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

4.4 Visualization Framework
• shallows::RenderTexture2D(texture_ptr tex) defines textures to store (shader/render)
results off screen
• shallows::Program and the derived shallows::GLProgram define a GLSL shader
object. A shader object can be invoked by simple command functions like ...::run()
or ...::activate() and initialized with the file containing the shader (or an application
internal string) by ...::readFile(const char*) or similar functions.
• Additional input for each shader can be submitted by functions like
...::setParamx*(const char *name,...) 1 and for input textures
...::setInputTexture(const char *name, ...) where char* name always refer
to a string similar to the variable’s/texture’s name as defined in a shader as
uniform variable; see next paragraph 4.4.1.2 for ”uniform variables”.
Basically, these four kinds of objects are the main requirements for using any shader
instead of an implementation with direct OpenGL commands. Nevertheless, these
classes should always be instanced with boost shared pointers [Abrahams2007] to ensure
a smart and correct memory management. Certainly there are also additionally
more complex functions available for special needs but with this basic equipment many
algorithms can be implemented.
GLSL
GLSL is a C-like high level language to perform even complex operation on graphics
hardware vertex or fragment processing units. In the next lists only the data types,
some important built-in functions and always available values and these values which
have to be set necessarily in each program are defined.
For using more of GLSL’s
capabilities the interested reader is referred to [Fernandes2007; Tatarchuk2004]. First
of all, listing 4.1 shows the simplest possible shader. Actually, these GLSL-shader does
nothing else than passing through values.
Listing 4.1: A very simple vertex and fragment shader in Shallows notation. They will
do nothing else than passing through the given input vertices and colorize interpolated
fragments between with a given texture.
1 [ Vertex shader ]
2
1 ”x*” can refer to 1f, 1i, ... 4fv, 4iv, Matrix4fv as type qualifier.
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