Contact
- Brian Paul (brian_e_paul 'at' yahoo.com)
+ Brian Paul (brian @ tungstengraphics.com)
Status
Last Modified Date: July 20, 2003
Author Revision: 1.0
- $Date: 2003/07/21 04:23:32 $ $Revision: 1.1 $
+ $Date: 2003/07/23 15:45:25 $ $Revision: 1.2 $
Number
only provides the minimal hooks required to implement a debugger.
There are facilities to do the following:
- 1. Query the current values of input, output and temporary registers.
- 2. Query the current program position during execution.
- 3. Have the GL call a user-specified function prior to executing
+ 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.
- The callback function can determine whether to return immediately (to
- continue program execution) or stop and process user commands.
From within the callback, the user may issue glGet* commands to
query current GL state. The GetProgramRegisterfvMESA function allows
- all program register values to be queried (such as temporaries,
- input attributes, and result registers).
+ current program values to be queried (such as temporaries, input
+ attributes, and result registers).
There are flags for enabling/disabling the program callbacks.
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?
+ 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
4. Is this extension amenable to hardware implementation?
- Unresolved, but we'd hope so. Perhaps the GL implementation
- will have to fall back to a software path when debugging.
+ 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)
Additions to Chapter 5 of the OpenGL 1.4 Specification (Special Functions)
- XXX Document ProgramCallbackMESA here
+ 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. Callbacks 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.
- Add to the list of functions which cannot be included in display
- lists: ProgramCallbackMESA.
+ 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)
- XXX document GetProgramRegisterfvMESA here
+ 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. GetProgramRegisterMESA may only be
+ called from within a callback function registered with
+ ProgramCallbackMESA.
+
+ <registerName> and <len> specify the string name of a program
+ register (such as "R3"), input attribute (such as "vertex.color"),
+ an output attribute (such as "result.texcoord[0]") or a user-
+ defined identifier. The current value of that variable is
+ returned as four floats in <v>.
Additions to Appendix A of the OpenGL 1.4 Specification (Invariance)
Note: INVALID_OPERAION IS NOT generated by GetProgramRegisterfvMESA,
GetBooleanv, GetDoublev, GetFloatv, or GetIntegerv if called between
- Begin and End.
- These functions may be called from the user-provided callback function
- which is called between Begin/End.
+ 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
NV_fragment_program).
INVALID_VALUE is generated by GetProgramRegisterfvMESA if <registerName>
- is not a recognized program register.
+ 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
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
-/* 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;
+ 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);
+ /* Get PC and current instruction string */
+ glGetIntegerv(GL_VERTEX_PROGRAM_POSITION_ARB, &pos);
- printf("Current position: %d\n", 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]);
- }
-}
+ 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...
- */
+ /*
+ * elsewhere...
+ */
- /* Register our debugger callback function */
- glProgramCallbackMESA(GL_VERTEX_PROGRAM_ARB, DebugCallback, NULL);
- glEnable(GL_VERTEX_PROGRAM_CALLBACK_MESA);
+ /* Register our debugger callback function */
+ glProgramCallbackMESA(GL_VERTEX_PROGRAM_ARB, DebugCallback, NULL);
+ glEnable(GL_VERTEX_PROGRAM_CALLBACK_MESA);
- /* define/bind a vertex program */
+ /* define/bind a vertex program */
- glEnable(GL_VERTEX_PROGRAM);
+ glEnable(GL_VERTEX_PROGRAM);
- /* render something */
- glBegin(GL_POINTS);
- glVertex2f(0, 0);
- glEnd();
+ /* render something */
+ glBegin(GL_POINTS);
+ glVertex2f(0, 0);
+ glEnd();
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