尝试使用javascript确定画布是否为空白

Question

我正在使用以下解决方案：如何检查画布是否为空白？但它不起作用。我的空白画布 URL 与新创建的画布 URL 不匹配，我无法弄清楚原因。它们是相同的尺寸，但它们的 .toDataURL 返回不同的东西，所以我无法判断它是否已被绘制。下面是我在空白画布上执行 .toDataURL 和在 .toDataURL 上执行时发生的情况的示例新创建的画布，如您所见，随着您继续前进，它们会有所不同。

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参考这里是功能：

function isCanvasBlank(canvas) {
    var blank = document.createElement('canvas');
    blank.width = canvas.width;
    blank.height = canvas.height;

    return canvas.toDataURL() == blank.toDataURL();
}

Answer 1

你得到的图像是不同的。第一个有白色背景，另一个是透明的。

这是造成差异的原因。

这是填充新画布的快速方法。

function isCanvasBlank(canvas) {
    var blank = document.createElement('canvas');
    blank.width = canvas.width;
    blank.height = canvas.height;

    var ctx = blank.getContext("2d");
    ctx.fillStyle = "#FFFFFF";
    ctx.fillRect(0, 0, blank .width, blank .height);
    return canvas.toDataURL() == blank.toDataURL();
}

或使用与小提琴相同的功能。 blank.getContext('2d').clearRect(0, 0, canvas.width, canvas.height);

function isCanvasBlank(canvas) {
    var blank = document.createElement('canvas');
    blank.width = canvas.width;
    blank.height = canvas.height;

    blank.getContext('2d').clearRect(0, 0, canvas.width, canvas.height);
    return canvas.toDataURL() == blank.toDataURL();
}