source/blender/draw/engines/eevee/shaders/volumetric_vert.glsl


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out vec4 vPos;

void main()
{
	/* Generate Triangle : less memory fetches from a VBO */
	int v_id = gl_VertexID % 3; /* Vertex Id */
	int t_id = gl_VertexID / 3; /* Triangle Id */

	/* Crappy diagram
	 * ex 1
	 *    | \
	 *    |   \
	 *  1 |     \
	 *    |       \
	 *    |         \
	 *  0 |           \
	 *    |             \
	 *    |               \
	 * -1 0 --------------- 2
	 *   -1     0     1     ex
	 **/
	vPos.x = float(v_id / 2) * 4.0 - 1.0; /* int divisor round down */
	vPos.y = float(v_id % 2) * 4.0 - 1.0;
	vPos.z = float(t_id);
	vPos.w = 1.0;

#ifdef USE_ATTR
	pass_attr(vec3(0.0));
#endif
}