在尝试了合成操作和在画布上绘制图像后,我现在试图删除图像和合成。我怎么做呢?
我需要清除画布重绘其他图像;这可能会持续一段时间,所以我不认为每次都画一个新的矩形是最有效的选择。
在尝试了合成操作和在画布上绘制图像后,我现在试图删除图像和合成。我怎么做呢?
我需要清除画布重绘其他图像;这可能会持续一段时间,所以我不认为每次都画一个新的矩形是最有效的选择。
当前回答
这些都是如何清除标准画布的好例子,但如果你使用的是paperjs,那么这将工作:
用JavaScript定义一个全局变量:
var clearCanvas = false;
从你的PaperScript定义:
function onFrame(event){
if(clearCanvas && project.activeLayer.hasChildren()){
project.activeLayer.removeChildren();
clearCanvas = false;
}
}
现在无论你在哪里设置clearCanvas为true,它都会从屏幕上清除所有的项目。
其他回答
如果你在画线条,请确保不要忘记:
context.beginPath();
否则这些行就不会被清除。
private clearCanvas() {
const canvas: HTMLCanvasElement = this.ctx.canvas
this.ctx.save()
this.ctx.setTransform(1, 0, 0, 1, 0, 0)
this.ctx.clearRect(0, 0, canvas.width, canvas.height)
this.ctx.restore()
}
This is a Free hand drawing Canvas with a Clear Canvas Button. See this live example of a canvas which you can draw on and also when required clear it for redrawing clearRect() is used to delete the prersent canvas and fillRect() is used to again draw the initial canvas which was clean and had no drawings on it. var canvas = document.getElementById("canvas"), ctx = canvas.getContext("2d"), painting = false, lastX = 0, lastY = 0, lineThickness = 1; canvas.width=canvas.height = 250; ctx.fillRect(0, 0, 250, 250); canvas.onmousedown = function(e) { painting = true; ctx.fillStyle = "#ffffff"; lastX = e.pageX - this.offsetLeft; lastY = e.pageY - this.offsetTop; }; canvas.onmouseup = function(e){ painting = false; } canvas.onmousemove = function(e) { if (painting) { mouseX = e.pageX - this.offsetLeft; mouseY = e.pageY - this.offsetTop; // find all points between var x1 = mouseX, x2 = lastX, y1 = mouseY, y2 = lastY; var steep = (Math.abs(y2 - y1) > Math.abs(x2 - x1)); if (steep){ var x = x1; x1 = y1; y1 = x; var y = y2; y2 = x2; x2 = y; } if (x1 > x2) { var x = x1; x1 = x2; x2 = x; var y = y1; y1 = y2; y2 = y; } var dx = x2 - x1, dy = Math.abs(y2 - y1), error = 0, de = dy / dx, yStep = -1, y = y1; if (y1 < y2) { yStep = 1; } lineThickness = 4; for (var x = x1; x < x2; x++) { if (steep) { ctx.fillRect(y, x, lineThickness , lineThickness ); } else { ctx.fillRect(x, y, lineThickness , lineThickness ); } error += de; if (error >= 0.5) { y += yStep; error -= 1.0; } } lastX = mouseX; lastY = mouseY; } } var button=document.getElementById("clear"); button.onclick=function clearcanvas(){ canvas=document.getElementById("canvas"), ctx = canvas.getContext('2d'); ctx.clearRect(0, 0, 250, 250); canvas.width=canvas.height = 250; ctx.fillRect(0, 0, 250, 250);} #clear{border-radius:10px; font-size:8px !important; position:absolute; top:1px;} #canvas{border-radius:10px} <link href="https://www.w3schools.com/w3css/4/w3.css" rel="stylesheet"/> <button id="clear" class="w3-padding w3-xxlarge w3-pink" type="button">Clear Canvas</button> <canvas id="canvas"></canvas>
我发现在我测试的所有浏览器中,最快的方法是用白色填充rect,或者任何你想要的颜色。我有一个非常大的显示器,在全屏模式下,clearRect非常慢,但fillRect是合理的。
context.fillStyle = "#ffffff";
context.fillRect(0,0,canvas.width, canvas.height);
缺点是画布不再是透明的。
我总是用
ctx.fillStyle = "rgb(255, 255, 255)";
ctx.fillRect(0, 0, canvas.width, canvas.height);
对于自定义颜色,和
ctx.clearRect(0, 0, canvas.width, canvas.height);
用于使画布透明时清除