MeshMatcapMaterial: update default matcap

[WestLangley]

Previously, if the matcap was not defined, the shader would render white:

We can actually improve on the default with a small change to the shader:

Just a suggestion... :-)

[mrdoob]

Interesting... Another option would be to generate a default matcap DataTexture?

[WestLangley]

Another option would be to generate a default matcap DataTexture?

Yes, this PR was in lieu of doing something like this:

const matcap = new THREE.DataTexture( new Uint8Array( [ 50, 50, 50, 200, 200, 200 ] ), 1, 2, THREE.RGBFormat );
matcap.encoding = THREE.LinearEncoding;
matcap.minFilter = THREE.LinearFilter;
matcap.magFilter = THREE.LinearFilter;
matcap.generateMipmaps = false;
matcap.needsUpdate = true;

The result is similar.

[mrdoob]

I think I prefer the DataTexture approach. The "dumber" the shaders are the better.

[Mugen87]

const matcap = new THREE.DataTexture( new Uint8Array( [ 50, 50, 50, 200, 200, 200 ] ), 1, 2, THREE.RGBFormat );

For the reasons mentioned in #22293 (comment), I suggest to not use RGBFormat in new code anymore. At some point, we should even consider to possible deprecate all RGB formats.

WebGPU does not support them anyway, see gpuweb/gpuweb#66.

[WestLangley]

So, @Mugen87 @mrdoob, it would be the renderer's responsibility to populate a default matcap if none is specified. This would be checked per-frame. Is that right?

//

FYI, you do not require that approach for the MeshToonMaterial gradient texture.

three.js/src/renderers/shaders/ShaderChunk/gradientmap_pars_fragment.glsl.js

Lines 9 to 25 in 1a241ef

	vec3 getGradientIrradiance( vec3 normal, vec3 lightDirection ) {
	// dotNL will be from -1.0 to 1.0
	float dotNL = dot( normal, lightDirection );
	vec2 coord = vec2( dotNL * 0.5 + 0.5, 0.0 );
	#ifdef USE_GRADIENTMAP
	return vec3( texture2D( gradientMap, coord ).r );
	#else
	return ( coord.x < 0.7 ) ? vec3( 0.7 ) : vec3( 1.0 );
	#endif
	}

I am implementing the same approach here.

[Mugen87]

The PR in its current form provides indeed the simpler solution. It would be nice to avoid the per-frame checks in the renderer.

[WestLangley]

@Mugen87 So, is that a tacit approval? :-)

[mrdoob]

Changed my mind 🤓

[mrdoob]

Thanks!