Add hint SDL_HINT_MOUSE_TOUCH_EVENTS for mouse events to generate touch events

controlling whether mouse events should generate synthetic touch events
By default SDL will *not* generate touch events for mouse events

include/SDL_hints.h

@@ -315,6 +315,18 @@ extern "C" {
  */
 #define SDL_HINT_TOUCH_MOUSE_EVENTS    "SDL_TOUCH_MOUSE_EVENTS"
 
+/**
+ *  \brief  A variable controlling whether mouse events should generate synthetic touch events
+ *
+ *  This variable can be set to the following values:
+ *    "0"       - Mouse events will not generate touch events
+ *    "1"       - Mouse events will generate touch events
+ *
+ *  By default SDL will *not* generate touch events for mouse events
+ */
+
+#define SDL_HINT_MOUSE_TOUCH_EVENTS    "SDL_MOUSE_TOUCH_EVENTS"
+
 /**
  *  \brief Minimize your SDL_Window if it loses key focus when in fullscreen mode. Defaults to true.
  *

include/SDL_touch.h

@@ -60,6 +60,9 @@ typedef struct SDL_Finger
 /* Used as the device ID for mouse events simulated with touch input */
 #define SDL_TOUCH_MOUSEID ((Uint32)-1)
 
+/* Used as the SDL_TouchID for touch events simulated with mouse input */
+#define SDL_MOUSE_TOUCHID ((Sint64)-1)
+
 
 /* Function prototypes */
 

src/events/SDL_mouse.c

@@ -37,6 +37,9 @@
 /* The mouse state */
 static SDL_Mouse SDL_mouse;
 
+/* for mapping mouse events to touch */
+static SDL_bool track_mouse_down = SDL_FALSE;
+
 static int
 SDL_PrivateSendMouseMotion(SDL_Window * window, SDL_MouseID mouseID, int relative, int x, int y);
 
@@ -104,6 +107,21 @@ SDL_TouchMouseEventsChanged(void *userdata, const char *name, const char *oldVal
     }
 }
 
+static void SDLCALL
+SDL_MouseTouchEventsChanged(void *userdata, const char *name, const char *oldValue, const char *hint)
+{
+    SDL_Mouse *mouse = (SDL_Mouse *)userdata;
+
+    if (hint && (*hint == '1' || SDL_strcasecmp(hint, "true") == 0)) {
+
+        SDL_AddTouch(SDL_MOUSE_TOUCHID, SDL_TOUCH_DEVICE_DIRECT, "mouse_input");
+
+        mouse->mouse_touch_events = SDL_TRUE;
+    } else {
+        mouse->mouse_touch_events = SDL_FALSE;
+    }
+}
+
 /* Public functions */
 int
 SDL_MouseInit(void)
@@ -127,6 +145,9 @@ SDL_MouseInit(void)
     SDL_AddHintCallback(SDL_HINT_TOUCH_MOUSE_EVENTS,
                         SDL_TouchMouseEventsChanged, mouse);
 
+    SDL_AddHintCallback(SDL_HINT_MOUSE_TOUCH_EVENTS,
+                        SDL_MouseTouchEventsChanged, mouse);
+
     mouse->cursor_shown = SDL_TRUE;
 
     return (0);
@@ -298,6 +319,17 @@ SDL_PrivateSendMouseMotion(SDL_Window * window, SDL_MouseID mouseID, int relativ
     int xrel;
     int yrel;
 
+    /* SDL_HINT_MOUSE_TOUCH_EVENTS: controlling whether mouse events should generate synthetic touch events */
+    if (mouse->mouse_touch_events) {
+        if (mouseID != SDL_TOUCH_MOUSEID && !relative && track_mouse_down) {
+            if (window) {
+                float fx = (float)x / (float)window->w;
+                float fy = (float)y / (float)window->h;
+                SDL_SendTouchMotion(SDL_MOUSE_TOUCHID, 0, fx, fy, 1.0f);
+            }
+        }
+    }
+
     if (mouseID != SDL_TOUCH_MOUSEID && mouse->relative_mode_warp) {
         int center_x = 0, center_y = 0;
         SDL_GetWindowSize(window, &center_x, &center_y);
@@ -443,6 +475,22 @@ SDL_PrivateSendMouseButton(SDL_Window * window, SDL_MouseID mouseID, Uint8 state
     Uint32 type;
     Uint32 buttonstate = mouse->buttonstate;
 
+    /* SDL_HINT_MOUSE_TOUCH_EVENTS: controlling whether mouse events should generate synthetic touch events */
+    if (mouse->mouse_touch_events) {
+        if (mouseID != SDL_TOUCH_MOUSEID && button == SDL_BUTTON_LEFT) {
+            if (window) {
+                float fx = (float)mouse->x / (float)window->w;
+                float fy = (float)mouse->y / (float)window->h;
+                if (state == SDL_PRESSED) {
+                    track_mouse_down = SDL_TRUE;
+                } else {
+                    track_mouse_down = SDL_FALSE;
+                }
+                SDL_SendTouch(SDL_MOUSE_TOUCHID, 0, track_mouse_down, fx, fy, 1.0f);
+            }
+        }
+    }
+
     /* Figure out which event to perform */
     switch (state) {
     case SDL_PRESSED:

src/events/SDL_mouse_c.h

@@ -93,6 +93,7 @@ typedef struct
     Uint32 double_click_time;
     int double_click_radius;
     SDL_bool touch_mouse_events;
+    SDL_bool mouse_touch_events;
 
     /* Data for double-click tracking */
     int num_clickstates;

src/events/SDL_touch.c

@@ -249,6 +249,8 @@ SDL_SendTouch(SDL_TouchID id, SDL_FingerID fingerid,
     {
         SDL_Mouse *mouse = SDL_GetMouse();
         if (mouse->touch_mouse_events) {
+            /* FIXME: maybe we should only restrict to a few SDL_TouchDeviceType */
+            if (id != SDL_MOUSE_TOUCHID) {
                 SDL_Window *window = SDL_GetMouseFocus();
                 if (window) {
                     if (down) {
@@ -270,6 +272,7 @@ SDL_SendTouch(SDL_TouchID id, SDL_FingerID fingerid,
                 }
             }
         }
+    }
 
     finger = SDL_GetFinger(touch, fingerid);
     if (down) {
@@ -339,6 +342,7 @@ SDL_SendTouchMotion(SDL_TouchID id, SDL_FingerID fingerid,
     {
         SDL_Mouse *mouse = SDL_GetMouse();
         if (mouse->touch_mouse_events) {
+            if (id != SDL_MOUSE_TOUCHID) {
                 SDL_Window *window = SDL_GetMouseFocus();
                 if (window) {
                     if (finger_touching == SDL_TRUE && track_touchid == id && track_fingerid == fingerid) {
@@ -349,6 +353,7 @@ SDL_SendTouchMotion(SDL_TouchID id, SDL_FingerID fingerid,
                 }
             }
         }
+    }
 
     finger = SDL_GetFinger(touch,fingerid);
     if (!finger) {