glPopMatrixNAMEglPushMatrix, glPopMatrix -- push and pop the current matrix stack
glPopMatrixNAMEglPushMatrix, glPopMatrix -- push and pop the current matrix stack
C SPECIFICATION
void glPushMatrix(void void)
C SPECIFICATION
void glPopMatrix(void void)
DEscriptION
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. 弹出栈顶的矩阵，并将其删除。这样，原来从栈顶数位于第二位的矩阵将成为栈顶矩阵。当前堆栈由函数glMatrixMode()指定。如果矩阵堆栈中只有一个矩阵，调用函数将导致错误。
ERRORS
GL_STACK_OVERFLOW is generated if glPushMatrix is called while the current matrix stack is full.
GL_STACK_UNDERFLOW is generated if glPopAttrib is called while the current matrix stack contains only a single matrix.
GL_INVALID_OPERATION is generated if glPushMatrix is called between a call to glBegin and the corresponding call to glEnd.
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