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

2.2 Advanced Graphics Processing
pass. Since passing back the results in the same render pass is currently only available
on late-breaking Nvidia G8x architectures, the programmer will have to by-pass this in
a way called multi-pass rendering .
• multi-pass rendering uses the output buffer or texture which was generated in on
render pass in the next render pass as input.
• single-pass rendering, in contrast, generates the final result in one render pass.
Additional to multi-pass rendering a technique called double buffering has to be used
due to most hardware’s disability to read and write to the same texture. This technique
switches two identical textures in each render pass. Depending on the frame rate of
the application these textures are subsequently exchanged and updated. Subsequently,
only one iteration step can be performed each frame but this for millions of parallel
iterations at once. Depending on the settling time of the system or an abort criterion,
such calculation updates of parallel systems can be performed much faster on nearly
all currently available graphics hardware cards than on a CPU with this method.
Despite these shortcomings there are also several comforts when programming
graphics hardware. For example a bilinear or trilinear interpolation, not only for a
texture, can be performed with hardware implemented units. This interpolation tends
to be really fast. Furthermore all in hardware implemented clipping mechanisms can
be used for many parts of standard algorithms which can imply another speedup.
Concluding, it must be noted that shader programs can not replace conventional
application programs due to the lack of high level languages but for problems with a high
arithmetic intensity as defined by equation 2.8. For sequential data access, GPU stream
processors can increase the performance remarkable. Since complex visualizations are
commonly linked to highly parallel costly calculations a programmable graphics card
is rather predestined for both: Calculation of the desired simulations and a subsequent
direct rendering of them.
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