Affinity Photo - How to mask shape with another shape non-destructively?

[rawalanche]

Hi,

I have a simple use case where I want to mask a shape with another shape non destructively. I am starting with a fresh, transparent document, and adding two rectangles:

Now, I'd like to perform a trivial action of using the black Rectangle layer as a mask for a blue Rectangle layer so that the black rectangle layer removes part of the blue Rectangle layer. 

If I just drag the black Rectangle layer as a mask layer of the blue Rectangle layer, I get an inverted effect where the black Rectangle area defines where the layer is visible, not invisible:

I am aware I can select both layers and go to Edit > Geometry > Subtract but that doesn't meet the criteria, as this action destroys both rectangle layers and converts them into a curve, which means I can no longer easily move around and adjust the masking rectangle.

I must be missing something, because this seems like a super trivial use case, yet I can't figure it out.

[firstdefence]

Use Layer > Create Compound

Change the rectangle layer geometry (Boolean) attribute to subtract

[rawalanche]

9 minutes ago, firstdefence said:

Use Layer > Create Compound

Change the rectangle layer geometry (Boolean) attribute to subtract

Uh, I must be missing something, but I don't see any "Compound" option in layer menu:

Is there any chance you've confused Affinity Photo with Affinity Designer?

[markw]

In AP go to Layer > Geometry (hold down alt key) and now choose the boolean action you want as a Compound.

[GarryP]

Note: Holding down ALT when choosing one of the Geometry functions from the menu doesn’t work in Windows. (It works when pressing the button in the Toolbar but not from the menu.) This is because ALT is the open/close menu key, so pressing ALT closes the menu.
An alternative is to use the button on the Toolbar but you may need to customise the Toolbar (menu “View → Customise Toolbar”) to get the buttons.

[rawalanche]

Thanks. This is a bit scary though. Given how basic this feature is, it's almost undiscoverable in the user interface :X

[kirkt]

You can also put the black rectangle in place on a layer directly above the blue shape and change the blend mode of the black rectangle to "Erase."  You can then group the two shapes together so you can move them as a unit, but you can still move the black rectangle relative to the blue shape (within the group) if you need to alter the knock out.  Grouping will also limit the "erase" effect of the black rectangle to just the blue shape, so that the black rectangle does not erase all of the layers under the group, just the blue shape in the group.

kirk

[rawalanche]

47 minutes ago, kirkt said:

You can also put the black rectangle in place on a layer directly above the blue shape and change the blend mode of the black rectangle to "Erase."  You can then group the two shapes together so you can move them as a unit, but you can still move the black rectangle relative to the blue shape (within the group) if you need to alter the knock out.  Grouping will also limit the "erase" effect of the black rectangle to just the blue shape, so that the black rectangle does not erase all of the layers under the group, just the blue shape in the group.

kirk

That seems to be easier. Thank you!

[JimmyJack]

16 minutes ago, rawalanche said:

That seems to be easier. Thank you!

Just be aware that using the Erase blend mode with result in rasterization on export. (...which may be fine for you).

You could also try a mask like the green below:

[firstdefence]

Oops! totally missed the Affinity Photo in the title Doh!! 

[lacerto]

4 hours ago, GarryP said:

Note: Holding down ALT when choosing one of the Geometry functions from the menu doesn’t work in Windows.

Alt + Ctrl (or Alt Gr) works. [But you do not get "Compound" text appended in the caption, as you do on macOS.]