# OpenGL Drawing more than one object using buffers

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I'm having difficulty drawing more than one object using buffers in OpenGL using objective-c with the Xcode programming interface. I know how to draw more than one object using buffers in DirectX because the buffers are actually objects, but using objective-C, which I'm relative new to, and OpenGL is making this task more difficult than it really has to be. So far I have been able to load all the files that I want to be displayed into the buffers (or at least I think all the data is being loaded into the buffers from what I can gather) but when it goes through the draw function it only displays one of the objects. Here's some of the code to show you what I have done so far. First I choose the files that I want to display.
		NSArray* filenames = [oPanel filenames];
numFiles = [filenames count];
glGenBuffers(NUM_BUFFERS, buffers);
for(currentBuffer = 0; currentBuffer < numFiles; currentBuffer++)
[self openFile: [filenames objectAtIndex: currentBuffer]];
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
glGetError();
printf("%i total vertices, %i total faces\n", totalVertices, totalFaces);
[self setNeedsDisplay: YES];

Once I load the data into my arrays, I bind them to the buffers. I tried to condense the code to only the most relevant parts of the code.
- (void) openFile: (NSString*) filename
{
//..declare variables
pFile = fopen([filename cStringUsingEncoding: NSASCIIStringEncoding], "rb");
fscanf(pFile, "%d %d\n", &numVertices, &numFaces); // number of vertices
printf("%d %d\n", numVertices, numFaces);
totalVertices += numVertices;
totalFaces += numFaces;
vCount[currentBuffer] = numVertices * 3;
iCount[currentBuffer] = numFaces * 3;
faceCount[currentBuffer] = numFaces;
GLfloat vertices[numVertices * 3];
GLfloat normals[numVertices * 3];
GLuint faces[numFaces * 3];
glGetError();

//VERTICES
for(i = 0; i < (numVertices * 3); i=i+3)
{
fscanf(pFile, "%f  %f  %f  %f\n", &x, &y, &z, &extra);

}

glBindBuffer(GL_ARRAY_BUFFER, buffers[VERTICES]);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_DYNAMIC_DRAW);
glVertexPointer(3, GL_FLOAT, 0, BUFFER_OFFSET(0));

data[currentBuffer][VERTICES] = vertices;

//INDICES
for(i = 0; i < (numFaces * 3); i+=3)
{
//set indices...
}
fclose( pFile );

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, buffers[INDICES]);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(faces), faces, GL_DYNAMIC_DRAW);

data[currentBuffer][INDICES] = faces;

//NORMALS
for(i = 0; i < numFaces * 3; i+=3)
{
//....calculate normals...
}
//vectorize
for(i = 0; i < numVertices; i+=3)
{
//..vectorize..
}

glBindBuffer(GL_ARRAY_BUFFER, buffers[NORMALS]);
glBufferData(GL_ARRAY_BUFFER, sizeof(normals), normals, GL_DYNAMIC_DRAW);
glNormalPointer(GL_FLOAT, 0, BUFFER_OFFSET(0));

data[currentBuffer][NORMALS] = normals;

//COLORS
for(i = 0; i < (numVertices * 3); i+=3)
{
//..set colors...
}

glBindBuffer(GL_ARRAY_BUFFER, buffers[COLORS]);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_DYNAMIC_DRAW);
glColorPointer(3, GL_FLOAT, 0, BUFFER_OFFSET(0));

//indices[currentBuffer] = faces;

data[currentBuffer][COLORS] = vertices;

And finally, once the data is loaded (which is working fine) it only draws one of the files that I chose instead of all the files I chose to be drawn.
//...set lighting...
for(i = 0; i < numFiles; i++)
{

glBufferSubData(GL_ARRAY_BUFFER, BUFFER_OFFSET(0), vCount, data[VERTICES]);
glDrawElements(GL_TRIANGLES, faceCount * 3, GL_UNSIGNED_INT, BUFFER_OFFSET(0));
}

Any help or links to websites that explains how to do this task would be greatly appreciated. [Edited by - Unreality on July 9, 2008 9:56:50 AM]

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I hope I'm not doing anything stupid since I've gotten no replies yet. It probably is something stupid though. Any links to where I can find how to do this would be great, I have looked for long hours and found none. Though specific help from anyone would also be greatly appreciated. I need to be able to get past this obstacle to continue with this important project.

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You might need to post more of your draw function. There's a lot of things that could make your other elements not visible, like camera position, blend modes etc.

What other tests have you done? Can you draw each 'file' manually? If you specify each file instead of using the loop, what happens? What if you switch the order around?

Bruce

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I'm sure it is not the camera position because I have loaded both files individually and they show completely fine. I'm also completely sure through lighting tests it is nothing else in the draw function. I'm pretty sure it's something to do with the buffers and how I'm inputting the data there or how I'm trying to access it. When you choose the files, it draws the last one you chose, and we have verified that it loads all the files we selected correctly through debug mode. I think it might be either overwriting the data in the buffer since it displays the last file we selected or it could be that we are not accessing the buffer data correctly.
Our main problem is that we do not know how to specify what we want to change (i.e. normals, vertices, colors) in the buffer. If we possibly specify what we want to change, we might be able to fix our problem too.

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http://www.opengl.org/registry/specs/ARB/vertex_buffer_object.txt

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