paint on multiple textures at once, and have a tracing overlay.

In the image editor it would be handy to paint on multiple images at once. For example when painting a colour image for the base colour, and a corresponding bump map at the same time. Otherwise it's difficult to get the alignment corresponding.

For the UI there could be a list of available images in a dropdown at the top, each with a checkbox to indicate if it should be drawn on from this single editor.

When the tools options are opened in the n panel, that same list at the top could be used to show the tool options for each image. So you could set a colour brush for the base colour texture, and a grayscale brush for the bump image texture.

To make painting easier, for example if working to a design, it could be possible to have a static overlay locked to the pixel area, and an option to use it as a non-moveable stencil or mask.