添加画布视图控件类用于相册集封面裁剪

- 将CropCanvas改造成CropCanvasView画布视图控件类
- 画布控件有宽度、高度和画布比例属性
- 初始化函数传入原始图片宽度、高度和图片比例
- 计算扩展高度和扩展宽度属性
- 画布高度和宽度取较大值
- 图片居中平铺到画布控件

gallery/src/main/java/cc/winboll/studio/gallery/CropCanvasView.java

@@ -0,0 +1,140 @@
+package cc.winboll.studio.gallery;
+
+import android.content.Context;
+import android.graphics.Bitmap;
+import android.graphics.Canvas;
+import android.graphics.Color;
+import android.graphics.Paint;
+import android.graphics.RectF;
+import android.util.AttributeSet;
+import android.view.View;
+
+public class CropCanvasView extends View {
+    private Paint imagePaint;
+    
+    private int imageWidth;
+    private int imageHeight;
+    private float coverRatio = 2.0f;
+    
+    private int extendHeight;
+    private int extendWidth;
+    private int canvasWidth;
+    private int canvasHeight;
+    
+    private RectF imageBounds = new RectF();
+    private RectF canvasBounds = new RectF();
+    private Bitmap originalBitmap;
+    
+    public CropCanvasView(Context context) {
+        super(context);
+        init();
+    }
+    
+    public CropCanvasView(Context context, AttributeSet attrs) {
+        super(context, attrs);
+        init();
+    }
+    
+    public CropCanvasView(Context context, AttributeSet attrs, int defStyleAttr) {
+        super(context, attrs, defStyleAttr);
+        init();
+    }
+    
+    private void init() {
+        imagePaint = new Paint();
+        imagePaint.setFilterBitmap(true);
+    }
+    
+    public void setImageBitmap(Bitmap bitmap) {
+        this.originalBitmap = bitmap;
+    }
+    
+    public void initCanvas(int imgWidth, int imgHeight, float ratio) {
+        this.imageWidth = imgWidth;
+        this.imageHeight = imgHeight;
+        this.coverRatio = ratio;
+        
+        float imgRatio = (float) imgWidth / imgHeight;
+        
+        if (coverRatio >= imgRatio) {
+            extendHeight = imgHeight;
+            extendWidth = (int) (imgHeight * coverRatio);
+        } else {
+            extendWidth = imgWidth;
+            extendHeight = (int) (imgWidth / coverRatio);
+        }
+        
+        canvasHeight = Math.max(imageHeight, extendHeight);
+        canvasWidth = Math.max(imageWidth, extendWidth);
+        
+        float left = (canvasWidth - imageWidth) / 2f;
+        float top = (canvasHeight - imageHeight) / 2f;
+        imageBounds.set(left, top, left + imageWidth, top + imageHeight);
+        canvasBounds.set(0, 0, canvasWidth, canvasHeight);
+        
+        requestLayout();
+        invalidate();
+    }
+    
+    public void scaleToView(int viewWidth, int viewHeight) {
+        if (viewWidth > 0 && viewHeight > 0 && canvasWidth > 0 && canvasHeight > 0) {
+            float scale = Math.max((float) viewWidth / canvasWidth, (float) viewHeight / canvasHeight);
+            canvasWidth = (int) (canvasWidth * scale);
+            canvasHeight = (int) (canvasHeight * scale);
+            
+            float left = (canvasWidth - imageWidth) / 2f;
+            float top = (canvasHeight - imageHeight) / 2f;
+            imageBounds.set(left, top, left + imageWidth, top + imageHeight);
+            canvasBounds.set(0, 0, canvasWidth, canvasHeight);
+            
+            requestLayout();
+            invalidate();
+        }
+    }
+    
+    public int getCanvasWidth() {
+        return canvasWidth;
+    }
+    
+    public int getCanvasHeight() {
+        return canvasHeight;
+    }
+    
+    public int getExtendWidth() {
+        return extendWidth;
+    }
+    
+    public int getExtendHeight() {
+        return extendHeight;
+    }
+    
+    public RectF getCanvasBounds() {
+        return new RectF(canvasBounds);
+    }
+    
+    public RectF getImageBounds() {
+        return new RectF(imageBounds);
+    }
+    
+    public float getCoverRatio() {
+        return coverRatio;
+    }
+    
+    @Override
+    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
+        int w = canvasWidth > 0 ? canvasWidth : 0;
+        int h = canvasHeight > 0 ? canvasHeight : 0;
+        setMeasuredDimension(w, h);
+    }
+    
+    @Override
+    protected void onDraw(Canvas canvas) {
+        super.onDraw(canvas);
+        
+        canvas.drawColor(Color.GREEN);
+        
+        if (originalBitmap != null && !originalBitmap.isRecycled()) {
+            canvas.drawBitmap(originalBitmap, imageBounds.left, imageBounds.top, imagePaint);
+        }
+    }
+}