Html5 Canvas Text

2023-02-14 09:10:40

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";

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：

使用实例：

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="utf-8" />

    <title>test</title>

    <!--<script type="text/javascript" src="modernizr-latest.js"></script>-->

    <script src="Js/modernizr-2.6.2.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;

                }

            }

            //添加阴影效果

            //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);

            //}

            //添加渐变效果

            //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);

            //}

            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 class="color" 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>

来源地址；

http://www.cnblogs.com/amtf/archive/2012/01/18/2324343.html

码农公寓

相关文章