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Graphics API Tracing

branch: dev
README.markdown

About apitrace

apitrace consists of a set of tools to:

  • trace OpenGL, OpenGL ES, Direct3D, and DirectDraw APIs calls to a file;

  • retrace OpenGL and OpenGL ES calls from a file;

  • inspect OpenGL state at any call while retracing;

  • visualize and edit trace files.

Obtaining apitrace

To obtain apitrace either download the latest binaries for your platform if available, or follow the instructions in INSTALL.markdown to build it yourself. On 64bits Linux and Windows platforms you'll need apitrace binaries that match the architecture (32bits or 64bits) of the application being traced.

Basic usage

Run the application you want to trace as

apitrace trace --api API /path/to/application [args...]

and it will generate a trace named application.trace in the current directory. You can specify the written trace filename by passing the --output command line option.

Problems while tracing (e.g, if the application uses calls/parameters unsupported by apitrace) will be reported via stderr output on Unices. On Windows you'll need to run DebugView to view these messages.

Follow the "Tracing manually" instructions below if you cannot obtain a trace.

View the trace with

apitrace dump application.trace

Replay an OpenGL trace with

glretrace application.trace

Pass the -sb option to use a single buffered visual. Pass --help to glretrace for more options.

Basic GUI usage

Start the GUI as

qapitrace application.trace

You can also tell the GUI to go directly to a specific call

qapitrace application.trace 12345

Advanced command line usage

Call sets

Several tools take CALLSET arguments, e.g:

apitrace dump --calls CALLSET foo.trace
glretrace -S CALLSET foo.trace

The call syntax is very flexible. Here are a few examples:

  • 4 one call

  • 1,2,4,5 set of calls

  • "1 2 4 5" set of calls (commas are optional and can be replaced with whitespace)

  • 1-100/2 calls 1, 3, 5, ..., 99

  • 1-1000/draw all draw calls between 1 and 1000

  • 1-1000/fbo all fbo changes between calls 1 and 1000

  • frame all calls at end of frames

  • @foo.txt read call numbers from foo.txt, using the same syntax as above

Tracing manually

Linux

On 64 bits systems, you'll need to determine ether the application is 64 bits or 32 bits. This can be done by doing

file /path/to/application

But beware of wrapper shell scripts -- what matters is the architecture of the main process.

Run the application you want to trace as

 LD_PRELOAD=/path/to/apitrace/wrappers/glxtrace.so /path/to/application

and it will generate a trace named application.trace in the current directory. You can specify the written trace filename by setting the TRACE_FILE environment variable before running.

The LD_PRELOAD mechanism should work with most applications. There are some applications, e.g., Unigine Heaven, which global function pointers with the same name as GL entrypoints, living in a shared object that wasn't linked with -Bsymbolic flag, so relocations to those globals function pointers get overwritten with the address to our wrapper library, and the application will segfault when trying to write to them. For these applications it is possible to trace by using glxtrace.so as an ordinary libGL.so and injecting into LD_LIBRARY_PATH:

ln -s glxtrace.so wrappers/libGL.so
ln -s glxtrace.so wrappers/libGL.so.1
ln -s glxtrace.so wrappers/libGL.so.1.2
export LD_LIBRARY_PATH=/path/to/apitrace/wrappers:$LD_LIBRARY_PATH
export TRACE_LIBGL=/path/to/real/libGL.so.1
/path/to/application

See the ld.so man page for more information about LD_PRELOAD and LD_LIBRARY_PATH environment flags.

To trace the application inside gdb, invoke gdb as:

gdb --ex 'set exec-wrapper env LD_PRELOAD=/path/to/glxtrace.so' --args /path/to/application

Android

The following instructions should work at least for Android Ice Scream Sandwitch:

For standalone applications the instructions above for Linux should work. To trace applications started from within the Android VM process (app_process aka zygote) you'll have to wrap this process and enable tracing dynamically for the application to be traced.

  • Wrapping the android main VM process:

    In the Android root /init.rc add the LD_PRELOAD setting to zygote's environment in the 'service zygote' section:

      service zygote ...
         setenv LD_PRELOAD /data/egltrace.so
         ...
    

