourceXNonNeg: mov [bp].lXAdvanceByOne,cx ;amount to add to source pointer to ; move by one in X mov [bp].lBaseAdvance,dx ;minimum amount to add to source ; pointer to advance in X each time ; the dest advances one in Y push si ;push dest Y height, in fixedpoint form sub ax,ax push ax ;push 0 as fractional part of dest Y height mov ax,word ptr [di].SourceY sub ax,word ptr [bp].lSourceY ;low word of source Y height mov dx,word ptr [di].SourceY+2 sbb dx,word ptr [bp].lSourceY+2 ;high word of source Y height push dx ;push source Y height, in fixedpoint form push ax call _FixedDiv ;scale source Y height to dest Y height add sp,8 ;clear parameters from stack mov word ptr [bp].lSourceStepY,ax ;remember source Y step for mov word ptr [bp].lSourceStepY+2,dx ; 1-pixel destination X step mov cx,[_TexMapWidth] ;assume source Y advances non-negative and dx,dx ;which way does source Y advance? jns short SourceYNonNeg ;non-negative neg cx ;negative cmp ax,0 ;is the whole step exactly an integer? jz short SourceYNonNeg ;yes inc dx ;no, truncate to integer in the direction of ; 0, because otherwise we'll end up with a ; whole step of 1-too-large magnitude SourceYNonNeg: mov [bp].lYAdvanceByOne,cx ;amount to add to source pointer to ; move by one in Y mov ax,[_TexMapWidth] ;minimum distance skipped in source imul dx ; image bitmap when Y steps (ignoring add [bp].lBaseAdvance,ax ; carry from the fractional part); ; add into total minimum source ; advance amount ; Advance 1/2 step in the stepping direction, to space scanned pixels evenly ; between the left and right edges. (There's a slight inaccuracy in dividing ; negative numbers by 2 by shifting rather than dividing, but the inaccuracy ; is in the least significant bit, and we'll just live with it.) mov ax,word ptr [bp].lSourceStepX mov dx,word ptr [bp].lSourceStepX+2 sar dx,1 rcr ax,1 add word ptr [bp].lSourceX,ax adc word ptr [bp].lSourceX+2,dx mov ax,word ptr [bp].lSourceStepY mov dx,word ptr [bp].lSourceStepY+2 sar dx,1 rcr ax,1 add word ptr [bp].lSourceY,ax adc word ptr [bp].lSourceY+2,dx ; Clip bottom edge if necessary. mov bx,[di].DestY cmp bx,[_ClipMaxY] jl short BottomEdgeClipped mov bx,[_ClipMaxY] BottomEdgeClipped: ; Clip top edge if necssary mov si,[bp].TopEdge mov di,[si].DestY cmp di,[_ClipMinY] jge short TopEdgeClipped ; Top clipping is necessary; advance the source accordingly neg di add di,[_ClipMinY] ;ClipMinY - DestY ;first, advance the source in X push di ;push ClipMinX - DestX, in fixedpoint form sub ax,ax push ax ;push 0 as fractional part of ClipMinX-DestX push word ptr [bp].lSourceStepX+2 push word ptr [bp].lSourceStepX call _FixedMul ;total source X stepping in clipped area add sp,8 ;clear parameters from stack add word ptr [bp].lSourceX,ax ;step the source X past clipping adc word ptr [bp].lSourceX+2,dx ;now advance the source in Y push di ;push ClipMinX - DestX, in fixedpoint form sub ax,ax push ax ;push 0 as fractional part of ClipMinX-DestX push word ptr [bp].lSourceStepY+2 push word ptr [bp].lSourceStepY call _FixedMul ;total source Y stepping in clipped area add sp,8 ;clear parameters from stack add word ptr [bp].lSourceY,ax ;step the source Y past clipping adc word ptr [bp].lSourceY+2,dx mov di,[_ClipMinY] ;start Y coordinate in dest after clipping TopEdgeClipped: ; Calculate actual clipped destination drawing height. sub bx,di ; Scan down the destination column, updating the source image position ; accordingly. ; Point to the initial source image pixel, adding 0.5 to both X and Y so that ; we can truncate to integers from now on but effectively get rounding. add word ptr [bp].lSourceY,8000h ;add 0.5 mov ax,word ptr [bp].lSourceY+2 adc ax,0 mul [_TexMapWidth] ;initial scan line in source image add