javascripthtmlwebdragbootstrap-5
HTML javascript, dragging method in canvas
I made a square grid using HTML canvas and I am implementing a drag mechanism, such that the user can draw only rectangles by dragging over the grid.
In the below solution, the user can draw non-rectangle shapes, depending on how the user drags.
An additional question : The grid can be of any size and the drag operation is laggy for large rectangles. Any performance improvement suggestions for that ?
Here are my code of html and javascript
function getSquare(canvas, evt) {
var rect = canvas.getBoundingClientRect();
return {
x: 1 + (evt.clientX - rect.left) - (evt.clientX - rect.left)%10,
y: 1 + (evt.clientY - rect.top) - (evt.clientY - rect.top)%10
};
}
function emptySquare(context) {
context.rect(0, 0, canvas.width, canvas.height);
context.fillStyle = "#ffffff"
context.fill();
context.strokeStyle = "#ddd";
context.stroke();
}
function range(start, end) {
var ans = [];
if (end > start) {
for (let i = start; i <= end; i += 10) {
ans.push(i);
}
} else {
emptySquare(context);
for (let i = start; i >= end; i -= 10) {
ans.push(i);
}}
return ans;
}
function drawBoard(context) {
for (var x = 0.5; x < 20001; x += 10) {
context.moveTo(x, 0);
context.lineTo(x,20000);
}
for (var y = 0.5; y < 20001; y += 10) {
context.moveTo(0, y);
context.lineTo(20000, y);
}
context.strokeStyle = "#ddd";
context.stroke();
}
function fillSquare(context, x, y){
context.fillStyle = "#70B7B5";
context.fillRect(x,y,9,9);
}
var canvas = document.getElementById('myBoard');
var context = canvas.getContext('2d');
var A;
drawBoard(context);
var isDrag= false;
// drawBoard(context);
canvas.addEventListener('mousedown', function(evt) {
var mousePos = getSquare(canvas, evt);
isDrag=true;
fillSquare(context, mousePos.x, mousePos.y);
previousPos = mousePos;
}, false);
canvas.addEventListener('mousemove', function(evt) {
if (isDrag) {
var mousePos = getSquare(canvas, evt);
var x_dist = range(previousPos.x, mousePos.x);
var y_dist = range(previousPos.y, mousePos.y);
for (x in x_dist) {
for (y in y_dist) {
fillSquare(context, x_dist[x], y_dist[y]);
}
}
}
}, false);
canvas.addEventListener('mouseup', function(evt) {
if (isDrag){
isDrag = false;
}
}, false);var canvas = document.getElementById('myBoard');
var context = canvas.getContext('2d');
// drawBoard(context);
var isDrag=false;
canvas.addEventListener('mousedown', function(evt) {
var mousePos = getSquare(canvas, evt);
isDrag=true;
fillSquare(context, mousePos.x, mousePos.y);
previousPos = mousePos;
}, false);
canvas.addEventListener('mousemove', function(evt) {
if (isDrag) {
var mousePos = getSquare(canvas, evt);
var x_dist = range(previousPos.x, mousePos.x);
var y_dist = range(previousPos.y, mousePos.y);
for (x in x_dist) {
for (y in y_dist) {
fillSquare(context, x_dist[x], y_dist[y]);
}
}
}
}, false);
canvas.addEventListener('mouseup', function(evt) {
if (isDrag){
isDrag = false;
}
}, false);<head>
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<link href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css" rel="stylesheet">
<link rel="stylesheet" href="./assets/css/style.css">
<meta charset="utf-8">
</head>
<body>
<nav class="navbar navbar-expand-lg navbar-dark bg-dark">
<div class="container-fluid">
<a class="navbar-brand" href="index.html">t</a>
<button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarNavAltMarkup" aria-controls="navbarNavAltMarkup" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarNavAltMarkup">
<div class="navbar-nav">
<a class="nav-link" aria-current="page" href="index.html">Home</a>
<a class="nav-link" href="#">About Us</a>
<a class="nav-link" href="Myblock.html">Mk</a>
</div>
<div class="navbar-nav ms-auto mb-2 mb-lg-0">
<a class="nav-link" href="login.html">Login</a>
</div>
</div>
</div>
</nav>
<div>
<div class="modal fade bd-example-modal-lg" id="exampleModal" tabindex="-1" aria-labelledby="exampleModalLabel" aria-hidden="true">
<div class="modal-dialog modal-lg">
<div class="modal-content">
<div class="modal-header">
<h5 class="modal-title" id="exampleModalLabel">간판 구입</h5>
<button type="button" class="btn-close" data-bs-dismiss="modal" aria-label="Close"></button>
</div>
<div class="modal-body">
<form action="" method="POST" enctype="multipart/form-data">
<div class="container">
<div class="row">
