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How can I get Illustrator to respect the rounded corners on the top shape when creating a mask?


Question

I have two shapes (left) and I have added rounded corners to the rectangle on the top one using the "Rounded Corners" menu item.

When I select the two shapes and choose "create mask" I want Illustrator to make a mask of the actual shape with the rounded corners and not of the rectangle that existed before I added the rounded corner effect.

However Illustrator gives me the actual result (middle). I want the desired result (right).

How can I do this?

example of desired and actual result

This is what my layers palette looks like:

layers palette screenshot

2015/08/17
1
6
8/17/2015 4:49:00 PM

Accepted Answer

I am not certain why Illustrator does this, but there is no question that it does. Here are two workarounds that you can use:

  1. Change the Order of Operations - First create a regular, unrounded rectangle and apply it as a clipping mask onto the other shape. Only then apply the Rounded Corners effect to the mask. This works for me in CS4.

  2. Create an Opacity Mask Instead - Create your rounded rectangle as before, but color it white with no stroke. Then select the shape to be masked, go to the Transparency panel, and use the little menu icon at the top-right to select ‘Make Opacity Mask’. This will create an opacity mask, which you will see as a black square in the Transparency panel. Cut your rounded rectangle, then select the opacity mask (black square) and paste the rounded rectangle inside. You have to select the opacity mask to work inside it, and then select the square to the left of it in order to resume working on your illustration. It’s a mutually exclusive drawing context, kind of like in Photoshop. Always switch back from the opacity mask, otherwise you will get confused as to why your mouse clicks aren’t doing anything.

2011/11/11
6
11/11/2011 7:04:00 AM

Expand your shape before using it as a mask and it should work correctly.

To expand your shape, select it and then go to the 'Object' menu and click on 'Expand'.

Expanding will permanently modify the shape to have rounded corners whereas just adding the rounded corners as an effect will only temporarily modify the shape to have rounded corners.

2011/11/16