##
Porter-Duff Group

Industry standard compositing operators.

DST:
  The destination is left untouched. Only the destination will be present in the output. Math formula is the same as that used by Porter-Duff and SVG; there is no Gimp equivalent.
DST_ATOP:
  The part of the destination lying inside of the source is composited over the source. The destination outside the source is dropped. You will see the existing canvas is only kept where the shapes overlap. Math formula is the same as that used by Porter-Duff and SVG; there is no Gimp equivalent.
DST_IN:
  The part of the destination lying inside of the source is displayed. This effectively allows for cutting out the background using the current layer/feature as a mask. You will see the new shape is drawn only where both the source and the destination overlap. Math formula is the same as that used by Porter-Duff and SVG; there is no Gimp equivalent.
DST_OUT:
  The part of the destination lying outside of the source is displayed. This is basically a reverse mask, compared to destination-in. You will see the existing content is kept where it doesn't overlap the source. Math formula is the same as that used by Porter-Duff and SVG; there is no Gimp equivalent.
DST_OVER:
  The destination is composited over the source. Math formula is the same as that used by Porter-Duff and SVG; there is no Gimp equivalent.
SRC:
  The source is copied. The destination is not used as input. Only the source will be present in the output. Math formula is the same as that used by Porter-Duff & SVG; there is no Gimp equivalent.
SRC_ATOP:
  The part of the source lying inside of the destination is composited over the destination. The source outside the destination is dropped. You will see the existing canvas is only kept where the shapes overlap. Math formula is the same as that used by Porter-Duff and SVG; no Gimp equivalent.
SRC_IN:
  The part of the source lying inside of the destination is displayed. This effectively allows the destination to act as a mask for the layer/feature being shown. You will see the new shape is drawn only where both the source and the destination canvas overlap. Math formula is the same as that used by Porter-Duff and SVG; there is no Gimp equivalent.
SRC_OUT:
  The part of the source lying outside of the destination is displayed. This is basically a reverse mask, compared to source-in. You will see the new shape is drawn where it doesn't overlap the destination. Math formula is the same as that used by Porter-Duff and SVG; there is no Gimp equivalent.
SRC_OVER:
  The source is composited over the destination. Math formula is the same as that used by Porter-Duff and SVG; there is no Gimp equivalent.