Скачать или смотреть How to Prevent Scaling of Arrow Heads in Fabric.js 3.6.6

Learn how to maintain the size of arrow heads while allowing line length adjustment in Fabric.js. This guide provides effective solutions and code examples.
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This video is based on the question https://stackoverflow.com/q/64082532/ asked by the user 'MarekDm' ( https://stackoverflow.com/u/13271317/ ) and on the answer https://stackoverflow.com/a/64126989/ provided by the user 'Adam M.' ( https://stackoverflow.com/u/2052173/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

If you're working with Fabric.js, you might be familiar with some common challenges that arise when creating interactive canvas graphics. One such issue is ensuring that arrow heads (triangles) maintain their size while allowing the line to adjust its length during scaling. This is a common requirement for diagramming tools and can occasionally lead to frustration when the default behavior of grouped objects doesn't meet expectations. In this post, we'll walk you through a concise solution to prevent arrow heads from scaling while still maintaining the ability to manipulate the line length.

Understanding the Problem

When you group a line and triangles (used as arrow heads) in Fabric.js and try to scale or rotate the group, the triangles also resize due to the group’s scaling transformation. This behavior is often not desired, especially when you want the arrow heads to retain their original dimensions.

Challenge Highlights

Scaling Issue: The arrow heads increase or decrease in size along with the line when the group is scaled.

Manipulation: You want the ability to rotate and resize the line while keeping the triangle sizes consistent.

Compatibility: The solution should work seamlessly within the Fabric.js 3.6.6 environment.

Solution Overview

To tackle this problem, the solution involves listening to the object:scaling event in Fabric.js and adjusting the scaling of the arrow heads back to their intended sizes. The resizing of the triangles is achieved by calculating and resetting their scale based on the group’s current scaling state. Here’s how to implement this effectively.

Step-by-Step Implementation

1. Setup Canvas and Arrow Group

First, set up your Fabric canvas and their initial objects which include a line and two triangle arrow heads.

[[See Video to Reveal this Text or Code Snippet]]

2. Adjust Arrows During Scaling

Implement the event listeners for the object:scaling and object:scaled events. Inside these event listeners, you will call a helper function that adjusts the size of the arrows.

[[See Video to Reveal this Text or Code Snippet]]

Complete HTML Code

To see the above script in action, make sure to include your canvas element in your HTML, along with a button to add arrows.

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By implementing the above solution, you can effectively prevent the arrow heads from scaling while still allowing users to adjust the length of the lines in Fabric.js. This ensures that your diagrams look polished and maintain the intended design and usability you require for your application.

Feel free to experiment with further customization around object control and scaling behaviors to fit the specific needs of your project. Happy coding!