Manual Data Formatting (Interleaving Buffer Data)

[DanielSaucen]

Hello once more all,

To the point, I have three sets of data I want to merge and upload to a buffer, those sets being Vertex, Normal, and Texcoord.
Do you know of an efficient, or more viable way to combine those three sets into one, than what I am presenting below?
Is this a correct technique, or am I not comprehending the index structure well enough?

I plan on formating my three sets of data to correspond with my index pattern, being the standard (VNTVNTVNTVNT) or (Vertex,Normal,Texcoord).
OpenGL Context, 4.0+.

	int* Indices = Mesh->Index;
 
	int size = Mesh->Index_count;
	float* Interleaved = new float[size];
 
	for(int i=0; i<size;)
	{
		Interleaved[i] = Mesh->VERTEX.mData  [Indices[i]];
		i++;
		Interleaved[i] = Mesh->NORMAL.mData  [Indices[i]];
		i++;
		Interleaved[i] = Mesh->TEXCOORD.mData[Indices[i]];
		i++;
	}
 
	// I believe both the interleaved and index buffers to have the same element count.
 
        GLuint Buffer_Interleaved,Buffer_Index;
 
	glGenBuffers(1,&amp;Buffer_Interleaved);
	glGenBuffers(1,&amp;Buffer_Index);
 
	glBindBuffer(GL_ARRAY_BUFFER,Buffer_Interleaved);
	glBufferData(GL_ARRAY_BUFFER,size*sizeof(float),Interleaved,GL_STATIC_DRAW);
 
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,Buffer_Index);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER,size*sizeof(int),Indices,GL_STATIC_DRAW);
 
	delete [] Interleaved;

Additionally, I would like to know how to use glDrawElements() with my newly formatted data.
Books and web references are lacking a good amount of clarity to me.

Any relative words of wisdom are words enough to suffice thanks.

[Alfonse Reinheart]

Pedantic grammar note: Index is the singular form of indices. "Indice" or "indicie" is not a word.

[DanielSaucen]

Haha, I knew something felt wrong when writing it.
I'll get to fixing my many errors.

Every bit helps, though I still need the above questions to be addressed.

[tonyo_au]

by merge do you mean display as one mesh? It makes a difference when displaying

[DanielSaucen]

Sorry, to clarify:

I am dealing with a mesh object, that is split into the three components that make it drawable, being Vertex, Normal, and Texcoord. I simply want to combine the three elements into a single buffer, though I'm not exactly sure how, after combined, to specify the pattern to let OpenGL know the offsets.

To sum my question up into two parts:
Is the above code I wrote (with Vertex[i] instead of Vertex[Index[i]]...ect), actually creating a valid format that matches my index pattern? (Vertex,Normal,Texcoord)

How do I use glVertexAttribPointer() before drawing to specify the correct offset for that single, combined, buffer object? I would very much appreciate a specific example, rather than yet another link to the wiki page that I've refereed to, and failed using.

Many thanks for your patience.

[aqnuep]

Not exactly, actually you have to do something like the following:

        int* Indices = Mesh->Index;
 
	int indexCount = Mesh->Index_count;
        int vertexCount = Mesh->Vertex_count;
 
        typedef struct _SvertexData {
            float vertex[4];
            float normal[3];
            float texcoord[2];
        } vertexData;
 
	vertexData* Interleaved = new vertexData[vertexCount ];
 
	for(int i=0; i<vertexCount; ++i)
	{
                Interleaved[i].vertex[0] = Mesh->VERTEX.mData[i*4+0];
                Interleaved[i].vertex[1] = Mesh->VERTEX.mData[i*4+1];
                Interleaved[i].vertex[2] = Mesh->VERTEX.mData[i*4+2];
                Interleaved[i].vertex[3] = Mesh->VERTEX.mData[i*4+3];
 
                Interleaved[i].normal[0] = Mesh->NORMAL.mData[i*3+0];
                Interleaved[i].normal[1] = Mesh->NORMAL.mData[i*3+1];
                Interleaved[i].normal[2] = Mesh->NORMAL.mData[i*3+2];
 
                Interleaved[i].texcoord[0] = Mesh->TEXCOORD.mData[i*2+0];
                Interleaved[i].texcoord[1] = Mesh->TEXCOORD.mData[i*2+1];
	}
 
        GLuint Buffer_Interleaved,Buffer_Index;
 
	glGenBuffers(1,&amp;Buffer_Interleaved);
	glGenBuffers(1,&amp;Buffer_Index);
 
	glBindBuffer(GL_ARRAY_BUFFER,Buffer_Interleaved);
	glBufferData(GL_ARRAY_BUFFER,vertexCount*sizeof(vertexData),Interleaved,GL_STATIC_DRAW);
 
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,Buffer_Index);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER,indexCount*sizeof(int),Indices,GL_STATIC_DRAW);
 
	delete [] Interleaved;
 
        glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, sizeof(vertexData), offsetof(vertexData, vertex));
        glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(vertexData), offsetof(vertexData, normal));
        glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, sizeof(vertexData), offsetof(vertexData, texcoord));

However, the code I wrote is completely based on assumptions as you haven't described how your data is layed out in the Mesh->VERTEX, Mesh->NORMAL and Mesh->TEXCOORD arrays. The actual, properly working code could be very different.

[aqnuep]

Do you know of an efficient, or more viable way to combine those three sets into one, than what I am presenting below?

Can you explain what do you mean by "an efficient" way? You are interested in how you should layout your GPU vertex data or you want to avoid the additional copy to the temporary array?

Btw, there are several problems with your code (at least as far as I understand how it should work):
1. You actually copying your data in Vx Nx Tx Vy Ny Ty etc. order which I think it's incorrect, but maybe I'm wrong. It's hard to figure out what you're doing.
2. You read the vertex data indexed by the indices, actually that defeats the purpose of hardware indexing and in this form only DrawArrays would work for you. You should remove the indirection (i.e. replace the array index "Indices[i]" simply with "i").

Additionally, I would like to know how to use glDrawElements() with my newly formatted data.
Books and web references are lacking a good amount of clarity to me.

The OpenGL specification clearly describes how DrawElements is working. You should give it a try. The spec is usually the best documentation.

Also, there are tons of sample applications all around the internet. Just use your favorite search engine and search for VBO samples.