class TGLOrthoCamera: public TGLCamera

 Construct orthographic camera with 'type' defining fixed view direction
 & orientation (in world frame):

 kXOY : X Horz. / Y Vert (looking towards +Z, Y up)
 kXOZ : X Horz. / Z Vert (looking towards +Y, Z up)
 kZOY : Z Horz. / Y Vert (looking towards +X, Y up)

 Construct orthographic camera.

 Destroy orthographic camera

 Setup camera limits suitible to view the world volume defined by 'box'
 and call Reset() to initialise camera.

 Reset the camera to defaults - trucking, zooming to reframe the world volume
 established in Setup(). Note: limits defined in Setup() are not adjusted.

 Dolly the camera - 'move camera along eye line, retaining lens focal length'.
 Arguments are:

 'delta' - mouse viewport delta (pixels) - +ive dolly in, -ive dolly out
 'mod1' / 'mod2' - sensitivity modifiers - see TGLCamera::AdjustAndClampVal()

 For an orthographic camera dollying and zooming are identical and both equate
 logically to a rescaling of the viewport limits - without center shift.
 There is no perspective foreshortening or lens 'focal length'.

 Returns kTRUE is redraw required (camera change), kFALSE otherwise.

 Zoom the camera - 'adjust lens focal length, retaining camera position'.
 Arguments are:

 'delta' - mouse viewport delta (pixels) - +ive zoom in, -ive zoom out
 'mod1' / 'mod2' - sensitivity modifiers - see TGLCamera::AdjustAndClampVal()

 For an orthographic camera dollying and zooming are identical and both equate
 logically to a rescaling of the viewport limits - without center shift.
 There is no perspective foreshortening or lens 'focal length'.

 Returns kTRUE is redraw required (camera change), kFALSE otherwise.

 Truck the camera - 'move camera parallel to film plane'. The film
 plane is defined by the EyePoint() / EyeDirection() pair. Define motion
 using center point (x/y) and delta (xDelta/yDelta) - the mouse motion.

 Returns kTRUE is redraw required (camera change), kFALSE otherwise.

 Note: Trucking is often mistakenly refered to as 'pan' or 'panning'.
 Panning is swivelling the camera on it's own axis - the eye point.

 Rotate the camera - 'swivel round the view volume center'.
 Ignored at present for orthographic cameras - have a fixed direction.
 Could let the user or external code create non-axis
 ortho projects by adjusting H/V rotations in future.

 Returns kTRUE is redraw required (camera change), kFALSE otherwise.

 Apply the camera to the current GL context, setting the viewport, projection
 and modelview matricies. After this verticies etc can be directly entered
 in the world frame. This also updates the cached frustum values, enabling
 all the projection, overlap tests etc defined in TGLCamera to be used.

 Arguments are:
 'box' - view volume box - ignored for ortho camera. Assumed to be same
 as one passed to Setup().
 'pickRect' - optional picking rect. If non-null, restrict drawing to this
 viewport rect.

 Configure the camera state

void TGLOrthoCamera::SetViewport(Int_t context)
Setup viewport, if it was changed, plus reset arcball.

'box' is the TGLPlotPainter's back box's coordinates.

User clicks somewhere (px, py).

Mouse movement.

User clicks somewhere (px, py).

Pan camera.

Viewport and projection.

Applies rotations and translations before drawing

viewport[0]

viewport[1]

viewport[2]

viewport[3]

Zoom in.

Zoom out.

 Write viewport dimensions on screen.

 Methods