StereoEffect: Handle clear differently.

[Mugen87]

Related issue: -

Description

I was testing what type of effects already work with WebGPURenderer(it's AsciiEffect and PeppersGhostEffect, btw). StereoEffect does not work because of the way the clear happens in render().

When defining a scissor area, WebGL honors it during the clear. That does not work with WebGPU where the clear value is loaded for the entire framebuffer.

StereoEffect clears now the entire framebuffer once before rendering the left and right view.

[Mugen87]

@WestLangley StereoCamera manipulates the projection matrices for the left and right eye to achieve an off-axis stereoscopic effect. It seems these changes do not work with WebGPU (using WebGPURenderer in webgl_effects_stereo produces a wrong image), probably because it has different NDC conventions. We have different code paths for WebGL and WebGPU in Matrix4.makePerspective() and we probably need something similar in StereoCamera. Do you know what part of the matrix computation in StereoCamera.update() must be changed to make it compatible to WebGPU?

[WestLangley]

@Mugen87 If I am not mistaken, StereoCamera does not know the correct coordinateSystem.

[Mugen87]

We can inject the coordinate system from outside, e.g. StereoEffect, AnaglyphEffect or ParallaxBarrierEffect. These classes have a reference to the renderer and can assign the value when creating a stereo camera.

[Mugen87]

The following line can be added to the constructor of StereoCamera.

this.coordinateSystem = WebGLCoordinateSystem;