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glGetPointerv

Started by cippyboy Jan 11, 2004 at 8:18 AM 7 replies 1k views

Original Post

Jan 11, 2004 at 8:18 AM

I`m trying to use this function but with no succes it seems glGetPointerv (GLenum pname, GLvoid* *params); The only way it works is as follows->

void **p;//offcourse it only compiles :)

glGetPointerv(GL_TEXTURE_COORD_ARRAY_POINTER,p);//Ups->Illegal Operation, Oh my, what have you done ?

//I also tryed

float **=new float*[size];//where size can be whatever

//->cannot convert from float ** to void **

So far I saw that this is the only OpenGL func that needs GLvoid** params ! I`m in despair right now so if you can please help me. Thanks in advance

Brother Bob

Mod

218

Brother Bob

Jan 11, 2004 at 8:30 AM

You want a pointer, so define a pointer. Then pass the address of that pointer.


GLfloat *p;
glGetPointerv(GL_WHATEVER_ARRAY_POINTER, (GLvoid **)&p);

cippyboy

Author

cippyboy

Jan 11, 2004 at 8:40 AM

Well... it compiles flawlessly(it`s booleanic anyways) but when I try to retrieve data from the pointer... breakpoint and exception happens(offcourse).


//I allocate 100 pieces... although after

GLfloat *texels=new GLfloat[100];
glGetPointerv(GL_TEXTURE_COORD_ARRAY_POINTER,(GLvoid**)&texels);//this fucntion

for(int y=0;y<100;y++)//the pointer points to 0x000000

{
  GLfloat n=texels[y];//Illegal operation ,I`m trying to retreive data that doesn`t exist

} 
}

Brother Bob

Mod

218

Brother Bob

Jan 11, 2004 at 10:56 AM

Well, to begin with, you''re leaking memory. The block of memory you allocate is lost when glGetPointerv assigns a new value to texels. Just pass the address of the pointer, and let OpenGL set it''s value.

When glGetPointerv returns, texels points to the array passed to glTexCoordPointer. Is this pointer properly set?

cippyboy

Author

cippyboy

Jan 12, 2004 at 2:16 AM

Well I generate texcoords with glTexGen and thats why I want the texcoords to be taken out... Im not passing any glTexCoordPointer... what would be the use of the function if you wore to get something you already have ?

Brother Bob

Mod

218

Brother Bob

Jan 12, 2004 at 3:32 AM

quote:
Original post by cippyboy
Well I generate texcoords with glTexGen and that`s why I want the texcoords to be taken out...

Then use the feedback buffer instead.

quote:
what would be the use of the function if you wore to get something you already have ?

Because sometimes you may not know where it is. Just because you set the pointer in one part of the program doesn't mean it's automatically available everywhere. You can query every state in OpenGL, so why should the vertex array pointers be an exception?

[edited by - Brother Bob on January 12, 2004 4:33:08 AM]

_DarkWIng_

Jan 12, 2004 at 3:40 AM

quote:
Original post by cippyboy
Well I generate texcoords with glTexGen and thats why I want the texcoords to be taken out... Im not passing any glTexCoordPointer... what would be the use of the function if you wore to get something you already have ?

What you are trying to do won''t work. You can only get data you set with gl*Pointer. If you use glTexGen texture coordinates are calculated when vertex is processed and ant before. Why not calculate tex coords by yourself (since you use glTexGen it''s usualy just a matrix multiplication)

You should never let your fears become the boundaries of your dreams.