Android 仿PhotoShop调色板应用(二) 透明度绘制之AlphaPatternDrawable

时间：2016-06-09 06:19:00 阅读：227 评论：0 收藏：0 [点我收藏+]

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这里讲一下如何实现PS调色板中的透明度选择条.首先说一下要点:

1. 透明度选择条实际上是基于白色(0xffffffff)和灰色(0xffcbcbcb)之间的颜色区间选取, 由此我们可以实现一个半透明颜色的选取

2.该应用不仅可以做透明度颜色选取，也可以在应用中实现半透明的图像效果

下面看一下代码，主要是基于Drawable的重写：

[java] view plain copy

/*
* 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.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 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 cahched.
*/
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;
}
}
}

Android 仿PhotoShop调色板应用(二) 透明度绘制之AlphaPatternDrawable

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原文地址：http://www.cnblogs.com/Free-Thinker/p/5571866.html

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