Android圆形头像的绘制(一)之绘制的几种方法

现在很多应用都有涉及到自定义图像，现在我们看下圆形图像是怎么绘制的。在绘制之前，我们需要对PorterDuff.Mode进行初步的了解，后面圆形图像的绘制会用到该方法，看下PorterDuff.Mode定义的枚举参数

public enum Mode {
/** [0, 0] */
CLEAR       (0),
/** [Sa, Sc] */
SRC         (1),
/** [Da, Dc] */
DST         (2),
/** [Sa + (1 - Sa)*Da, Rc = Sc + (1 - Sa)*Dc] */
SRC_OVER    (3),
/** [Sa + (1 - Sa)*Da, Rc = Dc + (1 - Da)*Sc] */
DST_OVER    (4),
/** [Sa * Da, Sc * Da] */
SRC_IN      (5),
/** [Sa * Da, Sa * Dc] */
DST_IN      (6),
/** [Sa * (1 - Da), Sc * (1 - Da)] */
SRC_OUT     (7),
/** [Da * (1 - Sa), Dc * (1 - Sa)] */
DST_OUT     (8),
/** [Da, Sc * Da + (1 - Sa) * Dc] */
SRC_ATOP    (9),
/** [Sa, Sa * Dc + Sc * (1 - Da)] */
DST_ATOP    (10),
/** [Sa + Da - 2 * Sa * Da, Sc * (1 - Da) + (1 - Sa) * Dc] */
XOR         (11),
/** [Sa + Da - Sa*Da,
Sc*(1 - Da) + Dc*(1 - Sa) + min(Sc, Dc)] */
DARKEN      (16),
/** [Sa + Da - Sa*Da,
Sc*(1 - Da) + Dc*(1 - Sa) + max(Sc, Dc)] */
LIGHTEN     (17),
/** [Sa * Da, Sc * Dc] */
MULTIPLY    (13),
/** [Sa + Da - Sa * Da, Sc + Dc - Sc * Dc] */
SCREEN      (14),
/** Saturate(S + D) */
ADD         (12),
OVERLAY     (15);
}

其中 Sa 代表source alpha ，即源 alpha 值 ，Da 代表 Destination alpha ，即 目标alpha值 ，Sc 代表 source color ，即源色值 ，Dc 代表 Destination color ，即目标色值，并且这所有的计算都以像素为单位，在某一种混合模式下，对每一个像素的alpha
和 color 通过对应算法进行运算，得出新的像素值。

ProterDuff.Mode16个枚举值代表的意思如下：

PorterDuff.Mode.CLEAR  所绘制不会提交到画布上。

PorterDuff.Mode.SRC 显示上层绘制图片

PorterDuff.Mode.DST 显示下层绘制图片

PorterDuff.Mode.SRC_OVER 正常绘制显示，上下层绘制叠盖。

PorterDuff.Mode.DST_OVER 上下层都显示。下层居上显示。

PorterDuff.Mode.SRC_IN  取两层绘制交集。显示上层。

PorterDuff.Mode.DST_IN 取两层绘制交集。显示下层。

PorterDuff.Mode.SRC_OUT 取上层绘制非交集部分。

PorterDuff.Mode.DST_OUT 取下层绘制非交集部分。

PorterDuff.Mode.SRC_ATOP 取下层非交集部分与上层交集部分

PorterDuff.Mode.DST_ATOP 取上层非交集部分与下层交集部分

PorterDuff.Mode.XOR 异或：去除两图层交集部分

PorterDuff.Mode.DARKEN 取两图层全部区域，交集部分颜色加深

PorterDuff.Mode.LIGHTEN 取两图层全部，点亮交集部分颜色

PorterDuff.Mode.MULTIPLY 取两图层交集部分叠加后颜色

PorterDuff.Mode.SCREEN 取两图层全部区域，交集部分变为透明色

看下16个枚举值展示的效果图：



实现的代码如下（代码来自ApiDemos/Graphics/XferModes）：

package com.dylan.porterduffdemo;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.RectF;
import android.graphics.Shader;
import android.graphics.Xfermode;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.View;

public class MainActivity extends AppCompatActivity {
static Bitmap makeDst(int w, int h) {
Bitmap bm = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(bm);
Paint p = new Paint(Paint.ANTI_ALIAS_FLAG);

p.setColor(0xFFFFCC44);
c.drawOval(new RectF(0, 0, w * 3 / 4, h * 3 / 4), p);
return bm;
}

