javascript - JQuery在画布图像上画线并重置线而不影响图像
问题描述
我有这个问题,我从输入字段上传图像并将其绘制到画布中。我有事件侦听器(mousemove
, click
, keydown
),当用户单击图像的任何部分时,该点是x1
,y1
坐标,当他们移动鼠标时,x2
每次y2
都会更新 , 。
问题是总是需要一条线,我用一个名为 的函数来管理它resetLine
,所以当x2
,y2
改变时,这条线会被重置,所以我们不会在每次鼠标移动时得到一堆连续的线。
问题在于我们正在绘制的图像,我重置线条的方式似乎也重置了图像,我认为这是预期的,所以我必须在每次鼠标移动时重新绘制图像,我认为这不是正确的方式要做到这一点,你也可以看到每次移动鼠标时图像都会闪烁。任何帮助,将不胜感激。
编辑:这是我之前制作的一个示例,但该图像是使用 javascript 制作的 css 背景 url 图像,但它有很多问题,我不得不开始使用画布绘制背景图像: https://angle-measurement.herokuapp。 com
这是我在 codepen 上制作的一个类似的: https ://codepen.io/Overflow0x/pen/yLaZxqm ,但它们都使用 css 的背景图像,而不是画布。
class APP {
constructor() {
this.$imageFileInput = $("#imageFileInput");
this.$lineWeight = $("#lineWeight");
this.$lineColor = $("#lineColor");
this.$reset = $("#reset");
this.$canvas = $("#canvas");
this.canvas = document.getElementById("canvas");
this.lineColor = "";
this.lineWidth = 3;
this.x1y1 = {
x: 4,
y: 8
};
this.x2y2 = {
x: 0,
y: 0
};
this.imageDataUrl = null;
this.imageWidth = 0;
this.imageHeight = 0;
this.ctx = this.canvas.getContext("2d");
this.y2X2MoveHandlerState = 0;
// 0 unregistered, 1, registered
}
setCanvasDimentions() {
this.ctx.canvas.width = (83 / 100) * window.innerWidth;
this.ctx.canvas.height = (60 / 100) * window.innerHeight;
}
registerX1Y1ClickHandler() {
var self = this;
self.$canvas.on('click', function(event) {
//console.log('registerX1Y2ClickHandler event\t', event);
console.log("click", event)
self.x1y1 = self.getMousePos(event);
self.log();
});
}
registerSaveLineClickHandler() {
var self = this;
$(document).keydown(function(e) {
console.warn(e);
if (e.keyCode == 83) {
// 's' button pressed...
self.toggleY2X2MoveHandler();
}
});
}
registerY2X2MoveHandler(mode = null) {
this.y2X2MoveHandlerState = 1;
var self = this;
self.$canvas.on('mousemove', function(event) {
console.log("mousemove", event);
self.x2y2 = self.getMousePos(event);
self.log();
self.resetLine();
self.draw_line();
self.draw_angle();
});
}
toggleY2X2MoveHandler() {
var self = this;
if (self.y2X2MoveHandlerState == 0) {
self.registerY2X2MoveHandler();
} else {
self.$canvas.off("mousemove");
self.y2X2MoveHandlerState = 0;
}
}
registerOnImageChangeHandler() {
var self = this;
self.$imageFileInput.on('change', function(event) {
console.log("image change", event);
const file = event.target.files[0];
self.getBase64Promise(file).then(function(result) {
self.imageDataUrl = result;
self.drawImage(result);
//self.ctx.canvas.style.backgroundImage = 'url(\'' + result + '\')';
}).catch(function(error) {
console.error("ikh\t", error)
self.error = error;
})
});
}
registerOnLineWeightChangeHandler() {
var self = this;
self.$lineWeight.on('change', function(event) {
self.lineWidth = event.target.value;
});
}
registerOnColorChangeHandler() {
var self = this;
self.$lineColor.on('change', function(event) {
self.lineColor = event.target.value;
});
}
registerOnResetHandler() {
var self = this;
self.$reset.on('click', function() {
var cords = {
x: 0,
y: 0
};
self.x1y1 = cords;
self.x2y2 = cords;
self.resetLine();
});
}
angle() {
var x1y1 = this.getObjectValuesAsArray(this.x1y1);
var x2y2 = this.getObjectValuesAsArray(this.x2y2);
var x1 = x1y1[0]
var y1 = x1y1[1]
var x2 = x2y2[0]
var y2 = x2y2[1]
var dy = y2 - y1;
var dx = x2 - x1;
var theta = Math.atan2(dy, dx); // range (-PI, PI]
theta *= 180 / Math.PI; // rads to degs, range (-180, 180]
//if (theta < 0) theta = 360 + theta; // range [0, 360)
theta = Number(theta).toPrecision(4);
return theta;
}
getBase64Promise(file) {
return new Promise(function(resolve, reject) {
var reader = new FileReader();
reader.readAsDataURL(file);
reader.onload = function() {
return resolve(reader.result);
};
reader.onerror = function(error) {
return reject(error);
};
});
}
getMousePos(event) {
var rect = this.$canvas.get(0).getBoundingClientRect();
return {
x: (event.clientX - rect.left) / (rect.right - rect.left) * this.ctx.canvas.width,
y: (event.clientY - rect.top) / (rect.bottom - rect.top) * this.ctx.canvas.height
};
}
/*
This code (getMousePos) takes into account both changing coordinates to canvas space
(evt.clientX - rect.left) and scaling when canvas logical size differs
from its style size
(/ (rect.right - rect.left) * canvas.width see: Canvas width and height in HTML5).
