Stuart.EditGroup.DisplayRegionMask C# (CSharp) Method

        public bool DisplayRegionMask(CanvasDrawingSession drawingSession, float zoomFactor, bool editInProgress)
        {
            if (!IsEnabled || !IsEditingRegion || !ShowRegion || regionMask == null)
                return false;

            if (editInProgress && RegionSelectionOperation == SelectionOperation.Replace)
                return false;

            drawingSession.Blend = CanvasBlend.SourceOver;

            if (!editInProgress)
            {
                // Gray out everything outside the region.
                var mask = new ColorMatrixEffect
                {
                    Source = GetRegionMask(),

                    ColorMatrix = new Matrix5x4
                    {
                        // Set RGB = gray.
                        M51 = 0.5f,
                        M52 = 0.5f,
                        M53 = 0.5f,

                        // Invert and scale the mask alpha.
                        M44 = -0.75f,
                        M54 = 0.75f,
                    }
                };

                drawingSession.DrawImage(mask);
            }

            // Magenta region border.
            var border = GetSelectionBorder(regionMask, zoomFactor);

            drawingSession.DrawImage(border);

            return true;
        }