Graphics Reference
In-Depth Information
Figure 1.2.
The actions of the overall graphics pipeline.
the CPU, are transformed into screen space by the vertex processor, are
assembled to go into the rasterizer, and are turned into pixels by the fragment
processor.
The graphics pipeline as described above includes a number of transfor-
mations noted in Figure 1.1: several modeling transformations, the viewing
transformation, and the projection transformation. The actual OpenGL imple-
mentation of the pipeline uses a more unified version of these transforma-
tions, however; the modeling and viewing transformations are combined into
the
ModelView transformation
, and new modeling transformations are multi-
plied into this as they are defined. A
transformation stack
is maintained for the
ModelView and Projection transformations, with the current version at the top
of the stack. The
glPushMatrix( )
and
glPopMatrix( )
operations let you save
and restore modeling environments. The
ModelViewProjection transformation
is
the product of the ModelView and Projection transformations, and is updated
whenever the ModelView transformation or Projection Transformation is
updated. The ModelViewProjection transformation is applied to individual
vertices to place them into clip space. The system also maintains another trans-
formation, the
Normal transformation
, calculated as the inverse of the transpose
of the ModelView transformation, which handles the problem of ensuring that
the normal can be correctly used for lighting and other operations. Later in the
chapter we will describe how this is done.
