Fire ‘shader:generate’ when a shader code gets generated

[mvaligursky]

The event shader:generate is fired on the GraphicsDevice when the shader definition is generated, just before the shader is compiled, to allow the user to inspect / modify the generated shader. Note that there is a further processing happening after this step, where defines are process (unused code is removed), a shader is converted to uniform format on some platforms (currently on WebGPU) and similar.

Typical use case:

• give materials a userId to recognise when its shader is getting compiled:

myMaterial.userId = 'redMaterial';

• listen to shader:generated events:

app.graphicsDevice.on('shader:generate', (info) => {
    if (info.userMaterialId)
        console.log('shader:generate', info);
});

This is the expected output, in this case the shader is compiled for a shadow pass and a forward pass. You can find relevant info in the `info.shaderPassInfo'. Note that there could be multiple shader compilations based on material settings / vertex format it's used on and similar.

[AndrewRayCode]

nit: it would be great if this had a type so consumers could at least typecast the event as pc.ShaderGenerateEvent or similar