Fabric.js canvas: How to find and get annotated objects based on coordinates?

Fabric.js canvas coordinate positioning label: efficient search and obtain

In Fabric.js graphical annotation application, it is crucial to quickly find and obtain annotated objects based on coordinates. This article will explain in detail how to use the Fabric.js feature to implement this function.

Goal: How to find and get the corresponding annotation object on the Fabric.js canvas based on specific coordinates?

Scheme: Fabric.js' getObjects() method returns an array of all objects on the canvas. We can traverse this array and use the coordinate information of the object to match.

step:

1. Get all objects: Use canvas.getObjects() to get an array of all objects in the canvas. Each object contains left and top attributes (representing the upper left corner coordinate).

2. traverse object array: Loop through the array returned by getObjects() .

3. Coordinate judgment: For each object, compare the target coordinates with the object coordinates. Since coordinates usually refer to the upper left corner, it is necessary to determine whether the target coordinates are within the object range based on the object type and size. For example, a rectangle needs to determine whether the coordinates are within the boundary of the rectangle. Different annotation objects need to adopt different judgment logic.

4. Get the target object: If the target coordinates are within the range of an object, the object is the target label object.

Example: Suppose the rectangular label object rect has left of 100, top of 50, width of 50, and height of 30. If the target coordinate is (120, 60), then the coordinate is located in the rectangle (100 ≤ 120 ≤ 150, 50 ≤ 60 ≤ 80).

With this method, you can efficiently find and get labeled objects in the Fabric.js canvas based on coordinates. Please write the corresponding coordinate comparison logic based on the actual labeled object type and shape.

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