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Visualization with OpenGL

Essential approaches to programming computer graphics with Open Graphics Language (OpenGL) graphics library are described. This document serves as the basis for exercises in PRACE Summer of HPC Visualization training. Rationale for giving introduction to OpenGL is that such knowledge is important when developing codes that require some specific visualization for which OpenGL can be handy. Programming Graphical Processing Unit (GPU) through shaders is an important technique to accelerate graphics and other embarrassing parallel problems. OpenGL evolved from immediate mode to GPU only processing with the advent of OpenGL Shading Language (GLSL). Introduction to the subject is given by recipes to follow, discussing important techniques for visualization that can also be extended to general GPU programming for parallel computing. Instead of jumping to the latest OpenGL specification we use minimum required OpenGL 2.1 with the extensions currently available on modest hardware and still be able to use modern OpenGL 3.1+ programming principles.


For the visualization of specific phenomena is usually not possible to use a general purpose visualization tools. Such cases occur especially in the visualization of engineering and physics problems. The modeling results are usually not only simple function plots but complex objects such as graphs, hierarchical structure, animation, motion mechanism, control channels, volume models of specific forms, ...

Through the time different standards were effective for computer graphics. This is mainly due to the complexity of implementation and closed code in the past. OpenGL remains the only widely accepted open standard, which was first introduced on Silicon Graphics workstations (SGI). There exist also a Microsoft Direct3D, which is limited to PCs with Windows and is not as easy to use as OpenGL, which is due to its openness and capacity provided on all operating systems and hardware platforms. OpenGL stagnated for some time with upgrades to the original SGI specification. Many extensions previously available from hardware vendors are now standardized with OpenGL 3+ where things dramatically changed. Immediate mode programming where communication from OS to GPU was regular practice and major obstacle to graphics performance. Programming knowledge of OpenGL 1.x is therefore not recommended for nowadays and can simply be forgotten and treated as legacy.

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