I'm trying to draw a graph in a shape of a butterfly on html canvas using javascript. Parametric equations of the graph are:
x=(e^(cost) -2cos4t+sin^5( t/12))sint
y=(e^(cost) -2cos4t+sin^5( t/12))cost
t e [0, 20.5]
I have been trying but i can't figure it out. Thanks for your help :)
Here is a minimal example of a Lissajous curve for drawing a parametrized 2D curve on a javascript canvas. You should be able to adapt this for your curve
// get the handles and info on the HTML elements
var canvas = document.getElementById('Canvas');
var width = canvas.width;
var height = canvas.height;
var context = canvas.getContext('2d');
// construct a local coordinate system that is
// slightly larger than [-1,1]x[-1,1]
context.translate(width/2, height/2);
context.scale(width/2.1, height/2.1);
context.lineWidth = 0.02;
// construct and draw the curve
context.beginPath();
context.moveTo(0,0);
for(var x = 0; x < 6*Math.PI; x += 0.05)
context.lineTo(Math.sin(3*x),Math.sin(4*x));
context.stroke();
<canvas id="Canvas" width = "200" height = "200" />
Related
I´ve been trying to make a desktop app (javascript, canvas) and draw 413.280 clickable circles in a certain pattern, but I can´t really figure out how to do it. I´m not convinced canvas is the best solution but I dont know how to solve this and get an app with a reasonable performance.
Here´s the layout I´m trying to get:
circle layout
I want 2 rows of circles within each line. the division in the middle is to be left empty.
Every left row has to be 588 circles.
Every right row has to be 560 circles
There are 180 lines on each side which means there's (588*2*180)= 211680 circles on the left side.
There's (560*2*180)=201600 circles on the right side.
can anyone point me in the right direction, maybe have a clue how I can solve this in the most efficient way possible? Thanks in advance.
EDIT: here's the JSFiddle I've got so far jsfiddle.net/cmxLoqej/2/
JavaScript
window.onload = draw;
function draw() {
var canvas = document.getElementById('canvas');
var c = canvas.getContext('2d');
var ycoordinate = 20;
//draw the line 180 times
for (var x = 1; x <= 180; x++) {
// draw the left side
for (var i = 1; i <= 1; i++){
c.strokeStyle = 'black';
c.moveTo(0,ycoordinate);
c.lineTo(6468,ycoordinate);
c.stroke();
ycoordinate = ycoordinate + 40;
}
}
var ycoordinate = 20;
//draw right side
for (var x = 1; x <= 180; x++) {
for (var j = 1; j <= 1; j++){
c.strokeStyle = 'black';
c.moveTo(6776,ycoordinate);
c.lineTo(canvas.width,ycoordinate);
c.stroke();
ycoordinate = ycoordinate + 40;
}
}
}
var canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');
var canvasPattern = document.createElement("canvas");
canvasPattern.width=11;
canvasPattern.height=20;
var contextPattern = canvasPattern.getContext("2d");
contextPattern.beginPath();
contextPattern.arc(5, 10, 5, 0, 2 * Math.PI, false);
contextPattern.strokeStyle = '#003300';
contextPattern.stroke();
var pattern = context.createPattern(canvasPattern,"repeat");
context.fillStyle = pattern;
context.fillRect(0, 20, 6468, 7160);
context.fill();
var canvas2 = document.getElementById('canvas');
var context2 = canvas.getContext('2d');
var canvasPattern2 = document.createElement("canvas");
canvasPattern2.width=11;
canvasPattern2.height=20;
var contextPattern2 = canvasPattern.getContext("2d");
contextPattern2.beginPath();
contextPattern2.arc(5, 10, 5, 0, 2 * Math.PI, false);
contextPattern2.strokeStyle = '#003300';
contextPattern2.stroke();
var pattern2 = context2.createPattern(canvasPattern2,"repeat");
context2.fillStyle = pattern;
context2.fillRect(6776, 20, 6160, 7160);
context2.fill();
HTML
<!DOCTYPE html>
<html>
<body>
<canvas {
id="canvas";
width= "12936" ;
height ="7400";
style= "border: 1px solid black;";
padding: 0;
margin: auto;
display: block;
}>
</canvas>
</body>
</html>
Use fill patterns of circles to create rectangular canvas images of
a single row of the left hand side
a single row of the right hand side
a combined row of each side
a single canvas of 180 rows
Use temporary CANVAS objects along the way as necessary to use the context2D.createPattern method. You should not need to add them to the DOM just to manipulate pixels.
