HTML5 Canvas学习---第八章 《Canvas文本API 2》
继续看Canvas中的文本属性
- Text Align：当textAlign属性设置为left或start，并文档是从左到右对齐的时候，文本会居左对齐，或文档方向是从右向左，属性设置为end。当textalign属性设置为right或end，并文档方向为从左向右时，文本居右对齐，或文档方向为从右向左的时候属性设置为start，它也会居右对齐。如果没有设置属性，默认为start。它的值有start, end, left, center, right。
简单的看一下例子
<!DOCTYPE html>
<html>
<body>
<canvas id="myCanvas" width="300" height="200" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.
</canvas>
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
// Create a red line in position 150
ctx.strokeStyle = "blue";
ctx.moveTo(150, 20);
ctx.lineTo(150, 170);
ctx.stroke();
ctx.font = "15px Arial";
// Show the different textAlign values
ctx.textAlign = "start";
ctx.fillText("textAlign=start", 150, 60);
ctx.textAlign = "end";
ctx.fillText("textAlign=end", 150, 80);
ctx.textAlign = "left";
ctx.fillText("textAlign=left", 150, 100);
ctx.textAlign = "center";
ctx.fillText("textAlign=center", 150, 120);
ctx.textAlign = "right";
ctx.fillText("textAlign=right", 150, 140);
</script>
</body>
</html>
- Text Baseline：跟textAlign基本上一样，只是它是垂直对齐的也就是沿着x轴对齐。它的值有
- top：文字的头部跟X轴对齐（y坐标）
- bottom：文字的底部对齐
- middle：居中对齐
- alphabetic：默认
- Hanging：跟top类似，但离x轴的距离更远一些（悬挂）
<!DOCTYPE html>
<html>
<body>
<canvas id="myCanvas" width="400" height="200" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.
</canvas>
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
//Draw a red line at y=100
ctx.strokeStyle = "blue";
ctx.moveTo(5, 100);
ctx.lineTo(395, 100);
ctx.stroke();
ctx.font = "20px Arial"
//Place each word at y=100 with different textBaseline values
ctx.textBaseline = "top";
ctx.fillText("Top", 5, 100);
ctx.textBaseline = "bottom";
ctx.fillText("Bottom", 50, 100);
ctx.textBaseline = "middle";
ctx.fillText("Middle", 120, 100);
ctx.textBaseline = "alphabetic";
ctx.fillText("Alphabetic", 190, 100);
ctx.textBaseline = "hanging";
ctx.fillText("Hanging", 290, 100);
</script>
</body>
</html>
这样，我们根据今天讲的两个内容及前面的文章里提到的透明度及阴影效果，更完善我们的文本控制器。
View Code
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>chp3-2</title>
<meta name="description" content="" />
<meta name="author" content="Administrator" />
<script>
window.addEventListener("load", eventWindowLoaded, false);
function eventWindowLoaded() {
canvasApp();
}
function canvasApp() {
var message = "your text";
var fillOrStroke = "fill";
var fontSize = "50";
var fontFace = "serif";
var fontWeight = "normal";
var fontStyle = "normal";
var textBaseline = "middle";
var textAlign = "center";
var shadowX = 1;
var shadowY = 1;
var shadowBlur = 1;
var shadowColor = "#000000";
var textAltha = 1;
var theCanvas = document.getElementById("canvas");
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("textFont");
formElement.addEventListener("change", textFontChanged, false);
formElement = document.getElementById("fontWeight");
formElement.addEventListener("change", fontWeightChanged, false);
formElement = document.getElementById("fontStyle");
formElement.addEventListener("change", fontStyleChanged, false);
formElement = document.getElementById("textBaseline");
formElement.addEventListener("change", textBaselineChanged, false);
formElement = document.getElementById("textAlign");
formElement.addEventListener("change", textAlignChanged, false);
formElement = document.getElementById("shadowX");
formElement.addEventListener("change", shadowXChanged, false);
formElement = document.getElementById("shadowY");
formElement.addEventListener("change", shadowYChanged, false);
formElement = document.getElementById("shadowBlur");
formElement.addEventListener("change", shadowBlurChanged, false);
formElement = document.getElementById("textAlpha");
formElement.addEventListener("change", textAlphaChanged, false);
drawScreen();
function drawScreen() {
context.clearRect(0, 0, theCanvas.width,theCanvas.height);
context.fillStyle = "#ffffaa";
// context.fillRect(0, 0, theCanvas.width, theCanvas.height);
context.strokeStyle = "#000000";
// context.strokeRect(5, 5, theCanvas.width-10, theCanvas.height-10);
context.font = "50px serif";
context.textBaseline = textBaseline;
context.textAlign = textAlign;
context.globalAlpha = textAlpha;
context.shadowColor = shadowColor;
context.shadowOffsetX = shadowX;
context.shadowOffsetY = shadowY;
context.shadowBlur = shadowBlur;
var metrics = context.measureText(message);
var textWidth = metrics.width;
context.font = fontWeight + " " + fontStyle + " " + fontSize + "px " + fontFace;
//canvas中间点
var xPosition =(theCanvas.width - textWidth)/2;
var yPosition = theCanvas.height/2;
switch(fillOrStroke) {
case "fill":
context.fillStyle="#ff0000";
context.fillText(message, xPosition, yPosition);
break;
case "stroke":
context.strokeStyle = "#FF0000";
context.strokeText(message, xPosition, yPosition);
break;
case "both":
context.fillStyle="#ff0000";
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 textFontChanged(e) {
var target = e.target;
fontFace = 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();
}
function textAlignChanged(e) {
var target = e.target;
textAlign = target.value;
drawScreen();
}
function textBaselineChanged(e) {
var target = e.target;
textBaseline = target.value;
drawScreen();
}
function shadowXChanged(e) {
var target = e.target;
shadowX = target.value;
drawScreen();
}
function shadowYChanged(e) {
var target = e.target;
shadowY = target.value;
drawScreen();
}
function shadowBlurChanged(e) {
var target = e.target;
shadowBlur = target.value;
drawScreen();
}
function shadowColorChanged(e) {
var target = e.target;
shadowColor = target.value;
drawScreen();
}
function textAlphaChanged(e) {
var target = e.target;
textAlpha = target.value;
drawScreen();
}
}
</script>
</head>
<body>
<div style="position: absolute; top:50px; left: 50px">
<canvas id="canvas" width="500"height="300">
</canvas>
<form>
Text:
<input id="textBox" placeholder="your text" />
<br>
Fill Or Stroke:
<select id="fillOrStroke">
<option value="fill">fill</option>
<option value="stroke">stroke</option>
<option value="both">both</option>
</select>
<br />
Font Style:
<select id="fontStyle">
<option value="normal">normal</option>
<option value="italic">italic</option>
<option value="oblique">oblique</option>
</select>
<br />
Font Weight:
<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 />
Text Font:
<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 />
Text Size:
<input type="range" id="textSize" min="0" max="200" step="1" value="50" />
<br>
Text Baseline
<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>
Text Align
<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>
<br>
Alpha:<input type="range" id="textAlpha" min="0" max="1" step="0.1" value="1" />
<br>
Shadow X:<input type="range" id="shadowX" min="-100" max="100" step="1" value="1" />
<br>
Shadow Y:<input type="range" id="shadowY" min="-100" max="100" step="1" value="1" />
<br>
Shadow Blur:<input type="range" id="shadowBlur" min="1" max="100" step="1" value="1" />
<br>
Shadow Color:<input class="color" id="shadowColor" value="#000000" />
</form>
</div>
</body>
</html>
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