DrawingContext Classe

Definição

public ref class DrawingContext abstract : System::Windows::Threading::DispatcherObject, IDisposable

public abstract class DrawingContext : System.Windows.Threading.DispatcherObject, IDisposable

type DrawingContext = class
    inherit DispatcherObject
    interface IDisposable

Public MustInherit Class DrawingContext
Inherits DispatcherObject
Implements IDisposable

Herança

Object

DispatcherObject

DrawingContext

Implementações

IDisposable

Exemplos

O exemplo a seguir recupera a DrawingContext de a DrawingVisual e o usa para desenhar um retângulo.

// Create a DrawingVisual that contains a rectangle.
private DrawingVisual CreateDrawingVisualRectangle()
{
    DrawingVisual drawingVisual = new DrawingVisual();

    // Retrieve the DrawingContext in order to create new drawing content.
    DrawingContext drawingContext = drawingVisual.RenderOpen();

    // Create a rectangle and draw it in the DrawingContext.
    Rect rect = new Rect(new System.Windows.Point(160, 100), new System.Windows.Size(320, 80));
    drawingContext.DrawRectangle(System.Windows.Media.Brushes.LightBlue, (System.Windows.Media.Pen)null, rect);

    // Persist the drawing content.
    drawingContext.Close();

    return drawingVisual;
}

' Create a DrawingVisual that contains a rectangle.
Private Function CreateDrawingVisualRectangle() As DrawingVisual
    Dim drawingVisual As New DrawingVisual()

    ' Retrieve the DrawingContext in order to create new drawing content.
    Dim drawingContext As DrawingContext = drawingVisual.RenderOpen()

    ' Create a rectangle and draw it in the DrawingContext.
    Dim rect As New Rect(New Point(160, 100), New Size(320, 80))
    drawingContext.DrawRectangle(Brushes.LightBlue, CType(Nothing, Pen), rect)

    ' Persist the drawing content.
    drawingContext.Close()

    Return drawingVisual
End Function

O exemplo seguinte demonstra o PushOpacity comando. O DrawingContext é obtido a partir de um DrawingGroup e apresentado usando um Image controlo.

using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Effects;

namespace SDKSample
{

    public class PushEffectExample : Page
    {

        public PushEffectExample()
        {
            Pen shapeOutlinePen = new Pen(Brushes.Black, 2);
            shapeOutlinePen.Freeze();

            // Create a DrawingGroup
            DrawingGroup dGroup = new DrawingGroup();

            // Obtain a DrawingContext from 
            // the DrawingGroup.
            using (DrawingContext dc = dGroup.Open())
            {
                // Draw a rectangle at full opacity.
                dc.DrawRectangle(Brushes.Blue, shapeOutlinePen, new Rect(0, 0, 25, 25));

                // Push an opacity change of 0.5. 
                // The opacity of each subsequent drawing will
                // will be multiplied by 0.5.
                dc.PushOpacity(0.5);

                // This rectangle is drawn at 50% opacity.
                dc.DrawRectangle(Brushes.Blue, shapeOutlinePen, new Rect(25, 25, 25, 25));
            }

            // Display the drawing using an image control.
            Image theImage = new Image();
            DrawingImage dImageSource = new DrawingImage(dGroup);
            theImage.Source = dImageSource;

            this.Content = theImage;
        }
    }
}

Imports System.Windows.Media.Animation
Imports System.Windows.Media.Effects

Namespace SDKSample

    Public Class PushEffectExample
        Inherits Page

        Public Sub New()
            Dim shapeOutlinePen As New Pen(Brushes.Black, 2)
            shapeOutlinePen.Freeze()

            ' Create a DrawingGroup
            Dim dGroup As New DrawingGroup()

            ' Obtain a DrawingContext from
            ' the DrawingGroup.
            Using dc As DrawingContext = dGroup.Open()
                ' Draw a rectangle at full opacity.
                dc.DrawRectangle(Brushes.Blue, shapeOutlinePen, New Rect(0, 0, 25, 25))

                ' Push an opacity change of 0.5.
                ' The opacity of each subsequent drawing will
                ' will be multiplied by 0.5.
                dc.PushOpacity(0.5)

                ' This rectangle is drawn at 50% opacity.
                dc.DrawRectangle(Brushes.Blue, shapeOutlinePen, New Rect(25, 25, 25, 25))
            End Using

            ' Display the drawing using an image control.
            Dim theImage As New Image()
            Dim dImageSource As New DrawingImage(dGroup)
            theImage.Source = dImageSource

            Me.Content = theImage

        End Sub

    End Class

End Namespace

Observações

Use a DrawingContext para preencher a Visual ou a Drawing com conteúdo visual.

Embora os DrawingContext métodos de desenho sejam semelhantes aos métodos de desenho do System.Drawing.Graphics tipo, funcionam de forma muito diferente: DrawingContext é usado com um sistema gráfico em modo retido, enquanto o System.Drawing.Graphics tipo é usado com um sistema gráfico em modo imediato. Quando usas os comandos de desenho de um DrawingContext objeto, estás na verdade a guardar um conjunto de instruções de renderização (embora o mecanismo exato de armazenamento dependa do tipo de objeto que fornece o DrawingContext) que serão posteriormente usadas pelo sistema gráfico; não estás a desenhar no ecrã em tempo real. Para mais informações sobre como funciona o sistema gráfico Windows Presentation Foundation (WPF), consulte WPF Graphics Rendering Overview.

Você nunca instancia diretamente um DrawingContext; no entanto, pode adquirir um contexto de desenho a partir de certos métodos, como DrawingGroup.Open e DrawingVisual.RenderOpen.

Ver também

• DrawingGroup
• Drawing