Modify the algorithm if needed as you learn. Happy coding!
Update (edit)
Running the code added to the question shows all circles being evenly spaced horizontally and vertically.
A simpler way of drawing the canvas may be to fill two rectangles that exactly cover the left and right areas of the canvas with the circle pattern, and draw the grid lines on the canvas afterwards instead of before.
Finding the circle clicked
A click event listener on the canvas is passed a mouse event object.
The classical way to determine which circle was clicked was to first perform arithmetic on the screenX and screenY event properties for screen position, window.scrollX and window.scrollY for document scroll amounts, and the position of the canvas within the document, to find where the click occured in the canvas.
Although not yet fully standardized, offsetX and offsetY properties of the mouse event object provide the result directly. The MDN reference shows fairly good cross browser support.
Then knowledge of canvas layout can be used to determine which rectangular circle pattern was clicked, and with a bit of algebra if the click is inside the circle.
How is it / is it possible to draw using the mouse a canvas using 3 axis(x,y,z).
I know that one can draw a canvas on 2 axis and I have done that successfully.
But I have no idea of how I shall draw it on 3 axis (for example a cube).
Following shows some 2d canvas drawing functionallity
$(canvas).on('mousemove', function(e) {
mousex = parseInt(e.clientX-canvasx);
mousey = parseInt(e.clientY-canvasy);
if(mousedown) {
ctx.beginPath();
if(tooltype=='draw') {
ctx.globalCompositeOperation = 'source-over';
ctx.strokeStyle = 'black';
ctx.lineWidth = 3;
} else {
ctx.globalCompositeOperation = 'destination-out';
ctx.lineWidth = 10;
}
ctx.moveTo(last_mousex,last_mousey);
ctx.lineTo(mousex,mousey);
ctx.lineJoin = ctx.lineCap = 'round';
ctx.stroke();
}
last_mousex = mousex;
last_mousey = mousey;
//Output
$('#output').html('current: '+mousex+', '+mousey+'<br/>last: '+last_mousex+', '+last_mousey+'<br/>mousedown: '+mousedown);
});
The full code https://jsfiddle.net/ArtBIT/kneDX/.
But how can I add a z axis and draw a 3d canvas for instance a cube.
With 2D it is simple, you have the X and Y coordinate of the mouse, and when a mouse button is clicked you can change pixels at that location in the canvas.
3D on the other hand is quite hard. Because of the extra dimension that does not exist on the 2D surface, you need to know how to control the 3D positions. And to make matters worse, with that third dimension comes all kinds of extra's that everyone likes to have: lightning and shadows, effects, focus, etc.
Simple drawing
In its most basic form, (set aside some arithmic) you can flatten the Z axis on the 2D surface with a single division. Suppose that you have a point in 3D which consists of three points on three axis (x3d, y3d, z3d) then you can do:
var x2d = x3d / z3d;
var y2d = y3d / z3d;
If you're new to 3D, you will want to play with this first. Here is a tutorial.
Advanced drawing
For just particles and lines this is rather straightforward, although you might want to use another perspective. But it gets more complicated soon when you use objects and want to rotate them in 3D space. This is why most people rely on an engine like three.js to do the 3D drawing for them.
Control 3D space
When drawing with the mouse, you need to map the 2D mouse movement to 3D for control. For examples, have a look a these 3D GUI's: Microsoft's Paint 3D, Google's Sketchup, and Blender. Note that the more kinds of mappings needs to be implemented (like scaling and other transformations) the more math is required.
