Mixing
get area of a polygon
-1
I'm trying to get the area of a polygone draw onclick in a canvas element
In the image above I try to get the area inside the red point which has a some opacity.
Is there anyway to do that "on the fly" which mean for each polygon draw.
I've already seen earcut.js which allow triangulation but I don't really understand how to get area whith this
var canvas = $('canvas');
var context = canvas[0].getContext('2d');
var imageObj = new Image();
imageObj.onload = function() {
$(canvas).attr({
width : this.width,
height: this.height
});
context.drawImage(imageObj,0,0);
};
imageObj.src = 'https://www.html5canvastutorials.com/demos/assets/darth-vader.jpg';
var clicks = ;
function drawPolygon(){
context.fillStyle = 'rgba(100,100,100,0.5)';
context.strokeStyle = "#df4b26";
context.lineWidth = 1;
context.beginPath();
context.moveTo(clicks[0].x, clicks[0].y);
for(var i=1; i < clicks.length; i++) {
context.lineTo(clicks[i].x,clicks[i].y);
}
context.closePath();
context.fill();
context.stroke();
};
function drawPoints(){
context.strokeStyle = "#df4b26";
context.lineJoin = "round";
context.lineWidth = 5;
for(var i=0; i < clicks.length; i++){
context.beginPath();
context.arc(clicks[i].x, clicks[i].y, 3, 0, 2 * Math.PI, false);
context.fillStyle = '#ffffff';
context.fill();
context.lineWidth = 5;
context.stroke();
}
};
function redraw(){
canvas.width = canvas.width; // Clears the canvas
context.drawImage(imageObj,0,0);
drawPolygon();
drawPoints();
};
canvas
.mouseup(function (e) {
clicks.push({
x: e.offsetX,
y: e.offsetY
});
redraw();
});<!DOCTYPE html>
<html lang="en" >
<head>
<meta charset="UTF-8">
<title>draw polygon with canvas</title>
<link rel="stylesheet" href="css/style.css">
</head>
<body>
<canvas width="600" height="400"></canvas>
<script src='http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js'></script>
<script src="js/index.js"></script>
</body>
</html>javascript math
asked Nov 20 '18 at 1:01
sonia makloufsonia maklouf
5852519
add a comment |
-1
I'm trying to get the area of a polygone draw onclick in a canvas element
In the image above I try to get the area inside the red point which has a some opacity.
Is there anyway to do that "on the fly" which mean for each polygon draw.
I've already seen earcut.js which allow triangulation but I don't really understand how to get area whith this
var canvas = $('canvas');
var context = canvas[0].getContext('2d');
var imageObj = new Image();
imageObj.onload = function() {
$(canvas).attr({
width : this.width,
height: this.height
});
context.drawImage(imageObj,0,0);
};
imageObj.src = 'https://www.html5canvastutorials.com/demos/assets/darth-vader.jpg';
var clicks = ;
function drawPolygon(){
context.fillStyle = 'rgba(100,100,100,0.5)';
context.strokeStyle = "#df4b26";
context.lineWidth = 1;
context.beginPath();
context.moveTo(clicks[0].x, clicks[0].y);
for(var i=1; i < clicks.length; i++) {
context.lineTo(clicks[i].x,clicks[i].y);
}
context.closePath();
context.fill();
context.stroke();
};
function drawPoints(){
context.strokeStyle = "#df4b26";
context.lineJoin = "round";
context.lineWidth = 5;
for(var i=0; i < clicks.length; i++){
context.beginPath();
context.arc(clicks[i].x, clicks[i].y, 3, 0, 2 * Math.PI, false);
context.fillStyle = '#ffffff';
context.fill();
context.lineWidth = 5;
context.stroke();
}
};
function redraw(){
canvas.width = canvas.width; // Clears the canvas
context.drawImage(imageObj,0,0);
drawPolygon();
drawPoints();
};
canvas
.mouseup(function (e) {
clicks.push({
x: e.offsetX,
y: e.offsetY
});
redraw();
});<!DOCTYPE html>
<html lang="en" >
<head>
<meta charset="UTF-8">
<title>draw polygon with canvas</title>
<link rel="stylesheet" href="css/style.css">
</head>
<body>
<canvas width="600" height="400"></canvas>
<script src='http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js'></script>
<script src="js/index.js"></script>
</body>
</html>javascript math
asked Nov 20 '18 at 1:01
sonia makloufsonia maklouf
5852519
Looks like you need to sum up the area of all the triangles received from earcut as you are looking for area of a irregular polygon.
