Name
MESA_trace
Name Strings
GL_MESA_trace
Contact
Bernd Kreimeier, Loki Entertainment, bk 'at' lokigames.com
Brian Paul, VA Linux Systems, Inc., brianp 'at' valinux.com
Status
Obsolete.
Version
Number
none yet
Dependencies
OpenGL 1.2 is required.
The extension is written against the OpenGL 1.2 Specification
Overview
Provides the application with means to enable and disable logging
of GL calls including parameters as readable text. The verbosity
of the generated log can be controlled. The resulting logs are
valid (but possibly incomplete) C code and can be compiled and
linked for standalone test programs. The set of calls and the
amount of static data that is logged can be controlled at runtime.
The application can add comments and enable or disable tracing of GL
operations at any time. The data flow from the application to GL
and back is unaffected except for timing.
Application-side implementation of these features raises namespace
and linkage issues. In the driver dispatch table a simple
"chain of responsibility" pattern (aka "composable piepline")
can be added.
IP Status
The extension spec is in the public domain. The current implementation
in Mesa is covered by Mesa's XFree86-style copyright by the authors above.
This extension is partially inspired by the Quake2 QGL wrapper.
Issues
(1) Is this Extension obsolete because it can
be implemented as a wrapper DLL?
RESOLVED: No. While certain operating systems (Win32) provide linkers
that facilitate this kind of solution, other operating systems
(Linux) do not support hierarchical linking, so a wrapper solution
would result in symbol collisions.
Further, IHV's might have builtin support for tracing GL execution
that enjoys privileged access, or that they do not wish to separate
the tracing code from their driver code base.
(2) Should the Trace API explicitely support the notion of "frames?
This would require hooking into glXSwapBuffers calls as well.
RESOLVED: No. The application can use NewTraceMESA/EndTraceMESA
and TraceComment along with external parsing tools to split the
trace into frames, in whatever way considered adequate.
(2a) Should GLX calls be traced?
PBuffers and other render-to-texture solutions demonstrate that
context level commands beyond SwapBuffers might have to be
traced. The GL DLL exports the entry points, so this would not
be out of the question.
(3) Should the specification mandate the actual output format?
RESOLVED: No. It is sufficient to guarantee that all data and commands
will be traced as requested by Enable/DisableTraceMESA, in the order
encountered. Whether the resulting trace is available as a readable
text file, binary metafile, compilable source code, much less which
indentation and formatting has been used, is up to the implementation.
For the same reason this specification does not enforce or prohibit
additional information added to the trace (statistics, profiling/timing,
warnings on possible error conditions).
(4) Should the comment strings associated with names and pointer (ranges)
be considered persistent state?
RESOLVED: No. The implementation is not forced to use this information
on subsequent occurences of name/pointer, and is free to consider it
transient state.
(5) Should comment commands be prohibited between Begin/End?
RESOLVED: Yes, with the exception of TraceCommentMESA. TraceCommentMESA
is transient, the other commands might cause storage of persistent
data in the context. There is no need to have the ability mark names
or pointers between Begin and End.
New Procedures and Functions
void NewTraceMESA( bitfield mask, const ubyte * traceName )
void EndTraceMESA( void )
void EnableTraceMESA( bitfield mask )
void DisableTraceMESA( bitfield mask )
void TraceAssertAttribMESA( bitfield attribMask )
void TraceCommentMESA( const ubyte* comment )
void TraceTextureMESA( uint name, const ubyte* comment )
void TraceListMESA( uint name, const ubyte* comment )
void TracePointerMESA( void* pointer, const ubyte* comment )
void TracePointerRangeMESA( const void* first,
const void* last,
const ubyte* comment )
New Tokens
Accepted by the <mask> parameter of EnableTrace and DisableTrace:
TRACE_ALL_BITS_MESA 0xFFFF
TRACE_OPERATIONS_BIT_MESA 0x0001
TRACE_PRIMITIVES_BIT_MESA 0x0002
TRACE_ARRAYS_BIT_MESA 0x0004
TRACE_TEXTURES_BIT_MESA 0x0008
TRACE_PIXELS_BIT_MESA 0x0010
TRACE_ERRORS_BIT_MESA 0x0020
Accepted by the <pname> parameter of GetIntegerv, GetBooleanv,
GetFloatv, and GetDoublev:
TRACE_MASK_MESA 0x8755
Accepted by the <pname> parameter to GetString:
TRACE_NAME_MESA 0x8756
Additions to Chapter 2 of the OpenGL 1.2.1 Specification (OpenGL Operation)
None.