Using three.js would help you out. See here: https://jsfiddle.net/bn890dtc/
The core code for drawing the line as your click and drag:
function onMouseMove(evt) {
if (renderer) {
var x = (event.clientX / window.innerWidth) * 2 - 1;
var y = -(event.clientY / window.innerHeight) * 2 + 1;
var z = 0
var vNow = new THREE.Vector3(x, y, z);
vNow.unproject(camera);
splineArray.push(vNow);
}
}
The line
vNow.unproject(camera);
will project your drawing into 3D space.
This function will update the line in 3D space:
function updatePositions() {
var positions = line.geometry.attributes.position.array;
var index = 0;
for ( var i = 0; i < splineArray.length; i ++ ) {
positions[ index ++ ] = splineArray[i].x;
positions[ index ++ ] = splineArray[i].y;
positions[ index ++ ] = splineArray[i].z;
}
}
I have two canvas elements and need them to be resized on buttons click.
<div class="sDetails"><div>
<div id="canvasDiv" style="width: 310px;"><canvas id="canvasGraph"></canvas></div></div>
<div class="kDetails"><div><div>
<div id="canvasDiv" style="width: 310px; height: 240px;"><canvas id="canvasGraph"></canvas></div></div>
and the script:
var sketch;var sketch_sl;var onPaint;var canvas=null;var ctx=null;var tmp_ctx=null;
function drawCanvas(div) {
canvas = document.querySelector(div + " #canvasGraph");
ctx = canvas.getContext('2d');
sketch = document.querySelector(div + " #canvasDiv");
sketch_sl = getComputedStyle(sketch);
canvas.width = parseInt(sketch_style.getPropertyValue('width'));
canvas.height = parseInt(sketch_style.getPropertyValue('height'));
tmp_canvas = document.createElement('canvas');
tmp_ctx = tmp_canvas.getContext('2d');
tmp_canvas.id = 'tmp_canvas';
tmp_canvas.width = canvas.width;
tmp_canvas.height = canvas.height;
sketch.appendChild(tmp_canvas);
the redraw function:
// here I must redraw my lines resized 2 times ( *cScale ) where cScale=2 or =1
function drawScales(ctx, canvas)
ctx.strokeStyle = 'green';
ctx.fillStyle = 'green';
ctx.beginPath();
ctx.moveTo(5, 0);
ctx.lineTo(0, canvas.height);
scaleStep = 24*cScale;
for some reason it works really bad, old positions stay.
Is there a way to completely delete the whole canvas and append it or redraw it completely?
I tried canvas.width=canvas.width, tried ctx.clearRect(0, 0, canvas.width, canvas.height);tmp_ctx.clearRect(0, 0, canvas.width, canvas.height);, tried $(".sDetails #canvasGraph")[0].reset();
logically, drawCanvas(".sDetails");drawLines(ctx, canvas); should redraw it from scratch but it will not.
Resize the canvas element's width & height and use context.scale to redraw the original drawings at their newly scaled size.
Resizing the canvas element will automatically clear all drawings off the canvas.
Resizing will also automatically reset all context properties back to their default values.
Using context.scale is useful because then the canvas will automatically rescale the original drawings to fit on the newly sized canvas.
Important: Canvas will not automatically redraw the original drawings...you must re-issue the original drawing commands.
