Z-order
Z-order ( English Z -order, also called " Z-order " ) is the order of overlapping two-dimensional objects, such as windows in graphical user interfaces or forms in vector graphics programs. One of the properties of typical interfaces is that windows may overlap one another. The Z-order then determines which will appear above the other.
Definition
The term " Z-order " refers to the sequence of objects along the Z axis. In analytical geometry, "X" typically refers to the horizontal axis ( " left and right "), " Y " on the vertical axis ( " up or down " ), and Z to the perpendicular to the other two stationary axis ( "front or back "). The window of a user interface can be thought of as a series of surfaces that are parallel to the surface of the screen. The windows are then stacked along the Z -axis and the Z-order determines the order of the windows from front to back.
Use
Three-dimensional objects can not be sorted in this way in general. For example, it is possible so to arrange the three pencils on a table such that the tip of each pin is located on the rear end of another pin. None of the pins is then transferred to the other because they all overlap each other. This can not happen with windows in a user interface, because each window is parallel to the screen and thus all of its points have the same depth. The windows can thus be stacked in a defined order.
Usually, a graphical user interface, users can influence the Z-order in that they select a window to bring it to the foreground (ie "above" or "before" all other windows ). Some window managers also allow interaction with windows that are not in the foreground, while others have a window always bring to the fore when it receives user input. Special window can be marked as " always on top ". These are then attached to the top of the Z-order, so that (with few exceptions) no other window can overlap.
In the processing of visible objects on a computer screen an object would be with a Z- order of 1 underneath an object with a Z- order of 2 or more. This corresponds to the generation of layers of objects, wherein the Z-order determines which object is located on another. An HTML page can use the CSS property "z - index" in the div element used to specify the z-order, so that objects can be placed over others.