OpenGL Programming Guide

Appendix CThe OpenGL Utility Library

Transforming Coordinates

The GLU includes routines that create matrices for standard perspective and orthographic viewing (gluPerspective() and gluOrtho2D()). In addition, a viewing routine allows you to place your eye at any point in space and look at any other point (gluLookAt()). These routines are discussed in Chapter 3 . In addition, the GLU includes a routine to help you create a picking matrix (gluPickMatrix()); this routine is discussed in Chapter 12 . For your convenience, the prototypes for these four routines are listed here.

void gluPerspective(GLdouble fovy, GLdouble aspect, GLdouble zNear, GLdouble zFar);

void gluOrtho2D(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top);

void gluLookAt(GLdouble eyex, GLdouble eyey, GLdouble eyez, GLdouble centerx, GLdouble centery, GLdouble centerz, GLdouble upx, GLdouble upy, GLdouble upz);

void gluPickMatrix(GLdouble x, GLdouble y, GLdouble width, GLdouble height, GLint viewport[4]);

In addition, GLU provides two routines that convert between object coordinates and screen coordinates, gluProject() and gluUnProject(). GLint gluProject(GLdouble objx, GLdouble objy, GLdouble objz, const GLdouble modelMatrix[16],const GLdouble projMatrix[16], const GLint viewport[4], GLdouble *winx, GLdouble *winy, GLdouble *winz);

Transforms the specified object coordinates objx, objy, and objz into window coordinates using modelMatrix, projMatrix, and viewport. The result is stored in winx, winy, and winz. A return value of GL_TRUE indicates success, and GL_FALSE indicates failure.

GLint gluUnProject(GLdouble winx, GLdouble winy, GLdouble winz, const GLdouble modelMatrix[16], const GLdouble projMatrix[16], const GLint viewport[4], GLdouble *objx, GLdouble *objy, GLdouble *objz);

Transforms the specified window coordinates winx, winy, and winz into object coordinates using modelMatrix, projMatrix, and viewport. The result is stored in objx, objy, and objz. A return value of GL_TRUE indicates success, and GL_FALSE indicates failure.

OpenGL Programming Guide