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glBufferSubData question

Started by FXACE Mar 13, 2011 at 1:57 PM 3 replies 1.4k views

Original Post

Mar 13, 2011 at 1:57 PM

Hi folks!!!

Situation: I have this variables : vec3 * vertices, *normals, * texture_coords; int num_vertices;

All this (vec3*) variables have different pointers. Can I pack it to one VBO without losing time for creating mixed array (vertices,normals,...)?

GLAPI void APIENTRY glBufferSubData (GLenum, GLintptr, GLsizeiptr, const GLvoid *);

What the second argument of glBufferSubData means? Is it a starting position (index) of allocated buffer where I want to update the data? If yes? how to work with it?

Thanks forward

karwosts

Mar 13, 2011 at 5:56 PM

http://www.opengl.org/sdk/docs/man/xhtml/glBufferSubData.xml

The arguments are explained in the documentation.

What do you mean "without losing time"? Yes you can pack all of your information into one buffer.

FXACE

Mar 13, 2011 at 6:14 PM

Thanks for reply, karwosts... I'd check this out.

What do you mean "without losing time"?

I mean to allocate the temporary array that would hold vector values like this:

vec3 *array = new vec3 [num_vertices*3]; // where '3' is: "vertices", "texcoords", "normals"
 
 // here I copy the data from "vertices", "texcoords", "normals" to "array"
 memcpy(array,vertices,sizeof(vec3)*num_vertices);
 memcpy((void*)(int(array)+sizeof(vec3)*num_vertices), normals, sizeof(vec3)*num_vertices);
 .............
 ..........
 
 at the end I sending "array" to VBO and deleting temporary variable

Now, by this argument GLintptr offset I can do this without allocating temporary array for them by this way:


 
 glBufferSubData( GL_ARRAY_BUFFER_ARB, 0, sizeof(vec3) * num_vertices, vertices);
 
 
 glBufferSubData( GL_ARRAY_BUFFER_ARB, sizeof(vec3) * num_vertices, sizeof(vec3) * num_vertices, normals);
 
 //and so on....

Thanks again!!!!

V-man

Mar 13, 2011 at 11:09 PM

It should work.
What is the problem you are having?

FXACE

Mar 15, 2011 at 4:56 PM

What is the problem you are having?

There is no problem. Everything OK.

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