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index.html
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width" />
<title>使用canvas模拟图像 object-fit，并支持旋转图片 </title>
</head>
<body>
<div>
测试的图片地址<input
type="text"
id="imgInput"
value="https://img11.360buyimg.com/imagetools/jfs/t1/194717/29/3901/78726/60a4d373E231e8129/d65a12481578a32b.png"
/>
</div>
<div>
容器宽度<input type="text" id="widthInput" value="375" /> 容器高度<input
type="text"
id="heightInput"
value="667"
/>
</div>
<div>
形式
<select id="typeSelect">
<option value="FILL">FILL</option>
<option value="FIT">FIT</option>
<option value="STRETCH">STRETCH</option>
</select>
</div>
<div><button onclick="createCanvas()">生成</button><button id="rotate" onclick="onRotate()">旋转</button></div>
<div id="imgResult"></div>
<canvas id="canvas"></canvas>
<script>
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
let rotation = 0;
const imgInput = document.getElementById("imgInput");
const widthInput = document.getElementById("widthInput");
const heightInput = document.getElementById("heightInput");
const typeSelect = document.getElementById("typeSelect");
const imgResult = document.getElementById("imgResult");
createCanvas()
function onRotate() {
rotation += 90;
createCanvas();
}
// 测试生成canvas
function createCanvas() {
const containerWidth = parseFloat(widthInput.value);
const containerHeight = parseFloat(heightInput.value);
ctx.clearRect(0, 0, containerWidth, containerHeight);
canvas.width = containerWidth;
canvas.height = containerHeight;
// 绘容器
ctx.rect(0, 0, containerWidth, containerHeight);
ctx.stroke();
// 绘图
const type = typeSelect.options[typeSelect.selectedIndex].value;
const img = document.createElement("img");
img.src = imgInput.value;
img.onload = function () {
imgResult.innerHTML =
"图片的宽：" + this.width + "; 图片的高：" + this.height;
const radians = (Math.PI / 180) * rotation;
const { width: cWidth, height: cHeight } = getBoundingDimentions(
containerWidth,
containerHeight,
radians
);
console.log(cWidth, cHeight);
ctx.translate(containerWidth / 2, containerHeight / 2);
ctx.rotate((Math.PI * rotation) / 180);
ctx.translate(-cWidth / 2, -cHeight / 2);
if (type === "STRETCH") {
ctx.drawImage(img, 0, 0, cWidth, cHeight);
} else {
const { sx, sy, swidth, sheight, x, y, width, height } =
getObjectFitSize(type, cWidth, cHeight, this.width, this.height);
ctx.drawImage(img, sx, sy, swidth, sheight, x, y, width, height);
}
};
}
/**
* 计算图片裁剪或者摆放位置
* @param {*} type FILL, FIT 暂时只兼容这两个模式
* @param {*} containerWidth 容器宽度
* @param {*} containerHeight 容器高度
* @param {*} imgWidth 图片宽度
* @param {*} imgHeight 图片高度
*/
function getObjectFitSize(
type = "FILL",
containerWidth,
containerHeight,
imgWidth,
imgHeight
) {
let radio = 1, // 容器与图片的比例
sx = 0, // 开始剪切的 x 坐标位置。
sy = 0, // 开始剪切的 y 坐标位置。
swidth = imgWidth, // 被剪切图像的宽度。
sheight = imgHeight, // 被剪切图像的高度。
x = 0, // 在画布上放置图像的 x 坐标位置。
y = 0, // 在画布上放置图像的 y 坐标位置。
width = containerWidth, // 要使用的图像的宽度（伸展或缩小图像）。
height = containerHeight; // 要使用的图像的高度（伸展或缩小图像）。
let cWHRatio = containerWidth / containerHeight;
let iWHRatio = imgWidth / imgHeight;
if (type === "FILL") {
// fill模式，需要裁剪
if (iWHRatio >= cWHRatio) {
// 横图，高先匹配，裁剪宽度
radio = containerHeight / imgHeight;
sx = (imgWidth - containerWidth / radio) / 2;
swidth = containerWidth / radio;
sheight = imgHeight;
} else {
// 竖图，宽先匹配，裁剪高度
radio = containerWidth / imgWidth;
sy = (imgHeight - containerHeight / radio) / 2;
swidth = imgWidth;
sheight = containerHeight / radio;
}
} else if (type === "FIT") {
if (iWHRatio >= cWHRatio) {
// 横图，宽先匹配，高度自适应
radio = containerWidth / imgWidth;
y = (containerHeight - imgHeight * radio) / 2;
height = imgHeight * radio;
} else {
// 竖图，高先匹配，宽度自适应
radio = containerHeight / imgHeight;
x = (containerWidth - imgWidth * radio) / 2;
width = imgWidth * radio;
}
}
return {
sx,
sy,
swidth,
sheight,
x,
y,
width,
height,
};
}
function getBoundingDimentions(width, height, rotation) {
const { cos, sin, abs } = Math;
/* eslint-disable max-len */
const widthAfterRotation =
abs(width * sin(rotation)) + abs(height * cos(rotation));
const heightAfterRotation =
abs(width * cos(rotation)) + abs(height * sin(rotation));
/* eslint-enable max-len */
return {
height: widthAfterRotation,
width: heightAfterRotation,
};
}
</script>
</body>
</html>