Copies rectangular part of SrcImage to DstImage.
function CopyRect(const SrcImage: TImageData; SrcX: LongInt; SrcY: LongInt; Width: LongInt; Height: LongInt; var DstImage: TImageData; DstX: LongInt; DstY: LongInt): Boolean;
Imaging (at line 216)
No blending is performed - alpha is simply copied to destination image. Operates also with negative X and Y coordinates. Note that copying is fastest for images in the same data format (and slowest for images in special formats).