– Narendra Mongiya
Nov 20 '18 at 1:45
add a comment |
-1
-1
-1
1
I'm trying to get the area of a polygone draw onclick in a canvas element
In the image above I try to get the area inside the red point which has a some opacity.
Is there anyway to do that "on the fly" which mean for each polygon draw.
I've already seen earcut.js which allow triangulation but I don't really understand how to get area whith this
var canvas = $('canvas');
var context = canvas[0].getContext('2d');
var imageObj = new Image();
imageObj.onload = function() {
$(canvas).attr({
width : this.width,
height: this.height
});
context.drawImage(imageObj,0,0);
};
imageObj.src = 'https://www.html5canvastutorials.com/demos/assets/darth-vader.jpg';
var clicks = ;
function drawPolygon(){
context.fillStyle = 'rgba(100,100,100,0.5)';
context.strokeStyle = "#df4b26";
context.lineWidth = 1;
context.beginPath();
context.moveTo(clicks[0].x, clicks[0].y);
for(var i=1; i < clicks.length; i++) {
context.lineTo(clicks[i].x,clicks[i].y);
}
context.closePath();
context.fill();
context.stroke();
};
function drawPoints(){
context.strokeStyle = "#df4b26";
context.lineJoin = "round";
context.lineWidth = 5;
for(var i=0; i < clicks.length; i++){
context.beginPath();
context.arc(clicks[i].x, clicks[i].y, 3, 0, 2 * Math.PI, false);
context.fillStyle = '#ffffff';
context.fill();
context.lineWidth = 5;
context.stroke();
}
};
function redraw(){
canvas.width = canvas.width; // Clears the canvas
context.drawImage(imageObj,0,0);
drawPolygon();
drawPoints();
};
canvas
.mouseup(function (e) {
clicks.push({
x: e.offsetX,
y: e.offsetY
});
redraw();
});<!DOCTYPE html>
<html lang="en" >
<head>
<meta charset="UTF-8">
<title>draw polygon with canvas</title>
<link rel="stylesheet" href="css/style.css">
</head>
<body>
<canvas width="600" height="400"></canvas>
<script src='http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js'></script>
<script src="js/index.js"></script>
</body>
</html>javascript math
asked Nov 20 '18 at 1:01
sonia makloufsonia maklouf
5852519
I'm trying to get the area of a polygone draw onclick in a canvas element
In the image above I try to get the area inside the red point which has a some opacity.
Is there anyway to do that "on the fly" which mean for each polygon draw.
