--- /dev/null
+Name
+
+ MESA_program_debug
+
+Name Strings
+
+ GL_MESA_program_debug
+
+Contact
+
+ Brian Paul (brian.paul 'at' tungstengraphics.com)
+
+Status
+
+ XXX - Not complete yet!!!
+
+Version
+
+ Last Modified Date: July 20, 2003
+ Author Revision: 1.0
+
+Number
+
+ TBD
+
+Dependencies
+
+ OpenGL 1.4 is required
+ The extension is written against the OpenGL 1.4 specification.
+ ARB_vertex_program or ARB_fragment_program or NV_vertex_program
+ or NV_fragment_program is required.
+
+Overview
+
+ The extension provides facilities for implementing debuggers for
+ vertex and fragment programs.
+
+ The concept is that vertex and fragment program debuggers will be
+ implemented outside of the GL as a utility package. This extension
+ only provides the minimal hooks required to implement a debugger.
+
+ There are facilities to do the following:
+ 1. Have the GL call a user-specified function prior to executing
+ each vertex or fragment instruction.
+ 2. Query the current program string's execution position.
+ 3. Query the current values of intermediate program values.
+
+ The main feature is the ProgramCallbackMESA function. It allows the
+ user to register a callback function with the GL. The callback will
+ be called prior to executing each vertex or fragment program instruction.
+
+ From within the callback, the user may issue Get* commands to
+ query current GL state. The GetProgramRegisterfvMESA function allows
+ current program values to be queried (such as temporaries, input
+ attributes, and result registers).
+
+ There are flags for enabling/disabling the program callbacks.
+
+ The current execution position (as an offset from the start of the
+ program string) can be queried with
+ GetIntegerv(GL_FRAGMENT_PROGRAM_POSITION_MESA, &pos) or
+ GetIntegerv(GL_VERTEX_PROGRAM_POSITION_MESA, &pos).
+
+
+IP Status
+
+ None
+
+Issues
+
+ 1. Is this the right model for a debugger?
+
+ It seems prudent to minimize the scope of this extension and leave
+ it up to the developer (or developer community) to write debuggers
+ that layer on top of this extension.
+
+ If the debugger were fully implemented within the GL it's not
+ clear how terminal and GUI-based interfaces would work, for
+ example.
+
+ 2. There aren't any other extensions that register callbacks with
+ the GL. Isn't there another solution?
+
+ If we want to be able to single-step through vertex/fragment
+ programs I don't see another way to do it.
+
+ 3. How do we prevent the user from doing something crazy in the
+ callback function, like trying to call glBegin (leading to
+ recursion)?
+
+ The rule is that the callback function can only issue glGet*()
+ functions and no other GL commands. It could be difficult to
+ enforce this, however. Therefore, calling any non-get GL
+ command from within the callback will result in undefined
+ results.
+
+ 4. Is this extension amenable to hardware implementation?
+
+ Hopefully, but if not, the GL implementation will have to fall
+ back to a software path when debugging. This may be acceptable
+ for debugging.
+
+ 5. What's the <data> parameter to ProgramCallbackMESA for?
+
+ It's a common programming practice to associate a user-supplied
+ value with callback functions.
+
+ 6. Debuggers often allow one to modify intermediate program values,
+ then continue. Does this extension support that?
+
+ No.
+
+
+New Procedures and Functions (and datatypes)
+
+ typedef void (*programcallbackMESA)(enum target, void *data)
+
+ void ProgramCallbackMESA(enum target, programcallbackMESA callback,
+ void *data)
+
+ void GetProgramRegisterfvMESA(enum target, sizei len,
+ const ubyte *registerName, float *v)
+
+New Tokens
+
+ Accepted by the <cap> parameter of Enable, Disable, IsEnabled,
+ GetBooleanv, GetDoublev, GetFloatv and GetIntegerv:
+
+ FRAGMENT_PROGRAM_CALLBACK_MESA 0x8bb1
+ VERTEX_PROGRAM_CALLBACK_MESA 0x8bb4
+
+ Accepted by the <pname> parameter GetBooleanv, GetDoublev,
+ GetFloatv and GetIntegerv:
+
+ FRAGMENT_PROGRAM_POSITION_MESA 0x8bb0
+ VERTEX_PROGRAM_POSITION_MESA 0x8bb4
+
+ Accepted by the <pname> parameter of GetPointerv:
+
+ FRAGMENT_PROGRAM_CALLBACK_FUNC_MESA 0x8bb2
+ FRAGMENT_PROGRAM_CALLBACK_DATA_MESA 0x8bb3
+ VERTEX_PROGRAM_CALLBACK_FUNC_MESA 0x8bb6
+ VERTEX_PROGRAM_CALLBACK_DATA_MESA 0x8bb7
+
+Additions to Chapter 2 of the OpenGL 1.4 Specification (OpenGL Operation)
+
+ None.
