How to implement canvas animation in uniapp

With the continuous development of mobile applications, animation has become an essential element of modern applications. As a drawing technology provided in HTML5, canvas is widely used to achieve various complex animation effects. Now, with the popularity of uniapp, we can also use the powerful capabilities of uniapp to easily achieve canvas animation effects. This article will introduce in detail how uniapp implements canvas animation.

1. Understanding canvas

Canvas is a new feature of HTML5. It is a drawing technology that can help us draw various shapes, patterns, complex scenes, etc. Compared with DOM operations, canvas's drawing performance is more powerful and can achieve more complex animation effects. The basis of canvas drawing is two commands: draw path and fill path, which is implemented based on JavaScript API.

The steps to implement canvas in uniapp are as follows:

1. Create a canvas in the uniapp project, the code is as follows:

<canvas id="myCanvas" style="width: 100%; height: 100%;"></canvas>

2. Get Canvas context, the code is as follows:

let ctx = uni.createCanvasContext('myCanvas')

3. Use JavaScript API to implement drawing operations in canvas context.

Below we will introduce the specific steps of implementing canvas animation in uniapp through example code.

2. Implementation steps

1. Define animation data

We first define the animation data, including the color, radius and movement speed of each circle, etc. , the code is as follows:

const data = [
  { color: '#0099CC', radius: 50, speed: 4, x: 0, y: 50 },
  { color: '#99CC00', radius: 70, speed: 3, x: 0, y: 100 },
  { color: '#FFBB33', radius: 60, speed: 5, x: 0, y: 150 },
  { color: '#FF4444', radius: 80, speed: 2, x: 0, y: 200 }
]

2. Draw a circle

First we need to draw each circle through the canvas context, the code is as follows:

function draw() {
  for (let i = 0; i < data.length; i++) {
    let item = data[i];
    ctx.beginPath();
    ctx.arc(item.x + item.radius, item.y + item.radius, item.radius, 0, Math.PI * 2, true)
    ctx.closePath()
    ctx.fillStyle = item.color;
    ctx.fill();
  }
  ctx.draw();
}

3. Update data and redraw

Next, we need to update the data that controls the circular animation and redraw it in the canvas context. The code is as follows:

function update() {
  for (let i = 0; i < data.length; i++) {
    let item = data[i];
    item.x += item.speed;
    if (item.x + item.radius >= window.innerWidth) {
      item.speed = -item.speed;
    } else if (item.x - item.radius <= 0) {
      item.speed = -item.speed;
    }
  }
  draw(); // 重新绘制
  setTimeout(update, 1000 / 60); //每秒重绘60次
}

4. Page monitoring

Finally, we monitor the canvas size changes in the onLoad life cycle of the page, automatically adapt to the screen width, and start the animation. The code is as follows:

onLoad() {
  ctx = uni.createCanvasContext('myCanvas');
  const query = uni.createSelectorQuery();
  query.select('#myCanvas').boundingClientRect(rect => {
    const canvas = document.getElementById('myCanvas');
    canvas.width = rect.width;
    canvas.height = rect.height;
  }).exec();
  update();
}

The complete code is as follows:

<script>
  let ctx = null;
  const data = [
    { color: '#0099CC', radius: 50, speed: 4, x: 0, y: 50 },
    { color: '#99CC00', radius: 70, speed: 3, x: 0, y: 100 },
    { color: '#FFBB33', radius: 60, speed: 5, x: 0, y: 150 },
    { color: '#FF4444', radius: 80, speed: 2, x: 0, y: 200 }
  ];

  function draw() {
    for (let i = 0; i < data.length; i++) {
      let item = data[i];
      ctx.beginPath();
      ctx.arc(item.x + item.radius, item.y + item.radius, item.radius, 0, Math.PI * 2, true)
      ctx.closePath()
      ctx.fillStyle = item.color;
      ctx.fill();
    }
    ctx.draw();
  }

  function update() {
    for (let i = 0; i < data.length; i++) {
      let item = data[i];
      item.x += item.speed;
      if (item.x + item.radius >= window.innerWidth) {
        item.speed = -item.speed;
      } else if (item.x - item.radius <= 0) {
        item.speed = -item.speed;
      }
    }
    draw();
    setTimeout(update, 1000 / 60); //每秒重绘60次
  }

  export default {
    onLoad() {
      ctx = uni.createCanvasContext('myCanvas');
      const query = uni.createSelectorQuery();
      query.select('#myCanvas').boundingClientRect(rect => {
        const canvas = document.getElementById('myCanvas');
        canvas.width = rect.width;
        canvas.height = rect.height;
      }).exec();
      update();
    },
  }
</script>

3. Summary

Through the above steps, we can see that with the help of uniapp's capabilities, we can easily achieve canvas animation effects, and at the same time, we can customize the animation style according to needs, which is very flexible and convenient. It is worth mentioning that uniapp also provides many rich components and plug-ins, which can be used to achieve more complex animation effects. It is a tool very suitable for mobile application development.

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