    Note that ICS will overwrite the /init.rc during each boot with the version in the recovery image. So you'll have to change the file in your ICS source tree, rebuild and reflash the device. Rebuilding/reflashing only the recovery image should be sufficient.

  • Copy egltrace.so to /data

    On the host:

      adb push /path/to/apitrace/build/wrappers/egltrace.so /data
    
  • Adjust file permissions to store the trace file:

    By default egltrace.so will store the trace in /data/app_process.trace. For this to work for applications running with a uid other than 0, you have to allow writes to the /data directory on the device:

      chmod 0777 /data
    
  • Enable tracing for a specific process name:

    To trace for example the Settings application:

      setprop debug.apitrace.procname com.android.settings
    

    In general this name will match what ps reports.

  • Start the application:

    If the application was already running, for example due to ICS's way of pre-starting the apps, you might have to kill the application first:

      kill <pid of app>
    

    Launch the application for example from the application menu.

Mac OS X

Run the application you want to trace as

DYLD_LIBRARY_PATH=/path/to/apitrace/wrappers /path/to/application

Note that although Mac OS X has an LD_PRELOAD equivalent, DYLD_INSERT_LIBRARIES, it is mostly useless because it only works with DYLD_FORCE_FLAT_NAMESPACE=1 which breaks most applications. See the dyld man page for more details about these environment flags.

Windows

When tracing third-party applications, you can identify the target application's main executable, either by:

  • right clicking on the application's icon in the Start Menu, choose Properties, and see the Target field;

  • or by starting the application, run Windows Task Manager (taskmgr.exe), right click on the application name in the Applications tab, choose Go To Process, note the highlighted Image Name, and search it on C:\Program Files or C:\Program Files (x86).

On 64 bits Windows, you'll need to determine ether the application is a 64 bits or 32 bits. 32 bits applications will have a *32 suffix in the Image Name column of the Processes tab of Windows Task Manager window.

Copy the appropriate opengl32.dll, d3d8.dll, or d3d9.dll from the wrappers directory to the directory with the application you want to trace. Then run the application as usual.

You can specify the written trace filename by setting the TRACE_FILE environment variable before running.

Emitting annotations to the trace

From OpenGL applications you can embed annotations in the trace file through the GL_GREMEDY_string_marker and GL_GREMEDY_frame_terminator GL extensions.

apitrace will advertise and intercept these GL extensions independently of the GL implementation. So all you have to do is to use these extensions when available.

For example, if you use GLEW to dynamically detect and use GL extensions, you could easily accomplish this by doing:

void foo() {

  if (GLEW_GREMEDY_string_marker) {
    glStringMarkerGREMEDY(0, __FUNCTION__ ": enter");
  }

  ...

  if (GLEW_GREMEDY_string_marker) {
    glStringMarkerGREMEDY(0, __FUNCTION__ ": leave");
  }

}

This has the added advantage of working equally well with gDEBugger.

From OpenGL ES applications you can embed annotations in the trace file through the GL_EXT_debug_marker extension.

For Direct3D applications you can follow the same procedure used for instrumenting an application for PIX

Dump GL state at a particular call

You can get a dump of the bound GL state at call 12345 by doing:

glretrace -D 12345 application.trace > 12345.json

This is precisely the mechanism the GUI obtains its own state.

You can compare two state dumps by doing:

apitrace diff-state 12345.json 67890.json

Comparing two traces side by side

apitrace diff trace1.trace trace2.trace

This works only on Unices, and it will truncate the traces due to performance limitations.

Recording a video with FFmpeg

You can make a video of the output by doing

glretrace -s - application.trace \
| ffmpeg -r 30 -f image2pipe -vcodec ppm -i pipe: -vcodec mpeg4 -y output.mp4

Trimming a trace

You can make a smaller trace by doing:

apitrace trim --callset 100-1000 -o trimed.trace applicated.trace

If you need precise control over which calls to trim you can specify the individual call numbers a plaintext file, as described in the 'Call sets' section above.

Profiling a trace

You can perform gpu and cpu profiling with the command line options:

  • -pgpu record gpu times for frames and draw calls.