I've already seen earcut.js which allow triangulation but I don't really understand how to get area whith this
var canvas = $('canvas');
var context = canvas[0].getContext('2d');
var imageObj = new Image();
imageObj.onload = function() {
$(canvas).attr({
width : this.width,
height: this.height
});
context.drawImage(imageObj,0,0);
};
imageObj.src = 'https://www.html5canvastutorials.com/demos/assets/darth-vader.jpg';
var clicks = ;
function drawPolygon(){
context.fillStyle = 'rgba(100,100,100,0.5)';
context.strokeStyle = "#df4b26";
context.lineWidth = 1;
context.beginPath();
context.moveTo(clicks[0].x, clicks[0].y);
for(var i=1; i < clicks.length; i++) {
context.lineTo(clicks[i].x,clicks[i].y);
}
context.closePath();
context.fill();
context.stroke();
};
function drawPoints(){
context.strokeStyle = "#df4b26";
context.lineJoin = "round";
context.lineWidth = 5;
for(var i=0; i < clicks.length; i++){
context.beginPath();
context.arc(clicks[i].x, clicks[i].y, 3, 0, 2 * Math.PI, false);
context.fillStyle = '#ffffff';
context.fill();
context.lineWidth = 5;
context.stroke();
}
};
function redraw(){
canvas.width = canvas.width; // Clears the canvas
context.drawImage(imageObj,0,0);
drawPolygon();
drawPoints();
};
canvas
.mouseup(function (e) {
clicks.push({
x: e.offsetX,
y: e.offsetY
});
redraw();
});<!DOCTYPE html>
<html lang="en" >
<head>
<meta charset="UTF-8">
<title>draw polygon with canvas</title>
<link rel="stylesheet" href="css/style.css">
</head>
<body>
<canvas width="600" height="400"></canvas>
<script src='http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js'></script>
<script src="js/index.js"></script>
</body>
</html>var canvas = $('canvas');
var context = canvas[0].getContext('2d');
var imageObj = new Image();
imageObj.onload = function() {
$(canvas).attr({
width : this.width,
height: this.height
});
context.drawImage(imageObj,0,0);
};
imageObj.src = 'https://www.html5canvastutorials.com/demos/assets/darth-vader.jpg';
var clicks = ;
function drawPolygon(){
context.fillStyle = 'rgba(100,100,100,0.5)';
context.strokeStyle = "#df4b26";
context.lineWidth = 1;
context.beginPath();
context.moveTo(clicks[0].x, clicks[0].y);
for(var i=1; i < clicks.length; i++) {
context.lineTo(clicks[i].x,clicks[i].y);
}
context.closePath();
context.fill();
context.stroke();
};
function drawPoints(){
context.strokeStyle = "#df4b26";
context.lineJoin = "round";
context.lineWidth = 5;
for(var i=0; i < clicks.length; i++){
context.beginPath();
context.arc(clicks[i].x, clicks[i].y, 3, 0, 2 * Math.PI, false);
context.fillStyle = '#ffffff';
context.fill();
context.lineWidth = 5;
context.stroke();
}
};
function redraw(){
canvas.width = canvas.width; // Clears the canvas
context.drawImage(imageObj,0,0);
drawPolygon();
drawPoints();
};
canvas
.mouseup(function (e) {
clicks.push({
x: e.offsetX,
y: e.offsetY
});
redraw();
});<!DOCTYPE html>
<html lang="en" >
<head>
<meta charset="UTF-8">
<title>draw polygon with canvas</title>
<link rel="stylesheet" href="css/style.css">
</head>
<body>
<canvas width="600" height="400"></canvas>
<script src='http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js'></script>
<script src="js/index.js"></script>
</body>
</html>var canvas = $('canvas');
var context = canvas[0].getContext('2d');
var imageObj = new Image();
imageObj.onload = function() {
$(canvas).attr({
width : this.width,
height: this.height
});
context.drawImage(imageObj,0,0);
};
imageObj.src = 'https://www.html5canvastutorials.com/demos/assets/darth-vader.jpg';
var clicks = ;
function drawPolygon(){
context.fillStyle = 'rgba(100,100,100,0.5)';
context.strokeStyle = "#df4b26";
context.lineWidth = 1;
context.beginPath();
context.moveTo(clicks[0].x, clicks[0].y);
for(var i=1; i < clicks.length; i++) {
context.lineTo(clicks[i].x,clicks[i].y);
}
context.closePath();
context.fill();
context.stroke();
};
function drawPoints(){
context.strokeStyle = "#df4b26";
context.lineJoin = "round";
context.lineWidth = 5;
for(var i=0; i < clicks.length; i++){
context.beginPath();
context.arc(clicks[i].x, clicks[i].y, 3, 0, 2 * Math.PI, false);
context.fillStyle = '#ffffff';
context.fill();
context.lineWidth = 5;
context.stroke();
}
};
function redraw(){
canvas.width = canvas.width; // Clears the canvas
context.drawImage(imageObj,0,0);
drawPolygon();
drawPoints();
};
canvas
.mouseup(function (e) {
clicks.push({
x: e.offsetX,
y: e.offsetY
});
redraw();
});<!DOCTYPE html>
<html lang="en" >
<head>
<meta charset="UTF-8">
<title>draw polygon with canvas</title>
<link rel="stylesheet" href="css/style.css">
</head>
<body>
<canvas width="600" height="400"></canvas>
<script src='http://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js'></script>
<script src="js/index.js"></script>
</body>
</html>javascript math
javascript math
asked Nov 20 '18 at 1:01
sonia makloufsonia maklouf
5852519
asked Nov 20 '18 at 1:01
sonia makloufsonia maklouf
5852519
edited Nov 20 '18 at 2:42
sonia maklouf
asked Nov 20 '18 at 1:01
sonia makloufsonia maklouf
5852519
asked Nov 20 '18 at 1:01
sonia makloufsonia maklouf
5852519
asked Nov 20 '18 at 1:01
sonia makloufsonia maklouf
5852519
5852519
Looks like you need to sum up the area of all the triangles received from earcut as you are looking for area of a irregular polygon.
