Stuart.EditGroup.EditRegionMask C# (CSharp) Method

        public void EditRegionMask(List<Vector2> points, float zoomFactor)
        {
            if (regionMask == null)
            {
                // Demand-create our region mask image.
                regionMask = new CanvasRenderTarget(SourceBitmap.Device, Parent.Size.X, Parent.Size.Y, 96);
            }
            else
            {
                // Back up the previous mask, to support undo.
                previousRegionMask = currentRegionMask;
            }

            // Prepare an ICanvasImage holding the edit to be applied.
            ICanvasImage editMask;

            if (RegionSelectionMode == SelectionMode.MagicWand)
            {
                // Magic wand selection is already an image.
                editMask = GetMagicWandMask(points, zoomFactor);
            }
            else
            {
                // Capture selection geometry into a command list.
                var commandList = new CanvasCommandList(regionMask.Device);

                using (var drawingSession = commandList.CreateDrawingSession())
                {
                    // If this was just a touch without move, treat it as selecting the entire image.
                    var dragRange = points.Select(point => Vector2.Distance(point, points[0])).Max() * zoomFactor;

                    if (dragRange < 10)
                    {
                        drawingSession.Clear(Colors.White);
                    }
                    else
                    {
                        // Draw selection geometry.
                        var geometry = GetSelectionGeometry(drawingSession, points);

                        drawingSession.FillGeometry(geometry, Colors.White);
                    }
                }

                editMask = commandList;
            }

            // Apply the edit.
            using (var drawingSession = regionMask.CreateDrawingSession())
            {
                CanvasComposite compositeMode;

                switch (RegionSelectionOperation)
                {
                    case SelectionOperation.Replace:
                        drawingSession.Clear(Colors.Transparent);
                        compositeMode = CanvasComposite.SourceOver;
                        break;

                    case SelectionOperation.Add:
                        compositeMode = CanvasComposite.SourceOver;
                        break;

                    case SelectionOperation.Subtract:
                        compositeMode = CanvasComposite.DestinationOut;
                        break;

                    case SelectionOperation.Invert:
                        compositeMode = CanvasComposite.Xor;
                        break;

                    default:
                        throw new NotSupportedException();
                }

                drawingSession.DrawImage(editMask, Vector2.Zero, regionMask.Bounds, 1, CanvasImageInterpolation.Linear, compositeMode);
            }

            // Back up the mask, so we can recover from lost devices.
            currentRegionMask = regionMask.GetPixelBytes();

            cachedRegionMask.Reset();

            CanUndo = true;
        }

        void Canvas_PointerReleased(object sender, PointerRoutedEventArgs e)
        {
            if (editingRegion == null)
            {
                return;
            }

            try
            {
                editingRegion.EditRegionMask(regionPoints, scrollView.ZoomFactor);
            }
            catch (Exception exception) when(canvas.Device.IsDeviceLost(exception.HResult))
            {
                canvas.Device.RaiseDeviceLost();
            }

            editingRegion = null;
            regionPoints.Clear();

            // Restore the manipulation mode so input goes to the parent ScrollViewer again.
            canvas.ManipulationMode = ManipulationModes.System;
            canvas.ReleasePointerCapture(e.Pointer);

            canvas.Invalidate();
            e.Handled = true;
        }