Flipped image when rendering to a MTLTexture

[Linfeng Li]

not sure if it is a bug or is there a configuration to flip it.

1. created MTLTexture with [MTLDevice newTextureWithDescriptor:]

2. under a surfaceless context get the EGLImage via eglCreateImageKHR

3. get the GL texture by glEGLImageTargetTexture2DOES

4. create a frame buffer backed by the texture

5. make draw calls

6. glFinish

7. render the MTLTexture in Metal

the resulting image is flipped. The black box is the metal texture that I render onto where I drew a upward triangle with ANGLE.

I see that in https://github.com/google/angle/blob/16d65289e8681e8f9f6f372f1173951d56dca450/src/libANGLE/renderer/metal/SurfaceMtl.mm#L548

the frame buffer is only flipped with a window surface

[Ken Russell]

(Resending from correct email address)

This is probably expected behavior. OpenGL's coordinate system differs from most of the other native APIs', including Metal's. If a toggle were to be added, it might be best to implement the already-specified  https://registry.khronos.org/OpenGL/extensions/MESA/MESA_framebuffer_flip_y.txt for ANGLE's Metal backend.

-Ken

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[Linfeng Li]

I think so. should I open a feature request in https://bugs.chromium.org/p/angleproject/issues/list ?

[Linfeng Li]

reported here: https://bugs.chromium.org/p/angleproject/issues/detail?id=8248

[Ken Russell]

Thanks, added some labels and asked for an Xcode project on it.

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