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.fanfou.app.opensource.preferences.colorpicker;

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) {
        this.mRectangleSize = rectangleSize;
        this.mPaintWhite.setColor(0xffffffff);
        this.mPaintGray.setColor(0xffffffff);
        // mPaintGray.setColor(0xffcbcbcb);
    }

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

    /**
     * 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;
        }

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

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

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

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

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

                isWhite = !isWhite;
            }

            verticalStartWhite = !verticalStartWhite;

        }

    }

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

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

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

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

        generatePatternBitmap();

    }

    @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.");
    }

}