evdev: Batch mouse axis updates until SYN_REPORT

This is necessary for consistent position reports with absolute mice
and improves application performance with relative mice by cutting the
number of reported mouse motion events roughly in half.

src/core/linux/SDL_evdev.c

@@ -96,8 +96,12 @@ typedef struct SDL_evdevlist_item
 
     } * touchscreen_data;
 
+    /* Mouse state */
     SDL_bool high_res_wheel;
     SDL_bool high_res_hwheel;
+    SDL_bool relative_mouse;
+    int mouse_x, mouse_y;
+    int mouse_wheel, mouse_hwheel;
 
     struct SDL_evdevlist_item *next;
 } SDL_evdevlist_item;
@@ -361,16 +365,20 @@ SDL_EVDEV_Poll(void)
                             if (item->touchscreen_data->max_slots != 1)
                                 break;
                             item->touchscreen_data->slots[0].x = events[i].value;
-                        } else
-                            SDL_SendMouseMotion(mouse->focus, mouse->mouseID, SDL_FALSE, events[i].value, mouse->y);
+                        } else if (!item->relative_mouse) {
+                            /* FIXME: Normalize to input device's reported input range (EVIOCGABS) */
+                            item->mouse_x = events[i].value;
+                        }
                         break;
                     case ABS_Y:
                         if (item->is_touchscreen) {
                             if (item->touchscreen_data->max_slots != 1)
                                 break;
                             item->touchscreen_data->slots[0].y = events[i].value;
-                        } else
-                            SDL_SendMouseMotion(mouse->focus, mouse->mouseID, SDL_FALSE, mouse->x, events[i].value);
+                        } else if (!item->relative_mouse) {
+                            /* FIXME: Normalize to input device's reported input range (EVIOCGABS) */
+                            item->mouse_y = events[i].value;
+                        }
                         break;
                     default:
                         break;
@@ -379,26 +387,28 @@ SDL_EVDEV_Poll(void)
                 case EV_REL:
                     switch(events[i].code) {
                     case REL_X:
-                        SDL_SendMouseMotion(mouse->focus, mouse->mouseID, SDL_TRUE, events[i].value, 0);
+                        if (item->relative_mouse)
+                            item->mouse_x += events[i].value;
                         break;
                     case REL_Y:
-                        SDL_SendMouseMotion(mouse->focus, mouse->mouseID, SDL_TRUE, 0, events[i].value);
+                        if (item->relative_mouse)
+                            item->mouse_y += events[i].value;
                         break;
                     case REL_WHEEL:
                         if (!item->high_res_wheel)
-                            SDL_SendMouseWheel(mouse->focus, mouse->mouseID, 0, events[i].value, SDL_MOUSEWHEEL_NORMAL);
+                            item->mouse_wheel += events[i].value;
                         break;
                     case REL_WHEEL_HI_RES:
                         SDL_assert(item->high_res_wheel);
-                        SDL_SendMouseWheel(mouse->focus, mouse->mouseID, 0, events[i].value / 120.0f, SDL_MOUSEWHEEL_NORMAL);
+                        item->mouse_wheel += events[i].value;
                         break;
                     case REL_HWHEEL:
                         if (!item->high_res_hwheel)
-                            SDL_SendMouseWheel(mouse->focus, mouse->mouseID, events[i].value, 0, SDL_MOUSEWHEEL_NORMAL);
+                            item->mouse_hwheel += events[i].value;
                         break;
                     case REL_HWHEEL_HI_RES:
                         SDL_assert(item->high_res_hwheel);
-                        SDL_SendMouseWheel(mouse->focus, mouse->mouseID, events[i].value / 120.0f, 0, SDL_MOUSEWHEEL_NORMAL);
+                        item->mouse_hwheel += events[i].value;
                         break;
                     default:
                         break;
@@ -407,6 +417,19 @@ SDL_EVDEV_Poll(void)
                 case EV_SYN:
                     switch (events[i].code) {
                     case SYN_REPORT:
+                        /* Send mouse axis changes together to ensure consistency and reduce event processing overhead */
+                        if (item->mouse_x != 0 || item->mouse_y != 0) {
+                            SDL_SendMouseMotion(mouse->focus, mouse->mouseID, item->relative_mouse, item->mouse_x, item->mouse_y);
+                            item->mouse_x = item->mouse_y = 0;
+                        }
+                        if (item->mouse_wheel != 0 || item->mouse_hwheel != 0) {
+                            SDL_SendMouseWheel(mouse->focus, mouse->mouseID,
+                                               item->mouse_hwheel / (item->high_res_hwheel ? 120.0f : 1.0f),
+                                               item->mouse_wheel / (item->high_res_wheel ? 120.0f : 1.0f),
+                                               SDL_MOUSEWHEEL_NORMAL);
+                            item->mouse_wheel = item->mouse_hwheel = 0;
+                        }
+
                         if (!item->is_touchscreen) /* FIXME: temp hack */
                             break;
 
@@ -760,6 +783,7 @@ SDL_EVDEV_device_added(const char *dev_path, int udev_class)
     }
 
     if (ioctl(item->fd, EVIOCGBIT(EV_REL, sizeof(relbit)), relbit) >= 0) {
+        item->relative_mouse = test_bit(REL_X, relbit) && test_bit(REL_Y, relbit);
         item->high_res_wheel = test_bit(REL_WHEEL_HI_RES, relbit);
         item->high_res_hwheel = test_bit(REL_HWHEEL_HI_RES, relbit);
     }