Canvas has two sizes, the size of the element and the size of the drawing surface. The default size for both element and drawing surface is 300 x 150 screen pixels. To set the height and width canvas HTML5 has two attributes: Height: With the help of Height attribute we can set the height.
The width attribute specifies the width of the <canvas> element, in pixels. Tip: Use the height attribute to specify the height of the <canvas> element, in pixels. Tip: Each time the height or width of a canvas is re-set, the canvas content will be cleared (see example at bottom of page).
The HTML <canvas> height Attribute is used to specify the height of the <canvas> element in terms of pixels. Attribute Values: It contains single value pixels which specify the height of the canvas in terms of pixel. It has a Default value which is 150.
The canvas
DOM element has .height
and .width
properties that correspond to the height="…"
and width="…"
attributes. Set them to numeric values in JavaScript code to resize your canvas. For example:
var canvas = document.getElementsByTagName('canvas')[0];
canvas.width = 800;
canvas.height = 600;
Note that this clears the canvas, though you should follow with ctx.clearRect( 0, 0, ctx.canvas.width, ctx.canvas.height);
to handle those browsers that don't fully clear the canvas. You'll need to redraw of any content you wanted displayed after the size change.
Note further that the height and width are the logical canvas dimensions used for drawing and are different from the style.height
and style.width
CSS attributes. If you don't set the CSS attributes, the intrinsic size of the canvas will be used as its display size; if you do set the CSS attributes, and they differ from the canvas dimensions, your content will be scaled in the browser. For example:
// Make a canvas that has a blurry pixelated zoom-in
// with each canvas pixel drawn showing as roughly 2x2 on screen
canvas.width = 400;
canvas.height = 300;
canvas.style.width = '800px';
canvas.style.height = '600px';
See this live example of a canvas that is zoomed in by 4x.
var c = document.getElementsByTagName('canvas')[0];
var ctx = c.getContext('2d');
ctx.lineWidth = 1;
ctx.strokeStyle = '#f00';
ctx.fillStyle = '#eff';
ctx.fillRect( 10.5, 10.5, 20, 20 );
ctx.strokeRect( 10.5, 10.5, 20, 20 );
ctx.fillRect( 40, 10.5, 20, 20 );
ctx.strokeRect( 40, 10.5, 20, 20 );
ctx.fillRect( 70, 10, 20, 20 );
ctx.strokeRect( 70, 10, 20, 20 );
ctx.strokeStyle = '#fff';
ctx.strokeRect( 10.5, 10.5, 20, 20 );
ctx.strokeRect( 40, 10.5, 20, 20 );
ctx.strokeRect( 70, 10, 20, 20 );
body { background:#eee; margin:1em; text-align:center }
canvas { background:#fff; border:1px solid #ccc; width:400px; height:160px }
<canvas width="100" height="40"></canvas>
<p>Showing that re-drawing the same antialiased lines does not obliterate old antialiased lines.</p>
A canvas has 2 sizes, the dimension of the pixels in the canvas (it's backingstore or drawingBuffer) and the display size. The number of pixels is set using the the canvas attributes. In HTML
<canvas width="400" height="300"></canvas>
Or in JavaScript
someCanvasElement.width = 400;
someCanvasElement.height = 300;
Separate from that are the canvas's CSS style width and height
In CSS
canvas { /* or some other selector */
width: 500px;
height: 400px;
}
Or in JavaScript
canvas.style.width = "500px";
canvas.style.height = "400px";
The arguably best way to make a canvas 1x1 pixels is to ALWAYS USE CSS to choose the size then write a tiny bit of JavaScript to make the number of pixels match that size.
function resizeCanvasToDisplaySize(canvas) {
// look up the size the canvas is being displayed
const width = canvas.clientWidth;
const height = canvas.clientHeight;
// If it's resolution does not match change it
if (canvas.width !== width || canvas.height !== height) {
canvas.width = width;
canvas.height = height;
return true;
}
return false;
}
Why is this the best way? Because it works in most cases without having to change any code.