// create a bitmap with a rect, used for the "src" image
static Bitmap makeSrc(int w, int h) {
Bitmap bm = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(bm);
Paint p = new Paint(Paint.ANTI_ALIAS_FLAG);

p.setColor(0xFF66AAFF);
c.drawRect(w / 3, h / 3, w * 19 / 20, h * 19 / 20, p);
return bm;
}

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new SampleView(this));
}

private static class SampleView extends View {
private static final int W = 192;
private static final int H = 192;
private static final int ROW_MAX = 4;   // number of samples per row

private Bitmap mSrcB;
private Bitmap mDstB;
private Shader mBG;     // background checker-board pattern

private static final Xfermode[] sModes = {
new PorterDuffXfermode(PorterDuff.Mode.CLEAR),
new PorterDuffXfermode(PorterDuff.Mode.SRC),
new PorterDuffXfermode(PorterDuff.Mode.DST),
new PorterDuffXfermode(PorterDuff.Mode.SRC_OVER),
new PorterDuffXfermode(PorterDuff.Mode.DST_OVER),
new PorterDuffXfermode(PorterDuff.Mode.SRC_IN),
new PorterDuffXfermode(PorterDuff.Mode.DST_IN),
new PorterDuffXfermode(PorterDuff.Mode.SRC_OUT),
new PorterDuffXfermode(PorterDuff.Mode.DST_OUT),
new PorterDuffXfermode(PorterDuff.Mode.SRC_ATOP),
new PorterDuffXfermode(PorterDuff.Mode.DST_ATOP),
new PorterDuffXfermode(PorterDuff.Mode.XOR),
new PorterDuffXfermode(PorterDuff.Mode.DARKEN),
new PorterDuffXfermode(PorterDuff.Mode.LIGHTEN),
new PorterDuffXfermode(PorterDuff.Mode.MULTIPLY),
new PorterDuffXfermode(PorterDuff.Mode.SCREEN)
};

private static final String[] sLabels = {
"Clear", "Src", "Dst", "SrcOver",
"DstOver", "SrcIn", "DstIn", "SrcOut",
"DstOut", "SrcATop", "DstATop", "Xor",
"Darken", "Lighten", "Multiply", "Screen"
};

public SampleView(Context context) {
super(context);

mSrcB = makeSrc(W, H);
mDstB = makeDst(W, H);

// make a ckeckerboard pattern
Bitmap bm = Bitmap.createBitmap(new int[]{0xFFFFFFFF, 0xFFCCCCCC,
0xFFCCCCCC, 0xFFFFFFFF}, 2, 2,
Bitmap.Config.RGB_565);
mBG = new BitmapShader(bm,
Shader.TileMode.REPEAT,
Shader.TileMode.REPEAT);
Matrix m = new Matrix();
m.setScale(6, 6);
mBG.setLocalMatrix(m);
}

@Override
protected void onDraw(Canvas canvas) {
canvas.drawColor(Color.WHITE);

Paint labelP = new Paint(Paint.ANTI_ALIAS_FLAG);
labelP.setTextAlign(Paint.Align.CENTER);

Paint paint = new Paint();
paint.setFilterBitmap(false);

canvas.translate(15, 35);

int x = 0;
int y = 0;
for (int i = 0; i < sModes.length; i++) {
// draw the border
paint.setStyle(Paint.Style.STROKE);
paint.setShader(null);
canvas.drawRect(x - 0.5f, y - 0.5f,
x + W + 0.5f, y + H + 0.5f, paint);

// draw the checker-board pattern
paint.setStyle(Paint.Style.FILL);
paint.setShader(mBG);
canvas.drawRect(x, y, x + W, y + H, paint);

// draw the src/dst example into our offscreen bitmap
int sc = canvas.saveLayer(x, y, x + W, y + H, null,
Canvas.MATRIX_SAVE_FLAG |
Canvas.CLIP_SAVE_FLAG |
Canvas.HAS_ALPHA_LAYER_SAVE_FLAG |
Canvas.FULL_COLOR_LAYER_SAVE_FLAG |
Canvas.CLIP_TO_LAYER_SAVE_FLAG);
canvas.translate(x, y);
canvas.drawBitmap(mDstB, 0, 0, paint);
paint.setXfermode(sModes[i]);
canvas.drawBitmap(mSrcB, 0, 0, paint);
paint.setXfermode(null);
canvas.restoreToCount(sc);

// draw the label
canvas.drawText(sLabels[i],
x + W / 2, y - labelP.getTextSize() / 2, labelP);

x += W + 10;

// wrap around when we've drawn enough for one row
if ((i % ROW_MAX) == ROW_MAX - 1) {
x = 0;
y += H + 30;
}
}
}
}
}

