Algorithmic Solutions > LEDA > LEDA Guide > Windows and Panels > Clip Regions

Clip Regions

Clipping regions are used to restrict the effect of a drawing operation to a restricted area of a window.

Definition and Resetting

The following operations can be used to define clipping regions
  void W.set_clip_rectangle(double x0, double y0, double x1, double y1);
  void W.set_clip_ellipse(double x0, double y0, double r1, double r2);
The following operation resets the clipping area to the entire drawing section of the window
  void W.reset_clipping();


The following program generates a window W and creates a pixrect from the xpm data file <LEDA/pixmaps/leda_icon.xpm>. It uses the Input Operator >> to get a circle C and draws the pixrect inside C using the function draw_pix_circle().

On the right you see a screenshot from the program. Clicking on the picture shows the window in original size.

Example of Convex Hull
#include <LEDA/graphics/window.h>
#include <LEDA/geo/point.h>
#include <LEDA/geo/circle.h>
#include <LEDA/graphics/pixmaps/leda_icon.xpm>

using namespace leda;

void draw_pix_circle(window& W, const circle& C, char* prect)
  double x=p.xcoord(),y=p.ycoord(),r=C.radius();

  W.set_clip_ellipse(x,y,r,r); //sets clipping region
  W.center_pixrect(x,y,prect); //places pixrect with center at x,y
  W.reset_clipping();  //restores the clipping region to 
                       //entire drawing area of W

int main()
  window W(400,400,"Clipping a Pixmap");

  char* leda_pix=W.create_pixrect(leda_icon);		
  circle c;		
  while (W>>c) draw_pix_circle(W,c,leda_pix);
  return 0;

See also:

Drawing Operations

Windows and Panels

Basic Data Types for 2D Geometry

Pixrects (Pixmaps)

Input and Output Operators

Manual Pages:

Manual Page Windows

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