Fills given rectangle of image with given pixel fill data.

function FillRect(var Image: TImageData; 
                  X: LongInt; 
                  Y: LongInt; 
                  Width: LongInt; 
                  Height: LongInt; 
                  FillColor: Pointer): Boolean;

Imaging (at line 220)

Fill should point to the pixel in the same format as the given image is in.