I am attempting to write a LUT shader similar to this or this, but am encountering problems when trying to implement the blue channel portion of the lookup algorithm. Whenever I add it to my code, a lot of the pixels become miss-colored :
Here is what the original colors are supposed to be like without the shader enabled:
And without the blue offset enabled:
Here is the fragment shader which performs the mappings:
"void main() {",
" highp vec2 uv = vUv0; // variable_vertex.xy; // interpolated at pixel's center",
"",
"float blueOffset[9] = float[](0.,0.125,0.25,0.375,0.5,0.625,0.75,0.875,0.875);",
"vec4 color = texture2D(uColorBuffer,uv);",
"int blueIndexY= int(floor(color.b * 8.));",
"int blueIndexX = int(floor(mod(color.b * 64.,8.)));",
"float lutX = color.r /8. + blueOffset[blueIndexX] ;",
"float lutY =color.g /8. + blueOffset[blueIndexY];",
"float filterOffset = 0.5/512.;",
"vec2 newUV = vec2(lutX + filterOffset,lutY + filterOffset );",
"vec4 checkColor = texture2D(uLUTTexture,newUV);",
"gl_FragColor = checkColor;",
"}"
I used an array to store the potential values of the blue offset in order to get rid of some of the potential issues from casting/to get rid of some casts. I have also calculated the values directly in the code but the output is the same. I assume it is an issue with rounding but none of my fixes have worked 
.
Here is my scene: https://playcanvas.com/editor/scene/2181714