欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识！
您现在的位置是： 首页  >  web前端

Html5 Canvas中支持对text文本进行渲染的示例代码（图）

程序员文章站 2022-05-25 22:36:17
...
html5 canvas中支持对text文本进行渲染;
直接的理解就是把text绘制在画布上，并像图形一样处理它（可以加shadow、gradient、pattern、color fill等等）；
既然它的本质是文字，就会具有文字所特有的一些属性；本篇的侧重点也在于此；
不过，在最后会增加一些图形填充效果在text上应用的实例；

context.font:

[font style] [font weight] [font size] [font face]

字体属性的设置与css中的类似；
例：

context.font = "italic bold 24px serif"; context.font = "normal lighter 50px cursive";

context.measureText(message):
当我们提供一个文本message,调用此方法，
它会依据当前context设置的字体、大小等，返回一个文本的度量信息对象TextMetrics；
当前html5 canvas中TextMetrics对象，仅包含一个属性，就是width;
可以用来确定当前给定字符串文本的在当前环境下的宽度；
例如：

var metrics = context.measureText(message);
var textWidth = metrics.width;


fillText([text],[x],[y],[maxWidth]):
参数的意义：
text:要在canvas上要渲染的文本内容；
x,y:代表开始渲染的点的位置坐标；
maxWidth:代表最大宽度；

与之搭配的设置文本的颜色属性：fillStyle


strokeText([text],[x],[y],[maxWidth]):
参数的意义与fillText相同；与fillText相比，它指渲染文字的轮廓；
与之搭配的设置文本的颜色属性：strokeStyle


Canvas中有对文本对齐方式的支持,包括两个选项：水平Horizontal alignment与竖直Vertical alignment；
context.textAlign：文字水平对齐方式。可取属性值: start, end, left,right, center。默认值:start.
context.textBaseline：文字竖直对齐方式。可取属性值：top, hanging, middle,alphabetic, ideographic, bottom。默认值：alphabetic.

Horizontal alignment选项:center|start|end|left|right
例：context.textAlign = "center";

Vertical alignment选项：top|hanging|middle|alphabetic|ideographic|bottom
例：context.textBaseline = "top";

当我们把一段文本渲染在canvas上时，文本本身显示在画布上，会占据一个矩形块（看不见的矩形，我们暂且称其为IBox(invisible bounding box)）；

这里提到的对齐方式，都是针些这个文本所占据的这个IBox来操作的（IBox有，上，下，左，右四条边线）；

把字符串“HA”在画布的中心点位置(两条黑色直线相交点为中心)；textAlign为默认值，应用不同的textBaseline所产生的效果如下图：

Html5 Canvas中支持对text文本进行渲染的示例代码（图）

把字符串“HA”在画布的中心点位置(两条黑色直线相交点为中心)；textBaseline为默认值，应用不同的textAlign所产生的效果如下图：

Html5 Canvas中支持对text文本进行渲染的示例代码（图）

大家可以细细品味一下，它们的区别……

实例：

基本属性展示：

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>test</title>
<script type="text/javascript" src="modernizr-latest.js"></script>
<script type="text/javascript">
window.addEventListener("load", eventWindowLoaded, false);

function eventWindowLoaded() {
canvasApp();
}

function canvasSupport() {
return Modernizr.canvas;
}

function eventWindowLoaded() {
canvasApp();
}

function canvasApp() {
var message = "your text";
var fillOrStroke = "fill";
var fontSize = "50";
var fontFace = "serif";
var textFillColor = "#ff0000";
var textBaseline = "middle";
var textAlign = "center";
var fontWeight = "normal";
var fontStyle = "normal";

if(!canvasSupport()) {
return;
}

var theCanvas = document.getElementById("canvasOne");
var context = theCanvas.getContext("2d");
var formElement = document.getElementById("textBox");
formElement.addEventListener('keyup', textBoxChanged, false);
formElement = document.getElementById("fillOrStroke");
formElement.addEventListener('change', fillOrStrokeChanged, false);
formElement = document.getElementById("textSize");
formElement.addEventListener('change', textSizeChanged, false);
formElement = document.getElementById("textFillColor");
formElement.addEventListener('change', textFillColorChanged, false);
formElement = document.getElementById("textFont");
formElement.addEventListener('change', textFontChanged, false);
formElement = document.getElementById("textBaseline");
formElement.addEventListener('change', textBaselineChanged, false);
formElement = document.getElementById("textAlign");
formElement.addEventListener('change', textAlignChanged, false);
formElement = document.getElementById("fontWeight");
formElement.addEventListener('change', fontWeightChanged, false);
formElement = document.getElementById("fontStyle");
formElement.addEventListener('change', fontStyleChanged, false);

drawScreen();

function drawScreen() {
context.fillStyle = "yellow";
context.fillRect(0, 0, theCanvas.width, theCanvas.height);

context.lineWidth = 1;
context.beginPath();
context.moveTo(theCanvas.width / 2, 0);
context.lineTo(theCanvas.width / 2, theCanvas.height);
context.stroke();
context.closePath();

context.beginPath();
context.moveTo(0, theCanvas.height/2);
context.lineTo(theCanvas.width, theCanvas.height/2);
context.stroke();
context.closePath();

