VertexShaderGen: Sonic epsilon hack for OpenGL ES

[ghost]

#4164 moved the "Sonic epsilon hack" to vertex shaders. However, it was only done for targets with depth clamping. If this is not available, for example the target is OpenGL ES, the Sonic problem appears (https://bugs.dolphin-emu.org/issues/11897).

A version of the "Sonic epsilon hack" is added for targets without depth clamping.

[JMC47]

This has been tested on multiple Sonic Games. Appears to work. It's a small change so if there is some kind of weird regression, it's easy to change back. Looks good to me.

[SN902]

This hack fixes black screens in Sonic Unleashed and Black Knight.

[mirh]

https://stackoverflow.com/questions/7408855/clipping-planes-in-opengl-es-2-0
User-defined clipping can also be found natively in GLES devices supporting EXT_clip_cull_distance (my Adreno 630 phone does for example)

[JMC47]

Oh that's neat! Maybe we can fix this properly on GLES then.

[ghost]

There already can be found a mention of this extension in the Dolphin source:

dolphin/Source/Core/VideoBackends/OGL/OGLRender.cpp

Lines 506 to 507 in 5513d5f

	// TODO: Implement support for GL_EXT_clip_cull_distance when there is an extension for
	// depth clamping.

But does there exist an "extension for depth clamping"?

[ghost]

But does there exist an "extension for depth clamping"?

GL_EXT_depth_clamp. It does not have a large number of supporting devices.

[mirh]

Because it was basically just shipped for mesa purposes KhronosGroup/OpenGL-Registry#240
Not that it couldn't probably be implemented in most phones, but idk how much GLES is still being maintained there.

Btw hrydgard/ppsspp#11399 and hrydgard/ppsspp#14042 sound interesting.