Java中使用三角函数

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通过一个简单的demo，学习三角函数的简单使用

注：使用三角函数的时候，不要直接Math.sin(x)，这样是不对的，或者说，你传的30度，进去就不是30度了。要经过转换。详见代码

画一个播放用的view（一个圆，中间一个三角形）
1、效果图：
这里写图片描述
2、计算三角形坐标（拍的照片，有点模糊）

3、代码：
PlayIconView

package com.chen.demo;import android.content.Context;import android.graphics.Canvas;import android.graphics.Paint;import android.graphics.Path;import android.util.AttributeSet;import android.util.Log;import android.view.View;public class PlayIconView extends View {    //圆的画笔    private Paint circlePaint;    //圆的边    private Paint strokePaint;    private int view_width;    private int view_height;    //三角形左上角点坐标    private double point_1_x;    private double point_1_y;    //三角形右下角点坐标    private double point_2_x;    private double point_2_y;    //三角形右侧点坐标    private double point_3_x;    private double point_3_y;    private Paint trianglePaint;    private Path trianglePath;    public PlayIconView(Context context, AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);        init();    }    public PlayIconView(Context context) {        super(context);        init();    }    public PlayIconView(Context context, AttributeSet attrs) {        super(context, attrs);        init();    }    @Override    protected void onSizeChanged(int w, int h, int oldw, int oldh) {        super.onSizeChanged(w, h, oldw, oldh);        Log.e("chen", "onSizeChanged");        view_width = w;        view_height = h;        calculateCoordinate();    }    /**     * 计算坐标     */    private void calculateCoordinate() {        point_1_x = (1 / 2d - 1 / (4 * Math.tan(60 * Math.PI / 180))) * view_width;        point_1_y = view_width / 4d;        point_2_x = point_1_x;        point_2_y = view_width * 3 / 4d;        point_3_x = (1 / 2d + 1 / (4 * Math.sin(60 * Math.PI / 180))) * view_width;        point_3_y = view_height / 2d;        trianglePath.moveTo((float) point_1_x, (float) point_1_y);        trianglePath.lineTo((float) point_2_x, (float) point_2_y);        trianglePath.lineTo((float) point_3_x, (float) point_3_y);        trianglePath.close();    }    /**     * 初始化     */    private void init() {        //背景圆画笔        circlePaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);        circlePaint.setStyle(Paint.Style.FILL);        circlePaint.setColor(0x33000000);        //圆边画笔        strokePaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);        strokePaint.setStyle(Paint.Style.STROKE);        strokePaint.setStrokeWidth(1);        strokePaint.setColor(0xccffffff);        //三角形画笔        trianglePaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);        trianglePaint.setStyle(Paint.Style.FILL);        trianglePaint.setColor(0xffffffff);        //闭合区间路径        trianglePath = new Path();    }    @Override    protected void onDraw(Canvas canvas) {        canvas.drawCircle(view_width / 2f, view_height / 2f, view_width / 2f, circlePaint);        canvas.drawCircle(view_width / 2f, view_height / 2f, view_width / 2f - 1, strokePaint);        canvas.drawPath(trianglePath, trianglePaint);    }}

4、布局文件中使用：

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"                android:layout_width="match_parent"                android:layout_height="match_parent"                android:background="@mipmap/ic_launcher"    >    <com.chen.demo.PlayIconView        android:id="@+id/play_icon"        android:layout_width="40dp"        android:layout_height="40dp"        android:layout_centerInParent="true"        /></RelativeLayout>

5、Activity:

package com.chen.demo;import android.app.Activity;import android.os.Bundle;import android.view.Window;public class MainActivity extends Activity {    private PlayIconView play_icon;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        requestWindowFeature(Window.FEATURE_NO_TITLE);        setContentView(R.layout.activity_main);        play_icon = (PlayIconView) findViewById(R.id.play_icon);    }}

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