AlphaPatternDrawable.java

/*
* Copyright (C) 2010 Daniel Nilsson
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package com.scheffsblend.iconfilters;

import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.ColorFilter;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.Bitmap.Config;
import android.graphics.drawable.Drawable;

/**
 * This drawable will draw a simple white and gray chessboard pattern.
 * It's pattern you will often see as a background behind a
 * partly transparent image in many applications.
 * @author Daniel Nilsson
 */
public class AlphaPatternDrawable extends Drawable {

    private int mRectangleSize = 10;

    private Paint mPaint = new Paint();
    private Paint mPaintWhite = new Paint();
    private Paint mPaintGray = new Paint();

    private int numRectanglesHorizontal;
    private int numRectanglesVertical;

    /**
     * Bitmap in which the pattern will be cached.
     * This is so the pattern will not have to be recreated each time draw() gets called.
     * Because recreating the pattern i rather expensive. I will only be recreated if the
     * size changes.
     */
    private Bitmap          mBitmap;

    public AlphaPatternDrawable(int rectangleSize) {
        mRectangleSize = rectangleSize;
        mPaintWhite.setColor(0xffffffff);
        mPaintGray.setColor(0xffcbcbcb);
    }

    @Override
    public void draw(Canvas canvas) {
        canvas.drawBitmap(mBitmap, null, getBounds(), mPaint);
    }

    @Override
    public int getOpacity() {
        return 0;
    }

    @Override
    public void setAlpha(int alpha) {
        throw new UnsupportedOperationException("Alpha is not supported by this drawwable.");
    }

    @Override
    public void setColorFilter(ColorFilter cf) {
        throw new UnsupportedOperationException("ColorFilter is not supported by this drawwable.");
    }

    @Override
    protected void onBoundsChange(Rect bounds) {
        super.onBoundsChange(bounds);

        int height = bounds.height();
        int width = bounds.width();

        numRectanglesHorizontal = (int) Math.ceil((width / mRectangleSize));
        numRectanglesVertical = (int) Math.ceil(height / mRectangleSize);

        generatePatternBitmap();

    }

    /**
     * This will generate a bitmap with the pattern
     * as big as the rectangle we were allow to draw on.
     * We do this to chache the bitmap so we don't need to
     * recreate it each time draw() is called since it
     * takes a few milliseconds.
     */
    private void generatePatternBitmap(){

        if(getBounds().width() <= 0 || getBounds().height() <= 0){
            return;
        }

        mBitmap = Bitmap.createBitmap(getBounds().width(), getBounds().height(), Config.ARGB_8888);
        Canvas canvas = new Canvas(mBitmap);

        Rect r = new Rect();
        boolean verticalStartWhite = true;
        for (int i = 0; i <= numRectanglesVertical; i++) {

            boolean isWhite = verticalStartWhite;
            for (int j = 0; j <= numRectanglesHorizontal; j++) {

                r.top = i * mRectangleSize;
                r.left = j * mRectangleSize;
                r.bottom = r.top + mRectangleSize;
                r.right = r.left + mRectangleSize;

                canvas.drawRect(r, isWhite ? mPaintWhite : mPaintGray);

                isWhite = !isWhite;
            }

            verticalStartWhite = !verticalStartWhite;

        }

    }

}