Metal and indirect light

[jwwalker]

By playing with material_sandbox, I see that having a reasonable amount of indirect light is critical to making shiny metal look good; otherwise you see specular highlights and the rest is black. But when I try adding ambient light without a cube map, it does not seem to have any effect on metal, though it works as expected on dielectrics.

    math::float3 ambientColor = { 1.0f, 1.0f, 1.0f };
    _indirLight = IndirectLight::Builder()
		.intensity( 1000000.0f )
		.irradiance( 1, &ambientColor )
		.build( *_engine );
    _scene->setIndirectLight( _indirLight );

Am I doing something wrong?

[romainguy]

irradiance is only used for diffuse lighting. Metals only have specular reflections, you need to provide a cubemap for metals to work. But that cubemap only needs to be a few pixels large and can be only a solid color.

[jwwalker]

That would be set using the IndirectLight::Builder::reflections method? The docs for its cubemap parameter say "Each cubemap level encodes a the irradiance for a roughness level", so we have irradiance there too, which confuses me.

[romainguy]

Yes, by the way for irradiance() you must pass an array of 9*3 floats.

[jwwalker]

Wait, why do I need to pass 9*3 floats to irradiance()? The docs say that the number of bands must be 1, 2, or 3, and the size of the array of float3 is the square of that. So you're saying that the number of bands can't be 1 and must be 3? Under what conditions?

[jwwalker]

For benefit of any others reading this, here's working code that makes a simple ambient light that works on metal.

	static unsigned char oneWhitePixel[] = { 0xFF, 0xFF, 0xFF };
	backend::PixelBufferDescriptor whitePixBuf( oneWhitePixel, sizeof(oneWhitePixel),
		backend::PixelDataFormat::RGB, backend::PixelDataType::UBYTE );
	_whiteCube = Texture::Builder()
		.width(1)
		.height(1)
		.levels(1)
		.sampler( filament::backend::SamplerType::SAMPLER_CUBEMAP )
		.format( filament::backend::TextureFormat::RGB8 )
		.build( *_engine );
	backend::FaceOffsets offsets( 0 );
	_whiteCube->setImage( *_engine, 0, std::move(whitePixBuf), offsets );
	
	_indirLight = IndirectLight::Builder()
		.intensity( 20000.0f )
		.reflections( _whiteCube )
		.build( *_engine );