Drawing On a Graphic
Go Up to Overview of Graphics Programming
You do not need any components to manipulate the graphic objects of your application. You can construct, draw on, save, and destroy graphic objects without ever drawing anything on screen. In fact, your applications rarely draw directly on a form. More often, an application operates on graphics and then uses an image control component to display the graphic on a form.
Once you move the drawing of the application to the graphic in the image control, it is easy to add printing, clipboard, and loading and saving operations for any graphic objects. graphic objects can be bitmap files, drawings, icons or whatever other graphics classes that have been installed such as jpeg graphics.
Note: Because you are drawing on an offscreen image such as a TBitmap canvas, the image is not displayed until a control copies from a bitmap onto the control's canvas. That is, when drawing bitmaps and assigning them to an image control, the image appears only when the control has an opportunity to process its paint message. But if you are drawing directly onto the canvas property of a control, the picture object is displayed immediately.