From 33058f2b292b3a581333bdfb21b8f671898c5060 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:40:17 -0500 Subject: initial commit --- .../createlineargradient/index.html | 156 +++++++++++++++++++++ 1 file changed, 156 insertions(+) create mode 100644 files/zh-cn/web/api/canvasrenderingcontext2d/createlineargradient/index.html (limited to 'files/zh-cn/web/api/canvasrenderingcontext2d/createlineargradient') diff --git a/files/zh-cn/web/api/canvasrenderingcontext2d/createlineargradient/index.html b/files/zh-cn/web/api/canvasrenderingcontext2d/createlineargradient/index.html new file mode 100644 index 0000000000..d7e9536d37 --- /dev/null +++ b/files/zh-cn/web/api/canvasrenderingcontext2d/createlineargradient/index.html @@ -0,0 +1,156 @@ +--- +title: CanvasRenderingContext2D.createLinearGradient() +slug: Web/API/CanvasRenderingContext2D/createLinearGradient +translation_of: Web/API/CanvasRenderingContext2D/createLinearGradient +--- +
{{APIRef}}
+ +

CanvasRenderingContext2D.createLinearGradient()方法创建一个沿参数坐标指定的直线的渐变。

+ +

+ +

该方法返回一个线性 {{domxref("CanvasGradient")}}对象。想要应用这个渐变，需要把这个返回值赋值给 {{domxref("CanvasRenderingContext2D.fillStyle", "fillStyle")}} 或者 {{domxref("CanvasRenderingContext2D.strokeStyle", "strokeStyle")}}。

+ +

语法

+ +
CanvasGradient ctx.createLinearGradient(x0, y0, x1, y1);
+
+ +

createLinearGradient() 方法需要指定四个参数，分别表示渐变线段的开始和结束点。

+ +

参数

+ +
+
x0
+
起点的 x 轴坐标。
+
y0
+
起点的 y 轴坐标。
+
x1
+
终点的 x 轴坐标。
+
y1
+
终点的 y 轴坐标。
+
+ +

返回值

+ +
+
{{domxref("CanvasGradient")}}
+
一个根据指定线路初始化的线性 CanvasGradient 对象。
+
+ +

示例

+ +

使用线性渐变填充一个矩形

+ +

这个例子使用createLinearGradient() 方法初始化了一个线性渐变。在这个线性渐变中添加了三种色彩。最后，这个渐变被赋值给上下文对应的属性，实现了对矩形的填充。

+ +

HTML

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

JavaScript

+ +
var canvas = document.getElementById('canvas');
+var ctx = canvas.getContext('2d');
+
+// Create a linear gradient
+// The start gradient point is at x=20, y=0
+// The end gradient point is at x=220, y=0
+var gradient = ctx.createLinearGradient(20,0, 220,0);
+
+// Add three color stops
+gradient.addColorStop(0, 'green');
+gradient.addColorStop(.5, 'cyan');
+gradient.addColorStop(1, 'green');
+
+// Set the fill style and draw a rectangle
+ctx.fillStyle = gradient;
+ctx.fillRect(20, 20, 200, 100);
+ +

结果

+ +
+
Playable code
+ +
<canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas>
+<div class="playable-buttons">
+  <input id="edit" type="button" value="编辑" />
+  <input id="reset" type="button" value="重置" />
+</div>
+<textarea id="code" class="playable-code">
+var gradient = ctx.createLinearGradient(0,0,200,0);
+gradient.addColorStop(0,"green");
+gradient.addColorStop(1,"white");
+ctx.fillStyle = gradient;
+ctx.fillRect(10,10,200,100);</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('Filling_a_rectangle_with_a_linear_gradient', 700, 180) }}

+ +

规范描述

+ + + + + + + + + + + + + + +
规范状态备注
{{SpecName('HTML WHATWG', "scripting.html#dom-context-2d-createlineargradient", "CanvasRenderingContext2D.createLinearGradient")}}{{Spec2('HTML WHATWG')}}
+ +

浏览器兼容性

+ + + +

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

+ + + +

Gecko特性说明

+ + + +


+ 参见

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