如何为 CSS 渐变停止设置动画并平滑过渡到透明？

Question

我有下面的代码。如何平滑地过渡渐变停止？它只是突然从一个变为另一个。

我见过的大多数渐变动画示例似乎都使用渐变位置，但我相信改变渐变停止点也应该是可能的。

.test {
    display: inline-block;
    width: 300px;
    height: 300px;
    border-radius: 100%;
    background: conic-gradient(red, red);
    background-repeat: no-repeat;
    background-size: cover;
    background-position: center center;
    background-size: auto;
    -webkit-mask:radial-gradient(circle, transparent 50%, white calc(50% + 1px));

    animation:
        rotate
        4.5s
        ease-out
        0s
        infinite
        none
        running;
}

@keyframes rotate {
    0% {
        background-image: conic-gradient(red, red);
    }

    30% {
        background-image: conic-gradient(red 70%, transparent);
    }

    70% {
        background-image: conic-gradient(red 30%, transparent, transparent, transparent);
    }

    100% {
        background-image: conic-gradient(red, transparent);
    }
}

<div class="test"></div>

Answer 1

在这种特殊情况下，您可以像下面这样为背景色图层设置动画：

.test {
    display: inline-block;
    width: 300px;
    height: 300px;
    border-radius: 100%;
    background: 
      conic-gradient(red, transparent)
      red;
    -webkit-mask:radial-gradient(circle, transparent 50%, white calc(50% + 1px));

    animation:
        rotate
        4.5s
        ease-out
        0s
        infinite
        none
        running;
}
@keyframes rotate {
    100% {
        background-color:blue;
    }
}

<div class="test"></div>

更新

这是另一个结合不透明度和渐变动画的想法（有点小问题，但会尝试优化它）

.test {
  display: inline-block;
  width: 300px;
  height: 300px;
  border-radius: 100%;
  background: conic-gradient(red 70%, transparent);
  animation: grad1 3s linear infinite;
  -webkit-mask: radial-gradient(circle, transparent 50%, white calc(50% + 1px));
  position: relative;
}

.test::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  opacity: 1;
  background: conic-gradient(red, red);
  animation: 
    op 1s   linear infinite,
    grad 3s linear infinite;
}

@keyframes op {
  100% {
    opacity: 0;
  }
}

@keyframes grad {
  0%,
  33.32% {
    background: conic-gradient(red, red);
  }
  33.328%,
  66.65% {
    background: conic-gradient(red 70%, transparent);
  }
  66.658%,
  100% {
    background: conic-gradient(red 30%, transparent);
  }
}

@keyframes grad1 {
  0%,
  33.32% {
    background: conic-gradient(red 70%, transparent);
  }
  33.328%,
  66.65% {
    background: conic-gradient(red 30%, transparent);
  }
  66.658%,
  100% {
    background: conic-gradient(red, transparent);
  }
}

<div class="test"></div>

Answer 2

截至 2020 年 12 月 3 日，这仅适用于 Chrome 或 Edge 95+

可以使用 CSS @property.

设置渐变动画

@property --opacity {
  syntax: '<percentage>';
  initial-value: 100%;
  inherits: false;
}

.test {
    display: inline-block;
    position: absolute;
    border-radius: 100%;
    background-image: conic-gradient(
        red var(--opacity),
        red 10%,
        rgba(255, 0, 0, var(--opacity)),
        transparent,
        transparent
    );
    will-change: transform, background-image;
    width: 200px;
    height: 200px;
    mask:radial-gradient(circle, transparent 47%, white calc(47% + 1px));
    -webkit-mask:radial-gradient(circle, transparent 47%, white calc(47% + 1px));

    animation:
        conic-gradient
            4.5s
            ease-out
            0s
            infinite
            none
            running;
}

@keyframes conic-gradient {
    50% {
        --opacity: 0%;
    }

    85% {
        --opacity: 100%;
    }
}

<div class="test"></div>

如何为 CSS 渐变停止设置动画并平滑过渡到透明？

How do I animate a CSS gradient stop with a smooth transition to transparent?

css

animation

gradient

gradientstop