Excessive loading times using GPUParticles2D in projects exported for HTML5

[derdobs]

Tested versions

Reproducable in 4.2.1 stable and forward (not tested in older versions)

System information

Windows 11

Issue description

Using GPUParticles2D in projects exported for the web/HTML5 incur excessive loading times. A single (default) GPUParticles2D system with a gradienttexture2D needs around 2 seconds to load.

The behaviour was the same accross two computers (Gaming PC and Laptop), Browsers (Firefox, Chrome) and regardless of the "export with debug" box ticked when exporting the project.

In a more complex project with multiple GPUParticles2D nodes with textures, this delay makes GPUParticle2D systems virtually unusable. CPUParticle2D systems did not incur any noticeable loading delays.

Steps to reproduce

Minimal Setup:
Empty 2D Scene with a single GPUParticles2D emitter which renders a GradientTexture2D.
Export the project for the Web and run the result.

Minimal reproduction project (MRP)

particle-test.zip

[Calinou]

Shader compilation on WebGL is much slower than on desktop platforms (due to browsers using ANGLE among other things), so we probably need to figure out a way to simplify the particles shader on the web platform similar to what's been proposed for 2D lighting in #70691.

In the meantime, try displaying particles for a single frame when the project starts. This is the standard approach used to ensure all shaders are compiled before gameplay.

Reproducable in 4.2.1 stable and forward (not tested in older versions)

The web export always uses the Compatibility rendering method, as Vulkan doesn't run in web browsers.

[derdobs]

Thanks for the response. Displaying the particles for a frame is what I tried, but with 4 particle systems, this would freeze the browser for 30-60 seconds right after loading.
For now I switched to CPU particles when running the project on a web platform.