How to Make jQuery Drag/Resize Work with CSS Transform Scale?

jQuery Drag/Resize with CSS Transform Scale

This question centers around the issue of applying jQuery draggable and resizable plugins to child elements within a div that has a CSS transform (matrix) applied to it. The problem arises when the child elements are dragged or resized, as the adjustments made by jQuery are out of sync with the mouse's position by a factor corresponding to the applied scale.

The Solution

After some experimentation, the user found a solution that involved patching jQuery's draggable and resizable plugins. Here's a summary of the patched code:

• Monkey Patching mouseStart(): This patch ensures that the position of the helper element is calculated correctly by adjusting the mouse offset based on the element's transform scale.
• getViewOffset(): This function assists in correctly calculating the offset of the element under the applied transform.

The jQuery Drag/Resize Patch

The following code demonstrates the modification to the mouseStart() and generatePosition() functions in jQuery UI's draggable plugin:

function monkeyPatch_mouseStart() {

  // Monkey patch mouseStart function

  $.ui.draggable.prototype._mouseStart = function(event) {
    
    // Calculate adjusted offset
    this.offset = this.positionAbs = getViewOffset(this.element[0]);
  }

}

function generatePosition(event) {

  // Calculate adjusted position
  this.top = (
    pageY                               // Absolute mouse position
    - this.offset.click.top                         // Click offset
    - this.offset.relative.top                        // Element's initial position
    + ($.browser.safari && $.browser.version < 526 && this.cssPosition == 'fixed' ? 0 : ( this.cssPosition == 'fixed' ? -this.scrollParent.scrollTop() : ( this.scrollParent.scrollTop() ) ))
  );

  this.left = (
    pageX                                // Absolute mouse position
    - this.offset.click.left                        // Click offset
    - this.offset.relative.left                       // Element's initial position
    + ($.browser.safari && $.browser.version < 526 && this.cssPosition == 'fixed' ? 0 : ( this.cssPosition == 'fixed' ? -this.scrollParent.scrollLeft() : scrollIsRootNode ? 0 : this.scrollParent.scrollLeft() ))
  );
}

Alternative to jQuery

For those seeking alternatives to jQuery for handling drag and resize functionality, here are a few options to consider:

• Vanilla JavaScript: You can implement drag-and-drop functionality using native JavaScript events.
• React.js: React provides a set of hooks like useDrag and useResize for managing these interactions.
• Vue.js: Vuex supports drag-and-drop interactions through the useDrag() hook.

Further Improvement

The user also provides a solution involving callback handlers within the jQuery plugins. This method does not require patching the plugin code and utilizes scale factors to adjust the width, height, and position during drag and resize operations.

// Resizable callback handler
$(this).resizable({
    ...
    resize: function(event, ui) {
        // Adjust width and height relative to scale
        ui.size.width = ui.originalSize.width + (ui.size.width - ui.originalSize.width) / zoomScale;
        ui.size.height = ui.originalSize.height + (ui.size.height - ui.originalSize.height) / zoomScale;
    }
});

// Draggable callback handler
$(this).draggable({
    ...
    drag: function(event, ui) {
        // Adjust position relative to scale
        ui.position.left = ui.originalPosition.left + (ui.position.left - ui.originalPosition.left) / zoomScale;
        ui.position.top = ui.originalPosition.top + (ui.position.top - ui.originalPosition.top) / zoomScale;
    }
});

This alternative method is a convenient solution for managing drag and resize events in elements with applied transform scales without modifying the jQuery plugins themselves.

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