Web前端 Canvas图片加载拖拽缩放绘制多边形打点，坐标偏移获取和颜色获取例程

Posted 2022-01-07 Love丶伊卡洛斯

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前言

参考文章：
https://www.cnblogs.com/HPhone/p/3459957.html
https://blog.csdn.net/weixin_29065959/article/details/112268524
https://blog.csdn.net/poqe131/article/details/51012454
结合实际案例色度图进行功能拓展和运用。

功能说明

加载img下的色度图片，显示在canvas中，可以进行图片的拖拽，移动，缩放。
可以根据下放的输入框进行四边形顶点的确定，程序会自动进行连线。
鼠标点击图片会获取点击位置的颜色显示在右侧，并在下发显示坐标位置，和判断此点是否在四边形范围内。

工程下载

码云 GitHub

在线访问

码云page

效果图

核心源码

index.html

<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>
        XYZ色度图
    </title>
    <link rel="shortcut icon" href="img/favicon.ico" />
    <link rel="stylesheet" href="css/index.css">
	<script src="js/jquery-3.4.1.min.js"></script>
</head>
<body>
    <div id="title_div">
        <span>XYZ色度图</span>
    </div>
    <div id="canvas_div">
        <canvas id="canvas" width="1080" height="550">
        </canvas>
        <canvas id="canvas2" width="200" height="200">
        </canvas>
    </div>
    <div id="boundary_div">
        <span>边界点C(x,y):</span>
        <input class="input_common" id="C_x" type="text" value="0.0796">
        <input class="input_common" id="C_y" type="text" value="0.5129">
        <span>边界点M(x,y):</span>
        <input class="input_common" id="M_x" type="text" value="0.4026">
        <input class="input_common" id="M_y" type="text" value="0.4907">
        <span>边界点R(x,y):</span>
        <input class="input_common" id="R_x" type="text" value="0.6985">
        <input class="input_common" id="R_y" type="text" value="0.3013">
        <span>边界点RB(x,y):</span>
        <input class="input_common" id="RB_x" type="text" value="0.1568">
        <input class="input_common" id="RB_y" type="text" value="0.0291">
        <button class="button_common" type="button" onclick="set_boundary()">设置边界范围</button>
    </div>
    <div id="info_div">
        <span>x:</span>
        <input class="input_common" id="x_input" type="text" value="">
        <span>y:</span>
        <input class="input_common" id="y_input" type="text" value="">
        <button class="button_common" type="button" onclick="choose_xy_color()">选中此坐标颜色</button>
        <span id="is_inside_msg">选中坐标是否在范围内：</span>
        <span id="is_inside_ret">--</span>
    </div>
    <div id="bottom">
		<div id="copyright">
			<span>Copyright © </span>
			<span id="copyright_year">--</span>
			<span id="official" title="点击打开www.xxx.com"
				onclick="jump_to_official()">xxx</span>
			<span>, All Rights Reserved.</span>
		</div>
	</div>
</body>
<script src="js/index.js"></script>
</html>

index.js

/*
	参考文章：
	https://www.cnblogs.com/HPhone/p/3459957.html
	https://blog.csdn.net/weixin_29065959/article/details/112268524
	https://blog.csdn.net/poqe131/article/details/51012454
*/
var canvas, context;
var img, //图片对象
    imgIsLoaded, //图片是否加载完成;
    imgX = 0,
    imgY = 0,
    imgScale = 1;

var image_widht = 0;
var image_height = 0;

// 边界ABC的xy值
var arr_xy = [x: 0, y: 0, x: 0, y: 0, x: 0, y: 0, x: 0, y: 0];

(function init() 
    canvas = document.getElementById('canvas');
    context = canvas.getContext('2d');
    load_img();
)();

// 加载图片
function load_img() 
    img = new Image();
    img.src = "img/1.jpeg";
    // img.crossOrigin = 'Anonymous';
    img.onload = function() 
        imgIsLoaded = true;
        drawImage();
        image_width = img.width;
        image_height = img.height;
    


// 绘制图片
function drawImage() 
    context.clearRect(0, 0, canvas.width, canvas.height);
    context.drawImage(img, 0, 0, img.width, img.height, imgX, imgY, img.width * imgScale, img.height * imgScale);
    set_boundary();


// 监听canvas拖动事件
canvas.ontouchstart = function(event) 
	var touch = event.touches[0];
    var pos = window_to_canvas(canvas, touch.clientX, touch.clientY);
    canvas.ontouchmove = function(event) 
	    var touch = event.touches[0];
        canvas.style.cursor = "move";
        var pos1 = window_to_canvas(canvas, touch.clientX, touch.clientY);
        var x = pos1.x - pos.x;
        var y = pos1.y - pos.y;
        pos = pos1;
        imgX += x;
        imgY += y;
        drawImage();
    

    canvas.ontouchend = function() 
        canvas.ontouchmove = null;
        canvas.ontouchend = null;
        canvas.style.cursor = "default";
    
