rotation - OpenGL glMatrixMode(GL_PROJECTION) vs glMatrixMode(GL_MODELVIEW) -

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what difference between placing glrotatef() after glmatrixmode(gl_projection);

glmatrixmode(gl_projection); glloadidentity(); glrotatef(red, green, blue);

and placing glrotatef() after glmatrixmode(gl_modelview);

glmatrixmode(gl_modelview); glloadidentity(); glrotatef(red, green, blue);

from documentation:

glmatrixmode() specifies matrix current matrix.

gl_modelview - applies subsequent matrix operations modelview matrix stack.  gl_projection - applies subsequent matrix operations projection matrix stack.

what means?

if set current matrix mode projection (e.g glmatrixmode(gl_projection)), expected change projection matrix. naturally, 1 of them expected next line :

for orthographic projection:

  • glortho(gldouble left, gldouble right, gldouble bottom, gldouble top, gldouble near, gldouble far);
  • gluortho2d(gldouble left, gldouble right, gldouble bottom, gldouble top);

for perspective projection:

  • void glfrustum(gldouble left, gldouble right, gldouble bottom, gldouble top, gldouble near, gldouble far);
  • void gluperspective(gldouble fov, gldouble aspect, gldouble near, gldouble far);

if set current matrix mode modelview(e.g glmatrixmode(gl_modelview)), saying in modelview matrix , can apply basic operations transform objects :

  • glrotatef();
  • gltranslatef();
  • glscalef();

in question if use rotatef after gl_projection instead of gl_modelview, rotate projection matrix corrupt projection matrix.

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