This document provides an overview of the architecture and implementation of OpenGL and the Mesa 3D graphics library on Intel graphics hardware. It describes the interactions between the different components like the DRI and i965 drivers, and how OpenGL commands are translated to hardware operations. Key points covered include initialization, context creation, rendering commands, and the mapping of OpenGL states to hardware state blocks and relocations.

1. GLX, DRI, andi965
olv@LunarG.com
2014-05-06
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2. ltrace of glxgears
XOpenDisplay(nil) = dpy
glXChooseVisual(dpy, 0, 0x7fff3674ceb0, 0) = visual
XCreateWindow(dpy, 151, 0, 0) = win
glXCreateContext(dpy, visual, 0, 1) = ctx
glXMakeCurrent(dpy, win, ctx, 0xeff5) = 1
glXGetProcAddressARB(0x403d4c, 0x403d36, 0, 0xb11e2a) = 0x7fe222677464
...
glClear(0x4100, 0x7fff3674d020, 0xdde0c, 1) = 0
glCallList(3, 0xdc0490, 0x800001, 0xdc0490) = 0x7fa8b79ea040
...
glXSwapBuffers(dpy, win, 0x800001, 0x93a910) = 2
...
glXMakeCurrent(dpy, 0, 0, 3) = 1
glXDestroyContext(dpy, ctx, 0x7fe2228d6b60, 0) = 0
XDestroyWindow(dpy, win, 0x7fe2228d6b60, 0x8f3be0) = 1
XCloseDisplay(dpy) = <void>
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3. 3 / 20

4. libGL.so::__glXInitialize(Display *dpy)
Associate a struct glx_displaywith dpy,
GLXQueryVersion, mandatory
DRI2QueryVersion, required for direct rendering
DRI3QueryVersion, optional
libxcb-*
X protocol C-language Binding
and associate a struct glx_screenwith each of the display screens
GLXGetVisualConfigsand GLXGetFBConfigs
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5. libGL.so::__glXInitialize(Display *dpy)
For each display screen, when DRI2 is supported,
DRI2Connect
returns device name: /dev/dri/card<N>or /dev/dri/renderD<N>
driver name: use libudevand internal driver maps
loads i965_dri.soand exchange "extensions"
"extensions" are tables of function pointers
DRI drivers are window system agnostic
DRI loaders are window system dependent; to support a new window system,
only a new loader needs to be created
stable ABI
intelInitScreen2()
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6. libGL.so::CreateContext(Display *dpy,...)
Create a struct glx_context
brwCreateContext()
GLXCreateContextor GLXCreateNewContext
only when indirect rendering
visuals v.s. fbconfigs
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7. libGL.so::MakeContextCurrent(Display *dpy,...)
remember the current struct glx_context
GLXMakeCurrentor GLXMakeContextCurrent
only when indirect rendering
intelMakeCurrent()
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8. i965_dri.so::intelMakeCurrent(...)
dri2GetBuffersWithFormat()
returns the backing graphics buffers for the current drawable
The current drawable is some window created by XCreateWindow(). This is
window system dependendent and is thus defined provided by the DRI loader.
_glapi_set_dispatch()
set the dispatch table for glXXX()
_glapi_set_context()
set the implicit current context for glXXX()
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9. libGL.so::glXGetProcAddressARB(const GLubyte*)
_glapi_get_proc_address()
every entry in the dispatch table has a name, such as glBindFramebuffer
returns a function pointer that will use the named entry to jump into the DRI
driver
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10. libGL.so::glXSwapBuffers(...)
intel_dri2_flush_with_flags()
resolve (fast clear value, hiz, MSAA buffer, and etc.)
emit batch buffer
DRI2CopyRegion
ask server to emit another batch buffer to copy the content to the front buffer
DRI2SwapBuffers
ask server to make the presented buffer the front buffer of the window (zero-
copy)
when fullscreen, the server may tell the kernel to emit MI_DISPLAY_FLIPto
make the presented buffer the scan-out buffer
GLXSwapBuffers, only when indirect rendering
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11. Source map
.-- src
|-- egl --enable-egl
|-- gallium --enable-{openvg,opencl,xa,xvmc,vdpau,omx}
|-- gbm --enable-gbm
|-- glsl --enable-{opengl,glesv1,glesv2}
|-- glx --enable-glx
|-- loader
`-- mapi
| |-- es1api --enable-gles1
| |-- es2api --enable-gles2
| |-- glapi --enable-glx
| |-- shared-glapi
| `-- vgapi --enable-openvg
.
