html：canvas画布绘图简单入门-2

<canvas 
  width="600" 
  height="700" 
  style="width:800px; height:900px">
</canvas>

<canvas id="canvas"
            width="600"
            height="600"></canvas>
<script>
    let canvas = document.querySelector('#canvas');
    let ctx = canvas.getContext('2d');
    ctx.fillStyle = "red";
    ctx.fillRect(0, 0, 50, 50);
    let imageData = ctx.getImageData(0, 0, 50, 50);
    console.log(imageData);
    // 转换元素的颜色数组 RGBA  [红色, 绿色, 蓝色, alpha通道]
    // [255, 0, 0, 255]  => [0, 255, 255, 255]
    for (let i = 0; i< imageData.data.length; i += 4) {
        imageData.data[i] = 255 - imageData.data[i];
        imageData.data[i + 1] = 255 - imageData.data[i + 1];
        imageData.data[i + 2] = 255 - imageData.data[i + 2];
        imageData.data[i + 3] = 255;
    }
    console.log(imageData);
    ctx.putImageData(imageData, 100, 0);
</script>

<canvas id="canvas"
            width="600"
            height="600"></canvas>
    <script>
        let canvas = document.querySelector('#canvas');
        let ctx = canvas.getContext('2d');
        ctx.fillStyle = "red";
        ctx.fillRect(0, 0, 50, 50);
        // 移动原点坐标(0, 0) => (100, 0)
        ctx.translate(100, 0);
        ctx.fillStyle = "green";
        ctx.fillRect(0, 0, 50, 50);
    </script>

<canvas id="canvas"
            width="600"
            height="600"></canvas>
    <script>
        let canvas = document.querySelector('#canvas');
        let ctx = canvas.getContext('2d');
        // 将坐标轴顺时针旋转45角
        ctx.rotate(Math.PI / 180 * 45);
        ctx.fillStyle = "red";
        ctx.fillRect(25, -25, 50, 50);
    </script>

<canvas id="canvas"
            width="600"
            height="600"></canvas>
    <script>
        let canvas = document.querySelector('#canvas');
        let ctx = canvas.getContext('2d');
        ctx.fillStyle = "red";
        ctx.fillRect(0, 0, 50, 50);
        // 保存画笔状态
        ctx.save()
        // 坐标轴x, y都放大两倍
        ctx.scale(2, 2);
        ctx.fillStyle = "green";
        ctx.fillRect(50, 0, 50, 50);
        // 恢复画笔状态
        ctx.restore()
        ctx.fillRect(250, 0, 50, 50);
    </script>