I want to write some text over a gradient (to make a scale):
I have this so far:
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
// Create gradient
var grd = ctx.createLinearGradient(0,0,500,0);
grd.addColorStop(0,"red");
grd.addColorStop(0.5,"yellow");
grd.addColorStop(1,"green");
// Fill with gradient
ctx.font = "30px Arial";
ctx.fillText("Hello World",10,50);
ctx.fillStyle = grd;
ctx.fillRect(0,0,500,100);
<canvas id="myCanvas" width="500" height="100" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>
I can't see the text. How can I fix this?
I want to create this:
Where the circle is generated from some score that I give.
There are two issues:
You're drawing the background overtop of the text
You're drawing the background and text in the same gradient, so the text will be invisible on top of the background
Move the text-drawing after the rectangle, and change its color:
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
// Create gradient
var grd = ctx.createLinearGradient(0,0,500,0);
grd.addColorStop(0,"red");
grd.addColorStop(0.5,"yellow");
grd.addColorStop(1,"green");
// Fill with gradient
ctx.font = "30px Arial";
ctx.fillStyle = grd;
ctx.fillRect(0,0,500,100);
ctx.fillStyle = "#000";
ctx.fillText("Hello World",10,50);
<canvas id="myCanvas" width="500" height="100" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>
You may want to set the text last. I can see you are drawing the filled rectangle over the text you have already drawn. Try doing this instead:
<canvas id="myCanvas" width="500" height="100" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
// Create gradient
var grd = ctx.createLinearGradient(0,0,500,0);
grd.addColorStop(0,"red");
grd.addColorStop(0.5,"yellow");
grd.addColorStop(1,"green");
// Fill with gradient
ctx.fillStyle = grd;
ctx.fillRect(0,0,500,100);
//write text with canvas methods
c.fillStyle = '#000000';
c.font = "30px Arial";
c.fillText("Hello World",10,50);
</script>
You may also want to consider looking up canvas.textAlign and canvas.textBaseline properties for positioning the text;
Related
Why is clearRect() not fully clearing fillRect() when they have the same values in this example?
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = "red";
setInterval(function(){
let rect = {x:Math.random()*c.width, y:Math.random()*c.height}
ctx.fillRect(rect.x, rect.y, 5, 5);
ctx.clearRect(rect.x, rect.y, 5,5);
},500)
<canvas id="myCanvas" width="300" height="150" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>
Because of antialiasing.
You are drawing at non-integer coordinates, while you can't have half pixel rendered, so the pixels colors are shaded with some transparency to give this illusion of smaller pixels than a pixel.
However, clearRect() is also subject to this antialiasing, and thus will leave some translucent pixels.
To avoid this try to always draw at pixel integers when possible, and moreover, clear the whole canvas and redraw what needs to be at every frame.
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = "red";
setInterval(function() {
// clear all
ctx.clearRect(0, 0, c.width, c.height);
// redraw what needs to be
let rect = {
x: Math.random() * c.width,
y: Math.random() * c.height
}
ctx.fillRect(rect.x, rect.y, 5, 5);
}, 500)
<canvas id="myCanvas" width="300" height="150" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>
I am interested in making CSS filter's apply to a javascript canvas's image data. I have already found the canvas context filter. For example, this works with blur.
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
ctx.filter = 'blur(3px)';
ctx.font = '48px serif';
ctx.strokeText('Hello world', 50, 100);
<canvas id="canvas"></canvas>
While the code below doesn't work because if it did, then the whole screen would be white.
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
ctx.filter = 'brightness(1000%)';
ctx.font = '48px serif';
ctx.strokeText('Hello world', 50, 100);
<canvas id="canvas"></canvas>
Also, as a side note, I do not care to have my application available on non Chrome/FF browsers, so please don't mention this unless if you have a polyfill for it.
I have found the answer to my question: you have to draw the canvas onto itself to apply the filters.
var canvas1 = document.getElementById('canvas1');
var ctx1 = canvas1.getContext('2d');
var canvas2 = document.getElementById('canvas2');
var ctx2 = canvas2.getContext('2d');
ctx1.font = '48px serif';
ctx1.strokeStyle = 'red';
ctx1.strokeText('Hello world', 50, 50);
ctx1.filter = 'brightness(0%)';
ctx2.font = '48px serif';
ctx2.strokeStyle = 'red';
ctx2.strokeText('Hello world', 50, 50);
ctx2.filter = 'brightness(0%)';
ctx2.drawImage(canvas2, 0, 0);
Before<br />
<canvas id=1></canvas><br />
After<br />
<canvas id=2></canvas>
You don't see the brightness effect because text has black color for default.
