size of GLsizeiptr

[bluenote10]

I'm currently struggling to get any output from vertex buffer based rendering and I'm trying to find what could be the issue. A possible problem could be the call to glDrawArrays, which takes the somewhat unusual GLsizeiptr as parameter (some background on GLsizeiptr). One thing that confuses me is the size of GLsizeiptr, which is defined as int32 in the bindings. However, in the official <GL/glext.h> header, the definition is typedef ptrdiff_t GLsizeiptr;. Running the following quick check

{.emit: """
#include <stdio.h>
#include <stdlib.h>

void c_call()
{
  printf("Size of ptrdiff_t: %d\n", sizeof(ptrdiff_t));
}
proc c_call() {.importc, nodecl.}
c_call()
"""}

# Size of ptrdiff_t: 8

shows on my 64 bit system (Ubuntu 14.04) that the size of ptrdiff_t and thus GLsizeiptr should be 8.

I have modified the bindings to force int64 for GLsizeiptr, but unfortunately this has not fixed my general issue. I'm also surprised that using an int32 did not crash in the first place. Therefore I currently don't know which is correct.

[bluenote10]

Update: My actual issue is solved. It looks like it does not matter if GLsizeiptr set to 32 or 64 bit ints -- both cases have identical behavior in my tests. I have no idea though why both works, nor which one is "more correct".

Probably because it's the last argument, and it'll just happen to work if the 4 bytes that are outside the argument section of the stack are zero