vesa: don't switch to the current mode.

* If a mode change is requested, check if it is equivalent to the
  current one, and don't do anything in this case.

src/add-ons/accelerants/vesa/mode.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright 2005-2011, Axel Dörfler, [email protected].
+ * Copyright 2005-2015, Axel Dörfler, [email protected].
  * Distributed under the terms of the MIT License.
  */
 
@@ -162,6 +162,13 @@ vesa_set_display_mode(display_mode* _mode)
 	if (vesa_propose_display_mode(&mode, &mode, &mode) != B_OK)
 		return B_BAD_VALUE;
 
+	if (gInfo->shared_info->current_mode.virtual_width == mode.virtual_width
+		&& gInfo->shared_info->current_mode.virtual_height
+			== mode.virtual_height
+		&& gInfo->shared_info->current_mode.space == mode.space) {
+		return B_OK;
+	}
+
 	vesa_mode* modes = gInfo->vesa_modes;
 	for (uint32 i = gInfo->shared_info->vesa_mode_count; i-- > 0;) {
 		// search mode in VESA mode list
@@ -169,8 +176,9 @@ vesa_set_display_mode(display_mode* _mode)
 		if (modes[i].width == mode.virtual_width
 			&& modes[i].height == mode.virtual_height
 			&& get_color_space_for_depth(modes[i].bits_per_pixel)
-				== mode.space)
+				== mode.space) {
 			return ioctl(gInfo->device, VESA_SET_DISPLAY_MODE, &i, sizeof(i));
+		}
 	}
 
 	return B_UNSUPPORTED;