从上面的效果图可以知道，假设创建一个矩形的bitmap（这里用A表示）和一个圆形的bitmap（这里用B表示），并且让B在A里居中展示，在调用PorterDuff.Mode.SRC_IN或者PorterDuff.Mode.DST_IN,合并后的图像就是我们想要的圆形图像，下面我们按照这样的思路，用代码进行实现，我们先创建一个Activity，在自定义一个View，并将
View设置在setContentView里，代码如下：

public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
CircleImageView circleImageView = new CircleImageView(this);
setContentView(circleImageView);
}

private class CircleImageView extends ImageView {
public CircleImageView(Context context) {
this(context, null);
}

public CircleImageView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}

public CircleImageView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
}
}

运行代码，出来的界面是空白的，因为没有实现CircleImageView里的onDraw方法，下面我们实现onDraw方法，在实现onDraw方法之前，需要在CircleImageView的构造函数里进行初始化操作，获取将要绘制图片的bitmap，代码如下：

private void init() {
mSrcBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.test);
}

用PorterDuff.Mode.SRC_IN实现onDraw方法，代码如下：

@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Bitmap bitmap = createCirclrBitmapForSRC_IN();
if (bitmap != null) {
canvas.drawBitmap(bitmap, 0, 0, new Paint());
}
}

private Bitmap createCirclrBitmapForSRC_IN() {
if (mSrcBitmap != null) {
int width = mSrcBitmap.getWidth();
int height = mSrcBitmap.getHeight();
if (width > 0 && height > 0) {
//创建一个和图片大小差不多的正方形矩阵
int size = Math.min(width, height);
Bitmap bitmap = Bitmap.createBitmap(size, size, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);

Paint paint = new Paint();
int center = size / 2;
//在矩阵中心画圆，与矩阵的四边相切
canvas.drawCircle(center, center, center, paint);
//设置Xfermode为SRC_IN
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
//绘制图片
canvas.drawBitmap(mSrcBitmap, 0, 0, paint);
return bitmap;
}
}
return null;
}

用PorterDuff.Mode.DST_IN实现onDraw方法，代码如下：

@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Bitmap bitmap = createCirclrBitmapForDST_IN();
if (bitmap != null) {
canvas.drawBitmap(bitmap, 0, 0, new Paint());
}
}

<span style="white-space:pre">	</span>private Bitmap createCirclrBitmapForDST_IN() {
if (mSrcBitmap != null) {
int width = mSrcBitmap.getWidth();
int height = mSrcBitmap.getHeight();
if (width > 0 && height > 0) {
//创建一个和图片大小差不多的正方形矩阵
int size = Math.min(width, height);
Bitmap bitmap = Bitmap.createBitmap(size, size, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);

Paint paint = new Paint();
//绘制图片
canvas.drawBitmap(mSrcBitmap, 0, 0, paint);
//设置Xfermode为SRC_IN
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
//创建圆形bitmap，
b222
并画在canvas上
canvas.drawBitmap(createDstBitmap(size), 0, 0, paint);
return bitmap;
}
}
return null;
}</span>

private Bitmap createDstBitmap(int size) {
Bitmap bitmap = Bitmap.createBitmap(size, size, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
int center = size / 2;
Paint paint = new Paint();
paint.setColor(Color.WHITE);
canvas.drawCircle(center, center, center, paint);
return bitmap;
}</span>

运行代码，两个方法的效果图如下：



除上面两张方法实现圆形图像外，还有一种方法，记得上篇文章Android绘制之Canvas中的clipPath方法么？裁剪出一个圆形的canvas，在把bitmap画在canvas上，这样也能到达我们想要的效果，代码如下：

@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Bitmap bitmap = createCirclrBitmapForClip();
if (bitmap != null) {
canvas.drawBitmap(bitmap, 0, 0, new Paint());
}
}

<span style="white-space:pre">	</span>private Bitmap createCirclrBitmapForClip() {
if (mSrcBitmap != null) {
int width = mSrcBitmap.getWidth();
int height = mSrcBitmap.getHeight();
if (width > 0 && height > 0) {
int size = Math.min(width, height);
Bitmap bitmap = Bitmap.createBitmap(size, size, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
clipCirclePath(canvas, size);

Paint paint = new Paint();
canvas.drawBitmap(mSrcBitmap, 0, 0, paint);
return bitmap;
}
}
return null;
}</span>

private void clipCirclePath(Canvas canvas, int size) {
int center = size / 2;
Path path = new Path();
path.addCircle(center, center, center, Path.Direction.CW);
canvas.clipPath(path);
}

运行代码，效果图如下：



源码链接