A dither pattern is an 8×8, two-colour tile that stands in for the ordered Bayer dither: wherever a bit is set, the tool deposits the primary colour; wherever it’s clear, it deposits the secondary colour (or transparency, for the eraser). It’s the same tiling layout QuickDraw and MacPaint used for their brush patterns, which is why MacPaint pattern files import byte-for-byte.
A pattern and the Dither slider share one slot, and only one can be active at a time. Choosing a pattern overrides the slider’s level; moving the slider afterward clears the pattern and returns to a plain Bayer dither. When a pattern is active, the slider’s space shows a live preview of the tiled pattern instead of the level bar.
Open the patterns popover from the Brush section of the sidebar, next to the Dither control. It lists every pattern you’ve saved as a swatch grid, plus a “None (use dither slider)” option at the top to drop back to the plain Bayer dither.
Selecting: click a swatch to make it the active pattern (undoable). “None (use dither slider)” clears the pattern and is also undoable.
Capturing from a selection: with an active selection, click the capture button to turn its opaque pixels into a new pattern—a cell is “on” wherever the selection has an opaque pixel. A selection larger than 8×8 is tiled into several patterns, saved and named in sequence.
Deleting: with a saved pattern active, click the trash button and confirm to remove it.
Revealing: click the magnifying-glass button to reveal the active pattern’s file in the Finder—handy for renaming it, since there’s no rename control in the popover itself.
Dottie bundles no patterns of its own; the grid is empty until you import one or capture a selection.
Click the import button in the patterns popover and choose a file. Dottie recognises three kinds of source:
XPM files: the image is thresholded—an opaque, dark pixel becomes an “on” cell—and tiled into as many 8×8 patterns as the image needs.
MacPaint files: importing a MacPaint image (File > Import) brings in the picture and the file’s 38 header patterns as dither patterns in one step, since a MacPaint document always carries both. You can also import just the patterns, without the picture, from the patterns popover.
Any other raster image AppKit can open (PNG, GIF, BMP, and the like): the same thresholding rule applies, sliced from the image’s top-left corner into 8×8 tiles.
Patterns that would import as fully empty or fully solid are skipped, as are duplicates of a pattern you already have.
Saved patterns live in a Patterns folder as individual .dither-pattern files, one per pattern, mirroring how custom palettes are stored. Because Dottie is sandboxed, this folder lives inside the app’s private container rather than at a path you can type into Finder—use the reveal button in the popover to open it.
An active pattern replaces the Bayer dither everywhere dithering would normally apply: the brush tools, the shape tools, and fills.