Master's Thesis - Studierstube Augmented Reality Project - Graz ...

5.3 Visualization nodes and subgraphs
Figure 5.11: A double buffered ”Position Texture” stores the current position of each
particle and ”Attribute Texture” the color assigned to a certain velocity or the particle.
The ”Reset Texture” is used if no velocity value has been found of the particle left the
volume or if it exceeded its maximum lifetime. The initial positions which are stored in
this texture are predefined randomly but they can even be arranged so that for example
some kind of streak-line will result. The ”Field Texture” stores the current flow volume
for texture lookup and can be changed during rendering in case of 4D-volumes.
frame via the OpenGL API to the stream processors would cost over 50% of the framerate.
Consequently, they get stored in a display list during the initialization step. Over
all this simple particle effect performes - assuming a buffer-size of 1024x1024, which
refers to over one million particles - with a frame-rate between 100 and 150 frames per
second on the hardware described in section 6.1. The frame rate was evaluated with
an artificial flow dataset.
Listing 5.4: Pseudo shader code for the simplest form of a GPGPU particle system
applicable to a predefined 3D velocity texture.
1 init arbitrary positions in init = reset texture
2 init ages randomly in attribute texture
3
4 [ Fragment shader ] // output : attribute texture
5 uniform attribute_texture ;
6 uniform position_texture ;
7 uniform color_mapping_1D_texture ;
8
9 if age of particle