Fix continuous scrolling speed on Wayland

Wayland compositors seem to have standardized on 10 units per "wheel tick" for
continuous scroll events, so we need to convert these axis values to ticks by
dividing by 10 before reporting them in SDL_MOUSEWHEEL events.

src/video/wayland/SDL_waylandevents.c

@@ -58,6 +58,9 @@
 #include <unistd.h>
 #include <xkbcommon/xkbcommon.h>
 
+/* Weston uses a ratio of 10 units per scroll tick */
+#define WAYLAND_WHEEL_AXIS_UNIT 10
+
 typedef struct {
     // repeat_rate in range of [1, 1000]
     int32_t repeat_rate;
@@ -471,6 +474,9 @@ pointer_handle_axis_common_v1(struct SDL_WaylandInput *input,
                 return;
         }
 
+        x /= WAYLAND_WHEEL_AXIS_UNIT;
+        y /= WAYLAND_WHEEL_AXIS_UNIT;
+
         SDL_SendMouseWheel(window->sdlwindow, 0, x, y, SDL_MOUSEWHEEL_NORMAL);
     }
 }
@@ -528,7 +534,17 @@ pointer_handle_frame(void *data, struct wl_pointer *pointer)
 {
     struct SDL_WaylandInput *input = data;
     SDL_WindowData *window = input->pointer_focus;
-    float x = input->pointer_curr_axis_info.x, y = input->pointer_curr_axis_info.y;
+    float x, y;
+
+    if (input->pointer_curr_axis_info.is_x_discrete)
+        x = input->pointer_curr_axis_info.x;
+    else
+        x = input->pointer_curr_axis_info.x / WAYLAND_WHEEL_AXIS_UNIT;
+
+    if (input->pointer_curr_axis_info.is_y_discrete)
+        y = input->pointer_curr_axis_info.y;
+    else
+        y = input->pointer_curr_axis_info.y / WAYLAND_WHEEL_AXIS_UNIT;
 
     /* clear pointer_curr_axis_info for next frame */
     memset(&input->pointer_curr_axis_info, 0, sizeof input->pointer_curr_axis_info);