小知识，大挑战！本文正在参与“程序员必备小知识”创作活动。

1.Canvas提供的绘制函数

canvas.drawColor();
canvas.drawRGB();
canvas.drawRect();
canvas.drawRoundRect();
canvas.drawCircle();
canvas.drawPath();
canvas.drawLine();
canvas.drawArc();
canvas.drawOval();
canvas.drawPoint();
canvas.drawPoints();
canvas.drawText();
canvas.drawTextOnPath();
canvas.drawBitmap();

2.绘制背景

用于初始化和清空画布

//绘制颜色，默认模式
public void drawColor(@ColorInt int color) {
    super.drawColor(color);
}

//颜色绘制，设置mode
public void drawColor(@ColorInt int color, @NonNull PorterDuff.Mode mode) {
    super.drawColor(color, mode);
}

//参数0-255
public void drawARGB(int a, int r, int g, int b) {
    super.drawARGB(a, r, g, b);
}

//参数0-255
public void drawRGB(int r, int g, int b) {
    super.drawRGB(r, g, b);
}

第二个函数中用到PorterDuff.Mode，PorterDuff.Mode主要用于图像混合模式，后面细说

3.绘制矩形drawRect

//传入RectF 
public void drawRect(@NonNull RectF rect, @NonNull Paint paint) {
    super.drawRect(rect, paint);
}
//传入Rect
public void drawRect(@NonNull Rect r, @NonNull Paint paint) {
    super.drawRect(r, paint);
}

//把Rect的四个点坐标传入
public void drawRect(float left, float top, float right, float bottom, @NonNull Paint paint) {
    super.drawRect(left, top, right, bottom, paint);
}

Rect 和RectF都是提供一个矩形局域。
(1)精度不一样，Rect是使用int类型作为数值，RectF是使用float类型作为数值。
(2)两个类型提供的方法也不是完全一致。

Rect rect = new Rect(100,100,300,300);
RectF rectf = new RectF(100,400,300,600);

canvas.drawRect(rect, mPaint);
canvas.drawRect(rectf, mPaint);
canvas.drawRect(100, 700, 300, 900, mPaint);

4.绘制圆角矩形drawRoundRect

public void drawRoundRect(@NonNull RectF rect, float rx, float ry, @NonNull Paint paint) {
    super.drawRoundRect(rect, rx, ry, paint);
}

//不利用RectF,直接设置四个点
public void drawRoundRect(float left, float top, float right, float bottom, float rx, float ry,
        @NonNull Paint paint) {
    super.drawRoundRect(left, top, right, bottom, rx, ry, paint);
}

rect：RectF对象，一个矩形区域。
rx：x方向上的圆角半径。
ry：y方向上的圆角半径。
paint：绘制时所使用的画笔。

Rect rect = new Rect(100,100,300,300);
RectF rectf = new RectF(100,400,300,600);

canvas.drawRect(rect, mPaint);
canvas.drawRoundRect(rectf, 5, 20, mPaint);
canvas.drawRoundRect(100, 700, 300, 900, 20, 5, mPaint);

5.绘制圆形drawCircle

public void drawCircle(float cx, float cy, float radius, @NonNull Paint paint) {
    super.drawCircle(cx, cy, radius, paint);
}

参数解释：
cx：圆心x
cy：圆心y
radius：半径

canvas.drawCircle(500, 300, 100, mPaint);

6.绘制路径drawPath

public void drawPath(@NonNull Path path, @NonNull Paint paint) {
    super.drawPath(path, paint);
}

需要一个Path

Path path = new Path();
path.moveTo(100, 100);
path.lineTo(100, 200);
path.lineTo(200, 300);
mPaint2.setStrokeJoin(Paint.Join.MITER);
canvas.drawPath(path, mPaint2);

7.绘制直线drawLine

//提供起点，终点和画笔
public void drawLine(float startX, float startY, float stopX, float stopY,
        @NonNull Paint paint) {
    super.drawLine(startX, startY, stopX, stopY, paint);
}

public void drawLines(@Size(multiple = 4) @NonNull float[] pts, int offset, int count,
        @NonNull Paint paint) {
    super.drawLines(pts, offset, count, paint);
}

public void drawLines(@Size(multiple = 4) @NonNull float[] pts, @NonNull Paint paint) {
    super.drawLines(pts, paint);
}

绘制线的集合，参数中pts是点的集合，两个值代表一个点，四个值代表一条线，互相之间不连接。
offset跳过的点，count跳过之后要绘制的点的总数，可以用于集合中部分点的绘制。

canvas.drawLine(500, 500, 500, 300, mPaint);

float[] pos = {20, 30, 40 , 100, 120, 160, 200, 290};
canvas.drawLines(pos, mPaint);

