copy-pixels-with-mask-to-stream

Arguments: to-stream texture texture-info to-box-or-position from-box-or-nil mask-texture

This function is similar to copy-pixels-to-stream except it allows you to copy a non-rectangular image. This is done by passing a mask-texture. The texture defines which pixels should be copied and which should be left unchanged.

The first five arguments are the same as for copy-pixels-to-stream. The sixth argument is mask-bitmap, a 1-bit-per-pixel texture with a 1 wherever the texture should be transparent (destination is left alone) and a 0 wherever texture should modify the destination. This function works by erasing the destination wherever there is a 1 in mask-texture and then merging in texture with the paint operation. (Since the operation is predefined, there is no paint-operation argument.)

If you use load-pixmap to load a .ico (icon) file, the third returned value is a mask bitmap suitable for using as the mask-texture argument.

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Created 2012.5.30.