Android放大镜的实现
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。不过，一个问题如果只有一种解决方法的话，那未免有点令人沮丧，想玩点另类的都不行。
玩程序就得玩出个性，玩出激情。哈哈，废话太多，切回正题。
再来看看放大镜的另外一种实现吧
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：
