#pragma BLENDER_REQUIRE(common_view_lib.glsl)

uniform float sphere_size;
uniform int offset;
uniform ivec3 grid_resolution;
uniform vec3 corner;
uniform vec3 increment_x;
uniform vec3 increment_y;
uniform vec3 increment_z;
uniform vec3 screen_vecs[2];

flat out int cellOffset;
out vec2 quadCoord;

const vec2 pos[6] = vec2[6](vec2(-1.0, -1.0),
                            vec2(1.0, -1.0),
                            vec2(-1.0, 1.0),

                            vec2(1.0, -1.0),
                            vec2(1.0, 1.0),
                            vec2(-1.0, 1.0));

void main()
{
  int cell_id = gl_VertexID / 6;
  int vert_id = gl_VertexID % 6;

  vec3 ls_cell_location;
  /* Keep in sync with update_irradiance_probe */
  ls_cell_location.z = float(cell_id % grid_resolution.z);
  ls_cell_location.y = float((cell_id / grid_resolution.z) % grid_resolution.y);
  ls_cell_location.x = float(cell_id / (grid_resolution.z * grid_resolution.y));

  cellOffset = offset + cell_id;

  vec3 ws_cell_location = corner +
                          (increment_x * ls_cell_location.x + increment_y * ls_cell_location.y +
                           increment_z * ls_cell_location.z);

  quadCoord = pos[vert_id];
  vec3 screen_pos = screen_vecs[0] * quadCoord.x + screen_vecs[1] * quadCoord.y;
  ws_cell_location += screen_pos * sphere_size;

  gl_Position = ViewProjectionMatrix * vec4(ws_cell_location, 1.0);
  gl_Position.z += 0.0001; /* Small bias to let the icon draw without zfighting */
}