学习往往是枯燥的，如果能用一个有趣 Demo 来学习和练习技术，那对知识的掌握就会更牢固。我在学习 Canvas 绘制 API 的时候就是这样做的。
❞其实很简单
首先找到一张小黄人的图
然后调用 canvas.drawBitmap() 后画到画布上 好吧，一点都不好笑 - -。
正文 ↓
自定义MinionView extends View，定义以下成员变量，备用（可以先不看，后面的代码看到莫名其妙出来的变量再上来看下）
private float bodyWidth; private float bodyHeight; private static final float BODY_SCALE = 0.6f; // 身体主干占整个view的比重 private static final float BODY_WIDTH_HEIGHT_SCALE = 0.6f; // 身体的比例设定为 w:h = 3:5 private float mStrokeWidth = 4; // 描边宽度 private float offset; // 计算时，部分需要 考虑描边偏移 private float radius; // 身体上下半圆的半径 private int colorClothes = Color.rgb(32, 116, 160); // 衣服的颜色 private int colorBody = Color.rgb(249, 217, 70); // 身体的颜色 private int colorStroke = Color.BLACK; private RectF bodyRect = new RectF(); private float handsHeight;// 计算出吊带的高度时，可以用来做手的高度 private float footHeight; // 脚的高度，用来画脚部阴影时用重写 onSizeChanged 方法，尺寸变化时初始化一下绘制的参数（会经常看到一些奇怪的数字，用做比例换算，别问我怎么来的，目测 + 一点点微调得来的- -。）
private void initParams() { bodyWidth = Math.min(getWidth(), getHeight() * BODY_WIDTH_HEIGHT_SCALE) * BODY_SCALE; bodyHeight = Math.min(getWidth(), getHeight() * BODY_WIDTH_HEIGHT_SCALE) / BODY_WIDTH_HEIGHT_SCALE * BODY_SCALE; mStrokeWidth = Math.max(bodyWidth / 50, mStrokeWidth); offset = mStrokeWidth / 2; bodyRect.left = (getWidth() - bodyWidth) / 2; bodyRect.top = (getHeight() - bodyHeight) / 2; bodyRect.right = bodyRect.left + bodyWidth; bodyRect.bottom = bodyRect.top + bodyHeight; radius = bodyWidth / 2; footHeight = radius * 0.4333f; handsHeight = (getHeight() + bodyHeight) / 2 + offset - radius * 1.65f; }绘制参数好了，接下来就是一步步绘制几何图形了
显然身体是一个矩形加上，上下半圆，这边只要用一个圆角矩形，然后圆角的弧度半径用身体宽度的一半就可以达到这个效果了。把身体的矩形外存起来，后面经常要用到其相对位置进行对其它部位的定位，代码如下:
protected void onDraw(Canvas canvas) { ... drawBody(canvas); // 身体 drawBodyStroke(canvas); // 最后画身体的描边，可以摭住一些过渡的棱角 } private void drawBody(Canvas canvas) { mPaint.setColor(colorBody); mPaint.setStyle(Paint.Style.FILL); canvas.drawRoundRect(bodyRect, radius, radius, mPaint); } private void drawBodyStroke(Canvas canvas) { mPaint.setColor(colorStroke); mPaint.setStrokeWidth(mStrokeWidth); mPaint.setStyle(Paint.Style.STROKE); canvas.drawRoundRect(bodyRect, radius, radius, mPaint); }首先画 底下的半圆
rect.left = (getWidth() - bodyWidth) / 2 + offset; rect.top = (getHeight() + bodyHeight) / 2 - radius * 2 + offset; rect.right = rect.left + bodyWidth - offset * 2; rect.bottom = rect.top + radius * 2 - offset * 2; mPaint.setColor(colorClothes); mPaint.setStyle(Paint.Style.FILL); mPaint.setStrokeWidth(mStrokeWidth); canvas.drawArc(rect, 0, 180, true, mPaint);再画半圆上方的矩形, w 表示矩形离左边身体的距离，h 矩形的高
int h = (int) (radius * 0.5); int w = (int) (radius * 0.3); rect.left += w; rect.top = rect.top + radius - h; rect.right -= w; rect.bottom = rect.top + h; canvas.drawRect(rect, mPaint);上面的画完之后，要在衣服上面描一层黑色的边，用canvas.drawLines把线一条条画出来吧，这边要同时考虑画笔的描边宽度，否则会出现连接点有锯齿的感觉。（ 2020 注：这是当时最直接的想法，现在来看用 Path 来绘制，每个点用 rLineTo 去连接，代码会简单得多。）
