# Graphics program to display particles slowly drifting upwards
class SmokeProgram
	super ParticleProgram

	redef fun vertex_shader_core do return """
		vec4 c = center;
		c.y += dt * 1.0;
		c.x += dt * 0.1;

		gl_Position = c * mvp;
		gl_PointSize = scale / gl_Position.z * (pt+0.1);

		if (pt < 0.1)
			v_color *= pt / 0.1;
		else
			v_color *= 1.0 - pt*0.9;
	"""
end