Renders a material captured by rendering a sphere into a texture. The texture captures the sphere’s original shading as well as its environment. The MatCap shader then only has to map screen normals to coordinates on the sphere, so it is very fast to render.
This is useful for quickly previewing a model, with the ability to try different materials and lighting environments by simply swapping out the texture.
The sphere image.
Use MatCap Alpha
Output the texture image’s alpha as opacity.