我需要,如果用户用一根手指触摸画布控件,则绘图过程必须开始;如果用户用两根手指触摸画布控件,则画布区域必须滚动/平移。我怎样才能做到这一点?
谢谢
我们可以使用Pointer事件来检测UWP中的多个手指输入。例如:
<ScrollViewer x:Name="scrollViewer" VerticalScrollBarVisibility="Hidden" HorizontalScrollBarVisibility="Hidden"
VerticalScrollMode="Disabled" HorizontalScrollMode="Disabled">
<canvas:CanvasControl x:Name="canvasControl" Draw="CanvasControl_Draw" CreateResources="canvasControl_CreateResources" ClearColor="CornflowerBlue"
PointerPressed="canvasControl_PointerPressed" PointerReleased="canvasControl_PointerReleased" PointerExited="canvasControl_PointerReleased"
PointerCanceled="canvasControl_PointerPressed"
PointerMoved="canvasControl_PointerMoved" Width="1200">
</canvas:CanvasControl>
</ScrollViewer>
正如你所看到的,我放了ScrollViewer
出来的canvas:CanvasControl
,所以会在画布上能够滚动。后面的代码:
private CanvasRenderTarget renderTarget;
private async void CanvasControl_Draw(Microsoft.Graphics.Canvas.UI.Xaml.CanvasControl sender, Microsoft.Graphics.Canvas.UI.Xaml.CanvasDrawEventArgs args)
{
args.DrawingSession.DrawImage(renderTarget);
}
private void canvasControl_CreateResources(CanvasControl sender, Microsoft.Graphics.Canvas.UI.CanvasCreateResourcesEventArgs args)
{
renderTarget = new CanvasRenderTarget(sender, (float)sender.ActualWidth, (float)sender.ActualHeight);
}
private List<PointerPoint> m_pt = new List<PointerPoint>();
private void canvasControl_PointerPressed(object sender, PointerRoutedEventArgs e)
{
PointerPoint cp = e.GetCurrentPoint(canvasControl);
m_pt.Add(cp);
if (m_pt.Count == 2)
{
scrollViewer.HorizontalScrollMode = ScrollMode.Enabled;
scrollViewer.VerticalScrollMode = ScrollMode.Enabled;
}
}
private void canvasControl_PointerReleased(object sender, PointerRoutedEventArgs e)
{
if (m_pt.Count == 1)
canvasControl.Invalidate();
scrollViewer.HorizontalScrollMode = ScrollMode.Disabled;
scrollViewer.VerticalScrollMode = ScrollMode.Disabled;
m_pt.Clear();
}
private void canvasControl_PointerMoved(object sender, PointerRoutedEventArgs e)
{
if (m_pt.Count == 1)
{
var pt = e.GetCurrentPoint(canvasControl);
using (var ds = renderTarget.CreateDrawingSession())
{
ds.DrawCircle(new Vector2((float)pt.Position.X, (float)pt.Position.Y), 2, Colors.Black);
}
}
else
{
if (m_pt.Count > 2)
m_pt.Clear();
}
}
当用一根手指绘制时,在我的演示中,画布仅在释放指针时才会更新其布局。您可以更改代码,以使画布在每次移动指针时进行更新。但是我认为,您需要canvas:CanvasControl
用另一个Win2D控件替换,有关更多信息,您可以参考CanvasControl.Invalidate Method。
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