Draw a marker like google maps with TCanvas on Delphi

问题

On my application I need draw on TCanvas a "marker", like Google Maps marker (see the image).

I'd like use as parameters the radius, the height and the origin:

I don't have idea about algorithm to use. I can use an arc to draw the top, but how can I draw the bottom? Note: I need draw it both with GDI and GDI+ so any solution is welcome.

回答1:

Here is a quick example using a 200x200 PaintBox - it should at least give you an idea for the algorithm. I trust you can draw the black dot in the middle. Read up on Bezier Curves; PolyBezier defines cubic Bezier curves. (link)

Four points define a cubic Bezier curve - start, end, and two control points. Control points define the strength of curvature as the line moves from start to end.

var origin, innerL, midL, midR, lft, tp, rgt, innerR : TPoint;
    radius, hgt : integer;
begin    
  radius := 25;
  hgt := 90;    
  origin.X := 100;
  origin.Y := 180;
  //control points
  innerL.X := origin.X;
  innerL.Y := origin.Y - (hgt - radius) div 3;
  midL.X := origin.X - radius;
  midL.Y := origin.Y - 2*((hgt - radius) div 3);
  //top circle
  lft.X := origin.X - radius;
  lft.Y := origin.Y - (hgt - radius);
  tp.X := origin.X;
  tp.Y := origin.Y - hgt;
  rgt.X := origin.X + radius;
  rgt.Y := lft.Y;
  //control points
  midR.X := origin.X + radius;
  midR.Y := midL.Y;
  innerR.X := origin.X;
  innerR.Y := innerL.Y;

  PaintBox1.Canvas.Pen.Width := 2;
  PaintBox1.Canvas.PolyBezier([origin, innerL, midL, lft]);
  PaintBox1.Canvas.Arc(lft.X, tp.Y, rgt.X, rgt.Y + radius, rgt.X, rgt.Y, lft.X, lft.Y);
  PaintBox1.Canvas.PolyBezier([rgt, midR, innerR, origin]);
  //fill
  PaintBox1.Canvas.Brush.Color := clYellow;
  PaintBox1.Canvas.FloodFill(origin.X, origin.Y - radius,
                             Canvas.Pen.Color, TFillStyle.fsBorder);    
end;

To satisfy the point that you can do this with one bezier :

  // add four more control TPoints
  cornerL.X := lft.X;
  cornerL.Y := tp.Y + radius div 2;
  cL2.X := lft.X + radius div 2;
  cL2.Y := tp.Y;
  cR2.X := rgt.X - radius div 2;
  cR2.Y := tp.Y;
  cornerR.X := rgt.X;
  cornerR.Y := cornerL.Y;


  PaintBox1.Canvas.PolyBezier([origin, innerL, midL, lft,
                               cornerL, cL2, tp, cR2, cornerR, rgt,
                               midR, innerR, origin]);

来源：https://stackoverflow.com/questions/18340074/draw-a-marker-like-google-maps-with-tcanvas-on-delphi

标签

Delphi

gdi+

gdi

marker