问题
Thus far i have only used glDrawArrays and would like to move over to using an index buffer and indexed triangles. I am drawing a somewhat complicated object with texture coords, normals and vertex coords. All this data is gathered into a single interleaved vertex buffer and drawn using calls similar to ( Assuming all the serup is done correctly ):
glVertexPointer( 3, GL_FLOAT, 22, (char*)m_vertexData );
glNormalPointer( GL_SHORT, 22, (char*)m_vertexData+(12) );
glTexCoordPointer( 2, GL_SHORT, 22, (char*)m_vertexData+(18) );
glDrawElements(GL_TRIANGLES, m_numTriangles, GL_UNSIGNED_SHORT, m_indexData );
Does this allow for m_indexData to also be interleaved with the indices of my normals and texture coords as well as the standard position index array? Or does it assume a single linear list of inidices that apply to the entire vertex format ( POS, NOR, TEX )? If the latter is true, how is it possible to render the same vertex with different texture coords or normals?
I guess this question could also be rephrased into: if i had 3 seperate indexed lists ( POS, NOR, TEX ) where the latter 2 cannot be rearranged to share the same index list as the first, what is the best way to render that.
回答1:
You cannot have different indexes for the different lists. When you specify glArrayElement(3) then OpenGL is going to take the 3rd element of every list.
What you can do is play with the pointer you specify since essentially the place in the list which is eventually accessed is the pointer offset from the start of the list plus the index you specify. This is useful if you have a constant offset between the lists. if the lists are just a random permutation then this kind of play for every vertex is probably going to be as costy as just using plain old glVertex3fv(), glNormal3fv() and glTexCoord3fv()
回答2:
I am having similar trouble attempting to do the same in Direct3D 9.0
For my OpenGL 3 implementation it was rather easy, and my source code is available online if it might help you any... https://github.com/RobertBColton/enigma-dev/blob/master/ENIGMAsystem/SHELL/Graphics_Systems/OpenGL3/GL3model.cpp
来源：https://stackoverflow.com/questions/618829/opengl-gldrawelements-with-interleaved-buffers