Graphics Reference
In-Depth Information
Chapter 7
This chapter describes the types of primitives and geometric objects that
are supported by OpenGL ES, and explains how to draw them. It then
describes the primitive assembly stage, which occurs after the vertices of
a primitive are processed by the vertex shader. In the primitive assembly
stage, clipping, perspective divide, and viewport transformation operations
are performed. These operations are discussed in detail. The chapter
concludes with a description of the rasterization stage. Rasterization is the
process that converts primitives into a set of two-dimensional fragments,
which are processed by the fragment shader. These two-dimensional
fragments represent pixels that may be drawn on the screen.
Refer to Chapter 8, “Vertex Shaders,” for a detailed description of vertex
shaders. Chapter 9, “Texturing,” and Chapter 10, “Fragment Shaders,”
describe processing that is applied to fragments generated by the
rasterization stage.
A primitive is a geometric object that can be drawn using the
glDrawArrays
,
glDrawElements
,
glDrawRangeElements
,
glDrawArraysInstanced
, and
glDrawElementsInstanced
commands
in OpenGL ES. The primitive is described by a set of vertices that indicate
the vertex position. Other information, such as color, texture coordinates,
and geometric normal can also be associated with each vertex as generic
attributes.
