Re: Newbish Question regarding texturing VBOs

/* Create VBOs */

glGenBuffers(2, &_vertexBuffer); // change this to two buffers - one for VBO and the other for Texture Coords

glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);

glBufferData(GL_ARRAY_BUFFER, kSize * kSize * 4 * sizeof(GLfloat), NULL, GL_DYNAMIC_COPY);

glBindBuffer(GL_ARRAY_BUFFER, 1); // for textures

glBufferData(GL_ARRAY_BUFFER, kSize * kSize * 4 * sizeof(GLfloat), NULL, GL_DYNAMIC_COPY);

glBindBuffer(GL_ARRAY_BUFFER, 0); // for verts

I Draw to them via

// for textures

glBegin();

blah blah

glEnd();

glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, _vertexBuffer);

glReadPixels(0, 0, kSize, kSize, GL_RGBA, GL_FLOAT, NULL);

glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, 1); // use the second buffer for texturing. yay?

/* Copy the rendered pixels into the VBO */

glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, _vertexBuffer);

glReadPixels(0, 0, kSize, kSize, GL_RGBA, GL_FLOAT, NULL);

glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, 0); // use the first buffer for verts

Now, I am attempting to draw the vertex buffer with glDrawElements, using both the vert buffer and the pseudo texture buffer vert hack thingy (ahem :) )

glEnableClientState(GL_VERTEX_ARRAY);

glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);

glVertexPointer(4, GL_FLOAT, 0, NULL);

glBindBuffer(GL_ARRAY_BUFFER, 0);

glEnableClientState(GL_VERTEX_ARRAY);

glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);

glTexCoordPointer(4, GL_FLOAT, 0, NULL);

glBindBuffer(GL_ARRAY_BUFFER, 1);

glDrawElements(GL_TRIANGLES, (kSize - 1) * (kSize - 1) * 6, GL_UNSIGNED_INT, _indices);

glDisableClientState(GL_VERTEX_ARRAY);

Again, this is just me attempting to reverse engineer the example code and infer proper syntax. Ive consulted google and checked up on some other fora, however I am still at a loss - so I do appreciate any other guidance. Thanks in advance (again).

On Oct 31, 2007, at 5:54 PM, Stefan Dösinger wrote:

Am Mittwoch, 31. Oktober 2007 21:14:25 schrieb vade:

So, in short, how does one specify texture coordinates for the
glDrawElements without using interleaved buffers? Apologies if this is
self evident, this is a bit deeper into OpenGL than I normally go.
If I understand it correctly, using two vbos might be helpful: Create one vbo
with position data, and one with the texture coordinates, then load the
vertex streams like this:

glBindBuffer(positionVBO);
glVertexPointer(...);
glBindBuffer(textureVBO);
glTexCoordPointer(...);

It is no issue to source two vbos, and glBindBuffer is designed to be cheap to
allow exactly what the code above does. In this case you can have different
strides of the elements in both buffers and don't have to care about the
position data when rendering out your texcoords. The texcoords can be packed
in any way you want them.