DrawPanelBounds

This code draws the panel's visible bounds in red and total bounds in magenta during panel callbacks (and is visible in 2-d and 3-d). It draws the panels' visible bounds in green and total bounds in blue during the window callbacks and is only visible in 2-d.

XPLMRegisterDrawCallback( PostPanelCB, xplm_Phase_Panel, 0, 0);
XPLMRegisterDrawCallback( PostWindowCB, xplm_Phase_Window, 0, 0);

int 	PostPanelCB(
				XPLMDrawingPhase     inPhase,
				int                  inIsBefore,
				void *               inRefcon)
{
	// BEN SAYS: WARNING - Calling XPLMFindDataRef per frame is REALLY BAD! This is just dumb sample code.
	// Make sure in your code to FIND the dataref once and read it per callback!
	float vl = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_visible_pnl_l"));
	float vb = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_visible_pnl_b"));
	float vr = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_visible_pnl_r"));
	float vt = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_visible_pnl_t"));

	float tl = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_total_pnl_l"));
	float tb = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_total_pnl_b"));
	float tr = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_total_pnl_r"));
	float tt = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_total_pnl_t"));

	XPLMSetGraphicsState(0, 0, 0,   0, 0,  0, 0);
	glColor3f(1, 0, 0);

	glBegin(GL_LINE_LOOP);
	glVertex2f(vl+8, vb+8);
	glVertex2f(vl+8, vt-8);
	glVertex2f(vr-8, vt-8);
	glVertex2f(vr-8, vb+8);
	glEnd();

	glColor3f(1, 0, 1);

	glBegin(GL_LINE_LOOP);
	glVertex2f(tl+6, tb+6);
	glVertex2f(tl+6, tt-6);
	glVertex2f(tr-6, tt-6);
	glVertex2f(tr-6, tb+6);
	glEnd();

	return 1;
}

int 	PostWindowCB(
				XPLMDrawingPhase     inPhase,
				int                  inIsBefore,
				void *               inRefcon)
{
	// BEN SAYS: WARNING - Calling XPLMFindDataRef per frame is REALLY BAD! This is just dumb sample code.
	// Make sure in your code to FIND the dataref once and read it per callback!
	float vl = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_visible_win_l"));
	float vb = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_visible_win_b"));
	float vr = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_visible_win_r"));
	float vt = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_visible_win_t"));

	float tl = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_total_win_l"));
	float tb = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_total_win_b"));
	float tr = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_total_win_r"));
	float tt = XPLMGetDataf(XPLMFindDataRef("sim/graphics/view/panel_total_win_t"));

	XPLMSetGraphicsState(0, 0, 0,   0, 0,  0, 0);
	glColor3f(0, 1, 0);

	glBegin(GL_LINE_LOOP);
	glVertex2f(vl+2, vb+2);
	glVertex2f(vl+2, vt-2);
	glVertex2f(vr-2, vt-2);
	glVertex2f(vr-2, vb+2);
	glEnd();

	glColor3f(0, 1, 1);

	glBegin(GL_LINE_LOOP);
	glVertex2f(tl+4, tb+4);
	glVertex2f(tl+4, tt-4);
	glVertex2f(tr-4, tt-4);
	glVertex2f(tr-4, tb+4);
	glEnd();

	return 1;
}