利用Canvas实现在屏幕随机位置绘制10个大小(边长为10-160)颜色随机的空心五角星
16lz
2021-01-26
Android不但能够显示图片,而且还能够直至一些简单的二维绘图,其实对于我们常见的一些Android基本组件,如TextView、Button等都是系统绘制出来的,其绘制的操作在View类的onDraw(Canvas canvas) 方法中,每个组件都需要实现onDraw(Canvas canvas) 方法进行自定义绘制。
下面实现的是利用Canvas在屏幕随机位置绘制10个大小(边长为10-160)和颜色随机的空心五角星,先看下面的效果图:
利用中学三角函数相关知识,以最左边顶点为基准,五角星的各个拐点点坐标表示如下(草图):
XML文件 :
xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/wujiaoxing" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity"> android:layout_width="wrap_content" android:layout_height="wrap_content" />
MainActavity.java :
package com.example.myapplication;import androidx.appcompat.app.AppCompatActivity;import android.os.Bundle;public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); }}
CanvasView.java :
import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.util.AttributeSet;import android.view.View;import java.util.Random;public class CanvasView extends View { public CanvasView(Context context, AttributeSet attrs) { super(context, attrs); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); //自定义相关三角函数值 float sin18 = (float) Math.sin(18 * Math.PI / 180); float cos18 = (float) Math.cos(18 * Math.PI / 180); float sin36 = (float) Math.sin(36 * Math.PI / 180); float cos36 = (float) Math.cos(36 * Math.PI / 180); float sin27 = (float) Math.sin(27 * Math.PI / 180); float cos27 = (float) Math.cos(27 * Math.PI / 180); float sin54 = (float) Math.sin(54 * Math.PI / 180); float cos54 = (float) Math.cos(54 * Math.PI / 180); Paint paint = new Paint();//定义一个画笔对象 paint.setAntiAlias(true);//设置抗锯齿 paint.setStyle(Paint.Style.STROKE);//设置画笔风格 paint.setStrokeWidth(8);//设置画笔粗细 for(int i=0;i<10;i++) { //随机颜色(rgb)生成 int red = new Random().nextInt(255)+1; int green = new Random().nextInt(255)+1; int blue = new Random().nextInt(255)+1; paint.setColor(Color.rgb(red,green,blue)); //随机(x,y),a生成 float x = (float) (new Random().nextInt(800) + 40); float y = (float) (new Random().nextInt(130)*10+100); float a= (float) (new Random().nextInt(150)+11); //五角星边的绘制 canvas.drawLine(x, y, x + a, y, paint); canvas.drawLine(x + a, y, x + a + a * sin18, y - a * cos18, paint); canvas.drawLine(x + a + a * sin18, y - a * cos18, x + a + 2 * a * sin18, y, paint); canvas.drawLine(x + a + 2 * a * sin18, y, x + 2 * a + 2 * a * sin18, y, paint); canvas.drawLine(x + 2 * a + 2 * a * sin18, y, (x + 2 * a + 2 * a * sin18 - a * cos36), y + a * sin36, paint); canvas.drawLine(x + 2 * a + 2 * a * sin18 - a * cos36, y + a * sin36, x + (2 * a + 2 * a * sin18) * sin54, y + (2 * a + 2 * a * sin18) * cos54, paint); canvas.drawLine(x + (2 * a + 2 * a * sin18) * sin54, y + (2 * a + 2 * a * sin18) * cos54, x + a * sin54 - a * sin27 + a * cos27, y + a * (cos54 + cos27 - sin27), paint); canvas.drawLine(x + a * sin54 - a * sin27 + a * cos27, y + a * (cos54 + cos27 - sin27), x + a * sin54 - a * sin27, y + a * (cos54 + cos27), paint); canvas.drawLine(x + a * sin54 - a * sin27, y + a * (cos54 + cos27), x + a * sin54, y + a * (cos54), paint); canvas.drawLine(x + a * sin54, y + a * (cos54), x, y, paint); } }}
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