====== Functions to adjust the coordinate frame ======

===== mglVisualAngleCoordinates: Visual angle coordinates =====

**purpose:** Sets view transformation to correspond to visual angles (in degrees) given size and distance of display. Display must be open and have valid width and height (defined in MGL variable)\\ **usage:** mglVisualAngleCoordinates(physicalDistance,physicalSize);

^ argument ^ value ^
| physicalDistance | [distance] in cm |
| physicalSize | [width height] in cm |

  mglOpen
  mglVisualAngleCoordinates(57,[16 12]);

===== mglScreenCoordinates: Pixel coordinate frame =====

**purpose:** Set coordinate frame so that it is in pixels with 0,0 in the top left hand corrner\\ **usage:** mglScreenCoordinates()

===== mglTransform: Low-level function to adjust transforms =====

purpose: applies view transformations\\  usage: mglTransform(whichMatrix, whichTransform, [whichParameters])

^ argument ^ value ^
| whichMatrix | 'GL_MODELVIEW', 'GL_PROJECTION', or 'GL_TEXTURE' |
| whichTransform | 'glRotate', 'glTranslate', 'glScale','glMultMatrix', 'glFrustum', 'glOrtho','glLoadMatrix', 'glLoadIdentity', 'glPushMatrix','glPopMatrix', 'glDepthRange', or 'glViewport' |
| whichParameters | function-specific; see OpenGL documentation |

You can also specifiy one of GL_MODELVIEW, GL_PROJECTION, or GL_TEXTURE and a return variable current matrix values. If two outputs are specified, the result of the computation will be returned.

This function is usually not called directly, but called by mglVisualAngleCoordinates or mglScreenCoordinates to set the transforms

===== mglHFlip: Horizontally flip coordinates =====

**purpose:** flips coordinate frame horizontally, useful for when the display is viewed through a mirror\\ **usage:** mglHFlip()

  mglOpen
  mglVisualAngleCoordinates(57,[16 12]);
  mglHFlip
  mglTextSet('Helvetica',32,1,0,0,0,0,0,0,0);
  mglTextDraw('Mirror reversed',[0 0]);
  mglFlush;

===== mglVFlip: Vertically flip coordinates =====

**purpose:** flips coordinate frame vertically\\ **usage:** mglVFlip

  mglOpen
  mglVisualAngleCoordinates(57,[16 12]);
  mglVFlip
  mglTextSet('Helvetica',32,[1 1 1],0,0,0,0,0,0,0);
  mglTextDraw('Vertically flipped',[0 0]);
  mglFlush;