how to use GL_RGB9_E5 format?

Question

I am trying to use GL_RGB9_E5 format with 3D texture. For this I have created simple test to understand the usage of format. Somehow I am not getting what I expect. Following is test program

GLuint texture;
const unsigned int depth = 1;
const unsigned int width = 7;
const unsigned int height = 3;

glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_3D, texture);
const float color[3] = { 0.0f, 0.5f, 0.0f };
const rgb9e5 uColor = float3_to_rgb9e5(color);

GLuint * t1 = (GLuint*)malloc(width*height*depth* sizeof(GLuint));
GLuint * t2 = (GLuint*)malloc(width*height*depth* sizeof(GLuint));
int index = 0;
for (int i = 0; i < depth; i++)
    for (int j = 0; j < width; j++)
        for (int k = 0; k < height; k++)
        {
            t1[index] = uColor.raw;
            index++;
        }

glTexImage3D(GL_TEXTURE_3D, 0,
    GL_RGB9_E5,
    width, height, depth, 0,
    GL_RGB,
    GL_UNSIGNED_INT,
    (void*)t1);

glGetTexImage(GL_TEXTURE_3D, 0, GL_RGB, GL_UNSIGNED_INT_5_9_9_9_REV, t2);

index = 0;
for (int i = 0; i < depth; i++)
    for (int j = 0; j < width; j++)
        for (int k = 0; k < height; k++)
        {
            rgb9e5 t;
            t.raw = t2[index];
            index++;
        }

What I am expecting is what ever uColor.raw I am putting in t1 I get back same raw color in t2 .

I have taken float3_to_rgb9e5 method from Specification for GL_RGB9_E5 at bottom you can find code.

It would be great If someone can give me example for how to use it correctly or correct way of doing it.

Answer 1

    GL_RGB,
    GL_UNSIGNED_INT,

This means that you are passing 3-channel pixel data, where each channel is a normalized, 32-bit unsigned integer. But that's not what you're actually doing.

You're actually passing 3 channel data, which is packed into a 32-bit unsigned integer, such that the first 5 bits represent a floating-point exponent, followed by 3 sets of 9-bits, each representing the unsigned mantissa of a float. We spell that:

GL_RGB,
GL_UNSIGNED_INT_5_9_9_9_REV