Particles

I came down on OpenGL a little heavier than on D3D in the last post, so to redress the balance I have to say that OpenGL instancing is very nice indeed; much nicer than D3D.

Here's some code:

void R_DrawParticles (void)
{
 int i, j;
 particle_t *p;

 if (!r_newrefdef.num_particles) return;

 GL_UseProgram (gl_particleprog);

 glUniformMatrix4fv (u_partmatrix, 1, GL_FALSE, r_mvpmatrix.m[0]);
 glUniform3fv (u_partrorigin, 1, r_origin);
 glUniform3fv (u_partvpn, 1, vpn);
 glUniform3fv (u_partvright, 1, vright);
 glUniform3fv (u_partvup, 1, vup);

 GL_Enable ((BLEND_BIT | DEPTHTEST_BIT) | (gl_cull->value ? CULLFACE_BIT : 0));

 GL_EnableVertexAttribArrays (VAA0 | VAA1 | VAA2);
 glBindBuffer (GL_ARRAY_BUFFER, gl_particledynamicvbo);

 if (r_firstparticle + r_newrefdef.num_particles >= MAX_PARTICLES)
 {
  glBufferData (GL_ARRAY_BUFFER, MAX_PARTICLES * sizeof (particle_t), NULL, GL_STREAM_DRAW);
  r_firstparticle = 0;
 }

 glVertexAttribPointer (0, 3, GL_FLOAT, GL_FALSE, sizeof (particle_t), (void *) (r_firstparticle * sizeof (particle_t)));
 glVertexAttribPointer (1, 4, GL_UNSIGNED_BYTE, GL_TRUE, sizeof (particle_t), (void *) (r_firstparticle * sizeof (particle_t) + 12));

 if ((p = glMapBufferRange (GL_ARRAY_BUFFER, r_firstparticle * sizeof (particle_t), r_newrefdef.num_particles * sizeof (particle_t), BUFFER_MAP_BITS)) == NULL)
 {
  ri.Con_Printf (PRINT_ALL, "R_DrawParticles : glMapBufferRange failed\n");
  return;
 }

 memcpy (p, r_newrefdef.particles, r_newrefdef.num_particles * sizeof (particle_t));
 glUnmapBuffer (GL_ARRAY_BUFFER);

 glBindBuffer (GL_ARRAY_BUFFER, gl_particletexcoordvbo);
 glVertexAttribPointer (2, 2, GL_FLOAT, GL_FALSE, 0, (void *) 0);

 glVertexAttribDivisor (0, 1);
 glVertexAttribDivisor (1, 1);

 glDrawArraysInstanced (GL_TRIANGLE_FAN, 0, 4, r_newrefdef.num_particles);

 glVertexAttribDivisor (0, 0);
 glVertexAttribDivisor (1, 0);

 r_firstparticle += r_newrefdef.num_particles;
}