Bitmap.createBitmap实现裁剪图片适配屏幕

在编写MusicPlayer的过程中，播放歌曲时搜索歌手的图片，并动态地将图片设为当前Activity的背景。当图片大小与屏幕不适应时会导致图片被拉神效果很不好看。比如你的手机分辨率是320X480，而图片的分辨率是320X320，那么，该图片将被拉长。

       那么，如何放大图片的同时不影响其显示效果呢？

       网上有用 drawable.setTileModeXY(TileMode.REPEAT , TileMode.REPEAT )的方法来设置图片的平铺，但是我没有试验成功，

 

 

于是尝试了Bitmap.createBitmap方法。

       下面是Google官方文档对createBitmap方法的解释

public static Bitmap createBitmap (Bitmap source, int x, int y, int width, int height, Matrix m, boolean filter)

Added in API level 1

Returns an immutable bitmap from subset of the source bitmap, transformed by the optional matrix. The new bitmap may be the same object as source, or a copy may have been made. It is initialized with the same density as the original bitmap. If the source bitmap is immutable and the requested subset is the same as the source bitmap itself, then the source bitmap is returned and no new bitmap is created.

Parameters

source	The bitmap we are subsetting
x	The x coordinate of the first pixel in source
y	The y coordinate of the first pixel in source
width	The number of pixels in each row
height	The number of rows
m	Optional matrix to be applied to the pixels
filter	true if the source should be filtered. Only applies if the matrix contains more than just translation.

Returns

• A bitmap that represents the specified subset of source

Throws

IllegalArgumentException	if the x, y, width, height values are outside of the dimensions of the source bitmap.

各参数含义：

       surce：用来剪裁的图片源;

       x：剪裁x方向的起始位置;

       y：剪裁y方向的起始位置;

       width：剪裁的宽度;

       height：剪裁的高度;

       filer：不是很清楚它的作用 - -！

需要注意的是：必须满足条件：x+width<=bitmap.width()（图片源的原始宽度）否则会抛出IllegalArgumentException异常。

 

       我遇到的问题是图片为320X320，手机屏幕是320X480，需将图片按照手机屏幕的比例剪裁后再适当放大。这里的执行过程并非是先放大再剪裁。

下面是思路：

       一、获取手机屏幕宽高（width，height）与图片的宽高（widthDrawable，heightDrawable）；

       二、计算其比例，取大的。比如width/widthDrawable=1.0，height/heightDrawable=1.5，那么取scale=1.5；

       三、利用Matrix构建缩放矩阵：

                     Matrix matrix = new Matrix(); 

                     matrix.postScale(scale, scale);

       四、计算起始剪裁的位置x，y和剪裁宽度width,高度height；

       五、调用createBitmap方法，在原图片的基础上剪裁新的图片并缩放相应的比例。

 

下面是相关的代码：

@SuppressWarnings("deprecation")
private void setDrawable(Bitmap backGroundMap, RelativeLayout lrcBackGround) {
DisplayMetrics dm = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(dm);
int width = dm.widthPixels;
int height = dm.heightPixels;//获取屏幕的宽和高
Log.v("franco-width", "width = " + width);
Log.v("franco-height", "height = " + height);//320X480

int widthDrawable = backGroundMap.getWidth();
int heightDrawable = backGroundMap.getHeight();//获取背景图片的宽和高
Log.v("franco-widthDrawable", "widthDrawable = " + widthDrawable);
Log.v("franco-heightDrawable", "heightDrawable = " + heightDrawable);//320X320

float scaleWidth = (float)width/widthDrawable;
float scaleHeight = (float)height/heightDrawable;//宽高比
Log.v("franco", "scaleWidth = " + scaleWidth);
Log.v("franco", "scaleHeight = " + scaleHeight);//1.0:1.5

Bitmap resizeBmp;
Matrix matrix = new Matrix();
if(scaleWidth < scaleHeight) { float scale = scaleHeight;//取大的 matrix.postScale(scale, scale);//缩放比例 int xStart = (int)(widthDrawable-widthDrawable/scale)/2; Log.v("franco-xStart", "xStart = " + xStart); /* * Bitmap source：要从中截图的原始位图 * int x:起始x坐标 * int y：起始y坐标 * int width：要截的图的宽度 * int height：要截的图的宽度 * x+width must be <= bitmap.width()不然会报错 * 原理是先截图再缩放，而不是先缩放再截图！！ */ resizeBmp = Bitmap.createBitmap(backGroundMap, xStart, 0, (int)(widthDrawable/scale), heightDrawable, matrix, true); } else { float scale = scaleWidth; matrix.postScale(scale, scale); int yStart = (int)(scaleHeight-scaleHeight/scale)/2; Log.v("franco-yStart", "yStart = " + yStart); resizeBmp = Bitmap.createBitmap(backGroundMap, 0, yStart, widthDrawable, (int)(heightDrawable/scale), matrix, true); } //Bitmap 转化为 Drawable BitmapDrawable drawable = new BitmapDrawable(getResources(), resizeBmp); //drawable.setTileModeXY(TileMode.REPEAT, TileMode.REPEAT); lrcBackGround.setBackgroundDrawable(drawable); lrcBackGround.getBackground().setAlpha(150);//将背景该图片透明度设低，避免歌词显示效果不好,数值越大透明度越高 }

最后效果如下：

 

 

但是这样做必将会剪裁掉部分原图，如果不剪裁的话图片的比例会失真，期待更好地方案。