/**
     * Create a shader that draws a linear gradient along a line.
     *
     * @param x0           The x-coordinate for the start of the gradient line
     * @param y0           The y-coordinate for the start of the gradient line
     * @param x1           The x-coordinate for the end of the gradient line
     * @param y1           The y-coordinate for the end of the gradient line
     * @param colors       The sRGB colors to be distributed along the gradient line
     * @param positions    May be null. The relative positions [0..1] of
     *                     each corresponding color in the colors array. If this is null,
     *                     the the colors are distributed evenly along the gradient line.
     * @param tile         The Shader tiling mode
     * 
     * 
     * 翻譯過來：
     * x0，y0為漸變起點，x1，y1為漸變的終點
     * 
     * colors數(shù)組為兩點間的漸變顏色值，positions數(shù)組取值范圍是0~1
     * 傳入的colors[]長度和positions[]長度必須相等，一一對應(yīng)關(guān)系，否則報錯
     * position傳入null則代表colors均衡分布
     * 
     * tile有三種模式
     * Shader.TileMode.CLAMP：    邊緣拉伸模式，它會拉伸邊緣的一個像素來填充其他區(qū)域
     * Shader.TileMode.MIRROR：    鏡像模式，通過鏡像變化來填充其他區(qū)域
     * Shader.TileMode.REPEAT：重復(fù)模式，通過復(fù)制來填充其他區(qū)域
     */
LinearGradient(float x0, float y0, float x1, float y1, @NonNull @ColorInt int[] colors,
            @Nullable float[] positions, @NonNull TileMode tile)

LinearGradient(a的x坐標, a的y坐標, c的x坐標, c的y坐標, new int[]{Color.parseColor("#00FFFFFF"), Color.parseColor("#FFFFFFFF"), Color.parseColor("#00FFFFFF")}, new float[]{0f, 0.5f, 1f}, Shader.TileMode.CLAMP)

/**
 * author: caoyb
 * created on: 2021/12/20 15:13
 * description:
 */
public class ConfigLoadingView extends View {

    private Paint mPaint;
    private Path mPath;
    private LinearGradient mLinearGradient;
    private ValueAnimator mValueAnimator;

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

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

    public ConfigLoadingView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        mPaint = new Paint();
        mPath = new Path();
    }

    private void initPointAndAnimator(int w, int h) {
        Point point1 = new Point(0, 0);
        Point point2 = new Point(w, 0);
        Point point3 = new Point(w, h);
        Point point4 = new Point(0, h);

        mPath.moveTo(point1.x, point1.y);
        mPath.lineTo(point2.x, point2.y);
        mPath.lineTo(point3.x, point3.y);
        mPath.lineTo(point4.x, point4.y);
        mPath.close();

		// 斜率k
        float k = 1f * h / w;
        // 偏移
        float offset = 1f * w / 2;
		// 0f - offset * 2 為數(shù)值左邊界（屏幕外左側(cè)）， w + offset * 2為數(shù)值右邊界（屏幕外右側(cè)）
		// 目的是使光影走完一遍，加一些時間緩沖，不至于每次光影移動的間隔都那么急促
        mValueAnimator = ValueAnimator.ofFloat(0f - offset * 2, w + offset * 2);
        mValueAnimator.setRepeatCount(-1);
        mValueAnimator.setInterpolator(new LinearInterpolator());
        mValueAnimator.setDuration(1500);
        mValueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                float value = (float) animation.getAnimatedValue();
                mLinearGradient = new LinearGradient(value, k * value, value + offset, k * (value + offset),
                        new int[]{Color.parseColor("#00FFFFFF"), Color.parseColor("#1AFFFFFF"), Color.parseColor("#00FFFFFF")}, null, Shader.TileMode.CLAMP);
                mPaint.setShader(mLinearGradient);
                invalidate();
            }
        });
        mValueAnimator.start();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        initPointAndAnimator(widthSize, heightSize);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawPath(mPath, mPaint);
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        mValueAnimator.cancel();
    }
}