Object Picking not working on Firefox

[wbpaley]

At least on FF 62.0.3 (Objects do not change color when clicked.)
Updated to 63.0 (64-bit); same behavior.

Works fine on Chrome

[mosra]

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! 👍

[wbpaley]

Wow, Vlad--thanks for the instant response, understanding and (soon, I assume) fix! Impressed here.

…

On 10/28/2018 9:43 PM, Vladimír Vondruš wrote: 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 <https://magnum.graphics/showcase/mouseinteraction/> 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! 👍 — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <https://github.com/mosra/magnum-website/issues/8#issuecomment-433764154>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AADtw1uBjKIM-9Qq1KNQ4s5eGnCNfzvMks5upl06gaJpZM4X-OVd>.

[mosra]

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.

[mosra]

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

[mosra]

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).

[mosra]

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! 🎉