WPF TileBrush

WPF 的 TileBrush 有 BrushMappingMode.Absolute 與 BrushMappingMode.RelativeToBoundingBox 兩種模式：

Absolute 採用固定的像數，Tile 圖案不會隨著物件的伸展而改變大小與形狀：

RelativeToBoundingBox 則相對於物件的長寬比，因此數量是不變的：

除了 TileBrush.ViewportUnits 設定的差異外，若 Tile 的圖案採用向量而不是圖檔時，要特別注意 Absolute 的用法。Absolute 以像數計算，DrawingBrush 會畫不出東西來，必須轉成 ImageBrush 才能正常運作，以下是這兩段程式的差異。

BrushMappingMode.RelativeToBoundingBox:

 
        public MainWindow()
        {
            InitializeComponent();

            Rectangle exampleRectangle = new Rectangle();

            GeometryDrawing backgroundSquare =
                new GeometryDrawing(Brushes.White, null, new RectangleGeometry(new Rect(0, 0, 100, 100)));

            GeometryGroup aGeometryGroup = new GeometryGroup();
            aGeometryGroup.Children.Add(new RectangleGeometry(new Rect(0, 0, 50, 50)));
            aGeometryGroup.Children.Add(new RectangleGeometry(new Rect(50, 50, 50, 50)));

            LinearGradientBrush checkerBrush = new LinearGradientBrush();
            checkerBrush.GradientStops.Add(new GradientStop(Colors.Black, 0.0));
            checkerBrush.GradientStops.Add(new GradientStop(Colors.Gray, 1.0));

            GeometryDrawing checkers = new GeometryDrawing(checkerBrush, null, aGeometryGroup);

            DrawingGroup checkersDrawingGroup = new DrawingGroup();
            checkersDrawingGroup.Children.Add(backgroundSquare);
            checkersDrawingGroup.Children.Add(checkers);

            DrawingBrush myBrush = new DrawingBrush();
            myBrush.Drawing = checkersDrawingGroup;
            myBrush.ViewboxUnits = BrushMappingMode.RelativeToBoundingBox;
            myBrush.Viewport = new Rect(0, 0, 0.25, 0.25);
            myBrush.TileMode = TileMode.Tile;
            exampleRectangle.Fill = myBrush;

            TilePanel.Children.Add(exampleRectangle);
        }

BrushMappingMode.Absolute:

 
        public MainWindow()
        {
            InitializeComponent();

            Rectangle exampleRectangle = new Rectangle();

            GeometryDrawing backgroundSquare =
                new GeometryDrawing(Brushes.White, null, new RectangleGeometry(new Rect(0, 0, 100, 100)));

            GeometryGroup aGeometryGroup = new GeometryGroup();
            aGeometryGroup.Children.Add(new RectangleGeometry(new Rect(0, 0, 50, 50)));
            aGeometryGroup.Children.Add(new RectangleGeometry(new Rect(50, 50, 50, 50)));

            LinearGradientBrush checkerBrush = new LinearGradientBrush();
            checkerBrush.GradientStops.Add(new GradientStop(Colors.Black, 0.0));
            checkerBrush.GradientStops.Add(new GradientStop(Colors.Gray, 1.0));

            GeometryDrawing checkers = new GeometryDrawing(checkerBrush, null, aGeometryGroup);

            DrawingGroup checkersDrawingGroup = new DrawingGroup();
            checkersDrawingGroup.Children.Add(backgroundSquare);
            checkersDrawingGroup.Children.Add(checkers);

            DrawingImage image = new DrawingImage(checkersDrawingGroup);
            ImageBrush myBrush = new ImageBrush(image);
            myBrush.Stretch = Stretch.None;
            myBrush.TileMode = TileMode.Tile;
            myBrush.Viewport = new Rect(0, 0, 100, 100);
            myBrush.ViewportUnits = BrushMappingMode.Absolute;
            exampleRectangle.Fill = myBrush;

            TilePanel.Children.Add(exampleRectangle);
        }

[Reference]
WPF Brushes Overview
ImageBrush for a BackGround grid in WPF