word ptr [bp].lSourceX,8000h ;add 0.5 mov si,word ptr [bp].lSourceX+2 ;offset into source scan line adc si,ax ;initial source offset in source image add si,[_TexMapBits] ;SI points to the initial image pixel ; Point to initial destination pixel. mov ax,SCREEN_WIDTH mul di ;offset of initial dest scan line mov di,[_DestX] mov cx,di ;initial destination X shr di,1 shr di,1 ;X/4 = offset of pixel in scan line add di,ax ;offset of pixel in page add di,[_CurrentPageBase] ;offset of pixel in display memory ;DI now points to the first destination pixel and cl,011b ;CL = pixel's plane mov al,MAP_MASK mov dx,SC_INDEX mov ah,01h ;one plane bit in each nibble, so we'll get carry ; automatically when going from plane 3 to plane 0 shl ah,cl ;set the bit for the first pixel's plane to 1 out dx,ax ; If source Y step is negative, change over to working with non-negative ; values. cmp word ptr [bp].lYAdvanceByOne,0 jge short SYStepSet neg word ptr [bp].lSourceStepY not word ptr [bp].lSourceY SYStepSet: ; If source X step is negative, handle with a separate inner loop. cmp word ptr [bp].lXAdvanceByOne,0 jl short TexScanRToL ; Handles edges that go left to right through the source texture. mov cx,word ptr [bp].lSourceStepX shl ecx,16 ;upper word of ECX is fractional X advance mov cx,word ptr [bp].lSourceStepY shr cx,1 ;lower 15 bits of ECX are fractional Y ; advance, bit 15 is 0 mov dx,[bp].lSourceX shl edx,16 mov dx,[bp].lSourceY shr dx,1 ;upper 16 bits are X fractional coord, bit 15 ; is 0, lower 15 bits are Y fractional coord push ds ;preserve normal data segment mov ax,SCREEN_SEG mov ds,ax ;DS:DI->initial destination pixel mov ax,[bp].lYAdvanceByOne push bp ;preserve stack frame pointer ;***stack frame not available*** mov bp,[bp].lBaseAdvance xchg bp,si ;SS:BP->initial source texture pixel ;SI = minimum source advance per destination ; step inc bx ;round pixel-pair count up shr bx,1 ;# of pixel-pairs to texture map jc short TexScanLToRLoop ;even # of pixels push bx ;preserve pixel-pair count sub di,SCREEN_WIDTH ;preadjust back to compensate for ; built-in offset in odd-pixel code ; being jumped to jmp short TexScanLToRLoopOddEntry ;odd # of pixels ; Inner loop to draw a single texture-mapped vertical column, ; rather than a horizontal scanline. Maxed-out 16-bit version. ; ; At this point: ; AX = source pointer increment to advance one in Y ; BX = # of pixel-pairs to draw ; ECX = fractional Y advance in lower 15 bits of CX, ; fractional X advance in high word of ECX, bit ; 15 set to 0 ; EDX = fractional source texture Y coordinate in lower ; 15 bits of CX, fractional source texture X coord ; in high word of ECX, bit 15 set to 0 ; SI = sum of integral X & Y source pointer advances ; DS:DI = initial destination pointer ; SS:BP = initial source texture pointer ; Plane mask set to point to the plane containing this scan align 2 TexScanLToRLoop: push bx ;remember pixel-pair count mov bl,ss:[bp] ;get texture pixel mov ds:[di],bl ;set screen pixel add edx,ecx ;advance frac Y in DX, ; frac X in high word of EDX adc bp,si ;advance source pointer by integral ; X & Y amount, also accounting for ; carry from X fractional addition test dh,80h ;carry from Y fractional addition? jz short TSLToRL1 ;no add bp,ax ;yes, advance Y by one and dh,not 80h ;reset the Y fractional carry bit TSLToRL1: TexScanLToRLoopOddEntry: mov bl,ss:[bp] ;get texture pixel mov ds:[di+SCREEN_WIDTH],bl ;set screen pixel add edx,ecx ;advance frac Y in DX, ; frac X in high word of EDX adc bp,si ;advance source pointer by integral ; X & Y amount, also accounting for ; carry from X fractional addition test dh,80h ;carry from Y fractional addition? jz short TSLToRL2 ;no add bp,ax ;yes, advance Y by one and dh,not 80h ;reset