From c0019b7f4999cbcad64b9629aefc6b874d23fa3a Mon Sep 17 00:00:00 2001
From: Sam Lantinga <slouken@libsdl.org>
Date: Wed, 11 Oct 2017 13:31:21 -0700
Subject: [PATCH] Fixed bug 3871 - Touch events are not normalised on X11

Trent Gamblin

The documentation for SDL_TouchFingerEvent says that the x and y coordinates are normalised between 0-1. I've found that to be true on Windows, Android and iOS but on X11 they are in pixel coordinates. This patch fixes the issue. This was the cleanest way I could do it with what was available without changing things around a lot but you may know a better way.
---
 src/video/x11/SDL_x11xinput2.c | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/src/video/x11/SDL_x11xinput2.c b/src/video/x11/SDL_x11xinput2.c
index 654fb8445b9a6..a4a588201d1c8 100644
--- a/src/video/x11/SDL_x11xinput2.c
+++ b/src/video/x11/SDL_x11xinput2.c
@@ -73,6 +73,24 @@ xinput2_version_atleast(const int version, const int wantmajor, const int wantmi
 {
     return ( version >= ((wantmajor * 1000) + wantminor) );
 }
+
+static void
+xinput2_normalize_touch_coordinates(SDL_VideoData *videodata, Window window,
+    double in_x, double in_y, float *out_x, float *out_y)
+{
+   int i;
+   for (i = 0; i < videodata->numwindows; i++) {
+      SDL_WindowData *d = videodata->windowlist[i];
+      if (d->xwindow == window) {
+         *out_x = in_x / (d->window->w-1);
+         *out_y = in_y / (d->window->h-1);
+         return;
+      }
+   }
+   // couldn't find the window...
+   *out_x = in_x;
+   *out_y = in_y;
+}
 #endif /* SDL_VIDEO_DRIVER_X11_XINPUT2 */
 
 void
@@ -171,22 +189,31 @@ X11_HandleXinput2Event(SDL_VideoData *videodata,XGenericEventCookie *cookie)
 #if SDL_VIDEO_DRIVER_X11_XINPUT2_SUPPORTS_MULTITOUCH
         case XI_TouchBegin: {
             const XIDeviceEvent *xev = (const XIDeviceEvent *) cookie->data;
+            float x, y;
+            xinput2_normalize_touch_coordinates(videodata, xev->event,
+                                  xev->event_x, xev->event_y, &x, &y);
             SDL_SendTouch(xev->sourceid,xev->detail,
-                      SDL_TRUE, xev->event_x, xev->event_y, 1.0);
+                      SDL_TRUE, x, y, 1.0);
             return 1;
             }
             break;
         case XI_TouchEnd: {
             const XIDeviceEvent *xev = (const XIDeviceEvent *) cookie->data;
+            float x, y;
+            xinput2_normalize_touch_coordinates(videodata, xev->event,
+                                  xev->event_x, xev->event_y, &x, &y);
             SDL_SendTouch(xev->sourceid,xev->detail,
-                      SDL_FALSE, xev->event_x, xev->event_y, 1.0);
+                      SDL_FALSE, x, y, 1.0);
             return 1;
             }
             break;
         case XI_TouchUpdate: {
             const XIDeviceEvent *xev = (const XIDeviceEvent *) cookie->data;
+            float x, y;
+            xinput2_normalize_touch_coordinates(videodata, xev->event,
+                                  xev->event_x, xev->event_y, &x, &y);
             SDL_SendTouchMotion(xev->sourceid,xev->detail,
-                                xev->event_x, xev->event_y, 1.0);
+                                x, y, 1.0);
             return 1;
             }
             break;