<div class="col-md-12">
<div class="form-group">
<div class="preview-zone hidden">
<div class="box box-solid">
<div class="box-header with-border">
<div><b>미리보기</b></div>
<!-- <div class="box-tools pull-right">
<button type="button" class="btn btn-danger btn-xs remove-preview">
<i class="fa fa-times"></i> 초기화
</button>
</div> -->
</div>
<div class="box-body"></div>
</div>
</div>
<div class="dropzone-wrapper">
<div class="dropzone-desc">
<i class="glyphicon glyphicon-download-alt"></i>
<p>광고 이미지 선택 or 드래그해 옮겨 오세요.</p>
</div>
<input type="file" name="img_logo" class="dropzone">
</div>
</div>
</div>
</div>
</div>
<div class="form-group">
<label for="exampleInputEmail1">닉네임/이름</label>
<input type="email" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp" placeholder="닉네임/이름">
<label for="exampleInputEmail1">연락처</label>
<input type="email" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp" placeholder="핸드폰 번호">
<label for="exampleInputEmail1">구매희망 면적</label>
<input type="email" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp" placeholder="ex) 10 x 10 OR 100x100 ">
</div>
</form>
</div>
<div class="modal-footer">
<button type="button" class="btn btn-secondary" data-bs-dismiss="modal">닫기</button>
<button type="submit" class="btn btn-dark">적용하기</button>
</div>
</div>
</div>
</div>
<div>
<canvas id="myBoard" width="1440" height="1200"></canvas>
</div>
</hr>
<footer>
<p>© 2021 Nune Project</p>
</footer>
<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/js/bootstrap.bundle.min.js"></script>
<script type="text/javascript" src="./assets/js/mainBoard.js"></script>
<script type="text/javascript" src="./assets/js/drag_field.js"></script>
</body>Solution
Another approach to solve the lag issue is to make two canvases: one for the background grid lines and the other one for drawing the green rectangles.
<div>
<canvas id="bg" width="1440" height="1200"></canvas>
<canvas id="myBoard" width="1440" height="1200"></canvas>
</div>
Set the #bg canvas so that #myBoard is in front of it:
#bg {
position: absolute;
z-index: -1;
}
Then draw the grid lines on the #bg canvas:
const bg = document.getElementById('bg')
const bgContext = bg.getContext('2d')
drawBoard(bgContext)
Finally, move the emptySquare(context) function into the mousemove event callback and edit it as follows:
function emptySquare(context) {
context.clearRect(0, 0, canvas.width, canvas.height)
}
So it will only clear the #myBoard canvas while #bg stays the same without needing to redraw it each time.
Example:
const bg = document.getElementById('bg')
const bgContext = bg.getContext('2d')
drawBoard(bgContext)
function getSquare(canvas, evt) {
var rect = canvas.getBoundingClientRect()
return {
x: 1 + (evt.clientX - rect.left) - ((evt.clientX - rect.left) % 10),
y: 1 + (evt.clientY - rect.top) - ((evt.clientY - rect.top) % 10),
}
}
function emptySquare(context) {
context.clearRect(0, 0, canvas.width, canvas.height)
}
function range(start, end) {
var ans = []
if (end > start) {
for (let i = start; i <= end; i += 10) {
ans.push(i)
}
} else {
for (let i = start; i >= end; i -= 10) {
ans.push(i)
}
}
return ans
}
function drawBoard(context) {
for (var x = 0.5; x < 20001; x += 10) {
context.moveTo(x, 0)
context.lineTo(x, 20000)
}
for (var y = 0.5; y < 20001; y += 10) {
context.moveTo(0, y)
context.lineTo(20000, y)
}
context.strokeStyle = '#ddd'
context.stroke()
}
function fillSquare(context, x, y) {
context.fillStyle = '#70B7B5'
context.fillRect(x, y, 9, 9)
}
var canvas = document.getElementById('myBoard')
var context = canvas.getContext('2d')
var isDrag = false
canvas.addEventListener('mousedown', function(evt) {
var mousePos = getSquare(canvas, evt)
isDrag = true
fillSquare(context, mousePos.x, mousePos.y)
previousPos = mousePos
}, false)
canvas.addEventListener('mousemove', function(evt) {
if (isDrag) {
var mousePos = getSquare(canvas, evt)
var x_dist = range(previousPos.x, mousePos.x)
var y_dist = range(previousPos.y, mousePos.y)
emptySquare(context)
for (x in x_dist) {
for (y in y_dist) {
fillSquare(context, x_dist[x], y_dist[y])
}
}
}
}, false)
canvas.addEventListener('mouseup', function(evt) {
if (isDrag) {
isDrag = false
}
}, false)#bg {
position: absolute;
z-index: -1;
}<div>
<canvas id="bg" width="1440" height="1200"></canvas>
<canvas id="myBoard" width="1440" height="1200"></canvas>
</div>