DeleteScans.pas

unit DeleteScans;
 //Renate Schaaf 
//renates@xmission.com 

interface

 uses Windows, Graphics;

 procedure DeleteScansRect(Src, Dest: TBitmap; rs, rd: TRect);
   //scanline implementation of Stretchblt/Delete_Scans 
  //about twice as fast 
  //Stretches Src to Dest, rs is source rect, rd is dest. rect 
  //The stretch is centered, i.e the center of rs is mapped to the center of rd. 
  //Src, Dest are assumed to be bottom up 

implementation

 uses Classes, math;

 type
   TRGBArray = array[0..64000] of TRGBTriple;
   PRGBArray = ^TRGBArray;

   TQuadArray = array[0..64000] of TRGBQuad;
   PQuadArray = ^TQuadArray;

 procedure DeleteScansRect(Src, Dest: TBitmap; rs, rd: TRect);
 var
    xsteps, ysteps: array of Integer;
   intscale: Integer;
   i, x, y, x1, x2, bitspp, bytespp: Integer;
   ts, td: PByte;
   bs, bd, WS, hs, w, h: Integer;
   Rows, rowd: PByte;
   j, c: Integer;
   pf: TPixelFormat;
   xshift, yshift: Integer;
 begin
   WS := rs.Right - rs.Left;
   hs := rs.Bottom - rs.Top;
   w  := rd.Right - rd.Left;
   h  := rd.Bottom - rd.Top;
   pf := Src.PixelFormat;
   if (W = 0) or (H = 0) then Exit;
   if (pf <> pf32Bit) and (pf <> pf24bit) then
   begin
     pf := pf24bit;
     Src.PixelFormat := pf;
   end;
   Dest.PixelFormat := pf;
   if not (((w <= WS) and (h <= hs)) or ((w >= WS) and (h >= hs))) then
   //we do not handle a mix of up-and downscaling, 
  //using threadsafe StretchBlt instead. 
  begin
     Src.Canvas.Lock;
     Dest.Canvas.Lock;
     try
       SetStretchBltMode(Dest.Canvas.Handle, STRETCH_DELETESCANS);
       StretchBlt(Dest.Canvas.Handle, rd.Left, rd.Top, w, h,
         Src.Canvas.Handle, rs.Left, rs.Top, WS, hs, SRCCopy);
     finally
       Dest.Canvas.Unlock;
       Src.Canvas.Unlock;
     end;
     Exit;
   end;