//Text
context.textBaseline = textBaseline;
context.textAlign = textAlign;
context.font = fontWeight + " " + fontStyle + " " + fontSize + "px " + fontFace;
var xPosition = (theCanvas.width / 2);
var yPosition = (theCanvas.height / 2);
switch(fillOrStroke) {
case "fill":
context.fillStyle = textFillColor;
context.fillText(message, xPosition, yPosition);
break;
case "stroke":
context.strokeStyle = textFillColor;
context.strokeText(message, xPosition, yPosition);
break;
case "both":
context.fillStyle = textFillColor;
context.fillText(message, xPosition, yPosition);
context.strokeStyle = "#000000";
context.strokeText(message, xPosition, yPosition);
break;
}
}

function textBoxChanged(e) {
var target = e.target;
message = target.value;
drawScreen();
}

function fillOrStrokeChanged(e) {
var target = e.target;
fillOrStroke = target.value;
drawScreen();
}

function textSizeChanged(e) {
var target = e.target;
fontSize = target.value;
drawScreen();
}

function textFillColorChanged(e) {
var target = e.target;
textFillColor = "#" + target.value;
drawScreen();
}

function textFontChanged(e) {
var target = e.target;
fontFace = target.value;
drawScreen();
}

function textBaselineChanged(e) {
var target = e.target;
textBaseline = target.value;
drawScreen();
}

function textAlignChanged(e) {
var target = e.target;
textAlign = target.value;
drawScreen();
}

function fontWeightChanged(e) {
var target = e.target;
fontWeight = target.value;
drawScreen();
}

function fontStyleChanged(e) {
var target = e.target;
fontStyle = target.value;
drawScreen();
}

}
</script>
</head>
<body>
<div style="position: absolute; top: 50px; left: 50px;">
<canvas id="canvasOne" width="400" height="150">
Your browser does not support HTML5 Canvas.
</canvas>
<form>
<span>Text</span>
<input id="textBox"/>
<br/>
<span>Fill or Stroke</span>
<select id="fillOrStroke">
<option value="fill">fill</option>
<option value="stroke">stroke</option>
<option value="both">both</option>
</select>
<br/>
<span>Font</span>
<select id="textFont">
<option value="serif">serif</option>
<option value="sans-serif">sans-serif</option>
<option value="cursive">cursive</option>
<option value="fantasy">fantasy</option>
<option value="monospace">monospace</option>
</select>
<br/>
<span>font size</span>
<input type="range" id="textSize" min="0" max="200"    value="30"/>
<br/>
<span>font color</span>
<input id="textFillColor" value="FF0000"/>
<br/>
<span>font weight</span>
<select id="fontWeight">
<option value="normal">normal</option>
<option value="bold">bold</option>
<option value="bolder">bolder</option>
<option value="lighter">lighter</option>
</select>
<br/>
<span>font style</span>
<select id="fontStyle">
<option value="normal">normal</option>
<option value="italic">italic</option>
<option value="oblique">oblique</option>
</select>
<br/>
<span>textBaseLine</span>
<select id="textBaseline">
<option value="middle">middle</option>
<option value="top">top</option>
<option value="hanging">hanging</option>
<option value="alphabetic">alphabetic</option>
<option value="ideographic">ideographic</option>
<option value="bottom">bottom</option>
</select>
<br/>
<span>TextAlign</span>
<select id="textAlign">
<option value="center">center</option>
<option value="start">start</option>
<option value="end">end</option>
<option value="left">left</option>
<option value="right">right</option>
</select>
</form>
</div>
</body>
</html>

阴影效果： 

代换上面代码的drawScreen方法体

function drawScreen() {
context.fillStyle = "yellow";
context.fillRect(0, 0, theCanvas.width, theCanvas.height);
//Text
context.textBaseline = textBaseline;
context.textAlign = textAlign;
context.shadowColor = "#707070";
context.shadowOffsetX = 5;
context.shadowOffsetY = 5;
context.shadowBlur = 5;
context.font = fontWeight + " " + fontStyle + " " + fontSize + "px " + fontFace;
var xPosition = (theCanvas.width / 2);
var yPosition = (theCanvas.height / 2);
context.fillStyle = textFillColor;
context.fillText(message, xPosition, yPosition);
}

渐变效果：

代换View Code 代码段中的drawScreen方法

function drawScreen() {
context.fillStyle = "yellow";
context.fillRect(0, 0, theCanvas.width, theCanvas.height);
var gradient = context.createLinearGradient(0, 0, theCanvas.width, 0);
context.font = "italic bold 40px serif";
gradient.addColorStop(0, "#000000");
gradient.addColorStop(.5, "#FF0000");
gradient.addColorStop(1, "#00ff00");
var xPosition = (theCanvas.width / 2);
var yPosition = (theCanvas.height / 2);
context.fillStyle = gradient;
context.fillText("message", xPosition, yPosition);
}

以上就是Html5 Canvas中支持对text文本进行渲染的示例代码（图）的详细内容，更多请关注其它相关文章！

相关标签： Html5，Canvas，text

上一篇： 从浏览器输入URL回车发生了什么_html/css_WEB-ITnose

下一篇： javascript实现简单的贪吃蛇游戏_javascript技巧

推荐阅读