How do you adjust layer masks in Photopea?

You can adjust layer masks in Photopea by enabling/disabling them or making modifications to the layer the mask is applied to.

Here's a detailed explanation:

Enabling and Disabling Layer Masks

You can easily toggle a layer mask on or off to see how it affects the layer.

Right-click the mask thumbnail: A context menu appears.
Select Enable/Disable: Choose "Enable" to activate the mask or "Disable" to deactivate it.

Alternatively, the mask can be toggled by:
Clicking the mask thumbnail with the Shift key pressed. This is the shortcut for enabling or disabling the mask.

To further adjust a mask, you can directly edit the layer mask as if it were a grayscale image:

Select the Mask Thumbnail - Click on the mask thumbnail you wish to edit.
Using Drawing Tools:
Select a tool like the brush or paint bucket and use black, white, or shades of gray directly onto the layer mask.
Black: Makes areas of the layer transparent.
White: Makes areas of the layer fully visible.
Grays: Create varying degrees of transparency.
Applying filters - Photopea's filters can also be applied to the mask to create a variety of effects.
Layer adjustments: Adjusting brightness, contrast, and curves on a mask can subtly tweak the mask's effect.

When editing the layer itself, a rotation or scaling will also modify the effect of the mask, meaning you'll have to re-edit the mask to fit your new transformation.
When a mask is disabled, you can see the layer's full image.
Using the right-click menu will show a few more options including:
- Add Mask to selection which adds the mask to your selection and gives you selection lines around masked areas.
- Delete mask which deletes the mask altogether.

By combining the use of the enable/disable options and editing tools, you can precisely control the visibility of layers.