Per pixel lightning mean that you calculate the light illumination per pixel and not f.e. like gourad shading does per vertex and interpolate the color across the triangle. The vertex shader is optimized for per vertex operations and the pixel shader is optimized for per pixel operations that's why it is more suitable to do the matrix calulations on the vertexshader and lightning on the pixel shader.
the_prodigyMember Since 17 Jun 2013
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