package chroya.demo.magnifier;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Shader.TileMode;
import android.graphics.drawable.ShapeDrawable;
import android.graphics.drawable.shapes.OvalShape;
import android.view.MotionEvent;
import android.view.View;
/**
* 放大镜实现方式1
*
* @author chroya
*
*/
public class ShaderView extends View {
private Bitmap bitmap;
private ShapeDrawable drawable;
// 放大镜的半径
private static final int RADIUS = 80;
// 放大倍数
private static final int FACTOR = 3;
private Matrix matrix = new Matrix();
public ShaderView(Context context) {
super(context);
Bitmap bmp = BitmapFactory.decodeResource(getResources(),
R.drawable.show);
bitmap = bmp;
BitmapShader shader = new BitmapShader(Bitmap.createScaledBitmap(bmp,
bmp.getWidth() * FACTOR, bmp.getHeight() * FACTOR, true),
TileMode.CLAMP, TileMode.CLAMP);
// 圆形的drawable
drawable = new ShapeDrawable(new OvalShape());
drawable.getPaint().setShader(shader);
drawable.setBounds(0, 0, RADIUS * 2, RADIUS * 2);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
final int x = (int) event.getX();
final int y = (int) event.getY();
// 这个位置表示的是，画shader的起始位置
matrix.setTranslate(RADIUS - x * FACTOR, RADIUS - y * FACTOR);
drawable.getPaint().getShader().setLocalMatrix(matrix);
// bounds，就是那个圆的外切矩形
drawable.setBounds(x - RADIUS, y - RADIUS, x + RADIUS, y + RADIUS);
invalidate();
return true;
}
@Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawBitmap(bitmap, 0, 0, null);
drawable.draw(canvas);
}
}
基本原理就是使用ShapeDrawable构造一个圆形的drawable，然后它的paint的shader设置为将要放大的图片，然后就是简单的位置移动问题了。放大镜的半径和放大倍数都可以在代码里面修改，代码都有注释，应该很好理解了。
再来看看另一种实现放大镜的方法。
package chroya.demo.magnifier;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Path;
import android.graphics.Path.Direction;
import android.view.MotionEvent;
import android.view.View;
/**
* 放大镜实现方式2
*
* @author chroya
*
*/
public class PathView extends View {
private Path mPath = new Path();
private Matrix matrix = new Matrix();
private Bitmap bitmap;
// 放大镜的半径
private static final int RADIUS = 80;
// 放大倍数
private static final int FACTOR = 2;
private int mCurrentX, mCurrentY;
public PathView(Context context) {
super(context);
mPath.addCircle(RADIUS, RADIUS, RADIUS, Direction.CW);
matrix.setScale(FACTOR, FACTOR);
bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.show);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
mCurrentX = (int) event.getX();
mCurrentY = (int) event.getY();
invalidate();
return true;
}
@Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
// 底图
canvas.drawBitmap(bitmap, 0, 0, null);
// 剪切
canvas.translate(mCurrentX - RADIUS, mCurrentY - RADIUS);
canvas.clipPath(mPath);
// 画放大后的图
canvas.translate(RADIUS - mCurrentX * FACTOR, RADIUS - mCurrentY
* FACTOR);
canvas.drawBitmap(bitmap, matrix, null);
}
}
这里使用的是Path类，将canvas剪切出一块圆形区域，在其上绘制放大的部分。
两种方式的效果都一样，如图：