+
+Additions to Chapter 3 of the OpenGL 1.4 Specification (Rasterization)
+
+ None.
+
+Additions to Chapter 4 of the OpenGL 1.4 Specification (Per-Fragment
+Operations and the Frame Buffer)
+
+ None.
+
+Additions to Chapter 5 of the OpenGL 1.4 Specification (Special Functions)
+
+ In section 5.4 "Display Lists", page 202, add the following command
+ to the list of those that are not compiled into display lists:
+
+ ProgramCallbackMESA.
+
+
+ Add a new section 5.7 "Callback Functions"
+
+ The function
+
+ void ProgramCallbackMESA(enum target, programcallbackMESA callback,
+ void *data)
+
+ registers a user-defined callback function with the GL. <target>
+ may be FRAGMENT_PROGRAM_ARB or VERTEX_PROGRAM_ARB. The enabled
+ callback functions registered with these targets will be called
+ prior to executing each instruction in the current fragment or
+ vertex program, respectively. The callbacks are enabled and
+ disabled by calling Enable or Disable with <cap>
+ FRAGMENT_PROGRAM_ARB or VERTEX_PROGRAM_ARB.
+
+ The callback function's signature must match the typedef
+
+ typedef void (*programcallbackMESA)(enum target, void *data)
+
+ When the callback function is called, <target> will either be
+ FRAGMENT_PROGRAM_ARB or VERTEX_PROGRAM_ARB to indicate which
+ program is currently executing and <data> will be the value
+ specified when ProgramCallbackMESA was called.
+
+ From within the callback function, only the following GL commands
+ may be called:
+
+ GetBooleanv
+ GetDoublev
+ GetFloatv
+ GetIntegerv
+ GetProgramLocalParameter
+ GetProgramEnvParameter
+ GetProgramRegisterfvMESA
+ GetProgramivARB
+ GetProgramStringARB
+ GetError
+
+ Calling any other command from within the callback results in
+ undefined behaviour.
+
+
+Additions to Chapter 6 of the OpenGL 1.4 Specification (State and
+State Requests)
+
+ Add a new section 6.1.3 "Program Value Queries":
+
+ The command
+
+ void GetProgramRegisterfvMESA(enum target, sizei len,
+ const ubyte *registerName,
+ float *v)
+
+ Is used to query the value of program variables and registers
+ during program execution. GetProgramRegisterfvMESA may only be
+ called from within a callback function registered with
+ ProgramCallbackMESA.
+
+ <registerName> and <len> specify the name a variable, input
+ attribute, temporary, or result register in the program string.
+ The current value of the named variable is returned as four
+ values in <v>. If <name> doesn't exist in the program string,
+ the error INVALID_OPERATION is generated.
+
+Additions to Appendix A of the OpenGL 1.4 Specification (Invariance)
+
+ None.
+
+Additions to the AGL/GLX/WGL Specifications
+
+ None.
+
+GLX Protocol
+
+ XXX TBD
+
+Dependencies on NV_vertex_program and NV_fragment_program
+
+ If NV_vertex_program and/or NV_fragment_program are supported,
+ vertex and/or fragment programs defined by those extensions may
+ be debugged as well. Register queries will use the syntax used
+ by those extensions (i.e. "v[X]" to query vertex attributes,
+ "o[X]" for vertex outputs, etc.)
+
+Errors
+
+ INVALID_OPERATION is generated if ProgramCallbackMESA is called
+ between Begin and End.