mPaint.setColor(colorStroke); mPaint.setStyle(Paint.Style.FILL); mPaint.setStrokeWidth(mStrokeWidth); float[] pts = new float[20];// 5 条线 pts[0] = rect.left - w; pts[1] = rect.top + h; pts[2] = pts[0] + w; pts[3] = pts[1]; pts[4] = pts[2]; pts[5] = pts[3] + offset; pts[6] = pts[4]; pts[7] = pts[3] - h; pts[8] = pts[6] - offset; pts[9] = pts[7]; pts[10] = pts[8] + (radius - w) * 2; pts[11] = pts[9]; pts[12] = pts[10]; pts[13] = pts[11] - offset; pts[14] = pts[12]; pts[15] = pts[13] + h; pts[16] = pts[14] - offset; pts[17] = pts[15]; pts[18] = pts[16] + w; pts[19] = pts[17]; canvas.drawLines(pts, mPaint);画吊带 就是一个直角梯形，把梯形的四个顶点计算出来，使用canvas.drawPath将其画上去，然后纽扣用一个实心的小圆表示
// 画左吊带 path.reset(); path.moveTo(rect.left - w - offset, handsHeight); path.lineTo(rect.left + h / 4f, rect.top + h / 2f); final float smallW = w / 2f * (float) Math.sin(Math.PI / 4); path.lineTo(rect.left + h / 4f + smallW, rect.top + h / 2f - smallW); final float smallW2 = w / (float) Math.sin(Math.PI / 4) / 2; path.lineTo(rect.left - w - offset, handsHeight - smallW2); canvas.drawPath(path, mPaint); mPaint.setColor(colorStroke); mPaint.setStrokeWidth(mStrokeWidth); mPaint.setStyle(Paint.Style.STROKE); canvas.drawPath(path, mPaint); mPaint.setStyle(Paint.Style.FILL_AND_STROKE); canvas.drawCircle(rect.left + h / 5f, rect.top + h / 4f, mStrokeWidth * 0.7f, mPaint); // 画右吊带，代码差不多省略了，坐标对称画中间的口袋 是一个下面两边是圆角的圆角矩形，但是貌似不能直接画这样的圆角矩形，所以我就用土办法，不就是一个多边形吗，用canvas.drawPath来画，在圆角的地方添加圆弧过渡path.addArc
path.reset(); float radiusBigPocket = w / 2.0f; path.moveTo(rect.left + 1.5f * w, rect.bottom - h / 4f); path.lineTo(rect.right - 1.5f * w, rect.bottom - h / 4f); path.lineTo(rect.right - 1.5f * w, rect.bottom + h / 4f); path.addArc(rect.right - 1.5f * w - radiusBigPocket * 2, rect.bottom + h / 4f - radiusBigPocket, rect.right - 1.5f * w, rect.bottom + h / 4f + radiusBigPocket, 0, 90); path.lineTo(rect.left + 1.5f * w + radiusBigPocket, rect.bottom + h / 4f + radiusBigPocket); path.addArc(rect.left + 1.5f * w, rect.bottom + h / 4f - radiusBigPocket, rect.left + 1.5f * w + 2 * radiusBigPocket, rect.bottom + h / 4f + radiusBigPocket, 90, 90); path.lineTo(rect.left + 1.5f * w, rect.bottom - h / 4f - offset); canvas.drawPath(path, mPaint);左右两个小口袋也直接用一个小弧来解决掉
// 下边一竖，分开裤子 canvas.drawLine(bodyRect.left + bodyWidth / 2, bodyRect.bottom - h * 0.8f, bodyRect.left + bodyWidth / 2, bodyRect.bottom, mPaint); // 左边的小口袋 float radiusSmallPocket = w * 1.2f; canvas.drawArc(bodyRect.left - radiusSmallPocket, bodyRect.bottom - radius - radiusSmallPocket, bodyRect.left + radiusSmallPocket, bodyRect.bottom - radius + radiusSmallPocket, 80, -60, false, mPaint); // 右边小口袋 canvas.drawArc(bodyRect.right - radiusSmallPocket, bodyRect.bottom - radius - radiusSmallPocket, bodyRect.right + radiusSmallPocket, bodyRect.bottom - radius + radiusSmallPocket, 100, 60, false, mPaint);嗯，衣服画完了。
