The following sample code, modeled after the X‑Plane 11 Window API sample, will create a “modern”-style window. Note that as of X‑Plane 11.20, control over windows in VR is quite limited—you can move a window in and out of VR and change the window’s size, but that’s about it.

Note that some of the APIs used here are new to X-Plane 11.20b5—if you get a runtime error, ensure you’re on the latest release.

#include "XPLMDisplay.h"    // for window creation and manipulation
#include "XPLMGraphics.h"   // for window drawing
#include "XPLMDataAccess.h" // for the VR dataref
#include "XPLMPlugin.h"     // for XPLM_MSG_ENTERED_VR and XPLM_MSG_EXITING_VR message
#include "XPLMMenus.h"
#include <string.h>
#include <stdio.h> // for sprintf()
#if IBM
	#include <windows.h>
#endif
#if LIN
	#include <GL/gl.h>
#elif __GNUC__
	#include <OpenGL/gl.h>
#else
	#include <GL/gl.h>
#endif

#ifndef XPLM301
	#error This is made to be compiled against the XPLM301 SDK
#endif

static XPLMWindowID	g_window;
static XPLMMenuID g_menu_id;

void				create_window();
void				get_default_window_pos(int position_lbrt[4]);
void				exit_vr_mode();
void				draw(XPLMWindowID in_window_id, void * in_refcon);
void				draw_button(const char * text, float in_out_lbrt[4] /* you set the left and bottom, we'll set the right and top */);
int					handle_mouse(XPLMWindowID in_window_id, int x, int y, int is_down, void * in_refcon);
void				handle_menu(void * mRef, void * iRef);

int					dummy_mouse_handler(XPLMWindowID in_window_id, int x, int y, int is_down, void * in_refcon) { return 0; }
XPLMCursorStatus	dummy_cursor_status_handler(XPLMWindowID in_window_id, int x, int y, void * in_refcon) { return xplm_CursorDefault; }
int					dummy_wheel_handler(XPLMWindowID in_window_id, int x, int y, int wheel, int clicks, void * in_refcon) { return 0; }
void				dummy_key_handler(XPLMWindowID in_window_id, char key, XPLMKeyFlags flags, char virtual_key, void * in_refcon, int losing_focus) { }

XPLMDataRef g_vr_dref;
static float g_vr_button_lbrt[4] = {0, 0, 0, 0}; // left, bottom, right, top
static float g_size_button_lbrt[4] = {0, 0, 0, 0}; // left, bottom, right, top
static int g_last_mouse_xy[2] = {0, 0};

static int	coord_in_rect(float x, float y, float * bounds_lbrt)  { return ((x >= bounds_lbrt[0]) && (x < bounds_lbrt[2]) && (y < bounds_lbrt[3]) && (y >= bounds_lbrt[1])); }


PLUGIN_API int XPluginStart(
						char *		outName,
						char *		outSig,
						char *		outDesc)
{
	strcpy(outName, "VRSamplePlugin");
	strcpy(outSig, "xpsdk.examples.vrsampleplugin");
	strcpy(outDesc, "A test plug-in that demonstrates moving a window into VR.");

	create_window();
	
	g_vr_dref = XPLMFindDataRef("sim/graphics/VR/enabled");
	
	g_menu_id = XPLMCreateMenu("VR Sample", NULL, 0, handle_menu, NULL);
	XPLMAppendMenuItem(g_menu_id, "Toggle Into/Out of VR", (void *)"cmd_vr", 1);
	
	// If this dataref is for some reason not available,
	// we won't be able to move the window to VR anyway,
	// so go ahead an disable us!
	return g_vr_dref != NULL;
}

PLUGIN_API void	XPluginStop(void)
{
	// Since we created the window, we'll be good citizens and clean it up
	XPLMDestroyWindow(g_window);
	g_window = NULL;
}

PLUGIN_API void XPluginDisable(void) { }
PLUGIN_API int  XPluginEnable(void)  { return 1; }
PLUGIN_API void XPluginReceiveMessage(XPLMPluginID inFrom, int inMsg, void * inParam)
{
	if(inFrom == XPLM_PLUGIN_XPLANE && inMsg == XPLM_MSG_ENTERED_VR)
	{
		XPLMSetWindowPositioningMode(g_window, xplm_WindowVR, -1);
	}
	else if(inFrom == XPLM_PLUGIN_XPLANE && inMsg == XPLM_MSG_EXITING_VR && XPLMWindowIsInVR(g_window))
	{
		exit_vr_mode();
	}
}

void create_window()
{
	int position_lbrt[4];
	get_default_window_pos(position_lbrt);
	