8.绘制圆弧drawArc

public void drawArc(@NonNull RectF oval, float startAngle, float sweepAngle, boolean useCenter,
        @NonNull Paint paint) {
    super.drawArc(oval, startAngle, sweepAngle, useCenter, paint);
}

public void drawArc(float left, float top, float right, float bottom, float startAngle,
        float sweepAngle, boolean useCenter, @NonNull Paint paint) {
    super.drawArc(left, top, right, bottom, startAngle, sweepAngle, useCenter, paint);
}

RectF oval:生成弧的矩形，中心为弧的圆心
float startAngle：弧开始的角度，以X轴正方向为0度，顺时针
float sweepAngle：弧持续的角度
boolean useCenter:是否有弧的两边，True，还两边，False，只有一条弧

RectF rectF = new RectF(100, 100, 400, 400);
canvas.drawArc(rectF, 0, 270, false, mPaint2);

rectF = new RectF(500, 500, 800, 800);
canvas.drawArc(rectF, 0, 270, true, mPaint2);

9.绘制椭圆drawOval

public void drawOval(@NonNull RectF oval, @NonNull Paint paint) {
    super.drawOval(oval, paint);
}
public void drawOval(float left, float top, float right, float bottom, @NonNull Paint paint) {
    super.drawOval(left, top, right, bottom, paint);
}

在矩形框内画一个椭圆，如果是个正方形会画出一个圆。

RectF rectF = new RectF(100, 100, 400, 400);
canvas.drawOval(rectF, mPaint2);

rectF = new RectF(500, 500, 900, 800);
canvas.drawOval(rectF, mPaint2);

10.绘制点drawPoint

public void drawPoint(float x, float y, @NonNull Paint paint) {
    super.drawPoint(x, y, paint);
}

public void drawPoints(@Size(multiple = 2) float[] pts, int offset, int count,
        @NonNull Paint paint) {
    super.drawPoints(pts, offset, count, paint);
}

public void drawPoints(@Size(multiple = 2) @NonNull float[] pts, @NonNull Paint paint) {
    super.drawPoints(pts, paint);
}

只需要提供两个点一个坐标就可以绘制点。

canvas.drawPoint(100, 100, mPaint2);
        
float[] points = {30, 40, 50, 60, 70, 80};
canvas.drawPoints(points, mPaint2);

11.绘制文本drawText 沿路径绘制文本drawTextOnPath

public void drawText(@NonNull char[] text, int index, int count, float x, float y,
        @NonNull Paint paint) {
    super.drawText(text, index, count, x, y, paint);
}

public void drawText(@NonNull String text, float x, float y, @NonNull Paint paint) {
    super.drawText(text, x, y, paint);
}

public void drawText(@NonNull String text, int start, int end, float x, float y,
        @NonNull Paint paint) {
    super.drawText(text, start, end, x, y, paint);
}

public void drawText(@NonNull CharSequence text, int start, int end, float x, float y,
        @NonNull Paint paint) {
    super.drawText(text, start, end, x, y, paint);
}

canvas.drawText("MatumbaMan的博客",100,100,mTextPaint);

Path path = new Path();
path.addArc(new RectF(100, 100, 600, 600), 0, 260);
canvas.drawTextOnPath("MatumbaMan的博客", path, 10, 20, mTextPaint);

canvas.drawText("MatumbaMan的博客",100,100, mTextPaint);

drawTextOnPath
沿着一条 Path 来绘制文字
text 为所需要绘制的文字
path 为文字的路径
hOffset 文字相对于路径的水平偏移量，用于调整文字的位置
vOffset 文字相对于路径竖直偏移量，用于调整文字的位置

12.绘制bitmap drawBitmap

public void drawBitmap(@NonNull Bitmap bitmap, @Nullable Rect src, @NonNull RectF dst,
        @Nullable Paint paint) {
    super.drawBitmap(bitmap, src, dst, paint);
}

public void drawBitmap(@NonNull Bitmap bitmap, @Nullable Rect src, @NonNull Rect dst,
        @Nullable Paint paint) {
    super.drawBitmap(bitmap, src, dst, paint);
}

Rect src：指定绘制图片的区域
Rect dst或RectF dst：指定图片在屏幕上的绘制（显示）区域
首先指定图片区域，然后指定绘制图片的区域。

Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.rocket2);
canvas.drawBitmap(bitmap, 100, 100, mPaint);

Rect src = new Rect(0, 0, 100,100);
Rect dst = new Rect(200, 500, 300, 600);
canvas.drawBitmap(bitmap, src, dst, mPaint);

Android原生绘图（二）：Canvas