Canvas drawImage在拉伸时绘制不需要的像素

Question

我使用 drawImage 将 1x2 像素精灵拉伸为 300x2 水平线。

这曾经工作得很好，但最近我注意到 Chrome、Firefox 和 Edge 上有一个问题，drawImage 函数将开始包含 1x2 定义框之外的精灵数据。（顺便说一句，这不会发生在移动设备上）

在下面的链接中，绘制线条对于小长度来说效果很好，但是一旦长度超过 255 像素，它将开始绘制不需要的颜色（蓝色）。

JSFiddle；https://jsfiddle.net/y6bo1zfu/1/

任何人都知道这可能是什么原因造成的？这可能是一个已知的错误还是通过优化添加的意外功能？

尝试将图像拉伸为其默认宽度 256 倍是禁忌吗？

Answer 1

这是由硬件加速 (HWA)（即 GPU）引起的。您可以在自己的浏览器上禁用它，您会看到它会按预期工作。遗憾的是，您无法要求所有用户禁用 HWA。解决这个问题的一种简单方法是创建一个仅包含图像所需部分的 ImageBitmap。这非常简单，因为该createImageBitmap()方法接受 5 个参数版本createImageBitmap( source, sourceX, sourceY, sourceWidth, sourceHeight );并且drawImage()接受 5 参数版本drawImage( source, destinationX, destinationY, destinationWidth, destinationHeight );因此，您可以将 9 个参数版本重写drawImage()为drawImage(   await createImageBitmap( source, sourceX, sourceY, sourceWidth, sourceHeight ),  destinationX, destinationY, destinationWidth, destinationHeight)var rawImage = false;var testCanvas = document.createElement('canvas');testCanvas.width = 300;testCanvas.height = 20;var testContext = testCanvas.getContext("2d");testContext.imageSmoothingEnabled = false;document.body.appendChild( testCanvas );function loadImage(){  rawImage = new Image();  rawImage.onload = function(){    // Create the sprite image    createSpriteImage();        document.body.appendChild( rawImage );  }  rawImage.src = 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function createSpriteImage(){  testContext.drawImage(    await createImageBitmap(rawImage,      2,     // Source X for this part of the Sprite      1 ,    // Source Y for this part of the Sprite      1 ,    // Width of this part of the Sprite      2      // Height of this part of the Sprite    ),    0,        // The X position where to draw    0,        // The Y position where to draw    300 ,     // Width of the line    2      // Height of the line  );    testContext.drawImage(    await createImageBitmap(rawImage,      2,    // Source X for this part of the Sprite      1 ,   // Source Y for this part of the Sprite      1 ,   // Width of this part of the Sprite      2     // Height of this part of the Sprite    ) ,      0 ,       // The X position where to draw    3 ,       // The Y position where to draw    298 ,     // Width of the line    2    // Height of the line  );    testContext.drawImage(    await createImageBitmap(rawImage,      2,    // Source X for this part of the Sprite      1 ,   // Source Y for this part of the Sprite      1 ,   // Width of this part of the Sprite      2     // Height of this part of the Sprite    ) ,    0,        // The X position where to draw    6,        // The Y position where to draw    264 ,     // Width of the line    2         // Height of the line  );    testContext.drawImage(    await createImageBitmap(rawImage,      2,    // Source X for this part of the Sprite      1 ,   // Source Y for this part of the Sprite      1 ,   // Width of this part of the Sprite      2     // Height of this part of the Sprite    ),    0,        // The X position where to draw    9,        // The Y position where to draw    256 ,     // Width of the line    2         // Height of the line  );    testContext.drawImage(    await createImageBitmap(rawImage,      2,     // Source X for this part of the Sprite      1 ,    // Source Y for this part of the Sprite      1 ,    // Width of this part of the Sprite      2      // Height of this part of the Sprite    ),    0,       // The X position where to draw    12,      // The Y position where to draw    255 ,    // Width of the line    2 ,      // Height of the line  );    testContext.drawImage(    await createImageBitmap(rawImage,      2,     // Source X for this part of the Sprite      1 ,    // Source Y for this part of the Sprite      1 ,    // Width of this part of the Sprite      2      // Height of this part of the Sprite    ),    0,       // The X position where to draw    15,      // The Y position where to draw    100 ,    // Width of the line    2 ,      // Height of the line  );    testContext.drawImage(    await createImageBitmap(rawImage,      2,     // Source X for this part of the Sprite      1 ,    // Source Y for this part of the Sprite      1 ,    // Width of this part of the Sprite      2      // Height of this part of the Sprite    ),    0,       // The X position where to draw    18,      // The Y position where to draw    10 ,     // Width of the line    2 ,      // Height of the line  );}//loadImage();body,html {    margin: 0px;    background-color: #4f4f4f;}img{    display: block;    width: 50px;    height: 50px;    margin: 0px auto;  image-rendering: pixelated;}canvas{  display: block;    width: 300px;    height: 20px;    box-shadow: 1px 1px 4px black;    margin: 15px auto;    background-color: white;    border: 1px solid white;}而对于不支持 ImageBitmap 接口的浏览器，至少可以通过使用其他画布来对这种用法进行猴子修补。