Shader lookup textures

A popular feature among RetroArch users the ability to access external textures. This means we have several samplers available for use. In the config file, we define the textures as so:

textures = " foo ; bar"
foo = path_foo.png
bar = bar_foo.png
foo_linear = true # Linear filtering for foo.
bar_linear = true # Linear filtering for bar.

RetroArch PS3 uses PNG as the main format, RetroArch can use whatever if Imlib2 support is compiled in. If not, it’s restricted to lop-left ordered, non-RLE TGA.

From here on, foo and bar can be found as uniforms in the shaders. The texture coordinates for the lookup texture will be found in TEXCOORD1. This can simply be passed along with TEXCOORD0 in the vertex shader as we did with TEXCOORD0.

Here we make a fragment shader that blends in two background picture at a reduced opacity. Do NOT assign lookup textures to a certain TEXUNIT, Cg will assign a fitting texture unit to the sampler.

float4 main_fragment ( uniform sampler2D s0 : TEXUNIT0,
                       uniform sampler2D foo,
                       uniform sampler2D bar,
                       float2 tex : TEXCOORD0,
                       float2 tex_lut : TEXCOORD1) : COLOR
{
   float4 bg_sum = (tex2D(foo, tex_lut) + tex2D (bar , tex_lut)) * 0.15;
   return lerp (tex2D(s0, tex), bg_sum, bg_sum.a); // Alpha blending.
}

Results: a shader for drawing a background border