WebGPURenderer: Unable to render with orthographic camera.

The WebGPU sandbox uses the following perspective camera setup:

camera = new THREE.PerspectiveCamera( 70, window.innerWidth / window.innerHeight, 0.1, 10 );

The rendered result seems as expected. However if I switch to an orthographic camera like so…

const frustumSize = 10;
const aspect = window.innerWidth / window.innerHeight;

camera = new THREE.OrthographicCamera( 0.5 * frustumSize * aspect / - 2, 0.5 * frustumSize * aspect / 2, frustumSize / 2, frustumSize / - 2, 0, 10 );

…nothing is rendered anymore.

As far as I understand, this is caused by the fact that WebGPU has different coordinate system definitions than WebGL. So in WebGPU, the z coordinate in NDC space lies in the range [0,1] whereas in WebGL it is [-1,1].

That means the current projection matrices for both perspective and orthographic cameras are not computed correctly in Matrix4 in context of WebGPU. It seems these formulas are correct: https://metashapes.com/blog/opengl-metal-projection-matrix-problem/

@mrdoob I have no idea so far how to hide this complexity from the user. When creating a camera, the projection matrix is computed right away from the parameters. In order to provide a “correct” matrix, the camera would have to know in which context (WebGL, WebGPU) it is going to be used.

[Kangz]

Premultiplying the matrix would work.

As far as I understand, this is caused by the fact that WebGPU has different coordinate system definitions than WebGL. So in WebGPU, the z coordinate in NDC space lies in the range [0,1] whereas in WebGL it is [-1,1].

That’s correct. When you’ll do render-to-texture there will be another difference that means that you’ll need to flip-Y to keep the same rendering results as the WebGL path. (for rendering directly to the canvas there are two flips compared to WebGL that cancel out).

[WestLangley]

Maybe just premultiply the projection matrix by the appropriate transform matrix, as described in the link above, if webGPU is enabled.