Mask a shape in front of many small shapes in Illustrator CC

Question

I am working on the latest version of Adobe Illustrator CC with all the latest updates installed.

I have the following:

I would like the dome shape in front to act as a mask for the complex shapes behind. How can I do this? The shapes behind are 100s of small shapes and even though I grouped them all as one, I still can't get it to mask when I try various things in the Pathfinder panel.

Any help would be appreciated.

Answer 1

Make certain the Dome shape is on top of everything else.

Select all

On the Transparency Panel (Window > Transparency), click the Make Mask button. This will create an Opacity Mask rather than a clipping mask. Works much the same as a clipping mask but there are some differences.

While a basic clipping mask would also work. You might find, due to the complexity of the underlying objects, an opacity mask is more manageable. It's all still vector.

Answer 2

A clipping mask or opacity mask, as suggested by others, would work. But I think what you really want is a pattern fill.

1. There is a pretty obvious repetition going on with that big mass of complex shapes. Isolate one copy of the motif that's repeated. If you built all that stuff by drawing it once and duplicating it a lot, then this should be pretty easy.
2. Select that single copy of the motif, and drag it to the Swatches panel.
3. Select the dome shape, and choose the swatch you made in step 2.
4. If it looks messy when it repeats, double-click on the swatch to enter Pattern Editing mode, where you can tweak it. The arrow at the upper left of the main document window will leave Pattern Editing mode, as will hitting ESC; the button at the top of the Pattern Options palette will let you switch between editing the shapes that make up your pattern, and the invisible box that defines how it repeats. The other options should hopefully be pretty self-explanatory.