+
+ INVALID_ENUM is generated by ProgramCallbackMESA if <target> is not
+ a supported vertex or fragment program type.
+
+ Note: INVALID_OPERAION IS NOT generated by GetProgramRegisterfvMESA,
+ GetBooleanv, GetDoublev, GetFloatv, or GetIntegerv if called between
+ Begin and End when a vertex or fragment program is currently executing.
+
+ INVALID_ENUM is generated by ProgramCallbackMESA,
+ GetProgramRegisterfvMESA if <target> is not a program target supported
+ by ARB_vertex_program, ARB_fragment_program (or NV_vertex_program or
+ NV_fragment_program).
+
+ INVALID_VALUE is generated by GetProgramRegisterfvMESA if <registerName>
+ does not name a known program register or variable.
+
+ INVALID_OPERATION is generated by GetProgramRegisterfvMESA when a
+ register query is attempted for a program target that's not currently
+ being executed.
+
+
+New State
+
+ XXX finish
+
+(table 6.N, p. ###)
+ Initial
+ Get Value Type Get Command Value Description Sec. Attribute
+ --------- ---- ----------- ----- ----------- ---- ---------
+ FRAGMENT_PROGRAM_CALLBACK_MESA B IsEnabled FALSE XXX XXX enable
+ VERTEX_PROGRAM_CALLBACK_MESA B IsEnabled FALSE XXX XXX enable
+ FRAGMENT_PROGRAM_POSITION_MESA Z+ GetIntegerv -1 XXX XXX -
+ VERTEX_PROGRAM_POSITION_MESA Z+ GetIntegerv -1 XXX XXX -
+ FRAGMENT_PROGRAM_CALLBACK_FUNC_MESA P GetPointerv NULL XXX XXX -
+ VERTEX_PROGRAM_CALLBACK_FUNC_MESA P GetPointerv NULL XXX XXX -
+ FRAGMENT_PROGRAM_CALLBACK_DATA_MESA P GetPointerv NULL XXX XXX -
+ VERTEX_PROGRAM_CALLBACK_DATA_MESA P GetPointerv NULL XXX XXX -
+
+ XXX more?
+
+New Implementation Dependent State
+
+ None.
+
+Revision History
+
+ 8 July 2003
+ Initial draft. (Brian Paul)
+ 11 July 2003
+ Second draft. (Brian Paul)
+ 20 July 2003
+ Third draft. Lots of fundamental changes. (Brian Paul)
+ 23 July 2003
+ Added chapter 5 and 6 spec language. (Brian Paul)
+
+Example Usage
+
+ The following is a very simple example of how this extension may
+ be used to print the values of R0, R1, R2 and R3 while executing
+ vertex programs.
+
+
+ /* This is called by the GL when the vertex program is executing.
+ * We can only make glGet* calls from within this function!
+ */
+ void DebugCallback(GLenum target, GLvoid *data)
+ {
+ GLint pos;
+ GLuint i;
+
+ /* Get PC and current instruction string */
+ glGetIntegerv(GL_VERTEX_PROGRAM_POSITION_ARB, &pos);
+
+ printf("Current position: %d\n", pos);
+
+ printf("Current temporary registers:\n");
+ for (i = 0; i < 4; i++) {
+ GLfloat v[4];
+ char s[10];
+ sprintf(s, "R%d", i);
+ glGetProgramRegisterfvMESA(GL_VERTEX_PROGRAM_ARB, strlen(s), s, v);
+ printf("R%d = %g, %g, %g, %g\n", i, v[0], v[1], v[2], v[3]);
+ }
+ }
+
+
+ /*
+ * elsewhere...
+ */
+
+ /* Register our debugger callback function */
+ glProgramCallbackMESA(GL_VERTEX_PROGRAM_ARB, DebugCallback, NULL);
+ glEnable(GL_VERTEX_PROGRAM_CALLBACK_MESA);
+
+ /* define/bind a vertex program */
+
+ glEnable(GL_VERTEX_PROGRAM);
+
+ /* render something */
+ glBegin(GL_POINTS);
+ glVertex2f(0, 0);
+ glEnd();
+
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