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Graphics.DrawImage méthode (Image, Point[], Rectangle, GraphicsUnit, ImageAttributes, Graphics.DrawImageAbort)

 

Date de publication : novembre 2016

Dessine la partie mentionnée du Image spécifié à l'emplacement indiqué avec la taille précisée.

Espace de noms:   System.Drawing
Assembly:  System.Drawing (dans System.Drawing.dll)

public void DrawImage(
	Image image,
	Point[] destPoints,
	Rectangle srcRect,
	GraphicsUnit srcUnit,
	ImageAttributes imageAttr,
	Graphics.DrawImageAbort callback
)

Paramètres

image
Type: System.Drawing.Image

Image à dessiner.

destPoints
Type: System.Drawing.Point[]

Tableau de trois structures PointF qui définissent un parallélogramme.

srcRect
Type: System.Drawing.Rectangle

Structure Rectangle qui spécifie la partie de l'objet image à dessiner.

srcUnit
Type: System.Drawing.GraphicsUnit

Membre de l'énumération GraphicsUnit qui spécifie les unités de mesure utilisées par le paramètre srcRect.

imageAttr
Type: System.Drawing.Imaging.ImageAttributes

ImageAttributes qui spécifie des informations de recoloriage et de gamma pour l'objet image.

callback
Type: System.Drawing.Graphics.DrawImageAbort

Délégué Graphics.DrawImageAbort qui spécifie une méthode à appeler lors du dessin de l'image. Cette méthode est fréquemment appelée pour vérifier si l'exécution de la méthode DrawImage doit être arrêtée selon des critères déterminés par l'application.

Exception Condition
ArgumentNullException

image a la valeur null.

The destPoints parameter specifies three points of a parallelogram. The three T:System.Drawing.PointF structures represent the upper-left, upper-right, and lower-left corners of the parallelogram. The fourth point is extrapolated from the first three to form a parallelogram.

The srcRect parameter specifies a rectangular portion of the image object to draw. This portion is scaled and sheared to fit inside the parallelogram specified by the destPoints parameter.

This overload with the callback parameter provides the means to stop the drawing of an image once it starts according to criteria determined by the application. For example, an application could start drawing a large image and the user might scroll the image off the screen, in which case the application could stop the drawing.

The following code example is designed for use with Windows Forms, and it requires T:System.Windows.Forms.PaintEventArgse, which is a parameter of the E:System.Windows.Forms.Control.Paint event handler. The code first defines a callback method for the T:System.Drawing.Graphics.DrawImageAbort delegate; the definition is simplistic and merely tests to see whether the Overload:System.Drawing.Graphics.DrawImage method calls it with a null callBackData parameter. The main body of the example performs the following actions:

  • Creates an instance of the T:System.Drawing.Graphics.DrawImageAbort callback method:

  • Creates an image from a JPEG file SampImag.jpg in the folder of the example.

  • Creates points that define a parallelogram in which to draw the image.

  • Creates a rectangle to select the portion of the image to draw.

  • Sets the graphics drawing unit to pixel.

  • Draws the original image to the screen.

  • Creates an additional parallelogram in which to draw an adjusted image.

  • Creates and sets the attributes of the adjusted image to have a larger-than-usual gamma value.

  • Draws the adjusted image to the screen.

For the original, unadjusted parallelogram, the position locates the image on the screen, and the size of the rectangle and the size and shape of the parallelogram determines the scaling and shearing of the drawn image.

Because this example uses an overload that does not pass a callBackData parameter, the T:System.Drawing.Graphics.DrawImageAbort callback returns true, which causes the Overload:System.Drawing.Graphics.DrawImage method to end, and the exception-handling code included in the example prints out the exception text rather than drawing the image.


// Define DrawImageAbort callback method.
private bool DrawImageCallback1(IntPtr callBackData)
{

    // Test for call that passes callBackData parameter.
    if(callBackData==IntPtr.Zero)
    {

        // If no callBackData passed, abort DrawImage method.
        return true;
    }
    else
    {

        // If callBackData passed, continue DrawImage method.
        return false;
    }
}
private void DrawImageParaRectAttribAbort(PaintEventArgs e)
{

    // Create callback method.
    Graphics.DrawImageAbort imageCallback
        = new Graphics.DrawImageAbort(DrawImageCallback1);

    // Create image.
    Image newImage = Image.FromFile("SampImag.jpg");

    // Create parallelogram for drawing original image.
    Point ulCorner = new Point(100, 100);
    Point urCorner = new Point(550, 100);
    Point llCorner = new Point(150, 250);
    Point[] destPara1 = {ulCorner, urCorner, llCorner};

    // Create rectangle for source image.
    Rectangle srcRect = new Rectangle(50, 50, 150, 150);
    GraphicsUnit units = GraphicsUnit.Pixel;

    // Draw original image to screen.
    e.Graphics.DrawImage(newImage, destPara1, srcRect, units);

    // Create parallelogram for drawing adjusted image.
    Point ulCorner2 = new Point(325, 100);
    Point urCorner2 = new Point(550, 100);
    Point llCorner2 = new Point(375, 250);
    Point[] destPara2 = {ulCorner2, urCorner2, llCorner2};

    // Create image attributes and set large gamma.
    ImageAttributes imageAttr = new ImageAttributes();
    imageAttr.SetGamma(4.0F);
    try
    {
        checked
        {

            // Draw image to screen.
            e.Graphics.DrawImage(
                newImage,
                destPara2,
                srcRect,
                units,
                imageAttr,
                imageCallback);
        }
    }
    catch (Exception ex)
    {
        e.Graphics.DrawString(
            ex.ToString(),
            new Font("Arial", 8),
            Brushes.Black,
            new PointF(0, 0));
    }
}

.NET Framework
Disponible depuis 1.1
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