Transforming Shapes, Text, and Images转换形状、文本和图像

You can modify the transform attribute in the Graphics2D context to move, rotate, scale, and shear graphics primitives when they are rendered.可以在Graphics2D上下文中修改“变换”属性，以在渲染图形基本体时移动、旋转、缩放和剪切图形基本体。The transform attribute is defined by an instance of the AffineTransform class.transform属性由AffineTransform类的实例定义。An affine transform is a transformation such as translate, rotate, scale, or shear in which parallel lines remain parallel even after being transformed.仿射变换是一种变换，例如平移、旋转、缩放或剪切，其中平行线即使在变换后仍保持平行。

The Graphics2D class provides several methods for changing the transform attribute.Graphics2D类提供了几种更改变换属性的方法。You can construct a new AffineTransform and change the Graphics2D transform attribute by calling transform.可以通过调用transform构造新的AffineTransform并更改Graphics2D变换属性。

AffineTransform defines the following factory methods to make it easier to construct new transforms:

• getRotateInstance
• getScaleInstance
• getShearInstance
• getTranslateInstance

Alternatively you can use one of the Graphics2D transformation methods to modify the current transform. When you call one of these convenience methods, the resulting transform is concatenated with the current transform and is applied during rendering:

• rotate — to specify an angle of rotation in radians
• scale — to specify a scaling factor in the x and y directions
• shear — to specify a shearing factor in the x and y directions
• translate — to specify a translation offset in the x and y directions

You can also construct an AffineTransform object directly and concatenate it with the current transform by calling the transform method.

The drawImage method is also overloaded to allow you to specify an AffineTransform that is applied to the image as it is rendered. Specifying a transform when you call drawImage does not affect the Graphics2D transform attribute.

Example: Transform

The following program is the same as StrokeandFill, but also allows the user to choose a transformation to apply to the selected object when it is rendered.

Transform.java contains the complete code for this applet.

When a transform is chosen from the Transform menu, the transform is concatenated onto the AffineTransform at:

public void setTrans(int transIndex) {
    // Sets the AffineTransform.
    switch ( transIndex ) {
    case 0 :
        at.setToIdentity();
        at.translate(w/2, h/2);
        break;
    case 1 :
        at.rotate(Math.toRadians(45));
        break;
    case 2 :
        at.scale(0.5, 0.5);
        break;
    case 3 :
        at.shear(0.5, 0.0);
        break;
    }
}

Before displaying the shape corresponding to the menu choices, the application first retrieves the current transform from the Graphics2D object:

AffineTransform saveXform = g2.getTransform();

This transform will be restored to the Graphics2D after rendering.

After retrieving the current transform, another AffineTransform, toCenterAt, is created that causes shapes to be rendered in the center of the panel. The at AffineTransform is concatenated onto toCenterAt:

AffineTransform toCenterAt = new AffineTransform();
toCenterAt.concatenate(at);
toCenterAt.translate(-(r.width/2), -(r.height/2));

The toCenterAt transform is concatenated onto the Graphics2D transform with the transform method:

g2.transform(toCenterAt);

After rendering is completed, the original transform is restored using the setTransform method:

g2.setTransform(saveXform);