OpenGL: 3D resolution scaling does not scale the image to the full viewport size

[zaevi]

Godot version

4.0.beta8

System information

Win11, gl_compatibility

Issue description

Scaling 3D doesn't work on gl_compatibility renderer.

renderer=forward+, scale=0.5:

renderer=gl_compatibility, scale=0.5:

renderer=gl_compatibility, scale=0.5, running on web:

Steps to reproduce

see reproduction project below

Minimal reproduction project

web_3d_scaling.zip

[Calinou]

For reference, 3D resolution scaling was added to Vulkan rendering backends in #51870.

Implementing this in OpenGL has some caveats:

• The renderer is low-end-oriented. The mere act of splitting 2D buffers from 3D buffers has a noticeable overhead on the target hardware. In general, the fewer passes are run, the better.
  • We can probably use a separate, faster approach if the scale is 1.0, but this will make the code more complex.
• FSR 1.0 will most likely not be available, given it has a significant cost on mobile devices and integrated graphics.¹

It's still worth implementing this in OpenGL, but resolution scales close to 1.0 like 0.8 or 0.9 may not be worth it on all devices.

Footnotes

1. It is possible to implement FSR 1.0 using only OpenGL despite official support being limited to Direct3D 12 and Vulkan, but it requires support for newer Shader Model versions on the hardware. ↩

[clayjohn]

Fixed by #83976