Masks painted anywhere on the canvas; mask thumbnails' ground white or black (12.12b)

src/UI/CanvasThumbnail.h

@@ -13,8 +13,6 @@ inline constexpr double backingScale = 2;
 QSize fittedSize(QSizeF canvas, double box);
 // The checkerboard with the pixels placed; null: empty canvas.
 QPixmap layer(const QImage &image, const LayerTransform &transform, QSizeF canvas, double box);
-// The mask placed; its edge tone fills the rest.
+// The mask placed; its background fills the rest.
 QPixmap mask(const QImage &image, const LayerTransform &transform, QSizeF canvas, double box);
-// The mean gray, 0 to 1, of the outermost pixels.
-double edgeTone(const QImage &image);
 }