– Narendra Mongiya
Nov 20 '18 at 1:45
add a comment |
Looks like you need to sum up the area of all the triangles received from earcut as you are looking for area of a irregular polygon.
– Narendra Mongiya
Nov 20 '18 at 1:45
Looks like you need to sum up the area of all the triangles received from earcut as you are looking for area of a irregular polygon.
– Narendra Mongiya
Nov 20 '18 at 1:45
Looks like you need to sum up the area of all the triangles received from earcut as you are looking for area of a irregular polygon.
– Narendra Mongiya
Nov 20 '18 at 1:45
add a comment |
1 Answer
1
active
oldest
votes
1
There is very simple algorithm to calculate area of polygon with given vertex coordinates: Shoelace formula
A = 1/2* Sum((x[i+1] + x[i]) * ([y[i+1] - y[i]))
(note indexes wrap in circular manner, so x[n]=x[0])
that might be implemented in a single loop.
answered Nov 20 '18 at 2:36
MBoMBo
47.3k22949
add a comment |
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1 Answer
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1 Answer
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oldest
votes
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oldest
votes
1
There is very simple algorithm to calculate area of polygon with given vertex coordinates: Shoelace formula
A = 1/2* Sum((x[i+1] + x[i]) * ([y[i+1] - y[i]))
(note indexes wrap in circular manner, so x[n]=x[0])
that might be implemented in a single loop.
answered Nov 20 '18 at 2:36
MBoMBo
47.3k22949
add a comment |
1
There is very simple algorithm to calculate area of polygon with given vertex coordinates: Shoelace formula
A = 1/2* Sum((x[i+1] + x[i]) * ([y[i+1] - y[i]))
(note indexes wrap in circular manner, so x[n]=x[0])
that might be implemented in a single loop.
answered Nov 20 '18 at 2:36
MBoMBo
47.3k22949
add a comment |
1
1
1
There is very simple algorithm to calculate area of polygon with given vertex coordinates: Shoelace formula
A = 1/2* Sum((x[i+1] + x[i]) * ([y[i+1] - y[i]))
(note indexes wrap in circular manner, so x[n]=x[0])
that might be implemented in a single loop.
answered Nov 20 '18 at 2:36
MBoMBo
47.3k22949
There is very simple algorithm to calculate area of polygon with given vertex coordinates: Shoelace formula
A = 1/2* Sum((x[i+1] + x[i]) * ([y[i+1] - y[i]))
(note indexes wrap in circular manner, so x[n]=x[0])
that might be implemented in a single loop.
answered Nov 20 '18 at 2:36
MBoMBo
47.3k22949
answered Nov 20 '18 at 2:36
MBoMBo
47.3k22949
answered Nov 20 '18 at 2:36
MBoMBo
47.3k22949
answered Nov 20 '18 at 2:36
MBoMBo
47.3k22949
47.3k22949
add a comment |
add a comment |
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Looks like you need to sum up the area of all the triangles received from earcut as you are looking for area of a irregular polygon.
– Narendra Mongiya
Nov 20 '18 at 1:45