Additions to Chapter 3 of the OpenGL 1.2.1 Specification (OpenGL Operation)
None.
Additions to Chapter 4 of the OpenGL 1.2.1 Specification (OpenGL Operation)
None.
Additions to Chapter 5 of the OpenGL 1.2.1 Specification (Special Functions)
Add a new section:
5.7 Tracing
The tracing facility is used to record the execution of a GL program
to a human-readable log. The log appears as a sequence of GL commands
using C syntax. The primary intention of tracing is to aid in program
debugging.
A trace is started with the command
void NewTraceMESA( bitfield mask, const GLubyte * traceName )
<mask> may be any value accepted by PushAttrib and specifies a set of
attribute groups. The state values included in those attribute groups
is written to the trace as a sequence of GL commands.
<traceName> specifies a name or label for the trace. It is expected
that <traceName> will be interpreted as a filename in most implementations.
A trace is ended by calling the command
void EndTraceMESA( void )
It is illegal to call NewTraceMESA or EndTraceMESA between Begin and End.
The commands
void EnableTraceMESA( bitfield mask )
void DisableTraceMESA( bitfield mask )
enable or disable tracing of different classes of GL commands.
<mask> may be the union of any of TRACE_OPERATIONS_BIT_MESA,
TRACE_PRIMITIVES_BIT_MESA, TRACE_ARRAYS_BIT_MESA, TRACE_TEXTURES_BIT_MESA,
and TRACE_PIXELS_BIT_MESA. The special token TRACE_ALL_BITS_MESA
indicates all classes of commands are to be logged.
TRACE_OPERATIONS_BIT_MESA controls logging of all commands outside of
Begin/End, including Begin/End.
TRACE_PRIMITIVES_BIT_MESA controls logging of all commands inside of
Begin/End, including Begin/End.
TRACE_ARRAYS_BIT_MESA controls logging of VertexPointer, NormalPointer,
ColorPointer, IndexPointer, TexCoordPointer and EdgeFlagPointer commands.
TRACE_TEXTURES_BIT_MESA controls logging of texture data dereferenced by
TexImage1D, TexImage2D, TexImage3D, TexSubImage1D, TexSubImage2D, and
TexSubImage3D commands.
TRACE_PIXELS_BIT_MESA controls logging of image data dereferenced by
Bitmap and DrawPixels commands.
TRACE_ERRORS_BIT_MESA controls logging of all errors. If this bit is
set, GetError will be executed whereever applicable, and the result will
be added to the trace as a comment. The error returns are cached and
returned to the application on its GetError calls. If the user does not
wish the additional GetError calls to be performed, this bit should not
be set.
The command
void TraceCommentMESA( const ubyte* comment )
immediately adds the <comment> string to the trace output, surrounded
by C-style comment delimiters.
The commands
void TraceTextureMESA( uint name, const ubyte* comment )
void TraceListMESA( uint name, const ubyte* comment )
associates <comment> with the texture object or display list specified
by <name>. Logged commands which reference the named texture object or
display list will be annotated with <comment>. If IsTexture(name) or
IsList(name) fail (respectively) the command is quietly ignored.