  • -pcpu record cpu times for frames and draw calls.

  • -ppd record pixels drawn for each draw call.

The results from this can then be read by hand or analysed with a script.

scripts/profileshader.py will read the profile results and format them into a table which displays profiling results per shader.

For example, to record all profiling data and utilise the per shader script:

./glretrace -pgpu -pcpu -ppd foo.trace | ./scripts/profileshader.py

Advanced usage for OpenGL implementors

There are several advanced usage examples meant for OpenGL implementors.

Regression testing

These are the steps to create a regression test-suite around apitrace:

  • obtain a trace

  • obtain reference snapshots, by doing on a reference system:

    mkdir /path/to/reference/snapshots/
    glretrace -s /path/to/reference/snapshots/ application.trace
    
  • prune the snapshots which are not interesting

  • to do a regression test, do:

    glretrace -c /path/to/reference/snapshots/ application.trace
    

    Alternatively, for a HTML summary, use apitrace diff-images:

      glretrace -s /path/to/test/snapshots/ application.trace
      apitrace diff-images --output summary.html /path/to/reference/snapshots/ /path/to/test/snapshots/
    

Automated git-bisection

With tracecheck.py it is possible to automate git bisect and pinpoint the commit responsible for a regression.

Below is an example of using tracecheck.py to bisect a regression in the Mesa-based Intel 965 driver. But the procedure could be applied to any GL driver hosted on a git repository.

First, create a build script, named build-script.sh, containing:

#!/bin/sh
set -e
export PATH=/usr/lib/ccache:$PATH
export CFLAGS='-g'
export CXXFLAGS='-g'
./autogen.sh --disable-egl --disable-gallium --disable-glut --disable-glu --disable-glw --with-dri-drivers=i965
make clean
make "$@"

It is important that builds are both robust, and efficient. Due to broken dependency discovery in Mesa's makefile system, it was necessary invoke make clean in every iteration step. ccache should be installed to avoid recompiling unchanged source files.

Then do:

cd /path/to/mesa
export LIBGL_DEBUG=verbose
export LD_LIBRARY_PATH=$PWD/lib
export LIBGL_DRIVERS_DIR=$PWD/lib
git bisect start \
    6491e9593d5cbc5644eb02593a2f562447efdcbb 71acbb54f49089b03d3498b6f88c1681d3f649ac \
    -- src/mesa/drivers/dri/intel src/mesa/drivers/dri/i965/
git bisect run /path/to/tracecheck.py \
    --precision-threshold 8.0 \
    --build /path/to/build-script.sh \
    --gl-renderer '.*Mesa.*Intel.*' \
    --retrace=/path/to/glretrace \
    -c /path/to/reference/snapshots/ \
    topogun-1.06-orc-84k.trace

The trace-check.py script will skip automatically when there are build failures.

The --gl-renderer option will also cause a commit to be skipped if the GL_RENDERER is unexpected (e.g., when a software renderer or another GL driver is unintentionally loaded due to missing symbol in the DRI driver, or another runtime fault).

Side by side retracing

In order to determine which draw call a regression first manifests one could generate snapshots for every draw call, using the -S option. That is, however, very inefficient for big traces with many draw calls.

A faster approach is to run both the bad and a good GL driver side-by-side. The latter can be either a previously known good build of the GL driver, or a reference software renderer.

This can be achieved with retracediff.py script, which invokes glretrace with different environments, allowing to choose the desired GL driver by manipulating variables such as LD_LIBRARY_PATH, LIBGL_DRIVERS_DIR, or TRACE_LIBGL.

For example, on Linux:

./scripts/retracediff.py \
    --ref-env LD_LIBRARY_PATH=/path/to/reference/GL/implementation \
    --retrace /path/to/glretrace \
    --diff-prefix=/path/to/output/diffs \
    application.trace

Or on Windows:

python scripts\retracediff.py --retrace \path\to\glretrace.exe --ref-env TRACE_LIBGL=\path\to\reference\opengl32.dll application.trace

Links

About apitrace:

Direct3D

Open-source:

Closed-source:

OpenGL

Open-source:

Closed-source:

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