From 7a2af605c2c2b0d2e9bbb0b161eba8842acefbcb Mon Sep 17 00:00:00 2001 From: marha Date: Fri, 15 Jun 2012 08:28:24 +0200 Subject: fontconfig mesa pixman xserver git update 15 juni 2012 --- mesalib/docs/dispatch.html | 50 ++++++++++++++++++++++------------------------ 1 file changed, 24 insertions(+), 26 deletions(-) (limited to 'mesalib/docs/dispatch.html') diff --git a/mesalib/docs/dispatch.html b/mesalib/docs/dispatch.html index 620aecd74..e40b41a60 100644 --- a/mesalib/docs/dispatch.html +++ b/mesalib/docs/dispatch.html @@ -1,19 +1,20 @@ - - -GL Dispatch in Mesa - - - - -

GL Dispatch in Mesa

+ + + + + GL Dispatch in Mesa + + + +

GL Dispatch in Mesa

Several factors combine to make efficient dispatch of OpenGL functions fairly complicated. This document attempts to explain some of the issues and introduce the reader to Mesa's implementation. Readers already familiar -with the issues around GL dispatch can safely skip ahead to the overview of Mesa's implementation.

+with the issues around GL dispatch can safely skip ahead to the 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 @@ -46,8 +47,7 @@ differnt 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.

- -

2. Overview of Mesa's Implementation

Mesa uses two per-thread pointers. The first pointer stores the address of the context current in the thread, and the second pointer stores the @@ -75,7 +75,7 @@ table. void glVertex3f(GLfloat x, GLfloat y, GLfloat z) { const struct _glapi_table * const dispatch = GET_DISPATCH(); - + (*dispatch->Vertex3f)(x, y, z); } Sample dispatch function @@ -89,14 +89,14 @@ overhead that it adds to every GL function call.

3. Optimizations

A number of optimizations have been made over the years to diminish the performance hit imposed by GL dispatch. This section describes these optimizations. The benefits of each optimization and the situations where each can or cannot be used are listed.

3.1. Dual dispatch table pointers

The vast majority of OpenGL applications use the API in a single threaded manner. That is, the application has only one thread that makes calls into @@ -131,7 +131,7 @@ the common case.

Improved GET_DISPATCH Implementation -

3.2. ELF TLS

Starting with the 2.4.20 Linux kernel, each thread is allocated an area of per-thread, global storage. Variables can be put in this area using some @@ -161,7 +161,7 @@ extern __thread struct _glapi_table *_glapi_tls_Dispatch GLX_USE_TLS. Any platform capable of using TLS should use this as the default dispatch method.

3.3. Assembly Language Dispatch Stubs

Many platforms has difficulty properly optimizing the tail-call in the dispatch stubs. Platforms like x86 that pass parameters on the stack seem @@ -170,7 +170,7 @@ routines are very short, and it is trivial to create optimal assembly language versions. The amount of optimization provided by using assembly stubs varies from platform to platform and application to application. However, by using the assembly stubs, many platforms can use an additional -space optimization (see below).

+space optimization (see below).

The biggest hurdle to creating assembly stubs is handling the various ways that the dispatch table pointer can be accessed. There are four @@ -235,7 +235,7 @@ 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 -are typically generated by scripts (see below), this +are typically generated by scripts (see below), this isn't a significant problem.

Once a new assembly file is created, it must be inserted in the build @@ -245,8 +245,7 @@ step is to add the correct #ifdef magic to src/mesa/glapi/glapi_dispatch.c to prevent the C version of the dispatch functions from being built.

- -

3.4. Fixed-Length Dispatch Stubs

To implement glXGetProcAddress, Mesa stores a table that associates function names with pointers to those functions. This table is @@ -265,8 +264,7 @@ dispatch stub.

src/mesa/glapi/glapi.c just before glprocs.h is included.

- -

4. Automatic Generation of Dispatch Stubs

- - + + -- cgit v1.2.3