The operations (transformations) which one needs for the transformation stacks aren't general purpose 4D transformations they're really 3D transformations done in 4D homogenous space. When I implemented my matrix classes I omitted this functionality from the mat4 class and implemented them as part of the TStack class.
SAMPLE OPENGL PROGRAM IN C ON MACOS CODE
In the author's original matrix code functions used to perform model-view, and projection stack transformations were implemented as functions which operated on mat4 objects. Any attempt to pop the last entry off of the stack will cause the pop() method to throw an exception. The default constructor creates a stack with one entry containing the identity matrix. Since TStack implements a stack, it has, as one would expect, methods for pushing and popping the stack. By using the vector class template the transformation stack depth is only limited by the amount of memory which the application can access. Īt its core, the TStack class is a std::vector. I named my transformation stack class TStack. In this post I replace these hardcoded limits replacing fixed length arrays of mat4 entries with my own transformation stack class objects. For the model-view transformation stack I, personally, have never needed to have more than 32 entries, still others may need support for a deeper stack so hardcoding the model-view stack to 32 entries may be short sighted. That the original GFX module hardcodes a stack depth of 32 for the projection and texture stacks is almost certainly a waste. The projection, and texture stacks were only required to support a stack depth of at least 2. Legacy OpenGL required that the model-view stack would support a stack of at least 32 entries.
The author's implementation limits the stack depth of the model-view, projection, and texture transformation stacks to 32 entries each. The GFX module provided by the author mimics this legacy functionality, without support for the color transformation stack.
Using modern versions of OpenGL, such as OpenGL ES, the programmer either has to provide this functionality for himself, or use a library which provides the functionality for him. This functionality has been deprecated but the functionality is still needed by graphics programmers. The programmer selected which stack was operated on by these functions by calling the glMatrixMode() function. OpenGL provided a collection of functions which the programmer used to manipulate these transformation stacks. Later OpenGL added optional support for a color transformation stack via the ARB_imaging extension. Legacy OpenGL supported three transformation stacks: model-view, projection, and texture. This will be the last preparation step before I present rewriting the GFX module as a proper C++ class.Ī copy of the code as described in this post can be downloaded from GitHub using the tag tstack. Below I'll discuss replacing the last portion of the author's transformation code used in the GFX module with my own library.
SAMPLE OPENGL PROGRAM IN C ON MACOS ANDROID
This post continues the series discussing ways I've rewritten the sample code from the book Game and Graphics Programming for iOS and Android with OpenGL ES 2.0.
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