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 modes, GL_COLOR,
const(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 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 of glEnd.

glGet with argument GL_MATRIX_MODE glGet with argument GL_COLOR_MATRIX glGet with argument GL_MODELVIEW_MATRIX glGet with argument GL_PROJECTION_MATRIX glGet with argument GL_TEXTURE_MATRIX glGet with argument GL_COLOR_STACK_DEPTH 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