MeshLambertMaterial and HemisphereLight

[bunnybones1]

Hemisphere light and shadows appear applied in the wrong order on MeshLambertMaterial, in comparison to MeshPhongMaterial.

Here is a scene with a hemisphere light and a spotlight, using MeshPhongMaterial:

Here is the same setup, but the materials are MeshLambertMaterial:

Apparently, in phong's case, the shadows are applied before being re-illuminated with the hemisphere light, but in lambert's case, it looks like the hemisphere applies its illumination to the vertex color in the vertex shader, making it impossible to "re-illuminate" the shadow samples in the fragment shader. Passing an extra light color varying to the fragment for shadow re-illumination could be a solution. I'll try this and report back within a few days.

I should note that using Lambert with shadows and a hemisphere light has a relatively inexpensive but beautiful aesthetic.

I'm using THREE r100.

[Mugen87]

Can you please demonstrate the issue with a simple live example?

[WestLangley]

Hemisphere light and shadows appear applied in the wrong order on MeshLambertMaterial, in comparison to MeshPhongMaterial.

That is not exactly the issue. Hemisphere lights are treated as direct lights in the Lambert shader. However, they are not direct lights; they are indirect lights -- a poor man's model for global illumination.

In fact, the following two lights should provide the same illumination -- and they don't with MeshLambertMaterial when shadows are present:

new THREE.AmbientLight( 0xffffff, 1 );
new THREE.HemisphereLight( 0xffffff, 0xffffff, 1 );

Another problem is shadows in MeshLambertMaterial are a hack -- they mask all direct light. This is a consequence of performing lighting calculations in the vertex shader. We can't fix that.

However, we can fix the artifact you are seeing by correctly treating hemisphere lights as an indirect light source in the shader.