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How to process texture indices properly


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#1 Rld_   Members   -  Reputation: 1371

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Posted 15 February 2012 - 01:54 PM

Hey guys,

I've been working on loading some models and so far it's going alright, got me a nice model and everything seems to be working fine, except that I'm rather clueless on how to texture it properly.

I'm working with VBOs and I load my stuff from an .obj file. Just like the vertices, I need to draw UVs with the indices provided, but I don't know how to process them properly with opengl. I tried to do it the same way with just creating another IBO for the UVs, but I don't know if this is the right way and if it is, where to put it (as my model is simply black, it seems to fail).

I checked with GDebugger and the texture seems to be there and I also enabled it with glEnable( GL_TEXTURE_2D );

Any pointers in the right direction would be appreciated. This is what I have so far:

Rld::Mesh::Mesh( String a_FileName, String a_Name )
{
   testtexid = SOIL_load_OGL_texture("Data/diffuseF.png", SOIL_LOAD_AUTO, SOIL_CREATE_NEW_ID, SOIL_FLAG_MIPMAPS);
   m_Name = a_Name;
   Load(a_FileName);

   glGenBuffers(1, &m_VertexBuffer);
   glBindBuffer(GL_ARRAY_BUFFER, m_VertexBuffer);
   glBufferData(GL_ARRAY_BUFFER, sizeof(float3) * m_Vertices.size(), &m_Vertices[0], GL_STATIC_DRAW);

   glGenBuffers(1, &m_UVBuffer);
   glBindBuffer(GL_ARRAY_BUFFER, m_UVBuffer);
   glBufferData(GL_ARRAY_BUFFER, sizeof(float2) * m_UVs.size(), &m_UVs[0], GL_STATIC_DRAW);

   glGenBuffers(1, &m_NormalBuffer);
   glBindBuffer(GL_ARRAY_BUFFER, m_NormalBuffer);
   glBufferData(GL_ARRAY_BUFFER, sizeof(float3) * m_Normals.size(), &m_Normals[0], GL_STATIC_DRAW);

   glGenBuffers(1, &m_IndexBuffer);
   glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_IndexBuffer);
   glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(unsigned int) * m_Indices.size(), &m_Indices[0], GL_STATIC_DRAW);

   glBindBuffer( GL_ARRAY_BUFFER, 0 );
   glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, 0 );
}

void Rld::Mesh::Render()
{
   glColor3f(1.0f, 0.0f, 0.0f);
   glEnable( GL_TEXTURE_2D );


   glEnableVertexAttribArray(0);
   glBindBuffer(GL_ARRAY_BUFFER, m_VertexBuffer);
   glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

   //How do I process this with an index buffer?
   glEnableVertexAttribArray(1);
   glBindBuffer( GL_ARRAY_BUFFER, m_UVBuffer );
   glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 0, 0);

   glEnableVertexAttribArray(2);
   glBindBuffer( GL_ARRAY_BUFFER, m_NormalBuffer );
   glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, 0);

   glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, m_IndexBuffer );
   glDrawElements( GL_TRIANGLES, m_Indices.size(), GL_UNSIGNED_INT, 0 );

   glDisableVertexAttribArray(2);
   glDisableVertexAttribArray(1);
   glDisableVertexAttribArray(0);

   glBindBuffer( GL_ARRAY_BUFFER, 0 );
   glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, 0 );
   glBindTexture( GL_TEXTURE_2D, 0 );
}


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#2 karwosts   Members   -  Reputation: 832

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Posted 15 February 2012 - 02:31 PM

Unfortunately processing texture coordinates from obj models is not trivial. In opengl you only get one IBO which must be shared by all buffers (for a given vertex, position, color, texcoord, normal, must all be in the same index of the buffer).

Because obj gives each attribute its own set of indices, you will need to read in the data and rearrange/reindex everything such that all attribute buffers are aligned on a single index.

If you have trouble doing this, just search the forums and I'm sure you'll find hundreds of discussions on the topic. I think pretty much every opengl developer runs into this wall early in their development carrer.
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#3 Rld_   Members   -  Reputation: 1371

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Posted 15 February 2012 - 03:54 PM

Unfortunately processing texture coordinates from obj models is not trivial. In opengl you only get one IBO which must be shared by all buffers (for a given vertex, position, color, texcoord, normal, must all be in the same index of the buffer).

Because obj gives each attribute its own set of indices, you will need to read in the data and rearrange/reindex everything such that all attribute buffers are aligned on a single index.

If you have trouble doing this, just search the forums and I'm sure you'll find hundreds of discussions on the topic. I think pretty much every opengl developer runs into this wall early in their development carrer.


Hmm thanks, I feel kinda stupid seeing how many answer there have been already..

Anyway, from what I can come up with from the previous answers I simply "spread out" my UVs with duplicate entries into a buffer and left the rest as is (so my UVs don't actually need an index anymore). Will this be enough or will this work at all? The previous threads led me to believe it should work. If it should, I'm doing something wrong elsewhere. :)

#4 karwosts   Members   -  Reputation: 832

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Posted 15 February 2012 - 04:20 PM

I'm not sure if that's an adequate general-case solution. In some cases you may actually need to increase the size of the vertex/index buffer with new indices. In an original VBO, you can have a single position vector share two UV vectors. For example if you had a quad consisting of two triangles, with unique textures on each tri, it might look like this:

f 1/1 2/2 3/3
f 2/4 3/5 4/6

Originally you'll have a vbo/ibo of 4 vertices, but you'll end up needing 6 to represent the texcoords accurately. You'll probably need to toss the entire existing IBO and recreate one from scratch.
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#5 Rld_   Members   -  Reputation: 1371

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Posted 15 February 2012 - 04:34 PM

Ah yes, I see what you're going at. This will eventually be something that will happen with more complex models. Suddenly I don't like .obj files anymore.

