📉 Draggable Curve Control (English)

Conmajia 2012

Updated on Feb. 18, 2018

In Photoshop, there is a very powerful feature Curve Adjust, as shown in figure 1.

figure 1 Curve Adjust in Photoshop

You can adjust image parameters by adding, deleting or dragging nodes of the image curve.

Basically, such a curve is simple to implement:

• A curve is presented by a series of points which are called nodes
• Each node is an adjustable handle
• Mouse events handlers for each node

Detailed design procedure is omitted. The result is show in figure 2:

figure 2 Animated Example

Sample Codes

The Node list.

List<Point> points;

Deal with node handlers.

Rectangle getHandle(Point p)
{
    Rectangle rect = new Rectangle(
        p.X - 3,
        p.Y - 3,
        6,
        6);
    return rect;
}

Check for mouse position.

bool isHandle(Point p)
{
    foreach (Point pt in points)
    {
        if (isInside(p, getHandle(pt)))
        {
            downIndex = points.IndexOf(pt);
            downPoint = pt;
            current = pt;
            return true;
        }
    }

    return false;
}

Draw handlers.

void drawHandle(Graphics g, Point p)
{
    if (points.IndexOf(p) == downIndex)
        g.FillRectangle(
            Brushes.Black,
            getHandle(p));
    else
        g.DrawRectangle(
            Pens.Black,
            getHandle(p));
}

Draw the curve.

void drawCurve(Graphics g)
{
    g.DrawCurve(Pens.Black, points.ToArray());
}

Total sample source code: download

The End. \(\Box\)