[Java] [View] 绘制曲线（其实是函数）

前言

今天一时兴起，打算扔掉贝塞尔曲线，自己定义曲线，然后就做到函数上去了…

代码

package com.Diamond.canvas;

import android.view.View;
import android.content.Context;
import android.renderscript.Float2;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.Log;

public class CurveView extends View {
    public Bitmap bitmap;

    public CurveView(Context context, Float2 start, Float2 vec, Float2 vec2, int end_time) {
        super(context);

        bitmap = Bitmap.createBitmap(1080, 2160, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap);
        Paint paint = new Paint();

        paint.setARGB(255, 0, 0, 255);
        canvas.drawARGB(255, 255, 255, 255);
        Float2 position = start;
        for (int t = 0; t < end_time; t++) {
            Float2 last = new Float2(position.x, position.y);

            position.x += vec.x;
            position.y += vec.y;

            vec.x += vec2.x;
            vec.y += vec2.y;

            canvas.drawLine(last.x, last.y, position.x, position.y, paint);

            Log.d("" + t, position.x + "," + position.y);
        }
    }

    public CurveView(Context context, float start, float end,float step, String xexp, String yexp) {
        super(context);
        
        bitmap = Bitmap.createBitmap(1080, 2160, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap);
        Paint paint = new Paint();
        paint.setARGB(255, 0, 0, 255);
        canvas.drawARGB(255, 255, 255, 255);
        
        Float2 position = new Float2();
        position.x = anal(start,xexp);
        position.y = anal(start,yexp);
        for (float t = start + 1; t < end; t += step) {
            Float2 last = new Float2(position.x, position.y);
            
            position.x = anal(t,xexp);
            position.y = anal(t,yexp);
            
            canvas.drawLine(last.x,last.y,position.x,position.y,paint);
        }
    }

    public static float anal(float t, String exp) {
        float total = 0;
        String[] items = exp.split("[+]+");
        for (int i = 0; i < items.length; i++) {
            String sub = items[i];
            String number = "";
            float product = 1;
            for (int j = 0; j < sub.length(); j++) {
                char ch = sub.charAt(j);
                if (ch == 't') {
                    product *= t;
                } else if(ch == 'r') {
                    product *= 1.0f / t;
                } else if (ch == '*') {
                    if (number.length() > 0) {
                        float num = Float.parseFloat(number);
                        product *= num;
                    }
                    number = "";
                } else {
                    number += ch;
                }
            }
            if (number.length() > 0) {
                float num = Float.parseFloat(number);
                product *= num;
            }
            total += product;
        }
        return total;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawBitmap(bitmap, 0, 0, null);
        super.onDraw(canvas);           
    }
}

示例

 CurveView qf = new CurveView(this,-540,540,10,"t+540","-0.01*t*t+1080");

最初的想法

这个是我最初打算做的，用一个类似海龟（Turtle）的东西绘制，有速度以及速度增量，可以画出一些不知道怎么操作的曲线
额，第一个构造函数其实是Int2类型，被文本替换一不小心全替换掉了…

anal（analysis）

public static float anal(float t, String exp)
这个函数干掉了我许多脑细胞
功能挺简单的
变量是t，r是1/t，用于反比例函数
不支持开方什么的
示例：

anal(10,"t*t");
anal(10,"1*r");
anal(10,"t+-1");//因为只能写+，所以减法要+-

最后再把实现给各位看看，顺便水水字数

public static float anal(float t, String exp) {
        float total = 0;
        String[] items = exp.split("[+]+");
        for (int i = 0; i < items.length; i++) {
            String sub = items[i];
            String number = "";
            float product = 1;
            for (int j = 0; j < sub.length(); j++) {
                char ch = sub.charAt(j);
                if (ch == 't') {
                    product *= t;
                } else if(ch == 'r') {
                    product *= 1.0f / t;
                } else if (ch == '*') {
                    if (number.length() > 0) {
                        float num = Float.parseFloat(number);
                        product *= num;
                    }
                    number = "";
                } else {
                    number += ch;
                }
            }
            if (number.length() > 0) {
                float num = Float.parseFloat(number);
                product *= num;
            }
            total += product;
        }
        return total;
    }