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vec3 evalEnvironmentMap( in vec3 R, float roughness )
{
// convert R to spherical texture coordinates
vec2 tc = vec2( ( atan( R.x, -R.z ) + PI ) / ( PI_TWO ), acos( -R.y ) / PI );
vec2 envMapSize = vec2( textureSize( uEnvironmentTexture, 0 ) );
float envMapLevels = log2( max( envMapSize.x, envMapSize.y ) );
// simulate textureQueryLod
vec2 dx = dFdx( tc * envMapSize.x );
vec2 dy = dFdy( tc * envMapSize.y );
float px = dot( dx, dx );
float py = dot( dy, dy );
float maxlod = 0.5 * log2( max( px, py ) ); // log2(sqrt()) = 0.5*log2()
float minlod = 0.5 * log2( min( px, py ) );
//float lod = max(0.0, maxlod - min( maxlod - minlod, envMapLevels ));
float lod = max(0.0, min( minlod, envMapLevels ));
float roughLevel = mix( lod , envMapLevels, roughness );
return( textureLod( uEnvironmentTexture, tc, roughLevel ).rgb );
}
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