Textured glDrawElement

Question

I am having trouble getting my 3D model textured, I am just diving into 3D models as I have been using basic primitives for testing purposes and have been working on more engine specific code. I am however having trouble with the glDrawElements function, I know my texture is loaded properly as I am able to draw it to a quad (note the glBegin in comments). However, when using glDrawElements I do not get the texture drawn. It does show the colour of part of the texture (yellow), and when I remove the texturing code it returns the 3D model to the last colour that has been set, so it is doing something. I am thinking maybe it is something to do with my glVertexAttributePointer , I get what these functions do sort of.

glMatrixMode(GL_MODELVIEW);
    glMultMatrixf(m_Props.WorldMatrix.data);

    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);
    glEnableVertexAttribArray(2);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(VertexPTN), 0);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, sizeof(VertexPTN), (const GLvoid*)12);
    glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, sizeof(VertexPTN), (const GLvoid*)20);

    glBindBuffer(GL_ARRAY_BUFFER, pExtra->GetVB());
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, pExtra->GetIB());

    glScalef(0.05, 0.05, 0.05);

    glEnable(GL_TEXTURE_2D);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, pTexExtra->GetTexture());

     glDrawElements(GL_TRIANGLES, pExtra->GetIndexCount(), GL_UNSIGNED_INT, 0); 
     /*glBegin(GL_QUADS);
        glTexCoord2f(0, 0); glVertex3f(0.0f, 0.0f, 0.0f);
        glTexCoord2f(0, 1); glVertex3f(10.0f, 0.0f, 0.0f);
        glTexCoord2f(1, 1); glVertex3f(10.0f, 10.0f, 0.0f);
        glTexCoord2f(1, 0); glVertex3f(0.0f, 10.0f, 0.0f);
     glEnd();*/

    glDisable(GL_TEXTURE_2D);


    glDisableVertexAttribArray(2);
    glDisableVertexAttribArray(1);
    glDisableVertexAttribArray(0);

My VertexPTN class is simply a container for a Position, Texture Coordinate and Normal. So I am assuming as the positioning of my vectors in the class goes; Vector3f, Vector2f, Vector3f, I would set the last parameter of the glVertexAttributePointer to 0, 12, 20.

Is there any missunderstanding of anything that I am missing? I'm really not pro with openGL but I do understand a decent amount of the setup and basic rendering. What is causing my texture to not render to my mesh, an unset GL state?

Just a hint (not relevant to your problem (probably)): You should never hardcode memory structure offsets. Instead let the compiler figure it out. There's the `offsetof` macro of ANSI C for this: https://en.wikipedia.org/wiki/Offsetof – use that for the data parameter of a VBO. — datenwolf, May 15 '12 at 01:20

score 0 · Accepted Answer · answered May 15 '12 at 01:16

0

Some thoughts:

Are you using shaders? glVertexAttribPointer only works with shaders

If Yes: Are you certain that your inputs are 0, 1, and 2? If you don't set these before shader linking with glBindAttribLocation, they aren't guaranteed to be any particular values.
If No: You should be using glVertexPointer, glTexCoordPointer, etc instead of AttribPointer

Also if you're using shaders, then enabling/disable GL_TEXTURE_2D is redundant, it doesn't do anything.

answered May 15 '12 at 01:16

Tim

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I have no shaders whatsoever, so I suppose that is the reason it won't work. Also I have some test objects that simply use a diffuse colour, for some reason even without specifying glTexCoord's it made them all yellowish. I will look up using those, thank you. – user1294021 May 15 '12 at 01:56
I now have glVertexPointer(3, GL_FLOAT, sizeof(GL_FLOAT) * 3, &pExtra->GetVB()[0]); glNormalPointer(GL_FLOAT, sizeof(GL_FLOAT) * 3, &pExtra->GetNB()[0]); glTexCoordPointer(2, GL_FLOAT, sizeof(GL_FLOAT) * 2, &pExtra->GetTB()[0]); glDrawElements(GL_TRIANGLES, pExtra->GetIB().size(), GL_UNSIGNED_SHORT, &pExtra->GetIB()[0]);
I changed the Vertex Buffers from GLuint generated buffers to simple stl vectors that I pumped the vertices, normals, tex coords into. I then directly point gl to these vector's as they are contiguous. But now I don't even see my model, what am I doing wrong?
– user1294021 May 15 '12 at 02:36
@user1294021 You also will need to replace glEnableVertexAttribArray with various calls to glEnableClientState to enable GL_VERTEX_ARRAY, GL_TEXCOORD_ARRAY, and GL_NORMAL_ARRAY – Tim May 15 '12 at 05:56

Textured glDrawElement

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