   if pf = pf24bit then
   begin
     bitspp  := 24;
     bytespp := 3;
   end
   else
   begin
     bitspp  := 32;
     bytespp := 4;
   end;
   bs := (Src.Width * bitspp + 31) and not 31;
   bs := bs div 8; //BytesPerScanline Source 
  bd := (Dest.Width * bitspp + 31) and not 31;
   bd := bd div 8; //BytesPerScanline Dest 
  if w < WS then //downsample 
  begin
     //first make arrays of the skipsteps 
    SetLength(xsteps, w);
     SetLength(ysteps, h);
     intscale := round(WS / w * $10000);
     x1       := 0;
     x2       := (intscale + $7FFF) shr 16;
     c  := 0;
     for i := 0 to w - 1 do
     begin
       xsteps[i] := (x2 - x1) * bytespp;
       x1        := x2;
       x2        := ((i + 2) * intscale + $7FFF) shr 16;
       if i = w - 2 then
         c := x1;
     end;
     xshift   := min(max((WS - c) div 2, - rs.Left), Src.Width - rs.Right);
     intscale := round(hs / h * $10000);
     x1       := 0;
     x2       := (intscale + $7FFF) shr 16;
     c        := 0;
     for i := 0 to h - 1 do
     begin
       ysteps[i] := (x2 - x1) * bs;
       x1        := x2;
       x2        := ((i + 2) * intscale + $7FFF) shr 16;
       if i = h - 2 then
         c := x1;
     end;
     yshift := min(max((hs - c) div 2, - rs.Top), Src.Height - rs.Bottom);
     if pf = pf24bit then
     begin
       Rows := @PRGBArray(Src.Scanline[rs.Top + yshift])^[rs.Left + xshift];
       rowd := @PRGBArray(Dest.Scanline[rd.Top])^[rd.Left];
       for y := 0 to h - 1 do
       begin
         ts := Rows;
         td := rowd;
         for x := 0 to w - 1 do
         begin
           pRGBTriple(td)^ := pRGBTriple(ts)^;
           Inc(td, bytespp);
           Inc(ts, xsteps[x]);
         end;
         Dec(rowd, bd);
         Dec(Rows, ysteps[y]);
       end;
     end
     else
     begin
       Rows := @PQuadArray(Src.Scanline[rs.Top + yshift])^[rs.Left + xshift];
       rowd := @PQuadArray(Dest.Scanline[rd.Top])^[rd.Left];
       for y := 0 to h - 1 do
       begin
         ts := Rows;
         td := rowd;
         for x := 0 to w - 1 do
         begin
           pRGBQuad(td)^ := pRGBQuad(ts)^;
           Inc(td, bytespp);
           Inc(ts, xsteps[x]);
         end;
         Dec(rowd, bd);
         Dec(Rows, ysteps[y]);
       end;
     end;
   end
   else
   begin
     //first make arrays of the steps of uniform pixels 
    SetLength(xsteps, WS);
     SetLength(ysteps, hs);
     intscale := Round(w / WS * $10000);
     x1       := 0;
     x2       := (intscale + $7FFF) shr 16;
     c        := 0;
     for i := 0 to WS - 1 do
     begin
       xsteps[i] := x2 - x1;
       x1        := x2;
       x2        := ((i + 2) * intscale + $7FFF) shr 16;
       if x2 > w then
         x2 := w;
       if i = WS - 1 then
         c := x1;
     end;
     if c < w then //>is now not possible 
    begin
       xshift         := (w - c) div 2;
       yshift         := w - c - xshift;
       xsteps[WS - 1] := xsteps[WS - 1] + xshift;
       xsteps[0]      := xsteps[0] + yshift;
     end;
     intscale := round(h / hs * $10000);
     x1       := 0;
     x2       := (intscale + $7FFF) shr 16;
     c        := 0;
     for i := 0 to hs - 1 do
     begin
       ysteps[i] := (x2 - x1);
       x1        := x2;
       x2        := ((i + 2) * intscale + $7FFF) shr 16;
       if x2 > h then
         x2 := h;
       if i = hs - 1 then
         c := x1;
     end;
     if c < h then
     begin
       yshift         := (h - c) div 2;
       ysteps[hs - 1] := ysteps[hs - 1] + yshift;
       yshift         := h - c - yshift;
       ysteps[0]      := ysteps[0] + yshift;
     end;
     if pf = pf24bit then
     begin
       Rows := @PRGBArray(Src.Scanline[rs.Top])^[rs.Left];
       rowd := @PRGBArray(Dest.Scanline[rd.Top])^[rd.Left];
       for y := 0 to hs - 1 do
       begin
         for j := 1 to ysteps[y] do
         begin
           ts := Rows;
           td := rowd;
           for x := 0 to WS - 1 do
           begin
             for i := 1 to xsteps[x] do
             begin
               pRGBTriple(td)^ := pRGBTriple(ts)^;
               Inc(td, bytespp);
             end;
             Inc(ts, bytespp);
           end;
           Dec(rowd, bd);
         end;
         Dec(Rows, bs);
       end;
     end
     else
     begin
       Rows := @PQuadArray(Src.Scanline[rs.Top])^[rs.Left];
       rowd := @PQuadArray(Dest.Scanline[rd.Top])^[rd.Left];
       for y := 0 to hs - 1 do
       begin
         for j := 1 to ysteps[y] do
         begin
           ts := Rows;
           td := rowd;
           for x := 0 to WS - 1 do
           begin
             for i := 1 to xsteps[x] do
             begin
               pRGBQuad(td)^ := pRGBQuad(ts)^;
               Inc(td, bytespp);
             end;
             Inc(ts, bytespp);
           end;
           Dec(rowd, bd);
         end;
         Dec(Rows, bs);
       end;
     end;
   end;
 end;


 end.