爱华网glPushMatrix，编程函数。
glPushMatrixNAME
glPushMatrix,glPopMatrix-- push and pop the current matrix stack
C SPECIFICATION
void glPushMatrix(void void)
C SPECIFICATION
void glPopMatrix(void void)
DESCRIPTION
描述
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.
每个矩阵模式都有相应的矩阵堆栈。在GL_MODELVIEW（模型视图）模式中，堆栈深度至少是32。在其他两个模式，GL_PROJECTION（投影）和GL_TEXTURE（纹理）中，堆栈深度至少是2。
当前矩阵在任何模式中都是位于该模式的堆栈顶端的。
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.
glPushMatrix复制当前矩阵，并将其在堆栈中下压。也就是说，glPushMatrix调用后，栈顶的矩阵和栈顶的下一个矩阵是相同的。
glPopMatrixPOPsthe current matrix stack, replacing the current matrix with the one below it on the stack.
glPopMatrix弹出当前矩阵堆栈，用当前矩阵替换该矩阵的下一个矩阵。
Initially, each of the stacks contains one matrix, an identity matrix.
初始时，每个模式的堆栈中都只有一个矩阵，并且该矩阵是单位矩阵。
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. 将当前栈中所有的矩阵向下压一级，当前矩阵由函数glMatrixMode()指定。复制栈顶矩阵，并将其压入堆栈，这样堆栈中最上面两个矩阵的内容相同。如果压入的矩阵过多，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.
