WPF 基于Transform实现画布超出边界触发计算

有些场景需要对画布边界做界限控制，此时需要计算画布的四个方向的界限和极值

先看效果图：

画布在通过RenderTransform 做变换，由于在变换的过程中，实际的宽高没有改变，需要通过Transform实时记录变换的状态

1、图中用到了是对Canvas做 RenderTransform的变换，支持缩放和移动

2、最外层需要包一层Border,主要是限定画布的实际的宽高，因为Canvas在做变换的时候，实际的宽高并不改变，画布canvas的移动的偏移量是通过计算Canvas与Border的宽高相对的位置

3、

  <Border x:Name="canvasGrid">

        <Canvas x:Name="writeBorad" Width="1920" Height="1080" MouseDown="WriteBorad_OnMouseDown"  MouseWheel="UIElement_OnMouseWheel" Background="{StaticResource test}" MouseUp="WriteBorad_OnMouseUp"  MouseMove="UIElement_OnMouseMove" >
            <Canvas.RenderTransform>
                <TransformGroup>
                    <ScaleTransform x:Name="scale"></ScaleTransform>
                    <TranslateTransform x:Name="trans"></TranslateTransform>
                </TransformGroup>
            </Canvas.RenderTransform>

            <Button Width="60" Height="60" Canvas.Left="100" Canvas.Top="100"></Button>

        </Canvas>
    </Border>

后台计算逻辑：

 public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            Loaded += MainWindow_Loaded;

            this.writeBorad.Width = 3840;
            this.writeBorad.Height = 2160;
        }

        private void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            //取整设置成刚好的网格大小
            var drawBrush = this.writeBorad.Background as DrawingBrush;
            if (drawBrush != null)
            {
                var size = drawBrush.Viewport.Size;
                //横向判断取整
                var div = writeBorad.Width / size.Width;
                var rem = writeBorad.Width % size.Width;

                if (rem != 0)
                {
                    writeBorad.Width = size.Width *(Math.Floor(div) + 1);
                }
                //纵向判断取整
                div = writeBorad.Height / size.Height;
                rem = writeBorad.Height % size.Height;
                if (rem != 0)
                {
                    writeBorad.Height =size.Height* (Math.Floor(div) + 1);
                }
            }

            trans.X = -writeBorad.Width / 2;
            trans.Y = -writeBorad.Height / 2;
        }

        private void UIElement_OnMouseWheel(object sender, MouseWheelEventArgs e)
        {
            Point point = e.GetPosition(writeBorad);
            var delta = e.Delta * 0.001;
            DowheelZoom(null, point, delta);
        }

        double scaleSize = 1;
        private void DowheelZoom(System.Windows.Media.TransformGroup group, Point point, double delta)
        {
            //按住ctrl缩放
           // if (Keyboard.IsKeyDown(Key.LeftCtrl) || Keyboard.IsKeyDown(Key.RightCtrl))
            {
                if ((scale.ScaleX + delta) <= 1)
                {
                    //return;
                    scale.ScaleX = 1;
                    scale.ScaleY = 1;
                }
                else if (scale.ScaleX + delta > 5)
                {
                    scale.ScaleX = 5;
                    scale.ScaleY = 5;
                }
                else
                {
                    scale.ScaleX += delta;
                    scale.ScaleY += delta;
                }
                var targetX = point.X * (scale.ScaleX - 1);
                var targetY = point.Y * (scale.ScaleX - 1);

                trans.X = -targetX;
                trans.Y = -targetY;

                Console.WriteLine($"{trans.X}==={trans.Y}");
                scaleSize = scale.ScaleX;
            }
        }

        double tranX;
        double tranY;
        Point startPoint;

        //判断是否鼠标点击
        private bool isMouseDown;

        private void UIElement_OnMouseMove(object sender, MouseEventArgs e)
        {
            if(e.LeftButton!= MouseButtonState.Pressed || !isMouseDown) return;
            Point mousePoint = e.GetPosition(canvasGrid);

            var targetX = tranX + mousePoint.X - startPoint.X;
            var targetY = tranY + mousePoint.Y - startPoint.Y;

            trans.X = targetX;
            trans.Y = targetY;

            Console.WriteLine($"{trans.X}==={trans.Y}");

            //边界检测
            //缩放后的尺寸
            var scaleWidth = writeBorad.ActualWidth * scaleSize;
            var scaleHeight = writeBorad.ActualHeight * scaleSize;

            var gridWidth = canvasGrid.ActualWidth;
            var gridHeight = canvasGrid.ActualHeight;

            //x轴最小x坐标
            var minX = -(scaleWidth - gridWidth);

            //y轴最小坐标
            var minY = -(scaleHeight - gridHeight);

            double resetX = 0;
            double resetY = 0;

             //计算边界值
            //x轴左侧坐标越界,缓存到point点
            if (targetX > 0)
            {
                ////拖拽前在可拖动区域
                //if(trans.X<0)
                targetX = 0;
                resetX = targetX;
                isNeedResetX = true;
                Console.WriteLine("左侧越界了");
            }

            if (targetX < minX)
            {
                targetX = minX;
                resetX = targetX;
                isNeedResetX = true;
                Console.WriteLine("右侧越界了");
            }
            if (targetY > 0)
            {
                targetY = 0;
                resetY = targetY;
                isNeedResetY = true;
                Console.WriteLine("上侧越界了");
            }
            if (targetY < minY)
            {
                targetY = minY;
                resetY = targetY;
                Console.WriteLine("下侧越界了");
                isNeedResetY = true;
            }
            ResetPoint=new Point(resetX,resetY);

        }

        private Point ResetPoint;

        private bool isNeedResetX;

        private bool isNeedResetY;

        private void WriteBorad_OnMouseDown(object sender, MouseButtonEventArgs e)
        {
            isMouseDown = true;

            writeBorad.CaptureMouse();

            startPoint = e.GetPosition(canvasGrid);
            tranX = trans.X;
            tranY = trans.Y;
            isNeedResetX = false;
            isNeedResetY = false;
        }

        private void AddElement(Point position)
        {
            Button btn=new Button();
            btn.Height = 60;
            btn.Width = 60;
            Canvas.SetLeft(btn,position.X);
            Canvas.SetTop(btn, position.Y);

            writeBorad.Children.Add(btn);
        }

        private void WriteBorad_OnMouseUp(object sender, MouseButtonEventArgs e)
        {

            AddElement(e.GetPosition(writeBorad));

            isMouseDown = false;
            writeBorad.ReleaseMouseCapture();

            if (isNeedResetX)
            {
                trans.X = ResetPoint.X;
            }

            if (isNeedResetY)
            {
                trans.Y = ResetPoint.Y;
            }

            isNeedResetY = isNeedResetX = false;
            ResetPoint =new Point();

            if (isNeedResetY || isNeedResetX)
            {
                Console.WriteLine($"{trans.X}==={trans.Y}");
            }
        }
    }

总结：1、通过Border限定画布的实际宽高，画布做Transform做平移缩放，通过实时计算宽高来计算偏移量，从而计算是否触发边界

2、本次演示用到Canvas的 ScaleTransform 和  TranslateTransform 做的平移缩放的变换，后续修改为MatrixTransform，灵活性更高，支持多指触发 Manipulation 操作

3、后续增加超出边界触发回弹的效果，以及回弹动画的处理