Today: Polygon Models (or Meshes)
This is what we’ve been using so far
• today we’ll fill in some details
Evaluating polygon model representation
• ease of construction: Good
• ease of manipulation: Fair
• rendering efficiency: Excellent — direct hardware support
• compact description: Fair
Recall What Polygon Meshes Are
Explicit mesh description
• a list of polygonal faces F= ( f
1
, f
2
, …, f
n
)
• each polygon f
i
is a list of points
• this is sometimes called a “polygon soup” model
• vertices will be duplicated several times
Indexed mesh description
• a list of vertices V= ( p
1
, p
2
, …, p
m
)
• a list of polygons, each of which is a list of indices into V
• generally more space efficient
• requires random access to vertex set — usually not a problem
Some Sample Triangle Meshes Drawing 3-D Triangle Meshes
Very similar to closed curves
• emit a long list of vertices
• every triple assumed to be a face
• see also GL_QUADS
Also more efficient types
• fewer calls to glVertex()
• GL_TRIANGLE_STRIP
• GL_TRIANGLE_FAN
• GL_QUAD_STRIP
Drawing the Mesh:
glBegin(GL_TRIANGLES);
for(int j=0; j<n; j++)
{
glVertex3f(…);
glVertex3f(…);
glVertex3f(…);
}
glEnd();
