Creating a polygon with Konva js by connecting lines: a step-by-step guide

I am seeking a way to empower the user to sketch out a polygon using lines, creating the desired shape and then apply transformations to it (such as rotation and resizing).

What is the best method for implementing this functionality with Konvajs?

https://i.sstatic.net/In0di.png

Answer №1

Creating and modifying polygons with Konva is a straightforward process.

For a detailed guide, check out the tutorials on Konva.Polygon and Konva.Transformer. If you need help with user-input points, consider asking a separate question for that.

In Konva, a polygon is essentially a Konva.Line shape positioned at specific x,y coordinates of your choice. This positioning feature is common to all Konva shapes.

Typically, it's simpler to start the polygon at 0,0. The polygon's points are stored as a unique attribute. The initial point acts as a move-to command from the polygon's position, while subsequent points serve as draw-to commands, outlining the polygon's lines. A "closed" attribute connects the final point back to the first.

When dragging the polygon, there's no need to adjust the points since they're linked to the shape's position attribute.

To create a polygon, your code should capture the points designated by the user via mouse or touch input, then finalize the polygon when prompted.

All Konva shapes can be resized and rotated visually using a Konva.Transformer. However, note that the Transformer modifies the scale, not the actual width or height of the shape.

As the Transformer operates on the shape's transformation matrix and the points are enclosed within the shape, adjustments made by the Transformer won't affect the underlying points.

For further insights on the Transformer, refer to this informative blog post.

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