You can create the mask by projecting surface geometry onto the height field, or by intersecting the height field with a fog or SDF volume.
Connect a height field to the first input, and the geometry to the second input.
This node projects the outline of geometry into a mask field as 2D. To project the geometry into a height field mask field as 3D height, use Height Field Project.
Combine with Existing
How to combine this mask with any existing mask in the input.
Clear the existing mask and replace it with the new mask.
Add the values in this mask to any existing mask.
Subtract the values in this mask from any existing mask.
Set the mask values to the difference between the old mask and this mask.
Multiply the values of the old mask by the values in this mask. This might be useful to "scale" existing values while leaving empty areas alone.
Set the mask values to the maximum of the old mask and this mask.
Set the mask values to the minimum of the old mask and this mask.
Blend the old mask and this mask by a certain amount.
The amount to blend the old mask with what you draw, when Combine with existing is "blend". A value of
0 leaves the existing mask, a value of
1 replaces with the new mask, a value of
0.5 blends equally between the old and new mask.
Assume the second input is surface geometry, project it "down" onto the terrain to create the mask.
Assume the second input is a fog volume, create the mask where it intersects the terrain.
Assume the second input is an SDF volume, create the mask where it intersects the terrain.
Invert Mask: Invert Mask.
The maximum distance to project before deciding the projection has missed the height field, when Method is "project".
The value to set the the mask layer to where the geometry projects/intersects.
How to blur the edges of the mask. The effect is only visible when Blur radius is greater than 0.
Instead of blurring, expand the drawn shapes.
Instead of blurring, shrink the drawn shapes.
How much to blur/expand/shrink the edges of the filled shapes (depending on the Blur method). A value of 0 has no effect.
If a mask volume is wired into this node’s second input, this specifies which volume in the second input to use to mask this node’s effect, usually
mask. Click the "Add mask paint" button to paint the mask directly in the viewport (this automatically adds a paint node to the second input).
The name of the height volume to operate on, usually