It is often desirable to display the coordinate position or the dimensions along with the object. This would be helpful in ascertaining the location of the object, when mere visible accuracy of location may not be enough, but they may have to be positioned w.r.t. the actual coordinate system
The more difficult problem is that the coordinates need to keep changing as the figure is being dragged around and this demands rapid calculation on the part of the system.
Normally the dimensions are displayed only when the object is being manipulated or moved around and will stay only long enough for the user to take note of them. This ensures that they do not obscure the active parts of the picture, once the completed picture is on display
Selection of Objects
One of the important points to be addressed is to select parts of the picture for further operations. Once the selection is made properly, tasks like moving, deletion, copying is whatever can be done. But the actual selection process poses several problems
The first one is about the choice of coordinates. When a point is randomly chosen at the starting point of the selection process, the system should be able to properly identify its coordinates. The second problem is about how much is being selected. This can be indicated by selecting a number of points around the figure or by enclosing the portion selected by a rectangle.
The other method is to use multiple keys i.e. position the cursor at the first point of selection, press certain combination of keys, move the cursor to the final position and again press certain combination of keys, so that the figure lying in between them is selected.
The mouse facilitates the same operation by the use of multiple buttons on it. Once the selection is made, normally the system is supposed to display the portion selected so that user can know he has actually selected what he had wanted to. This feed back is done either by changing the color of the screen, modifying the brightness or by blinking.
This is one of the special cases of selection where the user would be able to choose and operate from a set of available commands / figures displayed on the screen. This concept is called the “menu” operation, where you select the item from those available on the menu card. The use of mouse an input technique normally implies menus being provided by the system. The menu concept helps the user to overcome the difficulty of having to draw simple and often used objects by providing them as a part of the system