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Evan2009

OpenGL Access Violation with glDrawElements

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Good morning everyone,

Recently I've been working on a project using OpenGL and right now I've been trying to draw a model using arrays. I've looked around for postings with a similar problem to mine but nothing I've found has seemed to work or doesn't apply to my situation. I keep getting an Access Violation when I hit glDrawElements within my CModel class's draw(). The first time the draw code runs it doesn't hit that access violation so I'm wondering if I forgot to enable or disable something after that code runs. If anyone can shed some light on this it would help me a lot. Thank you.

In my Init() I use

glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState( GL_NORMAL_ARRAY );
glEnableClientState( GL_TEXTURE_COORD_ARRAY );



Here is the draw code for CModel

for(int i = m_vMeshes.size() - 1; i >= 0; --i)
{
//Make sure texture is loaded, get handle
std::string szTex;
int texHandle;

//If the mesh has a texture
if(m_vMeshes->m_vTextureNames.size() != 0)
{
szTex = "data/Textures/" + m_vMeshes->m_vTextureNames[0];
texHandle = CTextureManager::GetInstance()->GetTextureHandle(szTex.c_str()); //TODO: Move elsewhere

//Bind Texture
if(texHandle != -1)
{
glEnable(GL_TEXTURE_2D);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texHandle);
}
}

glPushMatrix();
//TODO: Add Translate code here based on input
glNormalPointer(GL_FLOAT, 0, &m_vMeshes->GetNormals()[0]);
glTexCoordPointer(2, GL_FLOAT, 0, &m_vMeshes->GetTexCoords()[0]);
glVertexPointer( 3, GL_FLOAT, 0, &m_vMeshes->GetVertices()[0] );
glDrawElements( GL_TRIANGLES, (GLsizei)m_vMeshes->GetIndices().size(), GL_UNSIGNED_INT, &m_vMeshes->GetIndices()[0] );
glPopMatrix();

//Draw Points
glBegin(GL_POINTS);
for(unsigned int j = 0; j < m_vMeshes->GetVertices().size(); j++)
{
glVertex3f(m_vMeshes->GetVertices()[j].v[0], m_vMeshes->GetVertices()[j].v[1], m_vMeshes->GetVertices()[j].v[2]);
}
glEnd();
}

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Yes, I have and it works if the enable states are in the Init(). However, if those states are only enabled within Init() and disabled every time during my draw I'll never see my model. So something odd is happening in my render I just can't put my finger on it.

Edit: Here is the other render code.


//Setup Scene
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
establishProjectionMatrix(windowWidth, windowHeight);

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

glEnable(GL_LIGHTING);
glDisable(GL_BLEND);

//Update the scene from mouse control
glTranslatef(0.0f, 0.0f, zoom);
glRotatef(rotateX, 1.0f, 0.0f, 0.0f);
glRotatef(rotateY, 0.0f, 1.0f, 0.0f);

//Draw all lights in the scene
for(int i = 0; i < (int)CLight::lights.size(); i++)
{
CLight* test = CLight::lights;
CLight::lights->updateLight();
}

//Draw the model we're animating
model.DrawModel();

//Draw grid with no texture
glEnable(GL_BLEND);
glDisable(GL_TEXTURE_2D);
drawGrid();

//Draw Controls
glColor3f(1.0f, 1.0f, 1.0f);
glDisable(GL_LIGHTING);
setOrtho(windowWidth, windowHeight);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
displayFPS();
drawControls();

//Clean
glFlush();
SDL_GL_SwapBuffers();



Edit2:
If I enable and disable the vertex and normal array state around glDrawElements no access violation.
If I do the same thing with tex coord array then I will hit the access violation.

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You've got an invalid or overflowing pointer in one of your client states, most likely texcoords from your description, although if you're rendering anything else with different client states it may be an idea to check those too.

The first thing I would suggest doing is to check the value returned from m_vMeshes->GetIndices().size(). This should be equal to 3 x the number of your normals (as individual floats, not float[3]), 3 x the size of your positions (likewise) and 2 x the number of your texcoords (likewise).

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I am using 2D coordinates and right now I'm looking at what I have stored within my mesh and I see 2185 float[3] so 6555 floats and the same for my normals. My tex coords has 4370(2185*2) but my Indices is at 8385. Right now I'm looking through the code I made for the exporter. I'm loading the correct size according to the exported model's text file. It's the same exporter I used in a previous project of mine which worked but we were using a different method of rendering.

Edit: If my pointer was overflowing or invalid then wouldn't it give me an access violation the first time the code runs?

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So I got it to work but I'm not quite sure what I did. I took a break and came back, compiled a couple times and it stopped giving me an access violation. I've tried disabling the states right after my glDrawElements several times already but I don't understand why it started working now. But I still can't see the texture on my model yet nor are the lights affecting it.

Here is my end result.


for(int i = m_vMeshes.size() - 1; i >= 0; --i)
{
//Make sure texture is loaded, get handle
std::string szTex;
int texHandle;

//If the mesh has a texture
if(m_vMeshes->m_vTextureNames.size() != 0)
{
szTex = "data/Textures/" + m_vMeshes->m_vTextureNames[0];
texHandle = CTextureManager::GetInstance()->GetTextureHandle(szTex.c_str());

//Bind Texture
if(texHandle != -1)
{
glEnable(GL_TEXTURE_2D);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texHandle);
}
}

// Draw Model
glPushMatrix();
glEnableClientState( GL_VERTEX_ARRAY );
glEnableClientState( GL_NORMAL_ARRAY );
glEnableClientState( GL_TEXTURE_COORD_ARRAY );

glNormalPointer(GL_FLOAT, 0, &m_vMeshes->GetNormals()[0]);
glTexCoordPointer(2, GL_FLOAT, 0, &m_vMeshes->GetTexCoords()[0]);
glVertexPointer( 3, GL_FLOAT, 0, &m_vMeshes->GetVertices()[0] ); //NOTE: Remember the [0] at the end when using vectors

glEnable(GL_LIGHTING);
glDrawElements( GL_TRIANGLES, (GLsizei)m_vMeshes->GetIndices().size(), GL_UNSIGNED_INT, &m_vMeshes->GetIndices()[0] );

glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_NORMAL_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);

glDisable(GL_LIGHTING);
glPopMatrix();
}

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