protected void onDraw(Canvas canvas) { ... drawClothes(canvas);//衣服 } private void drawClothes(Canvas canvas) { //就是上面那一堆代码按顺序合起来啦。。。。。 }脚这部分比较简单，从身体的下方，一个竖直的矩形下来，再加上一个左边圆角的圆角矩形，还是通过画Path来实现。
private void drawFeet(Canvas canvas) { mPaint.setStrokeWidth(mStrokeWidth); mPaint.setColor(colorStroke); mPaint.setStyle(Paint.Style.FILL_AND_STROKE); float radiusFoot = radius / 3 * 0.4f; float leftFootStartX = bodyRect.left + radius - offset * 2; float leftFootStartY = bodyRect.bottom - offset; float footWidthA = radius * 0.5f;//脚宽度大-到半圆结束 float footWidthB = footWidthA / 3;//脚宽度-比较细的部分 // 左脚 path.reset(); path.moveTo(leftFootStartX, leftFootStartY); path.lineTo(leftFootStartX, leftFootStartY + footHeight); path.lineTo(leftFootStartX - footWidthA + radiusFoot, leftFootStartY + footHeight); rect.left = leftFootStartX - footWidthA; rect.top = leftFootStartY + footHeight - radiusFoot * 2; rect.right = rect.left + radiusFoot * 2; rect.bottom = rect.top + radiusFoot * 2; path.addArc(rect, 90, 180); path.lineTo(rect.left + radiusFoot + footWidthB, rect.top); path.lineTo(rect.left + radiusFoot + footWidthB, leftFootStartY); path.lineTo(leftFootStartX, leftFootStartY); canvas.drawPath(path, mPaint); // 右脚与左脚实现一致，坐标对称，代码略 }手我用的是一个等腰直角三角形来实现，斜边就是吊带到裤子，从直角顶点作高到斜边，通过小直角三角形的直角边相等就可以算出顶点的坐标。这个时候还是有个圆角，刚开始我实现的时候是像上面那些通过path.addArc加上圆角，但是这边计算好之后和原来的衔接一直有问题，在调了半天之后，偶然发现mPaint.setPathEffect(new CornerPathEffect(radiusHand));这个方法，可以使path的拐角用圆角来过渡，一下子就简单到爆了，果然科学技术是第一生产力。
private void drawHands(Canvas canvas) { ... // 左手 path.moveTo(bodyRect.left, handsHeight); path.lineTo(bodyRect.left - hypotenuse / 2, handsHeight + hypotenuse / 2); path.lineTo(bodyRect.left +offset, bodyRect.bottom - radius +offset); path.lineTo(bodyRect.left, handsHeight); canvas.drawPath(path, mPaint); mPaint.setStrokeWidth(mStrokeWidth); mPaint.setStyle(Paint.Style.STROKE); mPaint.setColor(colorStroke); canvas.drawPath(path, mPaint); // 右手略 ... // 手臂内侧拐点 path.reset(); mPaint.setStyle(Paint.Style.FILL); path.moveTo(bodyRect.left, handsHeight + hypotenuse / 2 - mStrokeWidth); path.lineTo(bodyRect.left - mStrokeWidth * 2, handsHeight + hypotenuse / 2 + mStrokeWidth * 2); path.lineTo(bodyRect.left, handsHeight + hypotenuse / 2 + mStrokeWidth); canvas.drawPath(path, mPaint); ... }反正就是各种画圆，或者弧形，嘴巴部分偷懒也就一条小弧一笔带过了，哈哈
private void drawEyesMouth(Canvas canvas) { // 眼睛中心处于上半圆直径 往上的高度偏移 float eyesOffset = radius * 0.1f; mPaint.setStrokeWidth(mStrokeWidth * 5); // 计算眼镜带弧行的半径 分两段，以便眼睛中间有隔开的效果 float radiusGlassesRibbon = (float) (radius / Math.sin(Math.PI / 20)); rect.left = bodyRect.left + radius - radiusGlassesRibbon; rect.top = bodyRect.top + radius - (float) (radius / Math.tan(Math.PI / 20)) - radiusGlassesRibbon - eyesOffset; rect.right = rect.left + radiusGlassesRibbon * 2; rect.bottom = rect.top + radiusGlassesRibbon * 2; canvas.drawArc(rect, 81, 3, false, mPaint); canvas.drawArc(rect, 