*/
getObjectValuesAsArray(obj) {
return Object.keys(obj).map(function(k) {
return obj[k]
});
}
resetLine() {
this.ctx.save();
this.ctx.globalCompositeOperation = 'copy';
this.ctx.strokeStyle = 'transparent';
this.ctx.beginPath();
this.ctx.lineTo(0, 0);
this.ctx.stroke();
this.drawImage(this.imageDataUrl);
this.ctx.restore();
}
drawImage(result) {
var self = this;
console.warn(result);
var img = $('<img>', {
src: result
});
img.on('load', function() {
console.warn("jq image\t", img);
self.imageWidth = img.get(0).naturalWidth;
self.imageHeight = img.get(0).naturalHeight;
self.ctx.canvas.width = img.get(0).naturalWidth;
self.ctx.canvas.height = img.get(0).naturalHeight;
self.ctx.clearRect(0, 0, self.ctx.canvas.width, self.ctx.canvas.height);
self.ctx.drawImage(img.get(0), 0, 0, self.ctx.canvas.width, self.ctx.canvas.height);
});
}
draw_line() {
this.ctx.strokeStyle = this.lineColor;
this.ctx.lineWidth = this.lineWidth;
var x1y1 = this.getObjectValuesAsArray(this.x1y1);
var x2y2 = this.getObjectValuesAsArray(this.x2y2);
//console.log("vectors x1y1\t", x1y1, "\t vectors x2y2", x2y2);
this.ctx.beginPath();
this.ctx.moveTo(x1y1[0], x1y1[1]);
this.ctx.lineTo(x2y2[0], x2y2[1]);
this.ctx.stroke();
//this.ctx.strokeRect(vectors[0], vectors[1], vectors[2], vectors[3]);
}
draw_angle() {
this.ctx.strokeStyle = this.lineColor;
this.ctx.lineWidth = this.lineWidth;
var x2y2 = this.getObjectValuesAsArray(this.x2y2);
//console.log("vectors x1y1\t", x1y1, "\t vectors x2y2", x2y2);
this.ctx.font = "18px DejaVuSansMono33-Regular";
this.ctx.fillStyle = this.lineColor;
var x2 = x2y2[0];
var y2 = x2y2[1];
var dx = x2;
var dy = y2;
var width = this.ctx.canvas.width;
var height = this.ctx.canvas.height;
console.warn("canvas width and height", width, height);
this.ctx.fillText(this.angle() + "°", dx, dy);
//this.ctx.strokeRect(vectors[0], vectors[1], vectors[2], vectors[3]);
}
log() {
console.log("x2y2\t", this.x2y2);
//console.log("ctx", this.ctx)
}
init() {
this.setCanvasDimentions();
this.registerX1Y1ClickHandler();
this.registerY2X2MoveHandler();
this.registerOnImageChangeHandler();
this.registerOnColorChangeHandler();
this.registerOnLineWeightChangeHandler();
this.registerSaveLineClickHandler();
this.registerOnResetHandler();
this.log();
}
};
$(document).ready(function() {
var app = new APP();
app.init();
});
@font-face {
font-family: 'DejaVuSansMono33-Regular';
font-style: normal;
font-weight: normal;
src: url("/static/DejaVuSansMono33-Regular.otf") format("truetype");
}
html,
body {
font-family: DejaVuSansMono33-Regular, "Helvetica Neue", sans-serif;
font-size: 14px;
background: "red";
height: 100%;
}
canvas#canvas {
height: 100%;
background-size: cover;
background-size: 100% 100%;
display: inline;
}
#measure {
position: absolute;
left: -10000px;
top: -100000px;
}
body {
text-align: center;
background: #f2f6f8;
}
#canvas-container {
height: 100%;
width: 100%;
text-align: center;
padding: 1rem;
background: none;
}
input[type="color"] {
-webkit-appearance: none;
border: none;
width: 32px;
height: 32px;
}
input[type="color"]::-webkit-color-swatch-wrapper {
padding: 0;
}
input[type="color"]::-webkit-color-swatch {
border: none;
}
.container {
height: 100% !important;
}
.section {
padding-bottom: 0px !important;
margin-bottom: 0px !important;
}
