The present invention relates to a system for displaying a multilayer image on a screen and, in particular, it relates to a technique for determining a request destination when a user points a position on the screen and makes a process request.
Hitherto, systems for displaying multilayer images are known. Such systems display a plurality of images through alphablending the images according to their respective transparency information and superposing them. The transparency information can be set for each point on the screen. Color information and the transparency information are combined to display one point on the screen. The transparency information set for each point on the screen is called an alpha value, which ranges from 0 (completely transparent) to 1 (opaque).
Problems sometimes occur on a display screen that displays a multilayer image when a user selects an object located in one layer. For example, suppose a semitransparent enlarging or reducing button is displayed on a map. In this case, even if the user clicks on the position of the button with a mouse, the display system cannot determine whether the click operation is for the button or for the map. This makes it difficult to determine the destination of the event indicative the click operation.
A simple solution is preparing an event-only filter for each layer. However, this solution is not practical, because the producer of its application must set the filters in consideration of the arrangement of the layers and the objects.
Another solution is using alpha values such as in a layer window, one of the user interfaces provided by Microsoft Windows® operating systems. The layer window allows mouse messages to pass through regions of an alpha value of zero. However, with the layered window, even a region with a low alpha value always receives a process request unless the alpha value is zero. When a plurality of alpha values other than zero is set for one layer, some regions of low alpha values are not regions selected by the user, so that they should not receive a process request. On the other hand, regions of high alpha values thus having clear images, such as text information, sometimes should not receive a process request.