Android CreateBitmap

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1. public class CreateBitmap extends Activity{  
2.     @Override  
3.     protected void onCreate(Bundle savedInstanceState) {  
4.         // TODO Auto-generated method stub  
5.         super.onCreate(savedInstanceState);  
6.         setContentView(new SampleView(this));  
7.     }  
8.       
9.     private class SampleView extends View{  
10.         private Bitmap[] mBitmaps;  
11.         private Bitmap[] mJPEGs;  
12.         private Bitmap[] mPNGs;  
13.         private int[] mColors;  
14.         private Paint mPaint;  
15.           
16.         private static final int WIDTH=50;  
17.         private static final int HEIGHT=50;  
18.         private static final int STRIDE=64;//must be >=WIDTH  
19.         public SampleView(Context context) {  
20.             super(context);  
21.             setFocusable(true);  
22.               
23.             mColors=initColors();  
24.             mBitmaps=new Bitmap[6];  
25.             mPaint=new Paint();  
26.             mPaint.setDither(true);  
27.               
28.             //these three are initialized with colors[]  
29.             mBitmaps[0]=Bitmap.createBitmap(mColors, 0, STRIDE, WIDTH, HEIGHT, Config.ARGB_8888);  
30.             mBitmaps[1]=Bitmap.createBitmap(mColors, 0, STRIDE, WIDTH, HEIGHT, Config.RGB_565);  
31.             mBitmaps[2]=Bitmap.createBitmap(mColors, 0, STRIDE, WIDTH, HEIGHT, Config.ARGB_4444);  
32.               
33.             //these three will have their colors[] set later.  
34.             mBitmaps[3]=Bitmap.createBitmap(WIDTH, HEIGHT, Config.ARGB_8888);  
35.             mBitmaps[4]=Bitmap.createBitmap(WIDTH, HEIGHT, Config.RGB_565);  
36.             mBitmaps[5]=Bitmap.createBitmap(WIDTH, HEIGHT, Config.ARGB_4444);  
37.               
38.             for (int i = 3; i <=5; i++) {  
39.                 mBitmaps[i].setPixels(mColors, 0, STRIDE, 0, 0, WIDTH, HEIGHT);  
40.             }  
41.               
42.             //now decode/encode using JPEG and PNG  
43.             mJPEGs=new Bitmap[mBitmaps.length];  
44.             mPNGs=new Bitmap[mBitmaps.length];  
45.             for (int i = 0; i < mBitmaps.length; i++) {  
46.                 mJPEGs[i]=codec(mBitmaps[i],Bitmap.CompressFormat.JPEG,80);  
47.                 mPNGs[i]=codec(mBitmaps[i],Bitmap.CompressFormat.PNG,0);  
48.             }  
49.         }  
50.           
51.         @Override  
52.         protected void onDraw(Canvas canvas) {  
53.             // TODO Auto-generated method stub  
54.             super.onDraw(canvas);  
55.             canvas.drawColor(Color.WHITE);  
56.               
57.             for (int i = 0; i < mBitmaps.length; i++) {  
58.                 canvas.drawBitmap(mBitmaps[i], 0, 0, null);  
59.                 canvas.drawBitmap(mJPEGs[i], 80,0, null);  
60.                 canvas.drawBitmap(mPNGs[i], 160, 0, null);  
61.                 canvas.translate(0, mBitmaps[i].getHeight());  
62.             }  
63.               
64.             //draw the color array directly,w/o(without) creating a bitmap object  
65.             canvas.drawBitmap(mColors, 0, STRIDE, 0, 0, WIDTH, HEIGHT, true, null);  
66.             canvas.translate(0, HEIGHT);  
67.             canvas.drawBitmap(mColors, 0, STRIDE, 0, 0, WIDTH, HEIGHT, true, mPaint);  
68.         }  
69.         private Bitmap codec(Bitmap bitmap, CompressFormat format, int quality) {  
70.             ByteArrayOutputStream baos=new ByteArrayOutputStream();  
71.             bitmap.compress(format, quality, baos);  
72.             byte[] data=baos.toByteArray();  
73.             return BitmapFactory.decodeByteArray(data, 0, data.length);  
74.         }  
75.         private int[] initColors() {  
76.             int[] colors=new int[STRIDE*HEIGHT];  
77.             for (int y = 0; y < HEIGHT; y++) {//use of x,y is legible then the use of i,j  
78.                 for (int x = 0; x < WIDTH; x++) {  
79.                     int r = x * 255 / (WIDTH - 1);  
80.                     int g = y * 255 / (HEIGHT - 1);  
81.                     int b = 255 - Math.min(r, g);  
82.                     int a = Math.max(r, g);  
83.                     colors[y*STRIDE+x]=(a<<24)|(r<<16)|(g<<8)|(b);//the shift operation generates the color ARGB  
84.                 }  
85.             }  
86.             return colors;  
87.         }  
88.           
89.     }  
90. }  

 

Bitmap中setPiexls的解释：

 

public void setPixels (int[] pixels, int offset, int stride, int x, int y, int width, int height)

Since:  API Level 1

Replace pixels in the bitmap with the colors in the array. Each element in the array is a packed int prepresenting a Color

Parameters

pixels	The colors to write to the bitmap
offset	The index of the first color to read from pixels[]
stride	The number of colors in pixels[] to skip between rows. Normally this value will be the same as the width of the bitmap, but it can be larger (or negative).
x	The x coordinate of the first pixel to write to in the bitmap.
y	The y coordinate of the first pixel to write to in the bitmap.
width	The number of colors to copy from pixels[] per row
height	The number of rows to write to the bitmap

Throws

IllegalStateException	if the bitmap is not mutable
IllegalArgumentException	if x, y, width, height are outside of the bitmap's bounds.
ArrayIndexOutOfBoundsException	if the pixels array is too small to receive the specified number of pixels.

生成颜色值数组的函数：

view plain

1. private int[] initColors() {  
2.             int[] colors=new int[STRIDE*HEIGHT];  
3.             for (int y = 0; y < HEIGHT; y++) {//use of x,y is legible then the use of i,j  
4.                 for (int x = 0; x < WIDTH; x++) {  
5.                     int r = x * 255 / (WIDTH - 1);  
6.                     int g = y * 255 / (HEIGHT - 1);  
7.                     int b = 255 - Math.min(r, g);  
8.                     int a = Math.max(r, g);  
9.                     colors[y*STRIDE+x]=(a<<24)|(r<<16)|(g<<8)|(b);//the shift operation generates the color ARGB  
10.                 }  
11.             }  
12.             return colors;  
13.         }