const ctx = document.querySelector("#c").getContext("2d");
function render(time) {
time *= 0.001;
resizeCanvasToDisplaySize(ctx.canvas);
ctx.fillStyle = "#DDE";
ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
ctx.save();
const spacing = 64;
const size = 48;
const across = ctx.canvas.width / spacing + 1;
const down = ctx.canvas.height / spacing + 1;
const s = Math.sin(time);
const c = Math.cos(time);
for (let y = 0; y < down; ++y) {
for (let x = 0; x < across; ++x) {
ctx.setTransform(c, -s, s, c, x * spacing, y * spacing);
ctx.strokeRect(-size / 2, -size / 2, size, size);
}
}
ctx.restore();
requestAnimationFrame(render);
}
requestAnimationFrame(render);
function resizeCanvasToDisplaySize(canvas) {
// look up the size the canvas is being displayed
const width = canvas.clientWidth;
const height = canvas.clientHeight;
// If it's resolution does not match change it
if (canvas.width !== width || canvas.height !== height) {
canvas.width = width;
canvas.height = height;
return true;
}
return false;
}
body { margin: 0; }
canvas { display: block; width: 100vw; height: 100vh; }
<canvas id="c"></canvas>
const ctx = document.querySelector("#c").getContext("2d");
function render(time) {
time *= 0.001;
resizeCanvasToDisplaySize(ctx.canvas);
ctx.fillStyle = "#DDE";
ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
ctx.save();
const spacing = 64;
const size = 48;
const across = ctx.canvas.width / spacing + 1;
const down = ctx.canvas.height / spacing + 1;
const s = Math.sin(time);
const c = Math.cos(time);
for (let y = 0; y <= down; ++y) {
for (let x = 0; x <= across; ++x) {
ctx.setTransform(c, -s, s, c, x * spacing, y * spacing);
ctx.strokeRect(-size / 2, -size / 2, size, size);
}
}
ctx.restore();
requestAnimationFrame(render);
}
requestAnimationFrame(render);
function resizeCanvasToDisplaySize(canvas) {
// look up the size the canvas is being displayed
const width = canvas.clientWidth;
const height = canvas.clientHeight;
// If it's resolution does not match change it
if (canvas.width !== width || canvas.height !== height) {
canvas.width = width;
canvas.height = height;
return true;
}
return false;
}
span {
width: 250px;
height: 100px;
float: left;
padding: 1em 1em 1em 0;
display: inline-block;
}
canvas {
width: 100%;
height: 100%;
}
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Praesent cursus venenatis metus. Mauris ac nibh at odio scelerisque scelerisque. Donec ut enim <span class="diagram"><canvas id="c"></canvas></span>
vel urna gravida imperdiet id ac odio. Aenean congue hendrerit eros id facilisis. In vitae leo ullamcorper, aliquet leo a, vehicula magna. Proin sollicitudin vestibulum aliquet. Sed et varius justo.
<br/><br/>
Quisque tempor metus in porttitor placerat. Nulla vehicula sem nec ipsum commodo, at tincidunt orci porttitor. Duis porttitor egestas dui eu viverra. Sed et ipsum eget odio pharetra semper. Integer tempor orci quam, eget aliquet velit consectetur sit amet. Maecenas maximus placerat arcu in varius. Morbi semper, quam a ullamcorper interdum, augue nisl sagittis urna, sed pharetra lectus ex nec elit. Nullam viverra lacinia tellus, bibendum maximus nisl dictum id. Phasellus mauris quam, rutrum ut congue non, hendrerit sollicitudin urna.
