Box cursors consisting of lines of identical thickness are displayed using a bit inverting technique so that overlapped portions of the cursors may be differentiated. Masks are prepared, one for each of the box cursors, which have patterns which, when exclusive ORed, result in a pattern including 1 bits. The box cursors are generated having lines corresponding to respective ones of the masks. Thus, even though box cursors may overlap on the display, the side or sides of the overlapping cursors will be displayed as a pattern of pel points corresponding to the pattern including 1 bits.
In a sequence program constructed by forming a ladder diagram on a display screen, an element corresponding to a minimum unit of the ladder diagram is arranged by a symbol element and a character element. Inputting and amending operations of the ladder diagram are performed by a first cursor for designating each element and a second cursor for designating the character element of the element designated by this first cursor.
The Viewable Object Processor of the present invention utilizes object handles that allow users to perform operations on windows and other viewable objects (e.g., move or resize a window) without having to depress a key (or key sequence) on a keyboard or a button on a pointing device such as a mouse. Essentially, object handles are specialized regions created on a display screen. Associated with each object handle is a particular geometric shape and a object handle type. The shape of each object handle identifies the bounds of the particular object handle. To perform an operation on a viewable object, a user need only cause the cursor to enter into the object handle region of a handle that corresponds to the operation that the user wishes to perform.
