From 33058f2b292b3a581333bdfb21b8f671898c5060 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:40:17 -0500 Subject: initial commit --- .../quadraticcurveto/index.html | 214 +++++++++++++++++++++ 1 file changed, 214 insertions(+) create mode 100644 files/zh-cn/web/api/canvasrenderingcontext2d/quadraticcurveto/index.html (limited to 'files/zh-cn/web/api/canvasrenderingcontext2d/quadraticcurveto') diff --git a/files/zh-cn/web/api/canvasrenderingcontext2d/quadraticcurveto/index.html b/files/zh-cn/web/api/canvasrenderingcontext2d/quadraticcurveto/index.html new file mode 100644 index 0000000000..d1794c5043 --- /dev/null +++ b/files/zh-cn/web/api/canvasrenderingcontext2d/quadraticcurveto/index.html @@ -0,0 +1,214 @@ +--- +title: CanvasRenderingContext2D.quadraticCurveTo() +slug: Web/API/CanvasRenderingContext2D/quadraticCurveTo +tags: + - Canvas + - CanvasRenderingContext2D +translation_of: Web/API/CanvasRenderingContext2D/quadraticCurveTo +--- +
{{APIRef}}
+ +

CanvasRenderingContext2D.quadraticCurveTo() 是 Canvas 2D API 新增二次贝塞尔曲线路径的方法。它需要2个点。 第一个点是控制点，第二个点是终点。 起始点是当前路径最新的点，当创建二次贝赛尔曲线之前，可以使用 moveTo() 方法进行改变。

+ +

语法

+ +
void ctx.quadraticCurveTo(cpx, cpy, x, y);
+
+ +

参数

+ +
+
cpx
+
控制点的 x 轴坐标。
+
cpy
+
控制点的 y 轴坐标。
+
x
+
终点的 x 轴坐标。
+
y
+
终点的 y 轴坐标。
+
+ +

示例

+ +

quadraticCurveTo 如何工作

+ +

这是一段绘制二次贝赛尔曲线的简单的代码片段。 控制点是红色，起点和终点是蓝色。

+ +

HTML

+ +
<canvas id="canvas"></canvas>
+
+ +

JavaScript

+ +
const canvas = document.getElementById('canvas');
+const ctx = canvas.getContext('2d');
+
+// Quadratic Bézier curve
+ctx.beginPath();
+ctx.moveTo(50, 20);
+ctx.quadraticCurveTo(230, 30, 50, 100);
+ctx.stroke();
+
+// Start and end points
+ctx.fillStyle = 'blue';
+ctx.beginPath();
+ctx.arc(50, 20, 5, 0, 2 * Math.PI);   // Start point
+ctx.arc(50, 100, 5, 0, 2 * Math.PI);  // End point
+ctx.fill();
+
+// Control point
+ctx.fillStyle = 'red';
+ctx.beginPath();
+ctx.arc(230, 30, 5, 0, 2 * Math.PI);
+ctx.fill();
+ + + +

{{ EmbedLiveSample('Using_the_quadraticCurveTo_method', 315, 165) }}

+ +

简单的二次曲线

+ +

此示例使用quadraticCurveTo()绘制了简单的二次Bézier曲线。

+ +

HTML

+ +
<canvas id="canvas"></canvas>
+
+ +

JavaScript

+ +

曲线从moveTo()指定的点开始: (20, 110)。 控制点位于(230, 150)。 曲线在(250, 20)处结束。

+ +
const canvas = document.getElementById('canvas');
+const ctx = canvas.getContext('2d');
+
+ctx.beginPath();
+ctx.moveTo(20, 110);
+ctx.quadraticCurveTo(230, 150, 250, 20);
+ctx.stroke();
+
+ +

结果

+ + + +
+
<canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas>
+<div class="playable-buttons">
+  <input id="edit" type="button" value="Edit" />
+  <input id="reset" type="button" value="Reset" />
+</div>
+<textarea id="code" class="playable-code">
+ctx.beginPath();
+ctx.moveTo(50,20);
+ctx.quadraticCurveTo(230, 30, 50, 100);
+ctx.stroke();</textarea>
+
+ +
var canvas = document.getElementById("canvas");
+var ctx = canvas.getContext("2d");
+var textarea = document.getElementById("code");
+var reset = document.getElementById("reset");
+var edit = document.getElementById("edit");
+var code = textarea.value;
+
+function drawCanvas() {
+  ctx.clearRect(0, 0, canvas.width, canvas.height);
+  eval(textarea.value);
+}
+
+reset.addEventListener("click", function() {
+  textarea.value = code;
+  drawCanvas();
+});
+
+edit.addEventListener("click", function() {
+  textarea.focus();
+})
+
+textarea.addEventListener("input", drawCanvas);
+window.addEventListener("load", drawCanvas);
+
+
+ +

{{ EmbedLiveSample('Trying_the_quadraticCurveTo_parameters', 700, 360) }}

+ +

规范描述

+ + + + + + + + + + + + + + +
SpecificationStatusComment
{{SpecName('HTML WHATWG', "scripting.html#dom-context-2d-quadraticcurveto", "CanvasRenderingContext2D.quadraticCurveTo")}}{{Spec2('HTML WHATWG')}}
+ +

浏览器兼容性

+ + + +

{{Compat("api.CanvasRenderingContext2D.quadraticCurveTo")}}

+ + -- cgit v1.2.3-54-g00ecf