	XPLMCreateWindow_t params = {};
	params.structSize = sizeof(params);
	params.left = position_lbrt[0];
	params.bottom = position_lbrt[1];
	params.right = position_lbrt[2];
	params.top = position_lbrt[3];
	params.visible = 1;
	params.drawWindowFunc = draw;
	params.handleMouseClickFunc = handle_mouse;
	params.handleRightClickFunc = dummy_mouse_handler;
	params.handleMouseWheelFunc = dummy_wheel_handler;
	params.handleKeyFunc = dummy_key_handler;
	params.handleCursorFunc = dummy_cursor_status_handler;
	params.refcon = NULL;
	params.layer = xplm_WindowLayerFloatingWindows;
	params.decorateAsFloatingWindow = xplm_WindowDecorationRoundRectangle;
	
	g_window = XPLMCreateWindowEx(&params);
	
	const int vr_is_enabled = XPLMGetDatai(g_vr_dref);
	XPLMSetWindowPositioningMode(g_window, vr_is_enabled ? xplm_WindowVR : xplm_WindowPositionFree, -1);
	
	XPLMSetWindowResizingLimits(g_window, 200, 200, 500, 500); // Limit resizing our window: maintain a minimum width/height of 200 boxels and a max width/height of 500
	XPLMSetWindowTitle(g_window, "Sample VR Window");
}

void get_default_window_pos(int position_lbrt[4])
{
	// We're not guaranteed that the main monitor's lower left is at (0, 0)...
	// we'll need to query for the global desktop bounds!
	int global_desktop_bounds[4]; // left, bottom, right, top
	XPLMGetScreenBoundsGlobal(&global_desktop_bounds[0], &global_desktop_bounds[3], &global_desktop_bounds[2], &global_desktop_bounds[1]);
	position_lbrt[0] = global_desktop_bounds[0] + 50;
	position_lbrt[1] = global_desktop_bounds[1] + 150;
	position_lbrt[2] = global_desktop_bounds[0] + 350;
	position_lbrt[3] = global_desktop_bounds[1] + 450;
}

void draw(XPLMWindowID in_window_id, void * in_refcon)
{
	XPLMSetGraphicsState(
			0 /* no fog */,
			0 /* 0 texture units */,
			0 /* no lighting */,
			0 /* no alpha testing */,
			1 /* do alpha blend */,
			1 /* do depth testing */,
			0 /* no depth writing */
	);

	int l, t, r, b;
	XPLMGetWindowGeometry(in_window_id, &l, &t, &r, &b);

	float col_white[] = {1.0, 1.0, 1.0};
	int char_height;
	XPLMGetFontDimensions(xplmFont_Proportional, NULL, &char_height, NULL);
	
	const int vr_is_enabled = XPLMGetDatai(g_vr_dref);
	if(vr_is_enabled)
	{
		// Position the button in the upper left of the window (sized to fit the button text)
		g_vr_button_lbrt[0] = l + 10;
		g_vr_button_lbrt[1] = t - char_height * 1.5;
		draw_button("Toggle VR", g_vr_button_lbrt);
		
		g_size_button_lbrt[0] = g_vr_button_lbrt[2] + 10;
		g_size_button_lbrt[1] = g_vr_button_lbrt[1];
		draw_button("Toggle Size", g_size_button_lbrt);
	}
	else // Draw some text to say VR isn't available
	{
		char * line1 = "VR must be enabled before you";
		char * line2 = "can toggle this window into VR.";
		XPLMDrawString(col_white, l, t - 2 * char_height, line1, NULL, xplmFont_Proportional);
		XPLMDrawString(col_white, l, t - 4 * char_height, line2, NULL, xplmFont_Proportional);
	}
}

void draw_button(const char * text, float in_out_lbrt[4] /* you set the left and bottom, we'll set the right and top */)
{
	// We draw our rudimentary button boxes based on the height of the button text
	int char_height;
	XPLMGetFontDimensions(xplmFont_Proportional, NULL, &char_height, NULL);
	
	in_out_lbrt[2] = in_out_lbrt[0] + XPLMMeasureString(xplmFont_Proportional, text, strlen(text)); // *just* wide enough to fit the button text
	in_out_lbrt[3] = in_out_lbrt[1] + (1.25f * char_height); // a bit taller than the button text
	
	// Draw the box around our rudimentary button
	float green[] = {0.0, 1.0, 0.0, 1.0};
	glColor4fv(green);
	glBegin(GL_LINE_LOOP);
	{
		glVertex2i(in_out_lbrt[0], in_out_lbrt[3]);
		glVertex2i(in_out_lbrt[2], in_out_lbrt[3]);
		glVertex2i(in_out_lbrt[2], in_out_lbrt[1]);
		glVertex2i(in_out_lbrt[0], in_out_lbrt[1]);
	}
	glEnd();
	
