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 net.margaritov.preference.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.PixelFormat;
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 final int mSquareSizePixels;

    private final Paint mPaint = new Paint();
    
    private final Paint mPaintLight = new Paint();
    private final Paint mPaintDark = new Paint();

    // TODO: what these are member variables and not local variables?
    private int numRectanglesHorizontal;
    private int numRectanglesVertical;

    /** Caches the pattern. */
    private Bitmap mBitmap;

    public AlphaPatternDrawable(int squareSizePixels) {
        this(squareSizePixels, 0xffcbcbcb, 0xffffffff);
    }  
   
    public AlphaPatternDrawable(int squareSizePixels, int darkColor, int lightColor) {
        mSquareSizePixels = squareSizePixels;
        mPaintDark.setColor(darkColor);
        mPaintLight.setColor(lightColor);
    }

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

    @Override
    public int getOpacity() {
        // TODO: should this be OPAQUE ?
        return PixelFormat.UNKNOWN;
    }

    @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();

        // Determine actual number of horizontal and vertical square (no fractions).
        numRectanglesHorizontal = (int) Math.ceil((width / mSquareSizePixels));
        numRectanglesVertical = (int) Math.ceil(height / mSquareSizePixels);

        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();
        for (int i = 0; i <= numRectanglesVertical; i++) {
            for (int j = 0; j <= numRectanglesHorizontal; j++) {
                final boolean isEven = (((i + j) % 2) == 0);

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

                canvas.drawRect(r, isEven ? mPaintLight : mPaintDark);
            }
        }

    }

}