GLSL Unsigned Int Values Not Retrieved Properly

Question

I have packed several values needed for shading a particular vertex into a single 32-bit uint. In the shader, it is unpacked like this:

vec3 color;
uint vertexData = data;
float sunlight, artificialLight;
bool occlusion;

artificialLight = float(vertexData & 31u);
vertexData = vertexData >> 5;
sunlight = float(vertexData & 31u);
vertexData = vertexData >> 5;
occlusion = bool(vertexData & 1u);
vertexData = vertexData >> 1;
color.b = float(vertexData & 127u);
vertexData = vertexData >> 7;
color.g = float(vertexData & 127u);
vertexData = vertexData >> 7;
color.r = float(vertexData & 127u);

The color produced by this extraction is much different from the originally intended color. For example:

130, 245, 90 --> 78, 125, 249   (These values are not exact)

I took the code and put it into my main c++ program and ran it with a debugger. It showed the right values.

130, 245, 90 --> 130, 245, 90 

EDIT

I have taken a uint produced by my compressor and directly inputted it into my shader like this

vertexData = 2179293184;

Every vertex is shaded with the color of green this value corresponds to. So apparently, there is something going wrong with the transmission of the values. What might be causing this?

Answer 1

I suspect your vertex data is being converted to float (and back again).

You should use glVertexAttribIPointer to upload integer vertex data without converting to floating point. From the documentation:

For glVertexAttribPointer, if normalized is set to GL_TRUE, it indicates that values stored in an integer format are to be mapped to the range [-1,1] (for signed values) or [0,1] (for unsigned values) when they are accessed and converted to floating point. Otherwise, values will be converted to floats directly without normalization.

For glVertexAttribIPointer, only the integer types GL_BYTE, GL_UNSIGNED_BYTE, GL_SHORT, GL_UNSIGNED_SHORT, GL_INT, GL_UNSIGNED_INT are accepted. Values are always left as integer values.