<link rel="stylesheet" type="text/css" media="screen" href="https://cdn.jsdelivr.net/npm/bulma@0.9.1/css/bulma.min.css">
<div class="container">
<section class="section">
<div class="columns">
<div class="column">
<div class="container">
<div id="canvas-container">
<canvas id="canvas"></canvas>
<div id="measure"></div>
</div>
</div>
</div>
</div>
</section>
<section class="section" style="padding-top: 10rem;">
<div class="columns">
<div class="column">
<div class="container">
<div class="field is-horizontal">
<div class="field-body">
<div class="field">
<div class="file is-dark">
<label class="file-label">
<input class="file-input" type="file" name="imageFileInput" id="imageFileInput">
<span class="file-cta">
<span class="file-label">Upload Picture</span>
</span>
</label>
</div>
</div>
<div class="field">
<button class="button is-dark" id="reset">Reset to initial coordinates</button>
</div>
<div class="field">
<label class="label is-expanded">Vector Color</label>
<div class="control">
<input class="input" type="color" name="lineColor" id="lineColor" value="#000000" />
</div>
</div>
<div class="field">
<label class="label">Vector Size</label>
<div class="control">
<input class="input" type="number" name="lineWeight" id="lineWeight" min="0" value="2" />
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</section>
</div>
<script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
解决方案
罪魁祸首显然是这个功能:
drawImage(result) {
var self = this;
console.warn(result);
var img = $('<img>', {
src: result
});
img.on('load', function() {
console.warn("jq image\t", img);
self.imageWidth = img.get(0).naturalWidth;
self.imageHeight = img.get(0).naturalHeight;
self.ctx.canvas.width = img.get(0).naturalWidth;
self.ctx.canvas.height = img.get(0).naturalHeight;
self.ctx.clearRect(0, 0, self.ctx.canvas.width, self.ctx.canvas.height);
self.ctx.drawImage(img.get(0), 0, 0, self.ctx.canvas.width, self.ctx.canvas.height);
});
}
但那里实际发生了什么?
好吧,除此之外resetLine()
,draw_angle()
它是 mouseMove 回调处理程序的一部分,因此每次鼠标移动都会执行。
所以:
var img = $('<img>', {
src: result
});
您正在创建一个新图像并使用:
img.on('load', function() {});
你实际上是在等待它被“加载”——每次鼠标移动。
这意味着您观察到的闪烁是由触发图像的 onload 事件并且您的画布最终获得要绘制的图像所花费的时间引起的。
修复相当简单。我建议设置一个类变量,例如
this.image=null;
并通过以下方式修改 drawImage() 函数:
- 如果
this.image
为null,则添加 onLoad 侦听器并将局部变量分配img
给this.image
- 如果
this.image
不为空,则将其用作参考而不是img
就像是:
drawImage(result) {
var self = this;
console.warn(result);
var img = $('<img>', {
src: result
});
if (this.image == null) {
img.on('load', function() {
console.warn("jq image\t", img);
self.imageWidth = img.get(0).naturalWidth;
self.imageHeight = img.get(0).naturalHeight;
self.ctx.canvas.width = img.get(0).naturalWidth;
self.ctx.canvas.height = img.get(0).naturalHeight;
self.ctx.clearRect(0, 0, self.ctx.canvas.width, self.ctx.canvas.height);
self.ctx.drawImage(img.get(0), 0, 0, self.ctx.canvas.width, self.ctx.canvas.height);
});
this.image = img;
} else {
img = this.image;
self.imageWidth = img.get(0).naturalWidth;
self.imageHeight = img.get(0).naturalHeight;
self.ctx.canvas.width = img.get(0).naturalWidth;
self.ctx.canvas.height = img.get(0).naturalHeight;
self.ctx.clearRect(0, 0, self.ctx.canvas.width, self.ctx.canvas.height);
self.ctx.drawImage(img.get(0), 0, 0, self.ctx.canvas.width, self.ctx.canvas.height);
}
}
顺便说一句 - 这绝不是最优雅的方式,它只是为了让你开始。
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