渐变色动画

Question

我想要达到的目标：

径向渐变，起始颜色和结束颜色随着时间的推移从一种定义的颜色平滑地变化到另一种定义的颜色。

到目前为止我所做的尝试：

像这样使用 ObjectAnimator：

        searchAnimator = ObjectAnimator.ofFloat(drawThread, new Property<DrawThread, Float>(Float.TYPE, "fraction") {
            @Override
            public Float get(DrawThread object) {
                return object.fraction;
            }

            @Override
            public void set(DrawThread object, Float value) {
                object.setFraction(value);
            }
        }, 0, 1);
        searchAnimator.setDuration(maxSearchDuration);
        searchAnimator.setInterpolator(new LinearInterpolator());

随着时间的推移，这将调用DrawThread.setFraction(value);。在线程内部，我使用SurfaceView 执行Canvas 绘图，如下所示：

mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setDither(true);
mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
radius = (int) Math.sqrt(canvas.getWidth() / 2 * canvas.getWidth() / 2 + canvas.getHeight() / 2 * canvas.getHeight() / 2);
//calculating colors for current fraction using ARGBEvaluator
int start = (int) argbEvaluator.evaluate(fraction, colors[0].start, colors[1].start);
int end = (int) argbEvaluator.evaluate(fraction, colors[0].end, colors[1].end);
//end
mPaint.setShader(new RadialGradient(canvas.getWidth() / 2, canvas.getHeight() / 2,
      radius, start, end, Shader.TileMode.CLAMP));
canvas.drawCircle(canvas.getWidth() / 2, canvas.getHeight() / 2, radius, mPaint);

问题：

1. 渐变不平滑。图片看起来颜色很浅
2. 性能非常低。我在全高清 Snapdragon 801 设备上获得了大约 16 FPS。

所以我想问的是在提高性能（甚至完全不同的方式）和提高图像质量方面的任何帮助。

Answer 1

您可以像这样在渐变中为颜色变化设置动画：

int colorFrom = ContextCompat.getColor(this, R.color.red);
int colorTo = ContextCompat.getColor(this, R.color.blue);
ValueAnimator colorAnimation = ValueAnimator.ofObject(new ArgbEvaluator(), colorFrom, colorTo);
colorAnimation.setDuration(2000);

int color1 = ContextCompat.getColor(this, R.color.red);
int color2 = ContextCompat.getColor(this, R.color.green);
GradientDrawable gradientDrawable = new GradientDrawable(
            GradientDrawable.Orientation.TOP_BOTTOM, new int[]{color1, color2});
gradientDrawable.setGradientType(GradientDrawable.LINEAR_GRADIENT);

colorAnimation.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {

        @Override
        public void onAnimationUpdate(ValueAnimator animator) {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
                gradientDrawable.setColors(new int[]{(int) animator.getAnimatedValue(), color2});
                viewWithGradientBg.setBackground(gradientDrawable);
            }
        }

    });

colorAnimation.start();

Kotlin 变体：

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    val colorFrom = ContextCompat.getColor(requireContext(), android.R.color.holo_red_dark)
    val colorTo = ContextCompat.getColor(requireContext(), android.R.color.holo_blue_dark)
    val colorAnimation = ValueAnimator.ofObject(ArgbEvaluator(), colorFrom, colorTo)
    colorAnimation.duration = 2000
    val color1 = ContextCompat.getColor(requireContext(), android.R.color.holo_red_dark)
    val color2 = ContextCompat.getColor(requireContext(), android.R.color.holo_blue_dark)
    val gradientDrawable = GradientDrawable(GradientDrawable.Orientation.TL_BR, intArrayOf(color1, color2))
    gradientDrawable.gradientType = GradientDrawable.RADIAL_GRADIENT
    colorAnimation.addUpdateListener { animator ->
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            gradientDrawable.colors = intArrayOf(animator.animatedValue as Int, color2)
            viewWithGradientBg.background = gradientDrawable
        }
    }
    gradientDrawable.gradientRadius = 140f;
    gradientDrawable.setGradientCenter(0.5f, 0.5f);
    colorAnimation.repeatCount = INFINITE
    colorAnimation.start()
}

Answer 2

也许这段伪代码有帮助：

private ValueAnimator colorAnimation;

  colorAnimation = ValueAnimator.ofObject(new ArgbEvaluator(), startColor, endColor); 
                                                          // you can add more colors here 

    colorAnimation.addUpdateListener(new AnimatorUpdateListener() {

        @Override
        public void onAnimationUpdate(ValueAnimator animator) {
            yourView.setBackgroundColor((Integer) animator
                    .getAnimatedValue());
        }

    });

    colorAnimation.setDuration(maxSearchDuration);
    colorAnimation.start();
}