OpenGL man pages
glPushMatrix, glPopMatrix - push and pop the current matrix stack
void glPushMatrix( void )
void glPopMatrix( void )
There is a stack of matrices for each of the matrix modes. In GL_MODELVIEW
mode, the stack depth is at least 32. In the other two modes,
GL_PROJECTION and GL_TEXTURE, the depth is at least 2. The current matrix
in any mode is the matrix on the top of the stack for that mode.
glPushMatrix pushes the current matrix stack down by one, duplicating the
current matrix. That is, after a glPushMatrix call, the matrix on the top
of the stack is identical to the one below it.
glPopMatrix pops the current matrix stack, replacing the current matrix
with the one below it on the stack.
Initially, each of the stacks contains one matrix, an identity matrix.
It is an error to push a full matrix stack, or to pop a matrix stack that
contains only a single matrix. In either case, the error flag is set and
no other change is made to GL state.
GL_STACK_OVERFLOW is generated if glPushMatrix is called while the current
matrix stack is full.
GL_STACK_UNDERFLOW is generated if glPopMatrix is called while the current
matrix stack contains only a single matrix.
GL_INVALID_OPERATION is generated if glPushMatrix or glPopMatrix is
executed between the execution of glBegin and the corresponding execution
glGet with argument GL_MATRIX_MODE
glGet with argument GL_MODELVIEW_MATRIX
glGet with argument GL_PROJECTION_MATRIX
glGet with argument GL_TEXTURE_MATRIX
glGet with argument GL_MODELVIEW_STACK_DEPTH
glGet with argument GL_PROJECTION_STACK_DEPTH
glGet with argument GL_TEXTURE_STACK_DEPTH
glGet with argument GL_MAX_MODELVIEW_STACK_DEPTH
glGet with argument GL_MAX_PROJECTION_STACK_DEPTH
glGet with argument GL_MAX_TEXTURE_STACK_DEPTH
glFrustum, glLoadIdentity, glLoadMatrix, glMatrixMode, glMultMatrix,
glOrtho, glRotate, glScale, glTranslate, glViewport
Fri Dec 6 11:18:03 EST 1996
Look here for legal stuff: Legal