# OpenGL VBO problem

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For the past few days I've been trying to get a a square to render using VBOs but, unfortunately, have not been able to. So, any help I could get would be much appreciated. Sorry in advance for this post being so long: I wanted to give enough information on the problem. Here's the problem: The square isn't rendering. I'm trying to render it using the primitive type GL_TRIANGLES. Of course, it has four vertices for the corners and 2 indicies to specify the top left triangle and bottom right triangle. Here's what I've done so far to try to solve the problem myself: I've compared the code I'm writing now to the code I've written before where I actually used VBOs and was successful. I've checked out several threads on VBOs on this forum and others. I've checked out several sites that had tutorials on VBO's and read the vertex array, display lists and VBOs chapter in the "OpenGL SuperBible" book. I've also been comparing my code to the VBO code samples in that book and on the sites with the tutorials. I've also run my program through the program gDEBugger and used the OpenGL function glGetError(). You guys are my last resort and I figure there must be something small that I'm missing that some fresh eyes would see. First, here's the output of gDEBugger's OpenGL calls history HTML log file. I've split it up into the setup and rendering to make it easier to read. I've also removed some of the calls that I thought were not related or useless; the comments are mine: // SETUP ... ... glGenBuffers(1, 0xE7648C) // generate buffer for vertices glGenBuffers(1, 0xE764EC) // generate buffer for indices glGenBuffers(1, 0xE7655C) // generate buffer for tex. coords: not used right now glBindBuffer(GL_ARRAY_BUFFER, 1) glBufferData(GL_ARRAY_BUFFER, 48, 0xE765B8, GL_STATIC_DRAW) glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 2) glBufferData(GL_ELEMENT_ARRAY_BUFFER, 24, 0xE76728, GL_STATIC_DRAW) ... ... // RENDERING glClear(0x4100) glPushMatrix() glMultMatrixf((1.00, 0.00, -0.00, 0.00) (-0.00, 1.00, -0.00, 0.00) (0.00, 0.00, 1.00, 0.00) (0.00, 0.00, 0.00, 1.00)) glTranslatef(-0.00, -0.00, -0.00) glTranslatef(0.00, 0.00, -2.00) // here's the VBO specific rendering: glEnableClientState(GL_VERTEX_ARRAY) glBindBuffer(GL_ARRAY_BUFFER, 1) glVertexPointer(3, GL_FLOAT, 0, 0x0) glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 2) glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0x0) glDisableClientState(GL_VERTEX_ARRAY) glBegin(GL_LINES) // drawing a line for testing purposes glVertex3f(0.50, 0.00, 0.00) glVertex3f(-0.50, 0.00, 0.00) glEnd() glBegin(GL_TRIANGLES) // used this to check winding order: it was fine glEnd() glPopMatrix() glGetError() wglSwapBuffers(0x1601202D) Here's my init code where I create the vertex and index buffers and add in the data:
void InitContextGL(void)
{
glClearColor(0.0f, 0.0f, 1.0f, 1.0f);

// the buffers are being generated in the constructor of CModel (see below).
testModel = new CModel;

// adding vertices to the vertex list
const float fHalfWidth = 1.0f;
const float fHalfHeight = 1.0f;
const float fDepth = 2.0f;
testModel->GetVertexData()->GetVertexList().reserve(4);
testModel->GetVertexData()->GetVertexList().push_back(new tVertex3f(-fHalfWidth, fHalfHeight, -fDepth)); // top left
testModel->GetVertexData()->GetVertexList().push_back(new tVertex3f(-fHalfWidth, -fHalfHeight, -fDepth)); // bottom left
testModel->GetVertexData()->GetVertexList().push_back(new tVertex3f(fHalfWidth, -fHalfHeight, -fDepth)); // bottom right
testModel->GetVertexData()->GetVertexList().push_back(new tVertex3f(fHalfWidth, fHalfHeight, -fDepth)); // top right
testModel->GetVertexData()->SetData(GL_STATIC_DRAW);

// creating a square using indicies
testModel->GetIndexData()->GetIndexList().reserve(2);
testModel->GetIndexData()->GetIndexList().push_back(new tIndex3n(3,0,1)); // top left triangle
testModel->GetIndexData()->GetIndexList().push_back(new tIndex3n(3,1,2)); // bottom right triangle
testModel->GetIndexData()->SetData(GL_STATIC_DRAW);
}


Here's the rendering specific code:

void RenderFrame(void)
{
Input(); // getting input

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glPushMatrix();
{
camera.ApplyCameraTransform();

glTranslatef(0.0f, 0.0f, -2.0f);
testModel->Render(); // this is where the VBO data is supposed
// to be rendering (see below for
// definition).

// drawing a line for test purposes (removed)
...

