add ability to reset rotation via signal + gamepad

The gamepad change isn't the best as it requires the window to be
focused, but it allows to use a wireless gamepad to reset the rotation
and position like using the w key on the keyboard. I currently hardcoded
the reset button to 6 on a joystick, which was equal to the select
button on my steam controller using sc-controller simulating an xbox
controller. Maybe the controller update isn't quite fit to stay and
should use the VR controllers instead & work without focus.

The more interesting part of this patch is adding signal handling of
SIGUSR1 or SIGUSR2 to do the same thing. This allows to simply run a
command like `killall -USR1 vr-video-player` to reset the rotation and
position even without window focus. This is especially useful for
example for adding a custom command action to KDE connect so you can
reset the VR view from your phone without needing to have any special
software.

However I believe even this signal handling should eventually be
replaced with some more advanced API like dbus or a unix socket to also
allow for more advanced features like changing tracked windows on the
fly.

2 files changed, 35 insertions, 3 deletions

diff --git a/README.md b/README.md
index b9ac1b2..bfb53a7 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,11 @@ If the video is not meant to be viewed as a sphere but as a rectangle, then pass
 If the video is flipped where the right eye is on the left side, then pass the `--right-left` option when running vr video player.\
 If the video is stretched, then pass the `--no-stretch`option when running vr video player. Note: This option only works when also using the `--flat` option.
 
-To rotate the video to be in front of you, pull the trigger on the vr controller or press `w` on your keyboard while the vr video player is focused.
+To rotate and move the video to be in front of you, pull the trigger on the vr controller or press `w` on your keyboard while the vr video player is focused. You can also use the select/back button on an xbox controller while the application is focused or send the SIGUSR1 signal to the application to do the same thing like using the following command:
+
+```
+killall -USR1 vr-video-player
+```
 
 # Games
 This vr video player can also be used to play games in VR to to get a 3D effect, and even for games that don't support VR.\
diff --git a/src/main.cpp b/src/main.cpp
index dddee0e..e2627e0 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -53,6 +53,7 @@ extern "C" {
 #include <vector>
 
 #include <unistd.h>
+#include <signal.h>
 #include <libgen.h>
 
 #ifndef _countof
@@ -107,6 +108,7 @@ public:
 	void ProcessVREvent( const vr::VREvent_t & event );
 	void RenderFrame();
 
+	void ResetRotation();
 	void SetupScene();
 	void AddCubeToScene( const glm::mat4 &mat, std::vector<float> &vertdata );
 	void AddCubeVertex( float fl0, float fl1, float fl2, float fl3, float fl4, std::vector<float> &vertdata );
@@ -543,7 +545,7 @@ bool CMainApplication::BInit()
 
 	XSelectInput(x_display, src_window_id, StructureNotifyMask);
 
-	if ( SDL_Init( SDL_INIT_VIDEO | SDL_INIT_TIMER ) < 0 )
+	if ( SDL_Init( SDL_INIT_VIDEO | SDL_INIT_TIMER | SDL_INIT_JOYSTICK ) < 0 )
 	{
 		printf("%s - SDL could not initialize! SDL Error: %s\n", __FUNCTION__, SDL_GetError());
 		return false;
@@ -978,6 +980,11 @@ void CMainApplication::RunMainLoop()
 	SDL_StartTextInput();
 	SDL_ShowCursor( SDL_DISABLE );
 
+	SDL_Joystick *controller = SDL_JoystickOpen(0);
+	if (!controller)
+		fprintf(stderr, "Could not open gamecontroller: %s\n", SDL_GetError());
+
+
 	while ( !bQuit )
 	{
 		bQuit = HandleInput();
@@ -985,6 +992,9 @@ void CMainApplication::RunMainLoop()
 		RenderFrame();
 	}
 
+	if (controller)
+		SDL_JoystickClose(controller);
+
 	SDL_StopTextInput();
 }
 
@@ -1069,6 +1079,14 @@ void CMainApplication::RenderFrame()
 	UpdateHMDMatrixPose();
 }
 
+//-----------------------------------------------------------------------------
+// Purpose: resets rotation & position of the screen
+//-----------------------------------------------------------------------------
+void CMainApplication::ResetRotation()
+{
+	m_bResetRotation = true;
+}
+
 
 //-----------------------------------------------------------------------------
 // Purpose: Compiles a GL shader program and returns the handle. Returns 0 if
@@ -2200,13 +2218,23 @@ void CGLRenderModel::Draw()
 	glBindVertexArray( 0 );
 }
 
+CMainApplication *pMainApplication;
+
+void reset_position(int signum)
+{
+	printf("ok\n");
+	pMainApplication->ResetRotation();
+}
 
 //-----------------------------------------------------------------------------
 // Purpose:
 //-----------------------------------------------------------------------------
 int main(int argc, char *argv[])
 {
-	CMainApplication *pMainApplication = new CMainApplication( argc, argv );
+	pMainApplication = new CMainApplication( argc, argv );
+
+	signal(SIGUSR1, reset_position);
+	signal(SIGUSR2, reset_position);
 
 	if (!pMainApplication->BInit())
 	{