Illustration with 2 canvases at same size (their sizes are controlled by range controls)
Illustration with left canvas resized larger
Illustration with right canvas resized larger
Here's example code and a Demo. This demo uses range elements to control the resizing, but you can also do the resizing+redrawing inside window.onresize
var canvas1=document.getElementById("canvas1");
var ctx1=canvas1.getContext("2d");
var canvas2=document.getElementById("canvas2");
var ctx2=canvas2.getContext("2d");
var originalWidth=canvas1.width;
var originalHeight=canvas1.height;
var scale1=1;
var scale2=1;
$myslider1=$('#myslider1');
$myslider1.attr({min:50,max:200}).val(100);
$myslider1.on('input change',function(){
var scale=parseInt($(this).val())/100;
scale1=scale;
redraw(ctx1,scale);
});
$myslider2=$('#myslider2');
$myslider2.attr({min:50,max:200}).val(100);
$myslider2.on('input change',function(){
var scale=parseInt($(this).val())/100;
scale2=scale;
redraw(ctx2,scale);
});
draw(ctx1);
draw(ctx2);
function redraw(ctx,scale){
// Resizing the canvas will clear all drawings off the canvas
// Resizing will also automatically clear the context
// of all its current values and set default context values
ctx.canvas.width=originalWidth*scale;
ctx.canvas.height=originalHeight*scale;
// context.scale will scale the original drawings to fit on
// the newly resized canvas
ctx.scale(scale,scale);
draw(ctx);
// always clean up! Reverse the scale
ctx.scale(-scale,-scale);
}
function draw(ctx){
// note: context.scale causes canvas to do all the rescaling
// math for us, so we can always just draw using the
// original sizes and x,y coordinates
ctx.beginPath();
ctx.moveTo(150,50);
ctx.lineTo(250,150);
ctx.lineTo(50,150);
ctx.closePath();
ctx.stroke();
ctx.fillStyle='skyblue';
ctx.beginPath();
ctx.arc(150,50,20,0,Math.PI*2);
ctx.closePath();
ctx.fill();
ctx.stroke();
ctx.beginPath();
ctx.arc(250,150,20,0,Math.PI*2);
ctx.closePath();
ctx.fill();
ctx.stroke();
ctx.beginPath();;
ctx.arc(50,150,20,0,Math.PI*2);
ctx.fill();
ctx.stroke();
}
$("#canvas1, #canvas2").mousemove(function(e){handleMouseMove(e);});
var $mouse=$('#mouse');
function handleMouseMove(e){
// tell the browser we're handling this event
e.preventDefault();
e.stopPropagation();
var bb=e.target.getBoundingClientRect();
mouseX=parseInt(e.clientX-bb.left);
mouseY=parseInt(e.clientY-bb.top);
if(e.target.id=='canvas1'){
$mouse.text('Mouse1: '+mouseX/scale1+' / '+mouseY/scale1+' (scale:'+scale1+')');
}else{
$mouse.text('Mouse2: '+mouseX/scale2+' / '+mouseY/scale2+' (scale:'+scale2+')');
}
}
body{ background-color: ivory; }
canvas{border:1px solid red;}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<div>Resize left canvas</div>
<input id=myslider1 type=range><br>
<div>Resize right canvas</div>
<input id=myslider2 type=range><br>
<h4 id=mouse>Mouse coordinates:</h4>
<canvas id="canvas1" width=300 height=300></canvas>
<canvas id="canvas2" width=300 height=300></canvas>
If you need scale-independent positions you could use normalized values ([0, 1]) instead and use the size of canvas as the scale factor. This way you can scale and store values without too much concern about the actual target size.
You would also be able to use the mouse positions almost as is and normalize by just dividing them on canvas size.
For example:
When rendering, a point of (1,1) will always draw in lower-right corner as you would do (1 * canvas.width, 1 * canvas.height).
When you store a point you would use the mouse position and divide it on the canvas dimension, for example, if I click in the lower right corner of a canvas of size 400x200, the points would be 400/400 = 1, 200/200 = 1.
Note that width and height would be exclusive (ie. width-1 etc.), but for sake of simplicity...