// rendering a white square to test winding order: it worked
// fine. (removed)
...
}
glPopMatrix();

// this function checks if there was an OpenGL error using glGetError and displays
// that error as a windows message box
CheckForOpenGLError(__FILE__, __LINE__);
}

void CModel::Render()
{
glEnableClientState(GL_VERTEX_ARRAY);

m_VertexData->PrepareForRender();

m_IndexData->Render();

glDisableClientState(GL_VERTEX_ARRAY);
}


You may be wondering where I'm calling glGenBuffers and what testModel->SetData(), m_VertexData->PrepareForRender(), and m_IndexData->Render() do. Here they are:
CModelData::CModelData()
{
// CVertexData and CIndexData (below) are derived off of CModelData, so
// they automatically get a buffer.
...
glGenBuffers(1, &m_uVertexBufferHandle);
}

void CModelData::BindBuffer()
{
glBindBuffer(GetTarget(), GetVertexBufferHandle());
}

...

void CVertexData::SetData(GLenum usage)
{
BindBuffer();
// tVertex3f is a struct that contains an array of 3 floats
glBufferData(GetTarget(), sizeof(tVertex3f) * m_VertexList.size(), &m_VertexList.front(), usage);
}

void CVertexData::SetVertexPointer()
{
glVertexPointer(3, GL_FLOAT, 0, 0);
}

void CVertexData::PrepareForRender()
{
BindBuffer();
SetVertexPointer();
}

...

void CIndexData::Render()
{
BindBuffer();
glDrawElements(GetPrimitiveType(), GetNumElementsToRender(), GetTypeOfValue(), GetBufferDrawOffset());
}

void CIndexData::SetData(GLenum usage)
{
BindBuffer();
// tIndex3n is a struct that contains an array of 3 integers
glBufferData(GetTarget(), sizeof(tIndex3n) * m_IndexList.size(), &m_IndexList.front(), usage);
SetNumElementsToRender(static_cast<GLsizei>(m_IndexList.size()) * GetNumIndexComponents());
}


Sorry if the code isn't very helpful with all of the function calls and it being split up so much (I'm going to be fixing it up). I'm hoping the gDEBugger log file will help if you want to know what values are getting passed to the OpenGL functions. Edit: removed glEnableClientState(GL_INDEX_ARRAY) and glDisableClientState(GL_INDEX_ARRAY) to reflect a change that V-man suggested [Edited by - Switch0025 on November 24, 2007 7:46:02 PM]

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Remove
glEnableClientState(GL_INDEX_ARRAY)
glDisableClientState(GL_INDEX_ARRAY)
since you aren't using color index arrays.

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Quote:
 Original post by V-manRemoveglEnableClientState(GL_INDEX_ARRAY)glDisableClientState(GL_INDEX_ARRAY)since you aren't using color index arrays.

GL_INDEX_ARRAY is used for index arrays (for vertices) not "color index arrays" (I believe your talking about GL_COLOR_ARRAY) as specified by the OpenGL documentation:
Quote:
 GL_INDEX_ARRAY If enabled, the index array is enabled for writing and used during rendering when glDrawArrays or glDrawElements is called. See glIndexPointer.

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No you are wrong. V-man is 100% correct. glIndexPointer is for color indexes.

Check the official documentation and see for yourself.

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Then I stand corrected. Thanks for the correction; I misunderstood the documentation. I have edited my code and my original post to reflect the change. However, my original problem still persists.

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hey

Firstly, I don't know if it's such a good idea to have removed things from the log file, hehe. What if something you removed was a key to identifying the problem? But i dunno, hehe.

Anyhows I think you should try unbinding your VBO's after you create them, and also after you render. Well I remember having probs with my VBO's, and I found things to work when I unbinded them :). I forget the exact details now though :\. I'm not sure what lead me to try this, I forget if I read about doing this from somewhere, or if it was just something I thought to try myself.

Incase you don't know, to unbind you just call glBindBuffer(), with the buffer ID as zero.

I also recommend you checkout http://www.spec.org/gwpg/gpc.static/vbo_whitepaper.html

edit
Other things to think about... are they being drawn inside the screen? have you tried drawing as points? is lighting enabled? (I think you should disable GL_LIGHTING for testing, and make sure to set your vertices color different to background) are textures enabled (again I think you should disable GL_TEXTURE_2D for testing). Hmm, maybe you should also try drawing with glBegin()/glEnd() in your render function???

cya

[Edited by - yosh64 on November 24, 2007 10:02:22 PM]

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Quote:
 Original post by yosh64Firstly, I don't know if it's such a good idea to have removed things from the log file, hehe. What if something you removed was a key to identifying the problem? But i dunno, hehe.

I agree, but I didn't want to make my post any longer then it was and most of it was wglGetProcAddress() calls and repeats of the rendering section.

I tried all of your suggestions but unfortunately I was unable to get it rendering. Putting the rendering code in between glBegin() and glEnd() causes an opengl error (that I "caught" using glGetError). The website you gave was one of the websites I checked out before I posted here but I'll have to go over it a little bit more. Thanks for your help, yosh64.

Edit: spelling mistakes

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Hey, I figured out the problem so if anyone else has this problem here's what happened and how to solve it:

The vertex list I had was holding pointers to the vertex/index structures and not the vertex/index structures themselves.

when it should have been:

std::vector<tVertex3f> m_VertexList; // good

BTW, tVertex3f is a structure that holds the X,Y,Z coordinate for a vertex.

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