MiSTer - Shadow Mask Editor

Load Mask


Preview Type

Background Type









  1. Create a folder named Shadow_Masks in the root of your MiSTer MicroSD Card.
  2. Copy & paste the above Mask Definition into a new text file (*.txt) inside of the Shadow_Masks folder.
  3. Select your Mask from the MiSTer GUI.

The Colour Palette

Each location in a Shadow Mask contains two sets of intensity information [shown as two squares in the editor]. The primary "on" set increases intensity of matching colour channels, causing them to appear brighter [the larger square]. The reverse "off" set deceases intensity of opposite colour channels, causing them to appear darker [the smaller square].

Preview Types

There are two ways to view a Shadow Mask with the editor. The Simple mode is very fast and intended for quick reference and composition. And the more CPU intensive Accurate mode that recreates the way MiSTer will render the Shadow Mask. Keep in mind: the position of the Preview window of the editor and sub-pixel layouts of the screens used will greatly affect the appearance of your Shadow Mask. What looks good on one screen may not look as good on another; it all comes down to the sub-pixel layouts of the screens.

Preview Type Feature Matrix
Matches MiSTer
Color Intensity
Rainbow Test Pattern
Background Images


Pencil P
Will allow you to mark locations on the Shadow Mask with the current active colour.
Eraser E
Will make the selected location on the Shadow Mask transparent, regardless of the current active colour.
Flood Fill F Shift+click
Will replace all the locations in the Shadow Mask that match the selected location with the current active colour.
Eye Dropper D Ctrl+click
Will replace the active colour with the selected location from the Shadow Mask.
Undo Ctrl+Z
Undo the last operation
Redo Ctrl+Shift+Z
Redo the last operation that was undone

Palette Controls

Add +
Increase intensities by one step.
Minus -
Decease intensities by one step.
Half /
Decease intensities by half.
Invert I
Swap "on"/"off" intensities.
Reset Esc
Revert changes to defaults.

Resolution Controls

Add +
Create entry for resolution.
Minus - Delete Backspace
Remove selected resolution.


Toogle Preview Type `
Download Definition Ctrl+Shift+S

Additional Information

Most items and tools on the editor interface have tooltips that appear when hovered over.

Chrome is noticeably faster than Firefox, but may cause erroneous anti-aliasing to appear in the preview area.