= 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.


== Introduction ==
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.