Object Picking not working on Firefox about magnum-examples HOT 6 CLOSED

Ahh, I see. An unfortunate limitation where Firefox doesn't allow a read format any other than GL_RGBA + GL_UNSIGNED_BYTE. I already worked around this for the Mouse Interaction example (that one behaves properly for you, right?), so I will just need to put the same workaround here.

Thanks a lot for the report! 👍

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Well, I thought the fix would be simple and so I delayed the fix until now. It turns out to be harder than I thought, hitting one weirdness after another. Investigation so far:

• Applying the same hack as in Mouse Interaction (RGBA + UNSIGNED_BYTE) seemingly works, but the readback returns values from the color buffer, not from the object ID buffer, like if glReadBuffer() wouldn't work at all (the same works correctly in Chromium-based browsers).
• The object ID buffer is R8UI, but Firefox complains when reading it as R8UI. IMPLEMENTATION_COLOR_READ_FORMAT + TYPE on Firefox returns RGBA_INTEGER + UNSIGNED_INT (reading from R8UI works correctly on Chromium-based browsers).
• Reading as RGBA_INTEGER + UNSIGNED_INT always returns a value of 46460, no matter where I click; changing the object ID buffer format to RGBA32UI (to match) doesn't help (again, this all works correctly on Chromium-based browsers).

Because it's unlikely I will find a magic solution to this in time for this release, I'm postponing to later.

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The PhongGLTest / FlatGLTest Magnum tests now integrate Object ID rendering as well and should be a much easier target to investigate Firefox issues.

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The example now uses a R32UI format for Object ID, so this could get revisited.

While investigating one vaguely related issue (trying to read depth for the mouse interaction example), I saw that the GLES3 specification (4.3.1, page 186) says that the only allowed glReadPixels format + type combinations are:

• RGBA + UNSIGNED_BYTE for normalized colors
• RGBA_INTEGER + INT for signed integer formats
• and RGBA_INTEGER + UNSIGNED_INT for unsigned integer formats

Not sure how this interacts with the fact that the Object ID buffer is just a single channel (browsers usually complain that the read type has to match exactly).

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This is finally fixed as of 52a5fae. While working on an unrelated issue with GL::Mesh tests on Firefox I tried this example again and the above-mentioned issue is no longer present:

Reading as RGBA_INTEGER + UNSIGNED_INT always returns a value of 46460

And Firefox now also prints understandable warnings when using anything else than full RGBA and a 32-bit type for buffer reading. Not sure at which point during the last three years Firefox fixed this, but what matters is that it indeed got fixed! 🎉

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