Ivor Horton's Beginning Visual C++ 2012

PROGRAMMING FOR THE MOUSE

To program the drawing of Sketcher elements in the way that I have discussed, you need to identify how the mouse will be used:

• Pressing a mouse button signals the start of a drawing operation.
• The location of the cursor when the mouse button is pressed provides a first defining point for the shape.
• A mouse movement after detecting that a mouse button has been pressed is a cue to draw a shape, and the cursor position provides a second defining point for the shape.
• Releasing the mouse button signals the end of the drawing operation and that the final version of the shape should be drawn using the last cursor position.

As you may have guessed, all the information about what is happening with the mouse and its buttons is provided by Windows in the form of messages sent to your program. The implementation of the process for drawing lines, rectangles, circles, and curves consists almost entirely of writing message handlers.

Messages from the Mouse

When the users of your program are drawing an element, they will interact with a particular document view. The view class is, therefore, the obvious place to put the message handlers for the mouse. Right-click the CSketcherView class name in Class View and then display its properties window by selecting Properties from the menu. If you then click the messages button (wait for the button tooltips to display if you don’t know which it is) you’ll see the list of IDs for the standard Windows messages that are sent to ...