Comment # 19
on bug 92309
from Kamil Páral
I believe you can automatically detect invalid input in some cases. If you receive an image in which R or G or B value is higher than A value, for any available pixel, you can be certain that the image does not have premultiplied alpha but straight alpha (this situation can never happen with premultiplied alpha, by definition). You can then assume a developer mistake and "fix" the image automatically. It might even resolve most of the usual cursor-related mistakes (we can clearly see colored boxes, while it's expected to be transparent, so those images have RGB>A for some pixels). However, this has downsides as well. It does not cover all cases (for images where all RGB are lower or equal to their respective A, you can't decide whether it is premultiplied or straight). The automatic detection and conversion might involve some performance hit. And it might not be a good API design, because trying to be overly helpful often leads to lowered predictability and more difficult debugging. But that would be someone else's call. I might also be talking utter nonsense because I have no expertise in graphics.
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