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Basic Lines and Shapes

The CDC class provides a series of drawing functions that correspond to Windows GDI drawing functions. Basic drawing functions include those that draw various (straight and curved) lines and those that draw shapes.

Many line drawing functions make use of the concept of the current position in the device context. The current position is a pair of coordinates that usually represents the endpoint of the last drawing operation. The current position can be set using the MoveTo member function and can be retrieved using the GetCurrentPosition member function.

Line drawing functions use the current pen for drawing the line. To draw a straight line, use the MoveTo and LineTo member functions. To draw an elliptical arc, use the Arc or ArcTo functions. The direction of the arc can be controlled using the SetArcDirection member function; (use GetArcDirection to retrieve the current setting).

The Polyline and PolylineTo functions can be used to draw a series of connected line segments; PolyPolyline is a function to draw several polylines in a single operation. Windows can also draw BŽzier curves; use the PolyBezier or PolyBezierTo member functions. Finally, a series of line segments and BŽzier curves can be drawn in a single operation using PolyDraw.

Shape functions include Rectangle, RoundRect, Ellipse, Chord, Pie, and Polygon. The shapes generated by these functions are shown in Figure 4. One additional function, PolyPolygon, enables the drawing of multiple polygons in a single operation.

4. Some basic shapes.

The PaintRgn function draws a region using the current brush. The DrawFocusRect function is used to draw a rectangle around an object to indicate that the object has the focus. The focus rectangle is drawn using the exclusive OR logical function, so calling DrawFocusRect for the second time effectively removes the focus rectangle. Note that if you scroll an area containing a focus rectangle, it is necessary to remove the focus rectangle first, scroll the area, and then redraw the focus rectangle.

MFC Example