White furnace test

The white furnace test is a classic sanity check for physically-based renderers. Place a perfectly reflective object inside a uniform white environment, and it should be indistinguishable from the background, no matter how metallic and rough. Any object that remains visible is a sign that the shader is creating or absorbing energy it shouldn't.

Bevy used to fail this test, meaning something was wrong with our shader math. Two bugs were responsible:

• Seams were visible when using GeneratedEnvironmentMapLight for certain surface orientations.
• Partially metallic materials absorbed energy, appearing darker than they should be.

After fixing those, Bevy passes the test. That means your materials will behave more correctly under image-based lighting.

A gray image has never been so exciting!