CODEWITHSUNDEEP
c#wpfcanvasmatinkcanvas
wikiCan
wikiCan

Reputation: 449

Draw arc between two lines. I need to calculate points

Lines and arc

I can't find a way to drawing ARC between two lines. My constraint is : I have to calculate this Arc stroke points. Because i am using InkCanvas and i have to draw this arc point by point, i can't put any object to screen or canvas. So I know i can draw any arc with PATH object and use ArcSegment. With this method yes i can draw arc but it isn't stroke point on the Canvas. For this reason i cannot delete or save it. Anyway i need calculate this arch point by point.

I have code for drawing circle on canvas like this :

Stroke GetCircleStroke(int centerX, int centerY, int radiusX, int radiusY,double angletoDraw=2.0)
        {
            StylusPointCollection strokePoints = new StylusPointCollection();

            int numTotalSteps = 180;

            for (int i = 0; i <= numTotalSteps; i++)
            {
                double angle = angletoDraw * Math.PI * (double)i / (double)numTotalSteps;
                StylusPoint sp = new StylusPoint();
                //compute x and y points
                sp.X = centerX + Math.Cos(angle) * radiusX;
                sp.Y = centerY - Math.Sin(angle) * radiusY;

                //add to the collection
                strokePoints.Add(sp);
            }

            Stroke newStroke = new Stroke(strokePoints);
            return newStroke;

        }

I can draw circle easly, but i couldn't find a way to draw an arc :(

We know center point X,Y and we know Line1 and Line2 coordinates. I just don't know what is that arc..

Could you please help me for calculate arc points like this way ?

Upvotes: 0

Views: 2533

Answers (1)

InBetween
InBetween

Reputation: 32760

You have a few concepts flying around like Line/Segment, Point, Circle, etc. Instead of making a mess of hard to understand code, let's try to breakdown the problem into smaller parts that are easier to digest.

You have a notion of Point, ok, lets implement one:

public struct Point2D //omitted equality logic
{
    public double X { get; }
    public double Y { get; }

    public Point2D(double x, double y)
    {
        X = x;
        Y = y;
    }

    public override string ToString() => $"{X:N3}; {Y:N3}";
}

Ok, we also have a notion of Segment or a delimitted Line:

public struct Segment2D
{
    public Point2D Start { get; }
    public Point2D End { get; }
    public double Argument => Math.Atan2(End.Y - Start.Y , End.X - Start.X);

    public Segment2D(Point2D start, Point2D end)
    {
        Start = start;
        End = end;
    }
}

And last, but not least, we have the notion of Circle:

public struct Circle2D
{
    private const double FullCircleAngle = 2 * Math.PI;
    public Point2D Center { get; }
    public double Radius { get; }

    public Circle2D(Point2D center, double radius)
    {
        if (radius <= 0)
            throw new ArgumentOutOfRangeException(nameof(radius));

        Center = center;
        Radius = radius;
    }

    public IEnumerable<Point2D> GetPointsOfArch(int numberOfPoints, double startAngle, double endAngle)
    {
        double normalizedEndAngle;

        if (startAngle < endAngle)
        {
            normalizedEndAngle = endAngle;
        }
        else
        {
            normalizedEndAngle = endAngle + FullCircleAngle;
        }

        var angleRange = normalizedEndAngle - startAngle;
        angleRange = angleRange > FullCircleAngle ? FullCircleAngle : angleRange;
        var step = angleRange / numberOfPoints;
        var currentAngle = startAngle;

        while (currentAngle <= normalizedEndAngle)
        {
            var x = Center.X + Radius * Math.Cos(currentAngle);
            var y = Center.Y + Radius * Math.Sin(currentAngle);
            yield return new Point2D(x, y);
            currentAngle += step;
        }
    }

    public IEnumerable<Point2D> GetPoints(int numberOfPoints)
        => GetPointsOfArch(numberOfPoints, 0, FullCircleAngle);
}

Study the implementation of GetPointsOfArch, it shouldn't be too hard to understand.

And now, to solve your problem, you would do:

var myCircle = new Circle2D(new Point2D(centerX, centerY), radius);
var line1 = ....
var line2 = ....
var archPoints = myCircle.GetPointsOfArch(number, line2.Argument, line1.Argument);

Isn't that much easier to read, follow and understand?

Upvotes: 4

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