CODEWITHSUNDEEP
objective-ciosopengl-esglkit
KK.
KK.

Reputation: 783

Can't display VBO with simple cube, seems like issue with buffers

Trying to modify this OpenGL and GLKit tutorial at raywenderlich.com, I am trying to render a cube from a wavefront obj file, without the per vertex color information and with surface normals. But the thing that is rendered looks nothing like a cube.

"(Not a) Cube"

For parsing an obj file I have a method (createDrawable) that goes through the obj and saves the info into a struct (Drawable) that contains four things: vertex buffer, index buffer, number of faces in the object and the transform matrix of the object. (Here are the header, .m file and the .obj file.)

- (Drawable)createDrawable: (NSString *)objFileName {
    ......
    ......

    // Parsed obj and put info in vertexData and indices arrays.

    Drawable _drawable;

    _drawable.numFaces = numFaces;

    glGenBuffers(1, &_drawable.vertexBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, _drawable.vertexBuffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertexData) * numFaces * 8, vertexData, GL_STATIC_DRAW);

    glGenBuffers(1, &_drawable.indexBuffer);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _drawable.indexBuffer);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices) * numFaces * 3, indices, GL_STATIC_DRAW);

    _drawable.matrix = GLKMatrix4Identity;
    _drawable.matrix = GLKMatrix4Translate(_drawable.matrix, 0.0f, 0.0f, 10.0f);

    return _drawable;
}

For rendering I am using another method (renderDrawable) that binds an object's buffers, sets pointers to them and then renders using glDrawElements(..).

- (void) renderDrawable: (Drawable)object {
    glBindBuffer(GL_ARRAY_BUFFER, object.vertexBuffer);
    glEnableVertexAttribArray(GLKVertexAttribPosition);        
    glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 0, (const GLvoid *) 0);
    glEnableVertexAttribArray(GLKVertexAttribTexCoord1);
    glVertexAttribPointer(GLKVertexAttribTexCoord1, 2, GL_FLOAT, GL_FALSE, 0, (const GLvoid *) 3);
    glEnableVertexAttribArray(GLKVertexAttribNormal);
    glVertexAttribPointer(GLKVertexAttribNormal, 3, GL_FLOAT, GL_FALSE, 0, (const GLvoid *) 5);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, object.indexBuffer);
    glDrawElements(GL_LINES, sizeof(object.indexBuffer) * 3 * object.numFaces, GL_UNSIGNED_BYTE, (const GLvoid *) object.indexBuffer);
}

I think I am doing something wrong with the buffers (part of createDrawable shown here and renderDrawable, in the .m file), but I just can't figure out what it is.

Upvotes: 0

Views: 396

Answers (2)

fen
fen

Reputation: 10125

I think that the "stride" param in glVertexArrayPointer should be set to 8 * sizeof(float) for instance (size of a single vertex)

glVertexAttribPointer(GLKVertexAttribNormal, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (const GLvoid *) 5);

when stride is 0 - that means attribs are stored in a continous way... but you have interleaved attribs so you must provide some more info to OpenGL.

Another issue: what is the sizeof(vertexData) * numFaces * 8... I think is should be: sizeof(vertexData) * numFaces * 3

And for index buffer: sizeof(indices) * numFaces * 3 - I think it should be sizeof(int) * numFaces * 3

int - type for indices, but you have GL_BYTE (that means that you can have only 256 different indices!)

when rendering: glDrawArrays - you have index buffer bound, so set the last param to NULL

Upvotes: 1

Tobias Schlegel
Tobias Schlegel

Reputation: 3970

I think you problem is that you pass GL_LINES to glDrawElements() instead of GL_TRIANGLES.

Upvotes: 1

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