From 696a356b14ac2426b8b8176d298f05204751862c Mon Sep 17 00:00:00 2001
From: Luca Bacci <luca.bacci982@gmail.com>
Date: Fri, 11 Jun 2021 19:37:17 +0200
Subject: [PATCH] Wintab: Fix coordinates in mixed-DPI setups

Fixes #753
---
 gdk/win32/gdkdevice-wintab.c       | 77 +++++++++++++++++++-----------
 gdk/win32/gdkdevice-wintab.h       |  5 ++
 gdk/win32/gdkdevicemanager-win32.c |  5 ++
 3 files changed, 59 insertions(+), 28 deletions(-)

diff --git a/gdk/win32/gdkdevice-wintab.c b/gdk/win32/gdkdevice-wintab.c
index 338479db43..0337cc0d42 100644
--- a/gdk/win32/gdkdevice-wintab.c
+++ b/gdk/win32/gdkdevice-wintab.c
@@ -220,18 +220,9 @@ _gdk_device_wintab_translate_axes (GdkDeviceWintab *device_wintab,
                                    gdouble         *x,
                                    gdouble         *y)
 {
-  GdkDevice *device;
-  GdkWindow *impl_window;
-  gint root_x, root_y;
-  gdouble temp_x, temp_y;
+  GdkDevice *device = GDK_DEVICE (device_wintab);
   gint i;
 
-  device = GDK_DEVICE (device_wintab);
-  impl_window = _gdk_window_get_impl_window (window);
-  temp_x = temp_y = 0;
-
-  gdk_window_get_origin (impl_window, &root_x, &root_y);
-
   for (i = 0; i < gdk_device_get_n_axes (device); i++)
     {
       GdkAxisUse use;
@@ -243,19 +234,55 @@ _gdk_device_wintab_translate_axes (GdkDeviceWintab *device_wintab,
         case GDK_AXIS_X:
         case GDK_AXIS_Y:
           if (gdk_device_get_mode (device) == GDK_MODE_WINDOW)
-            _gdk_device_translate_window_coord (device, window, i,
-                                                device_wintab->last_axis_data[i],
-                                                &axes[i]);
+            {
+              _gdk_device_translate_window_coord (device, window, i,
+                                                  device_wintab->last_axis_data[i],
+                                                  &axes[i]);
+
+              if (use == GDK_AXIS_X)
+                {
+                  *x = axes[i];
+                }
+              else
+                {
+                  *y = axes[i];
+                }
+            }
           else
-            _gdk_device_translate_screen_coord (device, window,
-                                                root_x, root_y, i,
-                                                device_wintab->last_axis_data[i],
-                                                &axes[i]);
-          if (use == GDK_AXIS_X)
-            temp_x = axes[i];
-          else if (use == GDK_AXIS_Y)
-            temp_y = axes[i];
-
+            {
+              GdkAtom label_atom;
+              GdkAxisUse use;
+              double min_value, max_value, resolution;
+              double device_val = device_wintab->last_axis_data[i];
+              double screen_val = 0.0;
+              double window_val = 0.0;
+              POINT client;
+
+              client.x = 0;
+              client.y = 0;
+              ClientToScreen (GDK_WINDOW_HWND (window), &client);
+
+              _gdk_device_get_axis_info (device, i,
+                                         &label_atom, &use,
+                                         &min_value, &max_value, &resolution);
+
+              if (use == GDK_AXIS_X)
+                {
+                  screen_val = device_wintab->screen_mapping_origin_x +
+                               (device_wintab->screen_mapping_width / (max_value - min_value)) *
+                               (device_val - min_value);
+                  window_val = screen_val - client.x;
+                  *x = axes[i] = window_val;
+                }
+              else
+                {
+                  screen_val = device_wintab->screen_mapping_origin_y +
+                               (device_wintab->screen_mapping_height / (max_value - min_value)) *
+                               (device_val - min_value);
+                  window_val = screen_val - client.y;
+                  *y = axes[i] = window_val;
+                }
+            }
           break;
         default:
           _gdk_device_translate_axis (device, i,
@@ -264,12 +291,6 @@ _gdk_device_wintab_translate_axes (GdkDeviceWintab *device_wintab,
           break;
         }
     }
-
-  if (x)
-    *x = temp_x;
-
-  if (y)
-    *y = temp_y;
 }
 
 static void
diff --git a/gdk/win32/gdkdevice-wintab.h b/gdk/win32/gdkdevice-wintab.h
index 9431215359..828dd198d6 100644
--- a/gdk/win32/gdkdevice-wintab.h
+++ b/gdk/win32/gdkdevice-wintab.h
@@ -39,6 +39,11 @@ struct _GdkDeviceWintab
 {
   GdkDevice parent_instance;
 
+  double screen_mapping_origin_x;
+  double screen_mapping_origin_y;
+  double screen_mapping_width;
+  double screen_mapping_height;
+
   gboolean sends_core;
   gint *last_axis_data;
   gint button_state;
diff --git a/gdk/win32/gdkdevicemanager-win32.c b/gdk/win32/gdkdevicemanager-win32.c
index 34c0083cb3..d22dd3e68d 100644
--- a/gdk/win32/gdkdevicemanager-win32.c
+++ b/gdk/win32/gdkdevicemanager-win32.c
@@ -633,6 +633,11 @@ _wintab_recognize_new_cursors (GdkDeviceManagerWin32 *device_manager,
           _gdk_device_add_slave (device_manager->core_pointer, GDK_DEVICE (device));
         }
 
+      device->screen_mapping_origin_x = lc.lcSysOrgX;
+      device->screen_mapping_origin_y = lc.lcSysOrgY;
+      device->screen_mapping_width = lc.lcSysExtX;
+      device->screen_mapping_height = lc.lcSysExtY;
+
       device->hctx = hctx;
       device->cursor = cursorix;
       (*p_WTInfoA) (WTI_CURSORS + cursorix, CSR_PKTDATA, &device->pktdata);
-- 
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