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 org.afzkl.colorpicker.drawables;

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

/**
 * This drawable that draws 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 final Paint mPaint = new Paint();
    private final Paint mPaintWhite = new Paint();
    private final Paint mPaintGray = new Paint();

    private int numRectanglesHorizontal;
    private int numRectanglesVertical;

    /**
     * Bitmap in which the pattern will be cahched.
     */
    private Bitmap mBitmap;

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

    @Override
    public void draw(final Canvas canvas) {
        final Bitmap b = getBitmap();
        if (b != null) {
            canvas.drawBitmap(b, null, getBounds(), mPaint);
        }
    }

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

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

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

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

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

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

    /**
     * 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 Bitmap getBitmap() {
        final Rect bounds = getBounds();
        final int width = bounds.width();
        final int height = bounds.height();

        if (width <= 0 || height <= 0) {
            return null;
        }
        if (mBitmap == null || mBitmap.isRecycled() || mBitmap.getWidth() != width || mBitmap.getHeight() != height) {
            if (mBitmap != null) {
                mBitmap.recycle();
            }
            mBitmap = Bitmap.createBitmap(width, height, Config.ARGB_8888);
            final Canvas canvas = new Canvas(mBitmap);
            generatePatternBitmap(canvas);
        }
        return mBitmap;
    }

    public void generatePatternBitmap(final Canvas canvas) {
        final 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;
        }
    }

}