Thanks for the clarification.

#6 Rld_   Members   -  Reputation: 1371

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Posted 16 February 2012 - 05:02 AM

I didn't want to start a new topic as it is somewhat related to this one. I am still stuck at the texturing part. I now have one Vertex buffer with position, normal and UV data and by using another model format I don't have to use indices anymore.

The model loads just fine, all the coords are loaded properly and so does the texture (if I am allowed to believe GDebugger). However, the texture refuses to show up and right now I am not sure if this has something to do with my VBO or just not handling texturing correctly. This is how the code looks:

Rld::Mesh::Mesh( String a_FileName, String a_Name )
{
   testtexid = SOIL_load_OGL_texture("Data/diffuseF.png", SOIL_LOAD_AUTO, SOIL_CREATE_NEW_ID, SOIL_FLAG_MIPMAPS);
   m_Name = a_Name;
   Load(a_FileName);

   glGenBuffers(1, &m_VertexBuffer);
   glBindBuffer(GL_ARRAY_BUFFER, m_VertexBuffer);
   glBufferData(GL_ARRAY_BUFFER, sizeof(vertex) * m_Vertices.size(), &m_Vertices[0], GL_STATIC_DRAW);

   glBindBuffer( GL_ARRAY_BUFFER, 0 );
}

void Rld::Mesh::Render()
{
   glColor3f(1.0f, 0.0f, 0.0f);
   glBindTexture(GL_TEXTURE_2D, testtexid);

   glBindBuffer(GL_ARRAY_BUFFER, m_VertexBuffer);
   glEnableVertexAttribArray(0);
   glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(vertex), BUFFER_OFFSET(0));
 
   glEnableVertexAttribArray(1);
   glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(vertex), BUFFER_OFFSET(12));
   
   glEnableVertexAttribArray(2);
   glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, sizeof(vertex), BUFFER_OFFSET(24));

   glDrawArrays(GL_TRIANGLES, 0, m_Vertices.size());

   glDisableVertexAttribArray(2);
   glDisableVertexAttribArray(1);
   glDisableVertexAttribArray(0);

   glBindBuffer( GL_ARRAY_BUFFER, 0 );
   glBindTexture( GL_TEXTURE_2D, 0 );
}

glEnable( GL_TEXTURE_2D ); is called during the initialization of openGL.

Something tells me I'm either missing something in regard to calling the texture properly or I offset in the wrong way. Any help would be much appreciated!

#7 karwosts   Members   -  Reputation: 832

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Posted 16 February 2012 - 11:51 AM

I don't personally see anything, maybe you could post more code. Do you have a shader? How do you know that AttribArray 1 is really the texcoord, do you have glGetAttribLocation somewhere, or glBindAttribLocation?
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#8 Rld_   Members   -  Reputation: 1371

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Posted 16 February 2012 - 12:17 PM

I don't personally see anything, maybe you could post more code. Do you have a shader? How do you know that AttribArray 1 is really the texcoord, do you have glGetAttribLocation somewhere, or glBindAttribLocation?


The code I gave is actually all there is when it comes to filling/using the VBO. I'm not working with shaders yet, starting from the bottom up and later on convert it with CG. The last part you mentioned, I put up in bold in the code, this is something I am not doing. I'm following the second edition of Beginning openGL Game Programming and this is pretty much the way it is done in there so I thought that would be all. It's very logical that I can't know. So how would I get to know what buffer is what?

On a side note, I know for a fact the UVs, positions and normals are right as I am able to draw them with glEnableClientState() and everything show up just fine. I can continue on that, but I would like to extend on this and not use deprecated code :)

#9 V-man   Members   -  Reputation: 805

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Posted 16 February 2012 - 02:49 PM

If you are going to use glVertexAttribPointer, then you need shaders.
Otherwise, use glVertexPointer, glNormalPointer and the like.
Sig: http://glhlib.sourceforge.net
an open source GLU replacement library. Much more modern than GLU.
float matrix[16], inverse_matrix[16];
glhLoadIdentityf2(matrix);
glhTranslatef2(matrix, 0.0, 0.0, 5.0);
glhRotateAboutXf2(matrix, angleInRadians);
glhScalef2(matrix, 1.0, 1.0, -1.0);
glhQuickInvertMatrixf2(matrix, inverse_matrix);
glUniformMatrix4fv(uniformLocation1, 1, FALSE, matrix);
glUniformMatrix4fv(uniformLocation2, 1, FALSE, inverse_matrix);

#10 Rld_   Members   -  Reputation: 1371

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Posted 16 February 2012 - 03:02 PM

If you are going to use glVertexAttribPointer, then you need shaders.
Otherwise, use glVertexPointer, glNormalPointer and the like.


Right, that clears it up. Thanks for the replies. Much appreciated!




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