Dev Blog

Summary ​

Conclusions ​

Windows Forms draws graphics with GDI+ through a Graphics object, which can be obtained for a window (in the Paint event), for a bitmap (Graphics.FromImage), and for a printer page (PrintPage). The window image is not stored, so the program keeps data in fields, draws everything in OnPaint, and calls Invalidate() after the data changes. Outlines are drawn with pens, fills with five kinds of brushes, and text with the DrawString method, aligned with StringFormat and measured with MeasureString. Pens, brushes, fonts, and images consume operating system resources and are released with the using statement. Coordinate transformations and the Matrix class let you draw in a convenient coordinate system, while GraphicsPath and Region let you build compound shapes, hit-test the mouse, and restrict the drawing area. Animation is based on a timer, and double buffering eliminates flicker. A drawing described as a list of shape objects is easy to edit with the mouse, save as PNG, print, and package as a custom control.

Self-check questions ​

  1. What is GDI+? Which namespaces contain its classes? On which operating systems does it work?
  2. What is the purpose of the Graphics class? On which surfaces can it draw?
  3. When is the Paint event raised? How does a Paint handler differ from overriding OnPaint?
  4. How do the Invalidate, Update, and Refresh methods differ?
  5. Why must you not draw through CreateGraphics in a button handler?
  6. How are the axes of the screen coordinate system oriented? What is the client area?
  7. What properties does a Pen have? What kinds of brushes are there in GDI+?
  8. Why must pens and brushes be released? Which objects must not be released?
  9. How do you draw text centered in a rectangle? What is the MeasureString method for?
  10. How do the TranslateTransform, RotateTransform, and ScaleTransform methods work? Why does their order matter?
  11. What is a GraphicsPath? How do you check whether the mouse cursor is inside a shape?
  12. What is flicker, and how do you eliminate it?
  13. How do you save a drawing to a PNG file? How does PNG differ from JPEG?
  14. How do you print several pages with PrintDocument?
  15. How do you create a custom control? What are the [Category], [Description], and [DefaultValue] attributes for?