bloom.c

```c
#define BLOOM_LEVELS 7

int size_bloom[BLOOM_LEVELS][2];

size_bloom[0][0] = MAX(viewport_size_quarter[0], 64);
size_bloom[0][1] = MAX(viewport_size_quarter[1], 64);

for(int i=1; i<BLOOM_LEVELS; i++) {
  size_bloom[i][0] = MAX(ize_bloom[i - 1][0] / 2, 1);
  size_bloom[i][1] = MAX(size_bloom[i - 1][1] / 2, 1);
}

GLuint textures[2]; // Initialize etc
GLuint framebuffers[2][BLOOM_LEVELS]; // Initialize etc

for(int i=0; i<2; i++) {
  // Bind texture[i]
  // You can use glTexImage2D as well if you can't use GL4 extensions
  // http://docs.gl/gl4/glTexStorage2D
  // `size_bloom` must match the sizes that OpenGL expects
  glTexStorage(GL_TEXTURE_2D, BLOOM_LEVELS, GL_RGB, size_bloom[0][0], size_bloom[0][1]);
}

for(int i=0; i<2; i++) {
  for(int j=0; j<BLOOM_LEVELS; j++) {
    // Bind framebuffer[i][j]
    glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, textures[i], j);
  }
}

/* RENDER POSTPROCESS FOR A SINGLE FRAME */

glViewport(0, 0, size_bloom[0][0], size_bloom[0][1]);
// Bind framebuffer[1][0]
// Bind bloom extract shader (the shader would have to output a texture where black = no bloom)
glDrawArrays(fullscreen_quad, ...);

// Bind blur shader
for(int i=0; i<BLOOM_LEVELS; i++) {
  glViewport(0, 0, size_bloom[i][0], size_bloom[i][1]);
  // Bind framebuffer[0][i]
  // Set uniform to signify X axis gaussian blur
  // Set uniform to specify which texture mipmap to source from (see next line)
  int i_previous = ((i == 0) ? i : (i - 1))
  // Set uniform for pixel scale of source texture (see next line)
  float pixel_scale = {1.0 / size_bloom[i_previous][0], 1.0 / size_bloom[i_previous][1]};
  glBindTexture(GL_TEXTURE_2D, textures[1]);
  glDrawArrays(fullscreen_quad, ...);
  
  // Bind framebuffer[1][i]
  // Set uniform to signify X axis gaussian blur
  // Set uniform to specify which texture mipmap to source from (in this case, the value of `i`)
  glBindTexture(GL_TEXTURE_2D, textures[0]);
  glDrawArrays(fullscreen_quad, ...);
}

glViewport(0, 0, size_bloom[0][0], size_bloom[0][1]);
// Bind framebuffer[0][0]
// Bind bloom merge shader (take all source images, additively blend all mipmaps with bicubic filtering)
glBindTexture(GL_TEXTURE_2D, textures[1]);
glDrawArrays(fullscreen_quad, ...);
```