WebGPU and Webgl return different pixel array lengths when using readRenderTargetPixelsAsync

[Kycklingris]

Description

When using r179.1 the WebGPURenderer returns a pixelArray of length 40 000 (for a RenderTarget of size (100, 100)) both when forceWebGL is set to false and true.

However when using r180 and forceWebGL is false it outputs a length of 51 088. With forceWebGL set to true, the pixelArray length is still 40 000.

Reproduction steps

1. Create a new WebGPURenderer with forceWebGL set to false
2. Create a new RenderTarget
3. Init the RenderTarget
4. read the pixels using readRenderTargetPixelsAsync
5. check the length of the pixelsArray length

Code

const renderer = new WebGPURenderer();
await renderer.init();

const rt = new RenderTarget(100, 100);
await renderer.initTextureAsync(rt.texture);

const pixels = await renderer.readRenderTargetPixelsAsync(rt, 0, 0, rt.width, rt.height);

console.log(pixels.length); // Outputs 51088

Live example

• jsfiddle-broken-r180
• jsfiddle-working-r179.1

Screenshots

No response

Version

r180

Device

Desktop

Browser

Chrome

OS

Windows

[Mugen87]

Yes, this has been changed on purpose since the readback with WebGPU was buggy. Please read the discussion in #31765 and #31658 (especially #31658 (comment) and below) to understand how the readback with WebGPU is supposed to work.