Commits on Dec 6, 2018

1. Use the texture filtering hardware to reduce the number of sample ope… …

   …rations in
   
   the blur shader.
   
   Linear filtering allows us to evaluate the formula
   
       k₀c₀ + k₁c₁                 (Formula 1)
   
   where c₀ and c₁ are the colors of adjacent texels and k₀ and k₁ are arbitrary
   factors (in this case, the results of evaluating the Gaussian function) with a
   single lookup. Linear filtering evaluates the following expression for some t
   between 0 and 1:
   
       lerp(c₀, c₁, t)
   
   It can be shown algebraically that Formula 1 is equivalent to:
   
                    ⎛           k₁  ⎞
       (k₀ + k₁)lerp⎜c₀, c₁, ───────⎟
                    ⎝        k₀ + k₁⎠
   
   Which can be readily evaluated by letting `t = k₁/(k₀ + k₁)` and performing a
   texture lookup.

   

   pcwalton committed Dec 6, 2018

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