OpenGL 4.2 (Compatibility Profile) - April 27, 2012

2.6. BEGIN/END PARADIGM 22
Processed
Vertices
Coordinates
Associated
Data
Point,
Line Segment, or
Polygon
(Primitive)
Assembly
Point culling;
Line Segment
or Polygon
Clipping
Color
Processing
Rasterization
Begin/End
State
Figure 2.3. Primitive assembly and processing.
colors may be affected or replaced by lighting, and texture coordinates are transformed
and possibly affected by a texture coordinate generation function. The
processing indicated for each current value is applied for each vertex that is sent to
the GL.
The methods by which vertices, normals, texture coordinates, fog coordinate,
generic attributes, and colors are sent to the GL, as well as how normals are transformed
and how vertices are mapped to the two-dimensional screen, are discussed
later.
Before colors have been assigned to a vertex, the state required by a vertex
is the vertex’s coordinates, the current normal, the current edge flag (see section
2.6.2), the current material properties (see section 2.13.2), the current fog coordinate,
the multiple generic vertex attribute sets, and the multiple current texture
coordinate sets. Because color assignment is done vertex-by-vertex, a processed
vertex comprises the vertex’s coordinates, its edge flag, its fog coordinate, its assigned
colors, and its multiple texture coordinate sets.
Figure 2.3 shows the sequence of operations that builds a primitive (point, line
segment, or polygon) from a sequence of vertices. After a primitive is formed, it
is clipped to a clip volume. This may alter the primitive by altering vertex coordinates,
texture coordinates, and colors. In the case of line and polygon primitives,
clipping may insert new vertices into the primitive. The vertices defining a primitive
to be rasterized have texture coordinates and colors associated with them.
OpenGL 4.2 (Compatibility Profile) - April 27, 2012