.
.
(continued)
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12. Source map
.-- src
`-- mesa --enable-{opengl,glesv1,glesv2}
|-- drivers
| |-- dri --enable-dri
| | |-- i915
| | |-- i965
| | `-- swrast
| |-- osmesa --enable-osmesa
| `-- x11
|-- main
|-- math
|-- program
|-- state_tracker
|-- swrast
|-- swrast_setup
|-- tnl
|-- tnl_dd
`-- vbo
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13. Configuring Mesa
The "golden" options are
APIS="--enable-{opengl,glesv1,glesv2}
--enable-glx --enable-dri
--disable-egl"
FEATURES="--enable-shared-glapi
--enable-glx-tls
--enable-texture-float"
DRIVERS="--with-dri-drivers=i965 --with-gallum-drivers="
$ ./configure $APIS $FEATURES $DRIVERS
CC="ccache gcc" CXX="ccache g++"
Or for 32-bit build,
$ ./configure $APIS $FEATURES $DRIVERS --enable-32-bit
CC="ccache gcc -m32" CXX="ccache g++ -m32"
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14. Dependencies
Install dependencies and latest libdrm
$ sudo apt-get build-dep mesa libdrm
$ sudo apt-get install ccache
$ git clone git://anongit.freedesktop.org/mesa/drm
$ mkdir drm/build-x86_64; cd drm/build-x86_64
$ ../configure --libdir='/usr/local/lib/x86_64-linux-gnu'
$ make -j4
$ sudo make install
Tell the dynamic linker where to find libdrm
$ echo /usr/local/lib/x86_64-linux-gnu > /etc/ld.so.conf.d/local.conf
$ sudo ldconfig
and tell Mesa build system where to find libdrm
$ export PKG_CONFIG_PATH=/usr/local/lib/x86_64-linux-gnu/pkgconfig
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15. Dependencies (32-bit)
Follow https://wiki.debian.org/Multiarch/HOWTO (not needed on Ubuntu?), and build
32-bit libdrm
$ sudo apt-get build-dep -a i386 libdrm
$ mkdir drm/build-i386; cd drm/build-i386
$ ../configure --libdir='/usr/local/lib/i386-linux-gnu'
--disable-cairo-tests
CC="gcc -m32"
$ make -j4
$ sudo make install
To install 32-bit dependencies for Mesa, or to get the list of possible dependencies and
install manually when the build-depfails
$ sudo apt-get build-dep -a i386 mesa
or
$ dpkg -l | cut -d' ' -f3 | grep :amd64 | sed 's/:amd64/:i386/'
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16. Options not mentioned yet
--enable-dri3enables support for DRI3protocol in libGL.so
--enable-xlib-glxreplaces libGL.soby one that does not require GLXnor DRI2/DRI3
protocols, and does not support hardware acceleration
--enable-debugenables debug build
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17. Using Mesa without installation
$ cat << EOF > mesa-setup-env
MESA_VARIANT=mesa
MESA_TOP="$HOME/fdo/mesa/$MESA_VARIANT"
export LD_LIBRARY_PATH="$MESA_TOP/lib"
export EGL_DRIVERS_PATH="$MESA_TOP/lib/egl"
export LIBGL_DRIVERS_PATH="$MESA_TOP/lib"
if [ -z "$MESA_PS1" ]; then
MESA_PS1=$PS1
fi
PS1="[$MESA_VARIANT] $MESA_PS1"
EOF
$ . mesa-setup-env
Remember to change $MESA_TOPto point to your Mesa source tree.
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18. i965_dri.so::{_mesa_Clear(),_mesa_CallList()}
brw_clear()
fast depth clear
fast color clear
meta clear
brw_draw_prims()
i965 draw function for GL functions that draw (such as glDrawElements())
brw_upload_state()
brw_predraw_resolve_buffers()
brw_postdraw_set_buffers_need_resolve()
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19. (GL states are converted to this at draw time. Each block is a buffer. Each arrow is a
relocation entry.)
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20. We've got some time left
INTEL_DEBUG=batch, INTEL_DEBUG=auband https://github.com/olvaffe/envytools
INTEL_DEBUG=shader_time
glretrace --pgpu
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