Callback interface

I just found this issue last night, while struggling with the OpenGL
interface. It does not solve all the issues, but I do not know when
I will get my test case finished. So, I should let you all know what
I found, in case it might be useful to others and maybe, someone
knows a "better" solution.

The callback logic in Src/IDE/Win32/Callback.f presumes that the
function's xt is located 4 bytes after the return address inside RUNCB:

         4 [EDX] EBX MOV \ get xt for tos

         ' CALLBACK >CODE CALL \ and run the word...

Normally, this is correctly accomplished by the defining word:

: CB: ( xt n -- ) \ Usage: xt n CB: <name>
    CREATE
    RUNCB ,CALL
    [+ASM] CELLS # RET NOP [-ASM]
    ( xt) , ;

However, this is dependent on what RET assembles:

: RET ( n # | -- )
    DUP IMM? IF DROP ?DUP IF C2 C,(A) W,(A) \ imm16
    EXIT THEN THEN C3 C,(A) ;

If you are really sharp, you see the problem, but I don't really want
to say how long I've been chasing it.

The problem is with a callback that does not have any parameters. In
that case, the RET assembles a C3 and the RUNCB logic calls garbage.

I solved the problem by commenting out the inner conditional within
RET and my OpenGL tests no longer crash as soon as I call the
glutMainLoop. The callback assigned to glutIdleFunc is called
immediately, with no parameters, and crashes before it executes any
of the user's code. ;(

This solution requires a remake of the SF executable, so for those
who do not have the full system, an update or some other solution is
required.

DaR

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Received on Tue Jan 16 2007 - 08:27:07 PST