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Html5 Canvas中支援對text文字進行渲染的範例程式碼（圖）

黄舟原創: 2017-03-28 15:50:193147瀏覽

html5 canvas中支援對text文字進行渲染;
直接的理解就是把text繪製在畫布上，並且像圖形一樣處理它（可以加shadow、gradient、pattern、color fill等等）；
#既然它的本質是文字，就會具有文字所特有的一些屬性；本篇的重點也在於此；
不過，在最後會增加一些圖形填充效果在text上應用的實例；

context.font:

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

字體屬性的設定與css中的類似;
範例：

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

context.measureText(message):
當我們提供一個文字message,呼叫此方法，
它會依據目前context設定的字型、大小等，傳回一個文字的度量資訊物件TextMetrics;
#當前html5 canvas中TextMetrics對象，只包含一個屬性，就是width;
可以用來確定目前給定字串文本的在目前環境下的寬度；
例如：

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

<!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(&#39;keyup&#39;, textBoxChanged, false);
formElement = document.getElementById("fillOrStroke");
formElement.addEventListener(&#39;change&#39;, fillOrStrokeChanged, false);
formElement = document.getElementById("textSize");
formElement.addEventListener(&#39;change&#39;, textSizeChanged, false);
formElement = document.getElementById("textFillColor");
formElement.addEventListener(&#39;change&#39;, textFillColorChanged, false);
formElement = document.getElementById("textFont");
formElement.addEventListener(&#39;change&#39;, textFontChanged, false);
formElement = document.getElementById("textBaseline");
formElement.addEventListener(&#39;change&#39;, textBaselineChanged, false);
formElement = document.getElementById("textAlign");
formElement.addEventListener(&#39;change&#39;, textAlignChanged, false);
formElement = document.getElementById("fontWeight");
formElement.addEventListener(&#39;change&#39;, fontWeightChanged, false);
formElement = document.getElementById("fontStyle");
formElement.addEventListener(&#39;change&#39;, 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>

## fillText([text],[x],[y],[maxWidth]):

#參數的意義：

text:要在canvas上要渲染的文字內容；x,y:代表開始渲染的點的位置座標；

##maxWidth:代表最大寬度;

與之搭配的設定文字的顏色屬性：fillStyle

#strokeText([text ],[x],[y],[maxWidth]):

參數的意義與fillText相同；與fillText相比，它指渲染文字的輪廓；
與之搭配的設定文字的色彩屬性：
strokeStyle#Canvas中有對文字對齊方式的支援,包括兩個選項：水平Horizontal alignment與垂直Vertical alignment；
#context.textAlign：文字水平對齊方式。可取屬性值: start, end, left,right, center。預設值:start.

######context.textBaseline######：文字垂直對齊方式。可取屬性值：top, hanging, middle,alphabetic, ideographic, ###bottom###。預設值：alphabetic.#######

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

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：

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：

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(&#39;keyup&#39;, textBoxChanged, false);
formElement = document.getElementById("fillOrStroke");
formElement.addEventListener(&#39;change&#39;, fillOrStrokeChanged, false);
formElement = document.getElementById("textSize");
formElement.addEventListener(&#39;change&#39;, textSizeChanged, false);
formElement = document.getElementById("textFillColor");
formElement.addEventListener(&#39;change&#39;, textFillColorChanged, false);
formElement = document.getElementById("textFont");
formElement.addEventListener(&#39;change&#39;, textFontChanged, false);
formElement = document.getElementById("textBaseline");
formElement.addEventListener(&#39;change&#39;, textBaselineChanged, false);
formElement = document.getElementById("textAlign");
formElement.addEventListener(&#39;change&#39;, textAlignChanged, false);
formElement = document.getElementById("fontWeight");
formElement.addEventListener(&#39;change&#39;, fontWeightChanged, false);
formElement = document.getElementById("fontStyle");
formElement.addEventListener(&#39;change&#39;, 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);
}

以上是Html5 Canvas中支援對text文字進行渲染的範例程式碼（圖）的詳細內容。更多資訊請關注PHP中文網其他相關文章！

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