CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

See one the three examples of how to set an index to a vertex:
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Triangulation_3/Chapter_main.html#Subsection_39.5.3

Then build the Alpha_shape from the triangulation.
Note that the vertex base in the alpha shape is
CGAL::Alpha_shape_vertex_base_3.

Sebastien.

On 03/14/2013 08:39 PM, Sidnei Basei wrote:
> Hi All,
>
> I'm trying to find a way to build vertex and index matrix after
> Alpha_Shape_3 triangulation.
>
> I want use OpenGL VBO buffer. For example, I need something like following:
> GLfloat vertices[][3] = {
> { -1.0, -1.0, -1.0 },
> { 1.0, -1.0, -1.0 },
> { 1.0, 1.0, -1.0 },
> { -1.0, 1.0, -1.0 },
> { -1.0, -1.0, 1.0 },
> { 1.0, -1.0, 1.0 },
> { 1.0, 1.0, 1.0 },
> { -1.0, 1.0, 1.0 }
> };
> GLubyte indices[][4] = {
> { 0, 1, 2, 3 },
> { 4, 7, 6, 5 },
> { 0, 4, 5, 1 },
> { 3, 2, 6, 7 },
> { 0, 3, 7, 4 },
> { 1, 5, 6, 2 }
> };
>
>
> I want use it in OpenGL, like this:
> glGenBuffers(NUM_BUFFERS, buffers);
> glBindBuffer(GL_ARRAY_BUFFER, buffers[VERTICES]);
> glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
> glVertexPointer(3, GL_FLOAT, 0, BUFFER_OFFSET(0));
> glEnableClientState(GL_VERTEX_ARRAY);
> glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, buffers[INDICES]);
> glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices,
> GL_STATIC_DRAW);
> glDrawElements(GL_QUADS, 24, GL_UNSIGNED_BYTE, BUFFER_OFFSET(0));
>
>
>
>
>
> My current Alpha_Shape_3 is:
>
> Alpha_shape_3::Alpha_shape_facets_iterator
> ffi=as.Alpha_shape_facets_begin();
> for( ; ffi!=as.Alpha_shape_facets_end();ffi++) {
>
> Triangle tr = as.triangle(*ffi);
>
> *I DON'T WANT TRIANGLE VERTICES COORDINATES. I WANT vertices MATRIZ and
> INDICES.*
>
> out->push_back(tr);
> }
>
>
>
> Any idea?
>
> Thank you a lot.
>
>
> --
> Sidnei Basei