Prashant Saxena wrote:
> Hi,
>
> I am creating a viewer to display Renderman (.rib) using PyOpenGL.
> I'll be using either vertex arrays or VBO to store and render the data.
>
> A 6 face polygonal cube in .rib format: (5 faces are quad and I
> purposely divided 4th face into 2 triangles before exporting from 3d
> application)
> PointsGeneralPolygons
> [ 4 4 4 4 3 3 4 ] #number of vertices in face
> [ 2 3 1 0 4 5 3 2 6 7 5 4 0 1 7 6 3 7
> 1 5 7 3 4 2 0 6 ] #vertex index
> "vertex point P" [ -4.470358 -4.1476117 3.9099706 4.470358
> -4.1476117 3.9099706 -4.470358 4.1476117 3.9099706 4.470358 4.1476117
> 3.9099706
> -4.470358 4.1476117 -3.9099706 4.470358 4.1476117 -3.9099706
> -4.470358 -4.1476117 -3.9099706 4.470358 -4.1476117 -3.9099706 ]
> "facevarying normal N" [ 0 0 1 0 0 1 0 0 1 0 0 1
> 0 1 0 0 1 0 0 1 0 0 1 0
> 0 0 -1 0 0 -1 0 0 -1 0 0 -1
> 0 -1 0 0 -1 0 0 -1 0 0 -1 0
> 1 0 0 1 0 0 1 0 0 1 0 0
> 1 0 0 1 0 0 -1 0 0 -1 0 0
> -1 0 0 -1 0 0 ]
> "facevarying float[2] st" [ 0.375 0.75 0.625 0.75 0.625 1 0.375 1
> 0.375 0.5 0.625 0.5
> 0.625 0.75 0.375 0.75 0.375 0.25 0.625 0.25 0.625 0.5 0.375 0.5
> 0.375 0 0.625 0 0.625 0..25 0.375 0.25 0.625 0.75 0.875 1
> 0.625 1 0.875 0.75 0.875 1 0.625 0.75 0.125 0.75 0.375 0.75
>
> Here normals and "st" (texture coord) are per face basis while
> vertices are object basis. In OpenGL we have three different pointers
> to feed this data in: glVertexPointer, glTexCoordPointer and
> glNormalPointer.
>
> 1. In above case I would be needing vertices array also per face basis
> to pass them into glVertexPointer, which I could do by parsing vertex
> index array and vertices. Do we have something in GL to overcome this
> problem and creting the mesh using the information as it's already
> there in the rib.
You generally are going to need equally-indexed arrays AFAIK. That is,
you need to be able to say "render vertex X from current arrays". When
you have that, you can use e.g. glDrawElements or glDrawRangeElements to
render the data-set. Although there might be some extension that allows
you to use different indices for the various arrays, I don't believe
anything in core allows you to do so.
In summary: yes, you will likely need to expand your vertex array.
> 2. Secondly we have quads as well as tris in this case. Is it possible
> to pass an array which contains both of them. For example:
> [[...],
> [a,b,c], #three verts of a triangle
> [a,b,c,d], #four vertices of a quad
You can pass them in in the same array/vbo and then use multiple calls
to glDrawElements to render the geometry.
HTH,
Mike
--
________________________________________________
Mike C. Fletcher
Designer, VR Plumber, Coder
http://www.vrplumber.com
http://blog.vrplumber.com
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