blendAdd.metal

kernel void blendAdd(
                  texture2d<float, access::write> outTex [[texture(0)]],
                  texture2d<float, access::read> inTex [[texture(1)]],
                  texture2d<float, access::read> inTex2 [[texture(2)]],
                  uint2 gid [[thread_position_in_grid]]) {
    float4 c = inTex.read(gid).rgba;
    float4 add = inTex2.read(gid).rgba;
    c.rgb += add.rgb;
    outTex.write(c.rgba, gid);
}