How to Cut Curves with Key Object in Affinity Designer

To cut curves or shapes using a "key object" as a knife in Affinity Designer, you can utilize a specific modifier key combination with your selected objects, as demonstrated with the geometry tools.

Here's the process based on the provided reference:

1. Select Both Objects: Ensure both the object you want to cut and the object you want to use as the "knife" (the key object) are selected on your canvas. Place the "knife" object where you want it to cut or intersect with the object beneath it.
2. Hold Modifier Key: Hold down the Option key on a Mac or the Alt key on a Windows keyboard.
3. Choose the Knife Layer: While holding the modifier key, click on the object (layer) you intend to use as the "knife."

This action tells Affinity Designer to use the object you clicked on as the tool to cut or modify the other selected object(s). This method is often used in conjunction with geometry operations like Subtract or Divide, allowing you to quickly achieve complex shapes by using one object to "cut into" another. For example, you can use a smaller shape to cut a hole or specific indentation into a larger shape underneath it.

Steps to Cut Using a Key Object

Follow these simple steps to perform the cut:

• Select the object you want to cut.
• Select the object you want to use as the knife.
• Hold down Option (Mac) or Alt (Windows).
• Click on the object you want to be the knife.

This interaction, as seen in the video reference around the 2:17 to 3:20 mark, allows one selected object to act as a cutting tool against another.

Understanding the Operation

While the reference describes the key combination and selecting the "knife" layer, this action typically triggers a geometry operation. Holding Option/Alt and clicking might streamline or modify the standard Subtract or Divide operations:

• Subtract: Removes the area of the top object from the bottom object. Using the modifier key and clicking the "knife" object might reverse this or ensure that specific object is the one doing the subtracting.
• Divide: Splits all selected objects into their component parts wherever they overlap. The modifier key method could be a quick way to initiate this or a similar cutting function.

Using the key object method simplifies the process of defining which object performs the cut when multiple objects are selected.