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glDrawElements - what i do wrong?

 
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LarryTM



Joined: 04 Jul 2006
Posts: 30
PostPosted: Fri Jul 28, 2006 2:01 am    Post subject: glDrawElements - what i do wrong? Reply with quote
Im trying to learn how to use glDrawElements, but i have a problem.

Here is my cube object :

Code:

#define NR_Box01 0
objects[NR_Box01].id = ID_TRIMESH;
objects[NR_Box01].vertex_count = 8;
objects[NR_Box01].faces_count = 12;
objects[NR_Box01].vertex_list = &Box01_vertex_list[0];
objects[NR_Box01].faces_list = &Box01_faces_list[0];
objects[NR_Box01].face_normals_list = &Box01_face_normals_list[0];
objects[NR_Box01].tex_coords_list = &Box01_tex_coords_list[0];
objects[NR_Box01].dim_x1 = -5.000000;
objects[NR_Box01].dim_x2 = 5.000000;
objects[NR_Box01].dim_y1 = -5.000000;
objects[NR_Box01].dim_y2 = 5.000000;
objects[NR_Box01].dim_z1 = -4.981750;
objects[NR_Box01].dim_z2 = 5.018250;

static xyz Box01_vertex_list[] =
{
{-5.000000, -5.000000, -4.981750},
{5.000000, -5.000000, -4.981750},
{-5.000000, 5.000000, -4.981750},
{5.000000, 5.000000, -4.981750},
{-5.000000, -5.000000, 5.018250},
{5.000000, -5.000000, 5.018250},
{-5.000000, 5.000000, 5.018250},
{5.000000, 5.000000, 5.018250}
};
static face Box01_faces_list[] =
{
0, 2, 3,
3, 1, 0,
4, 5, 7,
7, 6, 4,
0, 1, 5,
5, 4, 0,
1, 3, 7,
7, 5, 1,
3, 2, 6,
6, 7, 3,
2, 0, 4,
4, 6, 2
};
static xyz Box01_face_normals_list[] =
{
{0.000000, 0.000000, -1.000000},
{0.000000, 0.000000, -1.000000},
{0.000000, 0.000000, 1.000000},
{0.000000, 0.000000, 1.000000},
{0.000000, -1.000000, 0.000000},
{0.000000, -1.000000, 0.000000},
{1.000000, 0.000000, 0.000000},
{1.000000, 0.000000, 0.000000},
{0.000000, 1.000000, 0.000000},
{0.000000, 1.000000, 0.000000},
{-1.000000, 0.000000, 0.000000},
{-1.000000, 0.000000, 0.000000}
};
static coords Box01_tex_coords_list[] =
{
{0.999500, 0.000500, 0.000499},
{0.000499, 0.000500, 0.999500},
{0.000499, 0.000500, 0.000500},
{0.000499, 0.000500, 0.999500},
{0.999500, 0.999501, 0.000499},
{0.000499, 0.999501, 0.999500},
{0.000499, 0.999501, 0.000500},
{0.000499, 0.999501, 0.999500},
{0.999501, 0.000500, 0.000500},
{0.999500, 0.999501, 0.000500},
{0.000499, 0.999500, 0.000500},
{0.000499, 0.999500, 0.000500},
{0.000500, 0.000499, 0.000500},
{0.999501, 0.000500, 0.000500},
{0.000499, 0.000500, 0.999501},
{0.999500, 0.000499, 0.999501},
{0.999501, 0.999500, 0.999501},
{0.999501, 0.999500, 0.999501},
{0.000500, 0.999501, 0.999501},
{0.000499, 0.000500, 0.999501},
{0.000499, 0.000500, 0.000500},
{0.999500, 0.000500, 0.000499},
{0.999500, 0.999501, 0.000499},
{0.999500, 0.999501, 0.000499},
{0.000499, 0.999501, 0.000500},
{0.000499, 0.000500, 0.000500},
{0.000499, 0.000500, 0.999500},
{0.999500, 0.000500, 0.999501},
{0.999500, 0.999501, 0.999501},
{0.999500, 0.999501, 0.999501},
{0.000499, 0.000500, 0.999500},
{0.999500, 0.000500, 0.999501},
{0.999500, 0.999501, 0.999501},
{0.999500, 0.999501, 0.999501},
{0.000499, 0.000500, 0.000500},
{0.999500, 0.999501, 0.000499}
};


and here is my code :

Code:

unsigned int   m_nVBOVertices;   
unsigned int   m_nVBOTexCoords;   
unsigned int index_buf;

Init :

  glGenBuffersARB( 1, &m_nVBOVertices );   
   glBindBufferARB( GL_ARRAY_BUFFER_ARB, m_nVBOVertices );      
   glBufferDataARB( GL_ARRAY_BUFFER_ARB, objects[0].vertex_count*3*sizeof(float), objects[0].vertex_list, GL_STATIC_DRAW_ARB );
   
   glGenBuffersARB(1, &index_buf);
   glBindBufferARB(GL_ELEMENT_ARRAY_BUFFER_ARB, index_buf);
   glBufferDataARB(GL_ELEMENT_ARRAY_BUFFER_ARB, objects[0].faces_count*sizeof(GLushort), objects[0].faces_list, GL_STATIC_DRAW_ARB);

Draw:

glEnableClientState(GL_VERTEX_ARRAY);
glBindBufferARB( GL_ARRAY_BUFFER_ARB, m_nVBOVertices );
glVertexPointer( 3, GL_FLOAT, 0, (char *) NULL );     
glBindBufferARB(GL_ELEMENT_ARRAY_BUFFER_ARB, index_buf);   
               
glDrawElements(GL_TRIANGLES, objects[0].faces_count, GL_UNSIGNED_SHORT, 0);
glDisableClientState( GL_VERTEX_ARRAY );   
       


And I have one triangle on screen. Why? What I do wrong?

/lar
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Kojima



Joined: 26 Jun 2006
Posts: 275
PostPosted: Fri Jul 28, 2006 3:45 am    Post subject: Reply with quote
you're passing the amount of faces to drawelements, but as the name suggests, you actually have to pass how many elements there are.

i.e TriCount * 3
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