Example
In this example you can start with any size of the canvas, draw points which are normalized, change size of canvas and have the points redrawn proportionally relative to the original position.
var rng = document.querySelector("input"),
c = document.querySelector("canvas"),
ctx = c.getContext("2d"),
points = [];
// change canvas size and redraw all points
rng.onchange = function() {
c.width = +this.value;
render();
};
// add a new normalized point to array
c.onclick = function(e) {
var r = this.getBoundingClientRect(), // to adjust mouse position
x = e.clientX - r.left,
y = e.clientY - r.top;
points.push({
x: x / c.width, // normalize value to range [0, 1]
y: y / c.height
}); // store point
render(); // redraw (for demo)
};
function render() {
ctx.clearRect(0, 0, c.width, c.height); // clear canvas
ctx.beginPath(); // clear path
for(var i = 0, p; p = points[i]; i++) { // draw points as fixed-size circles
var x = p.x * c.width, // normalized to absolute values
y = p.y * c.height;
ctx.moveTo(x + 5, y);
ctx.arc(x, y, 5, 0, 6.28);
ctx.closePath();
}
ctx.stroke();
}
canvas {background:#ddd}
<h3>Click on canvas to add points, then resize</h3>
<label>Width: <input type="range" min=50 max=600 value=300></label><br>
<canvas></canvas>
I decided to use a scale variable to resize my scales. I resize the canvas canvas.width *= 2; and then I redraw my scales.
var scaleStep;
and use add it into the code: ctx.lineTo(12*24*cScale+12, canvas.height-24); where the scaling needs to be done.
The scaleStep is 2 when maximizing the canvas and 1 when returning to the original size.
I'd like to give a sprite an outline when the character gets healed/damaged/whatever but I can't think of a way to code this using the 2d canvas. If it were possible, I'd think it would be a global composite operation, but I can't think of a way to achieve it with one of them.
I did find this stackoverflow answer that recommends creating a fatter, solid color version of the original and put the original on top of it. That would give it an outline, but it seems like a lot of extra work especially considering I'm using placeholder art. Is there an easier way?
This question is different from the one linked because this is specifically about the HTML5 2D canvas. It may have a solution not available to the other question.
For what it's worth, I don't mind if the outline creates a wider border or keeps the sprite the same size, I just want the outline look.
Just draw your original image in 8 position around the original image
Change composite mode to source-in and fill with the outline color
Change composite mode back to source-over and draw in the original image at correct location
This will create a clean sharp outline with equal border thickness on every side. It is not so suited for thick outlines however. Image drawing is fast, especially when image is not scaled so performance is not an issues unless you need to draw a bunch (which in that case you would cache the drawings or use a sprite-sheet anyways).
Example:
var ctx = canvas.getContext('2d'),
img = new Image;
img.onload = draw;
img.src = "http://i.stack.imgur.com/UFBxY.png";
function draw() {
var dArr = [-1,-1, 0,-1, 1,-1, -1,0, 1,0, -1,1, 0,1, 1,1], // offset array
s = 2, // scale
i = 0, // iterator
x = 5, // final position
y = 5;
// draw images at offsets from the array scaled by s
for(; i < dArr.length; i += 2)
ctx.drawImage(img, x + dArr[i]*s, y + dArr[i+1]*s);
// fill with color
ctx.globalCompositeOperation = "source-in";
ctx.fillStyle = "red";
ctx.fillRect(0,0,canvas.width, canvas.height);
// draw original image in normal mode
ctx.globalCompositeOperation = "source-over";
ctx.drawImage(img, x, y);
}
<canvas id=canvas width=500 height=500></canvas>
Maybe it would be worth trying this :
• build a canvas 1.1 time bigger than the original sprite
• fill it with the outline color
• draw the sprite scaled by 1.1 on the canvas using destination-in globalCompositeOperation.
Then you have a bigger 'shadow' of your sprite in the outline color.
When you want to draw the outline :
• draw the 'shadow' (centered)
• draw your sprite within the shadow.
Depending on the convexity of your sprite, this will work more or less nicely, but i think it's worth trying since it avoids you doubling the number of input graphic files.
