We have a limited number of interpolants, and 2 were used for spotlights,
but this is a fairly uncommon case, so we move the calculation to the
fragment shader. A side effect of this is that we are not limited to
two spot-light anymore from the shader's point of view.
This essentially adds a vector transform per fragment, but on the other
hand, it removes communication between the vertex and fragment shader,
as well as interpolation of the position.
This fixes dynamic lighting and SSAO when a viewport is not in 0,0.
In practice this currently happens only when all post-processing is
disabled.
Instead of using gl_FragCoord we introduce a new API,
getNormalizedViewportCoord(), which as the name implies returns
normalized [0, 1] viewport coordinates with origin at the bottom-left,
on all platforms.
This is implemented in this PR by interpolating gl_Position.
* Add support for bent normals
Bent normals can be enabled via the bentNormal property of a material.
When specular occlusion is enabled, bent normals improve the quality
of the computation.
* Save a couple of multiplications in bent specular AO
This is a prep step for the upcoming morph feature and does not require
a bump to our material version number.
Stay tuned for a new sample app that demonstrates this feature.
This replaces the previous "curvature to roughness" method. Both are related
and rely on the screen space variance of geometric normals but this new
solution offers more control (the screen space variance and the clamping
threshold can be controlled).
In the public docs and materials API, Filament "variables" are custom
interpolants (outputs of VS, inputs of FS). However we internally used
"variables" to also refer to built-in VS inputs.
CodeGenerator had a generateVariable method and a generateVariables
method, which did something completely different. :)
