【Android UI】Path 测量 PathMeasure ⑤ ( PathMeasure#getSegment 函数 | 圆形进度条示例 )

open fun getSegment(
    startD: Float, 
    stopD: Float, 
    dst: Path!, 
    startWithMoveTo: Boolean
): Boolean

Given a start and stop distance, return in dst the intervening segment(s). 
If the segment is zero-length, return false, else return true. 
startD and stopD are pinned to legal values (0..getLength()). 
If startD >= stopD then return false (and leave dst untouched). 
Begin the segment with a moveTo if startWithMoveTo is true.

On android.os.Build.VERSION_CODES#KITKAT and earlier releases, 
the resulting path may not display on a hardware-accelerated Canvas. 
A simple workaround is to add a single operation to this path, such as dst.rLineTo(0, 0).

给定开始和停止距离，在dst中返回中间段。
如果段的长度为零，则返回false，否则返回true。
startD和stopD固定为合法值（0..getLength（））。
如果startD>=stopD，则返回false（并保持dst不变）。
如果startWithMoveTo为true，则以moveTo开始该段。

在android上。操作系统。建筑版本代码#KITKAT和早期版本，
结果路径可能不会显示在硬件加速画布上。
一个简单的解决方法是向该路径添加一个操作，例如dst。rLineTo（0，0）。

package kim.hsl.paintgradient.pathmeasure;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.LinearGradient;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PathMeasure;
import android.graphics.RectF;
import android.graphics.Shader;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;

import androidx.annotation.Nullable;

import kim.hsl.paintgradient.R;

public class PathMeasureView extends View {

    public static final String TAG = "PathMeasureView";

    /**
     * 画笔工具
     * 线性渐变渲染 需要设置给该 画笔工具
     */
    private Paint mPaint;

    private Bitmap mBitmap;

    /**
     * 曲线上的点
     */
    private float[] pos = {0F, 0F};
    
    /**
     * 曲线上点的切点
     */
    private float[] tan = {0F, 0F};

    /**
     * 前进百分比, 0F ~ 1F
     */
    private float mProgress;

    public PathMeasureView(Context context) {
        this(context, null);
    }

    public PathMeasureView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public PathMeasureView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initPaint();
        mBitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.ic_launcher);
        Log.i(TAG, "mBitmap : " +mBitmap);
    }

    /**
     * 初始化 画笔工具, 主要是设置该画笔的渲染
     */
    private void initPaint() {
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setColor(Color.GREEN);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeWidth(100);
    }

    @Override
    protected void onSizeChanged(int width, int height, int oldWidth, int oldHeight) {
        super.onSizeChanged(width, height, oldWidth, oldHeight);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        // 每次前进千分之五
        mProgress += 0.005;
        // 到达结束点后, 继续循环运动
        if (mProgress >= 1) mProgress = 0;

        canvas.drawColor(Color.WHITE);
        canvas.translate(getWidth() / 2, getHeight() / 2);

        // 绘制的 Path
        Path path = new Path();

        // 绘制圆形
        path.addCircle(0, 0, 300, Path.Direction.CW);
        mPaint.setColor(Color.GREEN);
        canvas.drawPath(path, mPaint);

        // 圆形曲线测量
        PathMeasure pathMeasure = new PathMeasure(path, false);

        // 截取一段 Path
        Path segment = new Path();
        pathMeasure.getSegment(
                0,
                mProgress * pathMeasure.getLength(),
                segment,
                true);

        mPaint.setColor(Color.RED);
        canvas.drawPath(segment, mPaint);


        // 触发下一次绘制
        invalidate();
    }

}