Feature request: Mask union

[Pr0methean]

I have an app where I load layers from SVGs, repaint them various colors, stack them, and output the results as PNGs. To minimize the memory consumed by intermediate results, I always union together masks that are being painted the same color for the same output PNG, unless I need to avoid doing so for Z-order reasons. Thus, being able to take the union of two masks via a tiny-skia routine rather than a loop I had to write myself, would be very useful.

As well, I could get by with fewer SVGs given subtraction and XOR operations on masks.

[RazrFalcon]

Yes, the Mask API is very primitive right now. Will add more operations.

[Pr0methean]

Another useful operation would be to multiply all pixels in an alpha mask by a fraction.

[RazrFalcon]

Can you explain the use case? And it would be easier to implement on your side via data_mut. I don't think SIMD would help here much.

[Pr0methean]

The use case would involve merging consecutive layers that have the same color but different opacity, so that the layers can be masks rather than pixmaps until they've been combined.

Also, would SIMD help at all in stacking two masks where one has the same alpha for the whole image? I'd use this to make stained-glass window textures (where the background is the same color as the frame but 75% transparent).

[Pr0methean]

And is there any chance that once from_pixmap is optimized, a version can be provided that would replace the contents of a mutably-borrowed Mask rather than create a new one? I'd use that with an object pool.

[RazrFalcon]

Will take a look.

a version can be provided that would replace the contents of a mutably-borrowed Mask rather than create a new one?

You mean something like Pixmap::to_mask(&self, mask_type: MaskType, mask: &mut Mask)?
Yes, reducing allocations the goal.

The current tiny-skia API is incredibly bare-bone, mainly because it contains only stuff I use in resvg. So any suggestions are welcome, as long as I have time implementing them.