</p>
const ctx = document.querySelector("#c").getContext("2d");
function render(time) {
time *= 0.001;
resizeCanvasToDisplaySize(ctx.canvas);
ctx.fillStyle = "#DDE";
ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
ctx.save();
const spacing = 64;
const size = 48;
const across = ctx.canvas.width / spacing + 1;
const down = ctx.canvas.height / spacing + 1;
const s = Math.sin(time);
const c = Math.cos(time);
for (let y = 0; y < down; ++y) {
for (let x = 0; x < across; ++x) {
ctx.setTransform(c, -s, s, c, x * spacing, y * spacing);
ctx.strokeRect(-size / 2, -size / 2, size, size);
}
}
ctx.restore();
requestAnimationFrame(render);
}
requestAnimationFrame(render);
function resizeCanvasToDisplaySize(canvas) {
// look up the size the canvas is being displayed
const width = canvas.clientWidth;
const height = canvas.clientHeight;
// If it's resolution does not match change it
if (canvas.width !== width || canvas.height !== height) {
canvas.width = width;
canvas.height = height;
return true;
}
return false;
}
// ----- the code above related to the canvas does not change ----
// ---- the code below is related to the slider ----
const $ = document.querySelector.bind(document);
const left = $(".left");
const slider = $(".slider");
let dragging;
let lastX;
let startWidth;
slider.addEventListener('mousedown', e => {
lastX = e.pageX;
dragging = true;
});
window.addEventListener('mouseup', e => {
dragging = false;
});
window.addEventListener('mousemove', e => {
if (dragging) {
const deltaX = e.pageX - lastX;
left.style.width = left.clientWidth + deltaX + "px";
lastX = e.pageX;
}
});
body {
margin: 0;
}
.frame {
display: flex;
align-items: space-between;
height: 100vh;
}
.left {
width: 70%;
left: 0;
top: 0;
right: 0;
bottom: 0;
}
canvas {
width: 100%;
height: 100%;
}
pre {
padding: 1em;
}
.slider {
width: 10px;
background: #000;
}
.right {
flex 1 1 auto;
}
<div class="frame">
<div class="left">
<canvas id="c"></canvas>
</div>
<div class="slider">
</div>
<div class="right">
<pre>
* controls
* go
* here
<- drag this
</pre>
</div>
</div>
const ctx = document.querySelector("#c").getContext("2d");
function render(time) {
time *= 0.001;
resizeCanvasToDisplaySize(ctx.canvas);
ctx.fillStyle = "#DDE";
ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
ctx.save();
const spacing = 64;
const size = 48;
const across = ctx.canvas.width / spacing + 1;
const down = ctx.canvas.height / spacing + 1;
const s = Math.sin(time);
const c = Math.cos(time);
for (let y = 0; y < down; ++y) {
for (let x = 0; x < across; ++x) {
ctx.setTransform(c, -s, s, c, x * spacing, y * spacing);
ctx.strokeRect(-size / 2, -size / 2, size, size);
}
}
ctx.restore();
requestAnimationFrame(render);
}
requestAnimationFrame(render);
function resizeCanvasToDisplaySize(canvas) {
// look up the size the canvas is being displayed
const width = canvas.clientWidth;
const height = canvas.clientHeight;
// If it's resolution does not match change it
if (canvas.width !== width || canvas.height !== height) {
canvas.width = width;
canvas.height = height;
return true;
}
return false;
}
body { margin: 0; }
canvas {
display: block;
width: 100vw;
height: 100vh;
position: fixed;
}
#content {
position: absolute;
margin: 0 1em;
font-size: xx-large;
font-family: sans-serif;
font-weight: bold;
text-shadow: 2px 2px 0 #FFF,
-2px -2px 0 #FFF,
-2px 2px 0 #FFF,
2px -2px 0 #FFF;
}
<canvas id="c"></canvas>
<div id="content">
<p>
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Praesent cursus venenatis metus. Mauris ac nibh at odio scelerisque scelerisque. Donec ut enim vel urna gravida imperdiet id ac odio. Aenean congue hendrerit eros id facilisis. In vitae leo ullamcorper, aliquet leo a, vehicula magna. Proin sollicitudin vestibulum aliquet. Sed et varius justo.
</p>
<p>
Quisque tempor metus in porttitor placerat. Nulla vehicula sem nec ipsum commodo, at tincidunt orci porttitor. Duis porttitor egestas dui eu viverra. Sed et ipsum eget odio pharetra semper. Integer tempor orci quam, eget aliquet velit consectetur sit amet. Maecenas maximus placerat arcu in varius. Morbi semper, quam a ullamcorper interdum, augue nisl sagittis urna, sed pharetra lectus ex nec elit. Nullam viverra lacinia tellus, bibendum maximus nisl dictum id. Phasellus mauris quam, rutrum ut congue non, hendrerit sollicitudin urna.
</p>
</div>
Because I didn't set the attributes the only thing that changed in each sample is the CSS (as far as the canvas is concerned)
Notes:
Thank you very much! Finally I solved the blurred pixels problem with this code:
<canvas id="graph" width=326 height=240 style='width:326px;height:240px'></canvas>
With the addition of the 'half-pixel' does the trick to unblur lines.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With