Take into account the zoom when applying the output transform

When converting output-relative coordinates (such as from an input
event) to global coordinates it now takes into account the zoom
transform. Previously this would only work for the primary pointer
because the transform doesn't affect the primary pointer position due
to that way zoom follows the mouse. Touch events and multiple pointers
were not working correctly.

https://bugs.freedesktop.org/show_bug.cgi?id=68620

src/compositor.c

@@ -3333,6 +3333,7 @@ weston_output_transform_coordinate(struct weston_output *output,
 {
 	wl_fixed_t tx, ty;
 	wl_fixed_t width, height;
+	float zoom_scale, zx, zy;
 
 	width = wl_fixed_from_int(output->width * output->current_scale - 1);
 	height = wl_fixed_from_int(output->height * output->current_scale - 1);
@@ -3373,8 +3374,23 @@ weston_output_transform_coordinate(struct weston_output *output,
 		break;
 	}
 
-	*x = tx / output->current_scale + wl_fixed_from_int(output->x);
-	*y = ty / output->current_scale + wl_fixed_from_int(output->y);
+	tx /= output->current_scale;
+	ty /= output->current_scale;
+
+	if (output->zoom.active) {
+		zoom_scale = output->zoom.spring_z.current;
+		zx = (wl_fixed_to_double(tx) * (1.0f - zoom_scale) +
+		      output->width / 2.0f *
+		      (zoom_scale + output->zoom.trans_x));
+		zy = (wl_fixed_to_double(ty) * (1.0f - zoom_scale) +
+		      output->height / 2.0f *
+		      (zoom_scale + output->zoom.trans_y));
+		tx = wl_fixed_from_double(zx);
+		ty = wl_fixed_from_double(zy);
+	}
+
+	*x = tx + wl_fixed_from_int(output->x);
+	*y = ty + wl_fixed_from_int(output->y);
 }
 
 static void