    //->console.log("canvas开始坐标 x="+imgX +" & y="+imgY);


// 监听canvas放大缩小事件
canvas.onmousewheel = canvas.onwheel = function(event) 
    var pos = window_to_canvas(canvas, event.clientX, event.clientY);
    event.wheelDelta = event.wheelDelta ? event.wheelDelta : (event.deltaY * (-40));
    if (event.wheelDelta > 0) 
        imgScale *= 2;
        imgX = imgX * 2 - pos.x;
        imgY = imgY * 2 - pos.y;
     else 
        imgScale /= 2;
        imgX = imgX * 0.5 + pos.x * 0.5;
        imgY = imgY * 0.5 + pos.y * 0.5;
    
    drawImage();
    //->console.log("canvas开始坐标 x="+imgX +" & y="+imgY);


// 监听canvas拖动事件
canvas.onmousedown = function(event) 
    var pos = window_to_canvas(canvas, event.clientX, event.clientY);
    canvas.onmousemove = function(event) 
        canvas.style.cursor = "move";
        var pos1 = window_to_canvas(canvas, event.clientX, event.clientY);
        var x = pos1.x - pos.x;
        var y = pos1.y - pos.y;
        pos = pos1;
        imgX += x;
        imgY += y;
        drawImage();
    

    canvas.onmouseup = function() 
        canvas.onmousemove = null;
        canvas.onmouseup = null;
        canvas.style.cursor = "default";
    
    //->console.log("canvas开始坐标 x="+imgX +" & y="+imgY);


// 监听canvas放大缩小事件
canvas.onmousewheel = canvas.onwheel = function(event) 
    var pos = window_to_canvas(canvas, event.clientX, event.clientY);
    event.wheelDelta = event.wheelDelta ? event.wheelDelta : (event.deltaY * (-40));
    if (event.wheelDelta > 0) 
        imgScale *= 2;
        imgX = imgX * 2 - pos.x;
        imgY = imgY * 2 - pos.y;
     else 
        imgScale /= 2;
        imgX = imgX * 0.5 + pos.x * 0.5;
        imgY = imgY * 0.5 + pos.y * 0.5;
    
    drawImage();
    //->console.log("canvas开始坐标 x="+imgX +" & y="+imgY);


// 监听canvas点击事件
canvas.onclick = function(event) 
    // 重新绘制
    drawImage();
    var pos = window_to_canvas(canvas, event.clientX, event.clientY);
    //实际点的坐标
    var isX = 0;
    var isY = 0;
    //实际选中坐标 肯定 = 点击的坐标 + canvas的坐标(必须为-数)
    var temp_canvas_x = imgX - imgX * 2;
    var temp_canvas_y = imgY - imgY * 2;

    //console.log("imgX = "+imgX + " & imgY = "+imgY);
    //console.log("temp_canvas_x = "+temp_canvas_x + " & temp_canvas_y = "+temp_canvas_y);

    if (imgScale == 1)  //原始尺寸
        isX = (pos.x + temp_canvas_x);
        isY = (pos.y + temp_canvas_y);
     else 
        if (imgScale > 1)  //被放大了,实际坐标需要/
            isX = (pos.x + temp_canvas_x) / imgScale;
            isY = (pos.y + temp_canvas_y) / imgScale;
         else  //被缩小了,坐标点放大
            isX = (pos.x + temp_canvas_x) * (1 / imgScale);
            isY = (pos.y + temp_canvas_y) * (1 / imgScale);
        
    

    //处理左上的是否超出图片范围
    if (isX < 0 || isY < 0) 
        console.log("请选择图片区域");
        //return;
    
    //处理右下区域,主要处理图片是否超出
    if (isX > image_width || isY > image_height) 
        console.log("超出图片尺度");
    
    console.log("点击的坐标点: x = "+isX + " & y = "+isY);
    console.log("图片完整的宽度 = "+image_width + " & 高度 = "+image_height);
    console.log("缩放级别: "+imgScale);

    var ctx = document.getElementById("canvas").getContext("2d");

    // 开始新路径
    ctx.beginPath();
    ctx.lineWidth = 3;
    ctx.strokeStyle = "black";
    // 画空心圆 arc(x,y,r,sAngle,eAngle,counterclockwise)
    ctx.arc(pos.x, pos.y, 3, 0, 360, false);
    ctx.stroke以上是关于Web前端 Canvas图片加载拖拽缩放绘制多边形打点，坐标偏移获取和颜色获取 例程的主要内容，如果未能解决你的问题，请参考以下文章 
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Web前端 Canvas图片加载拖拽缩放绘制多边形打点，坐标偏移获取和颜色获取 例程

前言