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function ImageCollisionTest(suf1, suf2: TDirectDrawSurface; const rect1, rect2: TRect;
  x1,y1,x2,y2: Integer; DoPixelCheck: Boolean): Boolean;

  Procedure AddXOffs(var r:TRect;ofs:Integer);
  begin
    r.Left  := r.Left  + ofs;
    r.Right := r.Right + ofs;
  end;

  ...
    if DoPixelCheck and Result then
  begin
    {  Get Overlapping rectangle  }
    with r1 do r1 := Bounds(Max(x2-x1, 0), Max(y2-y1, 0), Right-Left, Bottom-Top);
    with r2 do r2 := Bounds(Max(x1-x2, 0), Max(y1-y2, 0), Right-Left, Bottom-Top);
    
    // fix
    AddXOffs(r1,rect1.Left);
    AddXOffs(r2,rect2.Left);

    ClipRect(r1, rect1);
    ClipRect(r2, rect2);
   ...					

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function ImageCollisionTest(suf1, suf2: TDirectDrawSurface; const rect1, rect2: TRect;
  x1,y1,x2,y2: Integer; DoPixelCheck: Boolean): Boolean;

  function ClipRect(var DestRect: TRect; const DestRect2: TRect): Boolean;
  begin
    with DestRect do
    begin
      Left := Max(Left, DestRect2.Left);
      Right := Min(Right, DestRect2.Right);
      Top := Max(Top, DestRect2.Top);
      Bottom := Min(Bottom, DestRect2.Bottom);

      Result := (Left < Right) and (Top < Bottom);
    end;
  end;

type
  PRGB = ^TRGB;
  TRGB = packed record
    R, G, B: Byte;
  end;
var
  ddsd1, ddsd2: TDDSurfaceDesc;
  r1, r2: TRect;
  tc1, tc2: DWORD;
  x, y, w, h: Integer;
  P1, P2: Pointer;
begin
  r1 := rect1;
  with rect2 do r2 := Bounds(x2-x1, y2-y1, Right-Left, Bottom-Top);

  Result := OverlapRect(r1, r2);

  if (suf1=nil) or (suf2=nil) then Exit;

  if DoPixelCheck and Result then
  begin
    {  Get Overlapping rectangle  }
    with r1 do r1 := Bounds(Max(x2-x1, 0), Max(y2-y1, 0), Right-Left, Bottom-Top);
    with r2 do r2 := Bounds(Max(x1-x2, 0), Max(y1-y2, 0), Right-Left, Bottom-Top);

    ClipRect(r1, rect1);
    ClipRect(r2, rect2);

    w := Min(r1.Right-r1.Left, r2.Right-r2.Left);
    h := Min(r1.Bottom-r1.Top, r2.Bottom-r2.Top);

    ClipRect(r1, bounds(r1.Left, r1.Top, w, h));
    ClipRect(r2, bounds(r2.Left, r2.Top, w, h));
                               
    {  Pixel check !!!  }
    ddsd1.dwSize := SizeOf(ddsd1);
    if suf1.Lock(r1, ddsd1) then
    begin
      try
        ddsd2.dwSize := SizeOf(ddsd2);
        if (suf1=suf2) or suf2.Lock(r2, ddsd2) then
        begin
          try
            if suf1=suf2 then ddsd2 := ddsd1;
            if ddsd1.ddpfPixelFormat.dwRGBBitCount<>ddsd2.ddpfPixelFormat.dwRGBBitCount then Exit;
                                     
            {  Get transparent color  }
            tc1 := ddsd1.ddckCKSrcBlt.dwColorSpaceLowValue;
            tc2 := ddsd2.ddckCKSrcBlt.dwColorSpaceLowValue;

            case ddsd1.ddpfPixelFormat.dwRGBBitCount of
              8 : begin
                    for y:=0 to h-1 do
                    begin
                      P1 := Pointer(Integer(ddsd1.lpSurface)+y*ddsd1.lPitch);
                      P2 := Pointer(Integer(ddsd2.lpSurface)+y*ddsd2.lPitch);
                      for x:=0 to w-1 do
                      begin
                        if (PByte(P1)^<>tc1) and (PByte(P2)^<>tc2) then Exit;
                        Inc(PByte(P1));
                        Inc(PByte(P2));
                      end;
                    end;
                  end;
              16: begin
                    for y:=0 to h-1 do
                    begin
                      P1 := Pointer(Integer(ddsd1.lpSurface)+y*ddsd1.lPitch);
                      P2 := Pointer(Integer(ddsd2.lpSurface)+y*ddsd2.lPitch);
                      for x:=0 to w-1 do
                      begin
                        if (PWord(P1)^<>tc1) and (PWord(P2)^<>tc2) then Exit;
                        Inc(PWord(P1));
                        Inc(PWord(P2));
                      end;
                    end;
                  end;
              24: begin
                    for y:=0 to h-1 do
                    begin
                      P1 := Pointer(Integer(ddsd1.lpSurface)+y*ddsd1.lPitch);
                      P2 := Pointer(Integer(ddsd2.lpSurface)+y*ddsd2.lPitch);
                      for x:=0 to w-1 do
                      begin        
                        if ((PRGB(P1)^.R shl 16) or (PRGB(P1)^.G shl 8) or PRGB(P1)^.B<>tc1) and
                          ((PRGB(P2)^.R shl 16) or (PRGB(P2)^.G shl 8) or PRGB(P2)^.B<>tc2) then Exit;
                        Inc(PRGB(P1));
                        Inc(PRGB(P2));
                      end;
                    end;
                  end;
              32: begin
                    for y:=0 to h-1 do
                    begin
                      P1 := Pointer(Integer(ddsd1.lpSurface)+y*ddsd1.lPitch);
                      P2 := Pointer(Integer(ddsd2.lpSurface)+y*ddsd2.lPitch);
                      for x:=0 to w-1 do
                      begin
                        if (PDWORD(P1)^ and $FFFFFF<>tc1) and (PDWORD(P2)^ and $FFFFFF<>tc2) then Exit;
                        Inc(PDWORD(P1));
                        Inc(PDWORD(P2));
                      end;
                    end;
                  end;
            end;
          finally
            if suf1<>suf2 then suf2.UnLock;
          end;
        end;
      finally
        suf1.UnLock;
      end;
    end;

    Result := False;
  end;
end;					

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// fix  
    AddXOffs(r1,rect1.Left);  
    AddXOffs(r2,rect2.Left);