Though many particle systems can be modeled with points and lines, quadrilaterals (quads) combined with textures allow more interesting effects. The texture can contain extra surface detail and can be partially transparent to break up the regularity of the quad shape. A quad can be assigned a normal and a
Material node component to allow it to be affected by lighting in the scene.
The only danger with these additional features is that they may decelerate rendering. The example here only utilizes a single
Texture2D object and stores all the quads in a single
QuadArray, thereby reducing the overheads of texture and shape creation considerably.
The effect I'm after with this example is suitably gory: a fountain of blood corpuscles gushing up from the origin. Each "blood" particle is roughly spherical and oscillates slightly as it travels through the air.
Figure 21-6. A fountain of blood from the back
It's a mistake to represent the particles using
GeometryArray meshes; the number of vertices required for a reasonable blood cell would severely restrict the total number of particles that could be created. Instead the effect is achieved by trickery: the particle system is placed inside an