92 lines
2.8 KiB
Text
92 lines
2.8 KiB
Text
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Using Extensions
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----------------
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To use an OpenGL extension in the code is is necessary to include a refference
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to the extensions.hxx header file and add the following to the code (as an
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example):
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/* global variables */
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glPointParameterfProc glPointParameterfPtr = 0;
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glPointParameterfvProc glPointParameterfvPtr = 0;
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bool glPointParameterIsSupported = false;
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To be able to use these extensions the functions pointers have to be initialized
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by something like the following examplde code:
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if (SGIsOpenGLExtensionSupported("GL_EXT_point_parameters") )
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{
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glPointParameterIsSupported = true;
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glPointParameterfPtr = (glPointParameterfProc)
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SGLookupFunction("glPointParameterfEXT");
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glPointParameterfvPtr = (glPointParameterfvProc)
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SGLookupFunction("glPointParameterfvEXT");
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} else if ( SGIsOpenGLExtensionSupported("GL_ARB_point_parameters") ) {
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glPointParameterIsSupported = true;
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glPointParameterfPtr = (glPointParameterfProc)
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SGLookupFunction("glPointParameterfARB");
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glPointParameterfvPtr = (glPointParameterfvProc)
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SGLookupFunction("glPointParameterfvARB");
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} else
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glPointParameterIsSupported = false;
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If a function is supported the function pointers are now initialized.
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When using the functions (note that glPointParameterfvPtr() is used instead of
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glPointParameterfvEXT() )it is important to check whether the
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glPointParameterIsSupported is set to true:
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if ( distance_attenuation && glPointParameterIsSupported )
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{
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// Enable states for drawing points with GL_extension
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glEnable(GL_POINT_SMOOTH);
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float quadratic[3] = {1.0, 0.001, 0.0000001};
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// makes the points fade as they move away
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glPointParameterfvPtr(GL_DISTANCE_ATTENUATION_EXT, quadratic);
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glPointParameterfPtr(GL_POINT_SIZE_MIN_EXT, 1.0);
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}
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Adding Extensions
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-----------------
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To add an extension to the SimGear extension support code you normally only need
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to edit the extensions.hxx header file in the screen directory.
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Currently there are two extensions supported:
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* glPointParameterf
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* glActiveTexture
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Adding a new extension involves adding the defines assosiated with the extension
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(surrounded by the appropriate extension test):
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#ifndef GL_EXT_point_parameters
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# define GL_EXT_point_parameters 1
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# define GL_POINT_SIZE_MIN_EXT 0x8126
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# define GL_DISTANCE_ATTENUATION_EXT 0x8129
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#endif
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This is needed because not all OpenGL implementations define them correctly.
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The following step is to add a typedef for the function pointer:
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typedef void (APIENTRY * glPointParameterfProc)(GLenum pname, GLfloat param);
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The APIENTRY refference is only used by windows machines but is defined empty
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for all other platforms and hence needs to be added for cross platfrom
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compatibillity.
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