Hit Detection on a Line

I want to know if the mouse is over (hitting) a line. Therefore I created a Region object that holds the line and use the IsVisible() method to test if the mouse hits the line. It doesn't work! In the little program below I create two Regions: one is square, the other is a line. Hit testing works on the square-Region, not on the line-Region.

How can I do a hit-test over a line

//namespace HitTest
namespace HitTest
{

//class Form
class Form:System.Windows.Forms.Form
{

//two points that make up a line
System.Drawing.Point point1=new System.Drawing.Point(0,0);
System.Drawing.Point point2=new System.Drawing.Point(50,50);

//a rectangle
System.Drawing.Rectangle rectangle=new
System.Drawing.Rectangle(50,50,100,100);

//a line region
System.Drawing.Region line;

//a square region
System.Drawing.Region square;

//a brush
System.Drawing.Brush brush=System.Drawing.Brushes.White;

//constructor
Form()
{

//set style for double buffered graphics
SetStyle
(
System.Windows.Forms.ControlStyles.AllPaintingInWmPaint|
System.Windows.Forms.ControlStyles.DoubleBuffer|
System.Windows.Forms.ControlStyles.ResizeRedraw|
System.Windows.Forms.ControlStyles.UserPaint,
true
);

//get a GraphicsPath object
System.Drawing.Drawing2D.GraphicsPath graphicspath=new
System.Drawing.Drawing2D.GraphicsPath();

//add a line to the graphicspath
graphicspath.AddLine(0,0,50,50);

//use the graphicspath to define the line-region
line=new System.Drawing.Region(graphicspath);

//use the rectangle to define the square-region
square=new System.Drawing.Region(rectangle);

//prepare for mouse-input
MouseMove+=new System.Windows.Forms.MouseEventHandler(OnMouseMove);

//prepare for paint
Paint+=new System.Windows.Forms.PaintEventHandler(this.OnPaint);

}

//OnMouseMove
void OnMouseMove(object a,System.Windows.Forms.MouseEventArgs b)
{

//use White brush
brush=System.Drawing.Brushes.White;

if(square.IsVisible(b.X,b.Y))
{

//use Red brush if mouse is over square
brush=System.Drawing.Brushes.Red;
}

else if(line.IsVisible(b.X,b.Y))
{

//use Blue brush if mouse is over line
brush=System.Drawing.Brushes.Blue;
}

//force redraw
Invalidate();
}

//OnPaint
void OnPaint(object a,System.Windows.Forms.PaintEventArgs b)
{
b.Graphics.DrawLine(System.Drawing.Pens.Black,point1,point2);
b.Graphics.DrawRectangle(System.Drawing.Pens.Black,rectangle);
b.Graphics.FillRegion(brush,square);
}

//Main
public static void Main()
{
System.Windows.Forms.Application.Run(new Form());
}
}
}

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Hit Detection on a Line

Marian Drumea
Here is the same program with some minor modifications that DOES implement a hit test on a line (thanks to Stoitcho Goutsev)

//namespace HitTest
namespace HitTest
{

//class Form
class Form:System.Windows.Forms.Form
{

//two points that make up a line
System.Drawing.Point point1=new System.Drawing.Point(0,0);
System.Drawing.Point point2=new System.Drawing.Point(50,50);

//a rectangle
System.Drawing.Rectangle rectangle=new
System.Drawing.Rectangle(50,50,100,100);

//a square region
System.Drawing.Region square;

//a graphicspath
System.Drawing.Drawing2D.GraphicsPath graphicspath=new
System.Drawing.Drawing2D.GraphicsPath();

//a brush
System.Drawing.Brush brush=System.Drawing.Brushes.White;

//constructor
Form()
{

//set style for double buffered graphics
SetStyle
(
System.Windows.Forms.ControlStyles.AllPaintingInWmPaint|
System.Windows.Forms.ControlStyles.DoubleBuffer|
System.Windows.Forms.ControlStyles.ResizeRedraw|
System.Windows.Forms.ControlStyles.UserPaint,
true
);

//add a line to the graphicspath
graphicspath.AddLine(point1,point2);

//use the rectangle to define the square-region
square=new System.Drawing.Region(rectangle);

//prepare for mouse-input
MouseMove+=new System.Windows.Forms.MouseEventHandler(OnMouseMove);

//prepare for paint
Paint+=new System.Windows.Forms.PaintEventHandler(OnPaint);

}

//OnMouseMove
void OnMouseMove(object a,System.Windows.Forms.MouseEventArgs b)
{

//use White brush
brush=System.Drawing.Brushes.White;

if(square.IsVisible(b.X,b.Y))
{

//use Red brush if mouse is over square
brush=System.Drawing.Brushes.Red;
}

else if(graphicspath.IsOutlineVisible(b.X,b.Y,System.Drawing.Pens.Black))
{

//use Blue brush if mouse is over line
brush=System.Drawing.Brushes.Blue;
}

//force redraw
Invalidate();
}

//OnPaint
void OnPaint(object a,System.Windows.Forms.PaintEventArgs b)
{
b.Graphics.DrawLine(System.Drawing.Pens.Black,point1,point2);
b.Graphics.DrawRectangle(System.Drawing.Pens.Black,rectangle);
b.Graphics.FillRectangle(brush,rectangle);
}

//Main
public static void Main()
{
System.Windows.Forms.Application.Run(new Form());
}
}
}
Hit Detection on a Line

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