Question

我正在使用来自How to check if a canvas is blank?的解决方案，但是它不起作用。我的空白画布URL与新创建的画布URL不匹配，我无法弄清原因。它们是相同的尺寸，但是它们的.toDataURL返回的都是不同的东西，因此我无法告诉它是否已被绘制。下面是一个示例，当我在空白画布上执行.toDataURL并在.toDataURL上执行时会发生什么新创建的画布，您会看到它们随着继续前进而有所不同。

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此功能供参考：

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

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

Answer 1

生成的图像不同。第一个是白色背景，另一个是透明的。

这引起了差异。

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();
}

尝试使用JavaScript确定画布是否为空白

1 个答案: