glPopMatrix example c c++ java objc

Name

glPushMatrix , glPopMatrix - push and pop the current matrix stack

C Specification

void glPushMatrix(void)
void glPopMatrix(void)

Description

There is a stack of matrices for each of the matrix modes. In GL_MODELVIEW mode, the stack depth is at least 16. In the other 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.(glPopMatrix)
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.

Notes

Each texture unit has its own texture matrix stack. Use glActiveTexture to select the desired texture matrix stack.

Errors

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.

Associated Gets

glGetInteger with argument GL_MAX_MODELVIEW_STACK_DEPTH
glGetInteger with argument GL_MAX_PROJECTION_STACK_DEPTH
glGetInteger with argument GL_MAX_TEXTURE_STACK_DEPTH
glGetInteger with argument GL_MAX_TEXTURE_UNITS

Copyright

Copyright © 2003 Silicon Graphics, Inc.
This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.

See Also

glActiveTexture, glFrustum, glGetInteger, glLoadIdentity, glLoadMatrix, glMatrixMode, glMultMatrix, glOrtho, glRotate, glScale, glTranslate, glViewport


Example
----------------------------------------------------------------------------
void display(void)
{
  int pass;

  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  glPushMatrix();

      glEnable(GL_ALPHA_TEST);
      pass = 2;

{
      glDisable(GL_ALPHA_TEST);
      pass = 0;
    }

 
   glRotatef(view_h, 0, 1, 0);
    glRotatef(view_v, 1, 0, 0);

    do {
      if (pass == 2) {
        glAlphaFunc(GL_EQUAL, 1);
        glDepthMask(GL_TRUE);
        pass--;
      } else if (pass != 0) {
        glAlphaFunc(GL_NOTEQUAL, 1);
        glDepthMask(GL_FALSE);
        pass--;
     }
      draw_engine_pole();

      glPushMatrix();
        glTranslatef(0.5, 1.4, 0.0);
        draw_cylinder_head();
      glPopMatrix();

      glPushMatrix();
        glTranslatef(0.0, -0.8, 0.0);
        draw_crank();
      glPopMatrix();
    } while (pass > 0);

    glDepthMask(GL_TRUE);
    glutSwapBuffers();
  glPopMatrix();

}