the Y fractional carry bit TSLToRL2: ; Point to the next destination pixel. add di,SCREEN_WIDTH*2 ; Continue if there are any more dest pixels to draw. pop bx dec bx jnz short TexScanLToRLoop pop bp ;restore stack frame pointer ;***stack frame available*** pop ds ;restore normal data segment jmp short ScanDone ; Handles edges that go right to left through the source texture. align 2 TexScanRToL: mov cx,word ptr [bp].lSourceStepX neg cx ;make fractional X advance positive, so we can ; add both X and Y simultaneously shl ecx,16 ;upper word of ECX is fractional X advance mov cx,word ptr [bp].lSourceStepY shr cx,1 ;lower 15 bits of ECX are fractional Y ; advance, bit 15 is 0 mov dx,[bp].lSourceX not dx ;convert fraction X advance to counting-up ; mode, so we can add both X and Y ; simultaneously (since X goes right to left, ; fractional X would normally be advanced ; with subtraction) shl edx,16 mov dx,[bp].lSourceY shr dx,1 ;upper 16 bits are X fractional coord, bit 15 ; is 0, lower 15 bits are Y fractional coord push ds ;preserve normal data segment mov ax,SCREEN_SEG mov ds,ax ;DS:DI->initial destination pixel mov ax,[bp].lYAdvanceByOne push bp ;preserve stack frame pointer ;***stack frame not available*** mov bp,[bp].lBaseAdvance xchg bp,si ;SS:BP->initial source texture pixel neg si ;SI = minimum source advance per destination ; step, negated so we can use SBB in the inner ; loop inc bx ;round pixel-pair count up shr bx,1 ;# of pixel-pairs to texture map jc short TexScanRToLLoop ;even # of pixels push bx ;preserve pixel-pair count sub di,SCREEN_WIDTH ;preadjust back to compensate for ; built-in offset in odd-pixel code ; being jumped to jmp short TexScanRToLLoopOddEntry ;odd # of pixels ; Inner loop to draw a single texture-mapped vertical column, ; rather than a horizontal scanline. Maxed-out 16-bit version. ; ; At this point: ; AX = source pointer increment to advance one in Y ; BX = # of pixel-pairs to draw ; ECX = fractional Y advance in lower 15 bits of CX, ; fractional X advance in high word of ECX, bit ; 15 set to 0 ; EDX = fractional source texture Y coordinate in lower ; 15 bits of CX, fractional source texture X coord ; in high word of ECX, bit 15 set to 0 ; SI = sum of integral X & Y source pointer advances ; DS:DI = initial destination pointer ; SS:BP = initial source texture pointer ; Plane mask set to point to the plane containing this scan align 2 TexScanRToLLoop: push bx ;remember pixel-pair count mov bl,ss:[bp] ;get texture pixel mov ds:[di],bl ;set screen pixel add edx,ecx ;advance frac Y in DX, ; frac X in high word of EDX sbb bp,si ;advance source pointer by integral ; X & Y amount, also accounting for ; carry from X fractional addition test dh,80h ;carry from Y fractional addition? jz short TSRToLL1 ;no add bp,ax ;yes, advance Y by one and dh,not 80h ;reset the Y fractional carry bit TSRToLL1: TexScanRToLLoopOddEntry: mov bl,ss:[bp] ;get texture pixel mov ds:[di+SCREEN_WIDTH],bl ;set screen pixel add edx,ecx ;advance frac Y in DX, ; frac X in high word of EDX sbb bp,si ;advance source pointer by integral ; X & Y amount, also accounting for ; carry from X fractional addition test dh,80h ;carry from Y fractional addition? jz short TSRToLL2 ;no add bp,ax ;yes, advance Y by one and dh,not 80h ;reset the Y fractional carry bit TSRToLL2: ; Point to the next destination pixel. add di,SCREEN_WIDTH*2 ; Continue if there are any more dest pixels to draw. pop bx dec bx jnz short TexScanRToLLoop pop bp ;restore stack frame pointer ;***stack frame available*** pop ds ;restore normal data segment ScanDone: pop di ;restore caller's register variables pop si mov sp,bp ;deallocate local variables pop bp ;restore caller's stack frame ret _ScanOutLine endp end