compositor-x11: Update axis notifications to follow protocol

Axis events are in the same coordinate space as motion events, thus
measured in pixels. To emulate axis events for discrete events move the
axis by a number of pixels every step.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>

src/compositor-x11.c

@@ -50,6 +50,8 @@
 #include "compositor.h"
 #include "../shared/config-parser.h"
 
+#define DEFAULT_AXIS_STEP_DISTANCE wl_fixed_from_int(10)
+
 static char *output_name;
 static char *output_mode;
 static char *output_transform;
@@ -660,32 +662,34 @@ x11_compositor_deliver_button_event(struct x11_compositor *c,
 		button = BTN_RIGHT;
 		break;
 	case 4:
+		/* Axis are measured in pixels, but the xcb events are discrete
+		 * steps. Therefore move the axis by some pixels every step. */
 		if (state)
 			notify_axis(&c->core_seat,
 				    weston_compositor_get_time(),
 				    WL_POINTER_AXIS_VERTICAL_SCROLL,
-				      wl_fixed_from_int(1));
+				    -DEFAULT_AXIS_STEP_DISTANCE);
 		return;
 	case 5:
 		if (state)
 			notify_axis(&c->core_seat,
 				    weston_compositor_get_time(),
 				    WL_POINTER_AXIS_VERTICAL_SCROLL,
-				      wl_fixed_from_int(-1));
+				    DEFAULT_AXIS_STEP_DISTANCE);
 		return;
 	case 6:
 		if (state)
 			notify_axis(&c->core_seat,
 				    weston_compositor_get_time(),
 				    WL_POINTER_AXIS_HORIZONTAL_SCROLL,
-				      wl_fixed_from_int(1));
+				    -DEFAULT_AXIS_STEP_DISTANCE);
 		return;
 	case 7:
 		if (state)
 			notify_axis(&c->core_seat,
 				    weston_compositor_get_time(),
 				    WL_POINTER_AXIS_HORIZONTAL_SCROLL,
-				      wl_fixed_from_int(-1));
+				    DEFAULT_AXIS_STEP_DISTANCE);
 		return;
 	}