Vertex Shaders - Praise for OpenGL ES 30 Programming Guide - page 198

// Translate away from the viewer
esTranslate ( &modelview, 0.0, 0.0, -2.0 );
// Rotate the cube
esRotate ( &modelview, userData->angle, 1.0, 0.0, 1.0 );
First, the identity matrix is loaded into the modelview matrix using
esMatrixLoadIdentity . Then the identity matrix is concatenated with a
translation that moves the object away from the viewer. Finally, a rotation
is concatenated to the modelview matrix that rotates the object around
the vector (1.0, 0.0, 1.0) with an angle in degrees that is updated based on
time to rotate the object continuously.
Projection Matrix
The projection matrix takes the eye coordinates (computed from
applying the model-view matrix) and produces clip coordinates
as described in the Clipping section in Chapter 7. In fixed-function
OpenGL, this transformation was specified using glFrustum or
the OpenGL utility function gluPerspective . In the OpenGL ES
Framework API, we have provided two equivalent functions: esFrustum
and esPerspective . These functions specify the clip volume detailed
in Chapter 7. The esFrustum function describes the clip volume by
specifying the coordinates of the clip volume. The esPerspective
function is a convenience function that computes the parameters to
esFrustum using a field-of-view and aspect ratio description of the
viewing volume. The projection matrix is computed for Example 8-1 as
follows:
ESMatrix projection;
// Compute the window aspect ratio
aspect = (GLfloat) esContext->width /
(GLfloat) esContext->height;
// Generate a perspective matrix with a 60-degree FOV
// and near and far clip planes at 1.0 and 20.0
esMatrixLoadIdentity ( &projection);
esPerspective ( &projection, 60.0f, aspect, 1.0f, 20.0f );
Finally, the MVP matrix is computed as the product of the model-view
and projection matrices:
// Compute the final MVP by multiplying the
// model-view and projection matrices together
esMatrixMultiply ( &userData->mvpMatrix, &modelview,
&projection );