99, -3, false, mPaint); // 眼睛半径 float radiusEyes = radius / 3; mPaint.setColor(Color.WHITE); mPaint.setStrokeWidth(mStrokeWidth); mPaint.setStyle(Paint.Style.FILL); canvas.drawCircle(bodyRect.left + bodyWidth / 2 - radiusEyes - offset, bodyRect.top + radius - eyesOffset, radiusEyes, mPaint); canvas.drawCircle(bodyRect.left + bodyWidth / 2 + radiusEyes + offset, bodyRect.top + radius - eyesOffset, radiusEyes, mPaint); mPaint.setColor(colorStroke); mPaint.setStyle(Paint.Style.STROKE); canvas.drawCircle(bodyRect.left + bodyWidth / 2 - radiusEyes - offset, bodyRect.top + radius - eyesOffset, radiusEyes, mPaint); canvas.drawCircle(bodyRect.left + bodyWidth / 2 + radiusEyes + offset, bodyRect.top + radius - eyesOffset, radiusEyes, mPaint); final float radiusEyeballBlack = radiusEyes / 3; mPaint.setStyle(Paint.Style.FILL); canvas.drawCircle(bodyRect.left + bodyWidth / 2 - radiusEyes - offset, bodyRect.top + radius - eyesOffset, radiusEyeballBlack, mPaint); canvas.drawCircle(bodyRect.left + bodyWidth / 2 + radiusEyes + offset, bodyRect.top + radius - eyesOffset, radiusEyeballBlack, mPaint); mPaint.setColor(Color.WHITE); final float radiusEyeballWhite = radiusEyeballBlack / 2; canvas.drawCircle(bodyRect.left + bodyWidth / 2 - radiusEyes + radiusEyeballWhite - offset * 2, bodyRect.top + radius - radiusEyeballWhite + offset - eyesOffset, radiusEyeballWhite, mPaint); canvas.drawCircle(bodyRect.left + bodyWidth / 2 + radiusEyes + radiusEyeballWhite, bodyRect.top + radius - radiusEyeballWhite + offset - eyesOffset, radiusEyeballWhite, mPaint); // 画嘴巴，因为位置和眼睛有相对关系，所以写在一块 mPaint.setColor(colorStroke); mPaint.setStyle(Paint.Style.STROKE); mPaint.setStrokeWidth(mStrokeWidth); float radiusMonth = radius; rect.left = bodyRect.left; rect.top = bodyRect.top - radiusMonth / 2.5f; rect.right = rect.left + radiusMonth * 2; rect.bottom = rect.top + radiusMonth * 2; canvas.drawArc(rect, 95, -20, false, mPaint); }这是最后一步了，直接画一个非常扁的椭圆放在脚下面就可以了
不科学啊，长这么胖，为毛影子这么瘦（别在意这些细节） private void drawFeetShadow(Canvas canvas) { mPaint.setColor(getResources().getColor(android.R.color.darker_gray)); canvas.drawOval(bodyRect.left + bodyWidth * 0.15f, bodyRect.bottom - offset + footHeight, bodyRect.right - bodyWidth * 0.15f, bodyRect.bottom - offset + footHeight + mStrokeWidth * 1.3f, mPaint); }按层级依次调用上述的各种方法，画完收工。
@Override protected void onDraw(Canvas canvas) { drawFeetShadow(canvas); // 脚下的阴影 drawFeet(canvas); // 脚 drawHands(canvas); // 手 drawBody(canvas); // 身体 drawClothes(canvas); // 衣服 drawEyesMouth(canvas); // 眼睛,嘴巴 drawBodyStroke(canvas); // 最后画身体的描边，可以摭住一些过渡的棱角 }画完了，好像少了点什么。。。。。对了，头发。好吧，我画的是程序猿，哪来的头发 - -
❝至此，正常画风的小黄人已经画完了，但是吧，好不容易画好，好像没啥意思，脑洞大开一下吧。电影中的小黄人中病毒后是会变成紫色的，那我们用代码画，换个颜色还不是分分钟，不但要紫色，还要各种颜色。
❞然后效果就变成了这样。
看起来还有点小酷炫 希望大家喜欢，完整源码在 github ，可点击“阅读原文”查看推荐阅读RecyclerView的缓存复用机制你亲手写的代码，正在出卖你深夜，聊聊设计模式
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