GL Dispatch in Mesa
Several factors combine to make efficient dispatch of OpenGL functions @@ -17,7 +25,7 @@ href="#overview">overview of Mesa's implementation.
1. Complexity of GL Dispatch
Every GL application has at least one object called a GL context. -This object, which is an implicit parameter to ever GL function, stores all +This object, which is an implicit parameter to every GL function, stores all of the GL related state for the application. Every texture, every buffer object, every enable, and much, much more is stored in the context. Since an application can have more than one context, the context to be used is @@ -43,7 +51,7 @@ example, glFogCoordf may operate differently depending on whether or not fog is enabled.
In multi-threaded environments, it is possible for each thread to have a -differnt GL context current. This means that poor old glVertex3fv +different GL context current. This means that poor old glVertex3fv has to know which GL context is current in the thread where it is being called.
@@ -75,7 +83,7 @@ table. void glVertex3f(GLfloat x, GLfloat y, GLfloat z) { const struct _glapi_table * const dispatch = GET_DISPATCH(); - + (*dispatch->Vertex3f)(x, y, z); }-
-
- If GLX_USE_TLS is defined, method #4 is used. -
- If PTHREADS is defined, method #3 is used. -
- If WIN32_THREADS is defined, method #2 is used. -
- If none of the preceeding are defined, method #1 is used. +
- If GLX_USE_TLS is defined, method #3 is used. +
- If HAVE_PTHREAD is defined, method #2 is used. +
- If none of the preceding are defined, method #1 is used.
Two different techniques are used to handle the various different cases. On x86 and SPARC, a macro called GL_STUB is used. In the preamble of the assembly source file different implementations of the macro are -selected based on the defined preprocessor variables. The assmebly code +selected based on the defined preprocessor variables. The assembly code then consists of a series of invocations of the macros such as:
@@ -234,7 +241,7 @@ first technique, is to insert #ifdef within the assembly implementation of each function. This makes the assembly file considerably larger (e.g., 29,332 lines for glapi_x86-64.S versus 1,155 lines for glapi_x86.S) and causes simple changes to the function -implementation to generate many lines of diffs. Since the assmebly files +implementation to generate many lines of diffs. Since the assembly files are typically generated by scripts (see below), this isn't a significant problem. @@ -266,5 +273,6 @@ included.4. Automatic Generation of Dispatch Stubs
+