	// Draw the button text (pop in/pop out)
	float col_white[] = {1.0, 1.0, 1.0};
	XPLMDrawString(col_white, in_out_lbrt[0], in_out_lbrt[1] + 4, (char *)text, NULL, xplmFont_Proportional);
}

int	handle_mouse(XPLMWindowID in_window_id, int x, int y, XPLMMouseStatus mouse_status, void * in_refcon)
{
	if(mouse_status == xplm_MouseDown)
	{
		g_last_mouse_xy[0] = x;
		g_last_mouse_xy[1] = y;
		if(!XPLMIsWindowInFront(in_window_id))
		{
			XPLMBringWindowToFront(in_window_id);
		}
		else
		{
			const int vr_is_enabled = XPLMGetDatai(g_vr_dref);
			if(vr_is_enabled && coord_in_rect(x, y, g_vr_button_lbrt)) // user clicked the "toggle VR mode" button
			{
				if(XPLMWindowIsInVR(in_window_id))
				{
					exit_vr_mode();
				}
				else
				{
					XPLMSetWindowPositioningMode(in_window_id, xplm_WindowVR, 0);
				}
			}
			else if(vr_is_enabled && coord_in_rect(x, y, g_size_button_lbrt)) // user clicked "toggle size" btn
			{
				int width, height;
				XPLMGetWindowGeometryVR(in_window_id, &width, &height);
				width = width > 300 ? 300 : 500;
				height = height > 300 ? 300 : 500;
				XPLMSetWindowGeometryVR(in_window_id, width, height);
			}
		}
	}
	return 1;
}

void handle_menu(void * mRef, void * iRef)
{
	if(!strcmp((char *)iRef, "cmd_vr"))
	{
		if(XPLMWindowIsInVR(g_window))
		{
			exit_vr_mode();
		}
		else
		{
			XPLMSetWindowPositioningMode(g_window, xplm_WindowVR, 0);
		}
	}
}

void exit_vr_mode()
{
	XPLMSetWindowPositioningMode(g_window, xplm_WindowPositionFree, 0);
	// We need to also reposition the window; it doesn't get automatically moved back to the main monitor!
	int position_lbrt[4];
	get_default_window_pos(position_lbrt);
	XPLMSetWindowGeometry(g_window, position_lbrt[0], position_lbrt[3], position_lbrt[2], position_lbrt[1]);
}

9 comments on “VR Window Sample

  1. I am seriously confused. This seems to be the latest example, dated late 2018, yet it uses OpenGL commands like “glBegin” and “glEnd” from the early 90s who have become obsolete since programmable shaders have been introduced, around 2008.
    Is this really the way we are supposed to draw GUIs in Xplane?

    1. You can use any valid OpenGL drawing technique you want. The point of the example is to show you how to interact with X-Plane, _not_ to teach you how to use OpenGL. The OpenGL code shown isn’t even useful, it is meant to prove that user-based drawing is working with a minimal sample.

      1. Thanks for the reply. I noticed that the Widgets API does not include the current, modern GUI elements (or maybe I did something wrong). Is it planned to expose those via the Widgets API at any time in future?

        1. Widget windows can be opted in to “modern” windowing features like support for UI scaling and being popped out into a native OS window (see this note). But if you’re asking about styling windows to match X-Plane 11 text, buttons, etc., we don’t have a good solution right now. The backstory here is: between X-Plane 10 and 11, the back-end infrastructure for our internal GUI framework changed entirely, in a way that no longer matches the public widgets API at all. So long term, we need to either:

          • deprecate the existing API and create an entirely new one that more closely aligns with the internal GUI framework, or
          • bbbbbasically back-port all our new GUI components to the old system.

          The cost for either is measured in months of dev time, and we just haven’t had the resources to devote to it yet. :/

  2. I’ve got a problem: I already made a HUD via OpenGL. It works fine on the monitor. Now I’m trying to implement it as a HMD for VR.
    I used this sample code and the window worked fine on VR. Ben Sputnik wrote that any valid OpenGL drawing technique will work, but I can’t see my drawings of my HMD (same Code as the HUD).
    I can see my drawing on my monitor when I’m not able to see the window in VR. (Toggle VR)
    Any suggestions?

      1. I added a function called “draw_HMD” and called it inside the “draw” function. So it should be in the callback.
        When it still is on my monitor (before pressing Toggle VR), my speed is shown correctly and is refreshed each gametick.

        1. What about if you pop your window out (see the window API sample, specifically the call to XPLMSetWindowPositioningMode(in_window_id, xplm_WindowPopOut, 0))? My hypothesis here is that your code isn’t drawing correctly with respect to the window bounds; popping the window out will change the coordinate space for drawing in a similar way to VR.

          If popping the window out works okay, I’d say get me a minimal reproducible example plugin that has this issue and I can look into it. (You can either post it here, or email me at my first name at X-Plane.com.)

          1. Thanks for your suggestion. I already found my problem. It was kind a dumb mistake but now it is fixed 🙂
            Thanks Tyler!

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