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Support for transparent overlays #175
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The library is built on top of |
Thinking a little bit more about this, it may be possible to leverage the fact that the clipping region in the underlying dc is a region (which supports union operations with anything that can be drawn via a path) that might allow something cool to be done here. I'm probably not going to tackle it soon but just thought I'd mention it. |
Is it possible to add support for an overlay-like operation of "erasing" by overlaying a transparent image? For example, this would be useful for overlaying a doughnut shape over a colorful background while maintaining the background behind the center of the doughnut:
but with a transparent rather than solid green background for the center of the doughnut shape, allowing the green-blue split to be visible. I can think of two ways to expand the API to support this functionality:
(erase image scene)
where scene is the background, and image is the area to be replaced by transparent pixels. The color of image could be ignored, or perhaps the function could require that the color of image is'transparent
(circle 30 'overwrite 'transparent)
This option may introduce lots of corner cases for existing functions, and the'overwrite
mode would be ignored in all cases except during an overlay.Looking through the existing API, it seems that implementing this functionality could closely follow the existing overlay implementation, but I hope that others can suggest some additional feedback and propose better ways to proceed!
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