Support custom outputs for ShaderMaterial

Feature requests
, ,
3

Thanks for this suggestion. I did notice that using #extension GL_EXT_draw_buffers : require would suppress the preprocessor from adding the default glFragColor target though I’m not super keen on that API as GL_EXT_draw_buffers is designed for WebGL1 and doesn’t necessarily express what I’m trying to do when using a single framebuffer.
I wonder if there would be some value in adding a field to IShaderMaterialOptions which would suppress the default output, or perhaps doing something like:

#define CUSTOM_OUTPUT
layout (location = 0) out ivec4 outTarget;

This, however, only solves half of the problem though, because at the moment Babylon doesn’t support clearing render targets with an INT or UNSIGNED_INT type as it requires calling clearBufferiv and clearBufferuiv respectively.
I imagine this would only be a small change to ThinEngine.clear() along the lines of:

(...)
 if (this._currentRenderTarget) {
                const textureFormat = this._currentRenderTarget.texture?.format;
                if (textureFormat === Constants.TEXTUREFORMAT_R_INTEGER ||
                    textureFormat === Constants.TEXTUREFORMAT_RG_INTEGER ||
                    textureFormat === Constants.TEXTUREFORMAT_RGB_INTEGER || 
                    textureFormat === Constants.TEXTUREFORMAT_RGBA_INTEGER) {

                        const textureType = this._currentRenderTarget.texture?.type;
                        if (textureType === Constants.TEXTURETYPE_UNSIGNED_INTEGER ||
                            textureType === Constants.TEXTURETYPE_UNSIGNED_SHORT) {
                                this._gl.clearBufferuiv(this._gl.COLOR, 0, new Uint32Array([color.r, color.g, color.b, color.a]));
                            } else {
                                this._gl.clearBufferiv(this._gl.COLOR, 0, new Int32Array([color.r, color.g, color.b, color.a]))
                            }

                } else {
                    mode |= this._gl.COLOR_BUFFER_BIT;
                }
            } else {
                mode |= this._gl.COLOR_BUFFER_BIT;
            }
(...)

I appreciate your thoughts!