I just did a short try as proof-of-concept and it quite works :
http://jsbin.com/dogoroxelupo/1/edit?js,output
Before :
After :
html
<html>
<body>
<image src='http://www.gifwave.com/media/463554/cartoons-comics-video-games-sprites-scott-pilgrim-paul-robertson_200s.gif' id='spr'></image>
<canvas id='cv' width = 500 height= 500 ></canvas>
</body>
</html>
code
window.onload=function() {
var spr = document.getElementById('spr');
var margin = 4;
var gh = createGhost(spr, '#F80', margin);
var cv = document.getElementById('cv');
var ctx = cv.getContext('2d');
var outlined = true;
setInterval(function() {
ctx.clearRect(0,0,cv.width, cv.height);
if (outlined)
ctx.drawImage(gh, 0, 0)
ctx.drawImage(spr, 0, 0)
outlined = !outlined;
}, 400);
}
function createGhost (img, color, margin) {
var cv= document.createElement('canvas');
cv.width = img.width+2*margin;
cv.height = img.height + 2*margin;
var ctx = cv.getContext('2d');
ctx.fillStyle = color;
ctx.fillRect(0,0, cv.width, cv.height);
ctx.save();
ctx.globalCompositeOperation = 'destination-in';
var scale = cv.width/spr.width;
ctx.scale(cv.width/spr.width, cv.height/spr.height);
ctx.drawImage(img, -margin, -margin);
ctx.restore();
return cv;
}
You could use strokeRect method to outline the sprite after drawing it. It should be asy if you know your sprite's dimensions...
the example of the code below can be viewed here - http://dev.touch-akl.com/celebtrations/
What I have been trying to do is draw 2 images onto the canvas (glow and then flare. links for these images are below)
http://dev.touch-akl.com/celebtrations/wp-content/themes/beanstalk/img/flare.jpg
http://dev.touch-akl.com/celebtrations/wp-content/themes/beanstalk/img/blue-background.jpg
The goal is for the 'blue-background' image to sit on the canvas at the height and width of the container, and for the 'flare' image to be drawn ontop of this image with a blending mode and rotated with an animation to create a kind of twinkle effect.
My problem is that because the images I am using are rectangular when the 'flare' rotates at certain points you can see the edges of the layer underneath...
What I tried to do was find the diagonal width of the container using trigonometry and draw the 'flare' image at that width so that it always covered the whole canvas but alas you can still see the background layer at some points (but much less than before).
I need a way for the flare image to always cover the whole canvas, can anyone point me in the right direction please?
var banner = $('#banner'),
flare = document.getElementById('flare'),
glow = document.getElementById('glow'),
canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d"),
blendMode = "multiply";
$window.load(function(){
_canvasWidth = banner.outerWidth(),
_canvasHeight = banner.outerHeight();
canvas.width = _canvasWidth;
canvas.height = _canvasHeight;
var _flareSum = (_canvasWidth * _canvasWidth) + (_canvasHeight * _canvasHeight);
_flareWidth = Math.sqrt(_flareSum);
_angle = 0;
setInterval(function() {
_angle = _angle +0.25;
// draw the bg without a blend mode
ctx.globalCompositeOperation = "source-over";
ctx.drawImage(glow, 0, 0, _canvasWidth, _canvasHeight);
ctx.save();
// clear the canvas
// ctx.clearRect(0, 0, _canvasWidth, _canvasHeight);
ctx.translate( _canvasWidth/2, _canvasHeight); // move to center point
ctx.globalCompositeOperation = blendMode;
ctx.rotate(Math.PI / 180 * (_angle)); // 1/2 a degree
ctx.drawImage(flare, -_flareWidth/2, -_flareWidth/2, _flareWidth, _flareWidth); // redraw ia=mages
ctx.restore();
//console.log(_angle)
}, 1);
If I understand correctly, you need the shortest part of the flare to still cover the canvas when the flare is rotated at any angle.
Since you're only showing half the flare at any time, the shortest part of the flare is the distance from the flare center to the top of the flare:
var flareMinHeight = flare.height/2;
The longest length the flare must cover is from the flare rotation point to the top-left of the canvas.
var dx=rotationPointX;
var dy=rotationPointY;
var requiredLength=Math.sqrt(dx*dx+dy*dy);
So you will need to scale the flare to be at least the length computed above:
var minScale = requiredLength / flareMinHeight;