Specify a MIN_FILTER for render target textures #220
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Previously when rendering with Swiftshader, enabling the postprocessing pipeline would result in nothing being rendered to the screen. I narrowed down the issue due to Swiftshader not considering the postProcess_colorBuffer sampler as complete. This occurs because the default min filter for textures is GL_NEAREST_MIPMAP_LINEAR, which requires mipmaps, and the render target texture doesn't include those, so Swiftshader doesn't consider the texture to be complete when it's binding it to a sampler, resulting in it failing to bind. The OpenGL ES 3.1 spec is vague around this area, see section 8.16.1, which states that if the sampler min filter requires mipmaps and the texture doesn't include them the sampler may be considered incomplete, but it doesn't say what happens if the texture is incomplete by itself and complete after the sampler min filter overrides the texture min filter. Since the language is vague, and the current behavior is arguably incorrect, update OpenGLDriver::textureStorage to explicitly specify a min filter so that render target textures are considered complete standalone.
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We usually don't use |
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Yeah, in this situation the sampler is correct and initialized with a min filter of GL_LINEAR, but Swiftshader is failing because the texture itself isn't complete, per the check in swiftshader at: https://github.com/google/swiftshader/blob/a062f321768dc39a533188806c571cf8a9479ca7/src/OpenGL/libGLESv2/Context.cpp#L3090 |
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Romain, to confirm you're proposing making this change in OpenGLDriver::createRenderTarget instead? |
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Yes that's what I'm proposing. I just want to avoid messing with state as much as possible. |
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This workaround shouldn't be needed once the SwiftShader-side fix lands: https://swiftshader-review.googlesource.com/20529 |
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Oh nice! Filament is yet again a stress test against the OpenGL ES API :-) Given this new information, would you like me to continue on this fix? This is an uncommon scenario, with the combination of samplers, creating a texture without explicitly setting the glTexParameters, and using the incomplete texture, but it does appear to be accepted everywhere else. |
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I wouldn't mind doing the right thing here for render targets. Up to you :) |
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Using sampler objects instead of setting the texture's parameters is definitely the modern way of using OpenGL, and shouldn't be considered uncommon. It's a blatant bug in SwiftShader for not handling it correctly, and I'm happy Filament exposed it. I'll look into why dEQP didn't catch it. Concretely, I would advise against working around this bug. Our patch should land shortly. |
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Alright, thanks! |
Previously when rendering with Swiftshader, enabling the postprocessing
pipeline would result in nothing being rendered to the screen.
I narrowed down the issue due to Swiftshader not considering the
postProcess_colorBuffer sampler as complete. This occurs because the
default min filter for textures is GL_NEAREST_MIPMAP_LINEAR, which
requires mipmaps, and the render target texture doesn't include those,
so Swiftshader doesn't consider the texture to be complete when it's
binding it to a sampler, resulting in it failing to bind.
The OpenGL ES 3.1 spec is vague around this area, see section 8.16.1,
which states that if the sampler min filter requires mipmaps and the
texture doesn't include them the sampler may be considered incomplete,
but it doesn't say what happens if the texture is incomplete by itself
and complete after the sampler min filter overrides the texture min
filter.
Since the language is vague, and the current behavior is arguably
incorrect, update OpenGLDriver::textureStorage to explicitly specify a
min filter so that render target textures are considered complete
standalone.