The commands
void TracePointerMESA( void* pointer, const ubyte* comment )
void TracePointerRangeMESA( const void* first,
const void* last,
const ubyte* comment )
associate <comment> with the address specified by <pointer> or with
a range of addresses specified by <first> through <last>.
Any logged commands which reference <pointer> or an address between
<first> and <last> will be annotated with <comment>.
The command
void TraceAssertAttribMESA( bitfield attribMask )
will add GL state queries and assertion statements to the log to
confirm that the current state at the time TraceAssertAttrib is
executed matches the current state when the trace log is executed
in the future.
<attribMask> is any value accepted by PushAttrib and specifies
the groups of state variables which are to be asserted.
The commands NewTraceMESA, EndTraceMESA, EnableTraceMESA, DisableTraceMESA,
TraceAssertAttribMESA, TraceCommentMESA, TraceTextureMESA, TraceListMESA,
TracePointerMESA and TracePointerRangeMESA are not compiled into display lists.
Examples:
The command NewTraceMESA(DEPTH_BUFFER_BIT, "log") will query the state
variables DEPTH_TEST, DEPTH_FUNC, DEPTH_WRITEMASK, and DEPTH_CLEAR_VALUE
to get the values <test>, <func>, <mask>, and <clear> respectively.
Statements equivalent to the following will then be logged:
glEnable(GL_DEPTH_TEST); (if <test> is true)
glDisable(GL_DEPTH_TEST); (if <test> is false)
glDepthFunc(<func>);
glDepthMask(<mask>);
glClearDepth(<clear>);
The command TraceAssertAttribMESA(DEPTH_BUFFER_BIT) will query the state
variables DEPTH_TEST, DEPTH_FUNC, DEPTH_WRITEMASK, and DEPTH_CLEAR_VALUE
to get the values <test>, <func>, <mask>, and <clear> respectively.
The resulting trace might then look will like this:
{
GLboolean b;
GLint i;
GLfloat f;
b = glIsEnabled(GL_DEPTH_TEST);
assert(b == <test>);
glGetIntegerv(GL_DEPTH_FUNC, &i);
assert(i == <func>);
glGetIntegerv(GL_DEPTH_MASK, &i);
assert(i == <mask>);
glGetFloatv(GL_DEPTH_CLEAR_VALUE, &f);
assert(f == <clear>);
}
Additions to Chapter 6 of the OpenGL 1.2.1 Specification
(State and State Requests)
Querying TRACE_MASK_MESA with GetIntegerv, GetFloatv, GetBooleanv or
GetDoublev returns the current command class trace mask.
Querying TRACE_NAME_MESA with GetString returns the current trace name.
Additions to Appendix A of the OpenGL 1.2.1 Specification (Invariance)
The MESA_trace extension can be used in a way that does not affect data
flow from application to OpenGL, as well as data flow from OpenGL to
application, except for timing, possible print I/O. TRACE_ERRORS_BIT_MESA
will add additional GetError queries. Setting a trace mask with NewTraceMESA
as well as use of TraceAssertAttribMESA might cause additional state queries.
With the possible exception of performance, OpenGL rendering should not be
affected at all by a properly chosen logging operation.
Additions to the AGL/GLX/WGL Specifications
None.
GLX Protocol
None. The logging operation is carried out client-side, by exporting
entry points to the wrapper functions that execute the logging operation.
Errors
INVALID_OPERATION is generated if any trace command except TraceCommentMESA
is called between Begin and End.
New State
The current trace name and current command class mask are stored
per-context.
New Implementation Dependent State
None.
Revision History
* Revision 0.1 - Initial draft from template (bk000415)
* Revision 0.2 - Draft (bk000906)
* Revision 0.3 - Draft (bk000913)
* Revision 0.4 - Reworked text, fixed typos (bp000914)
* Revision 0.5 - Assigned final GLenum values (bp001103)
* Revision 0.6 - TRACE_ERRORS_BIT_MESA (bk000916)
* Revision 0.7 - Added MESA postfix (bk010126)