Brightness changes the concentration of selected color and mixes it with black color, so, for example, if you have red-colored text and brightness property 70%, then your text will have 70% red and 30% black color.
Just add color in strokeStyle:
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
ctx.filter = 'brightness(70%)';
ctx.font = '48px serif';
ctx.strokeStyle = 'red';
ctx.strokeText('Hello world', 50, 100);
<canvas id="canvas"></canvas>
I am learning drawing canvas and now I have task. I need to add an image within the inner circle. The image position needs to be inside the circle. Also I attached the image with this post. My code are:
<!DOCTYPE html>
<html>
<body>
<canvas id="myCanvas" width="200" height="100" style="border:1px solid #c3c3c3;">
Your browser does not support the HTML5 canvas tag.
</canvas>
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = "green";
ctx.fillRect(0,0,200,100);
var cicleT = document.getElementById("myCanvas");
var dtx = cicleT.getContext("2d");
dtx.arc(95,50,40,0,2*Math.PI);
dtx.stroke();
dtx.fillStyle = "red";
dtx.fill();
dtx.fillStyle = "black"; // font color to write the text with
var font = "bold 13px serif";
dtx.font = font;
dtx.textBaseline = "bottom";
dtx.fillText("Bangladesh",50,50, 95 ,25);
</script>
</body>
</html>
You can use ctx.clip to cut out the region you want to draw, and the following operation will be refined on the region, remember to restore when you complete the works that needs to be refined.
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.fillStyle = "green";
ctx.fillRect(0, 0, 200, 100);
ctx.arc(95,50,40,0,2*Math.PI);
ctx.stroke();
ctx.fillStyle = "red";
ctx.fill();
// For safety, I move the draw image and draw text to image.onload.
var image = document.createElement('img');
image.onload = function() {
var iw = image.width;
var ih = image.height;
var r = Math.sqrt(Math.pow(iw/2, 2) + Math.pow(ih/2, 2));
var ratio = 40 / r;
var tw = iw * ratio;
var th = ih * ratio;
// Use the same ctx is ok.
ctx.arc(95, 50, 40, 0, 2 * Math.PI);
ctx.stroke();
// Save the current state of context, which is not clipped yet.
ctx.save();
// Clip by the stroke.
ctx.clip();
// Draw image.
//
ctx.drawImage(image, 0, 0, iw, ih, 95 - tw/2, 50 - th/2, tw, th);
// Restore the context, otherwise the text will also be clipped.
ctx.restore();
ctx.fillStyle = "black"; // font color to write the text with
var font = "bold 13px serif";
ctx.font = font;
ctx.textBaseline = "bottom";
ctx.fillText("Bangladesh", 50, 50, 95, 25);
};
image.src = "https://i.stack.imgur.com/jy3YL.jpg";
<canvas id="myCanvas" width="200" height="100" style="border:1px solid #c3c3c3;">
Your browser does not support the HTML5 canvas tag.
</canvas>
I am working in Jquery.
I have 4 Cordinates , Width, Height, x Position and Y position.
How can i create a Square shape Using This
$('#box').drawRect(20,20,2,30,{color:'red'})
I tried this and Not Working. Looking for a Good Hand
Here is My Demo. http://fiddle.jshell.net/vbm2vhu4/
try using canvas tag in JavaScript..
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.rect(20, 20, 150, 100);
ctx.stroke();
<canvas id="myCanvas" width="300" height="150" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>
JSFIDDLE
JAVASCRIPT
Draw a circle
$(document).ready(function(){
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
var centerX = canvas.width / 2;
var centerY = canvas.height / 2;
var radius = 70;
context.beginPath();
context.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
context.fillStyle = 'green';
context.fill();
context.lineWidth = 5;
context.strokeStyle = '#003300';
context.stroke();
});
Drawing a rectangle requires canvas. You really do not need to use jquery for it. It can be well done with Javascript. I am attaching my example here.
<!DOCTYPE html>
<html>
<body>
<canvas id="myCanvas" width="300" height="150">
Browser does not support the HTML5 canvas tag.</canvas>
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
// Blue rectangle
ctx.beginPath();
ctx.lineWidth = "10";
ctx.strokeStyle = "blue";
ctx.rect(50, 50, 50, 50);
ctx.stroke();
</script>
</body>
</html>
Paste this into a notepad and save as .html and load it in your browser
or jsfiddle http://jsfiddle.net/ssbiswal1987/vsbak0mq/
Is there a way to rotate the existing content of HTML5 canvas by Javascript? I know it's possible to rotate an image that will be drawn on to canvas, but I want to rotate the content that has been drawn on to canvas, for example, a 200x200 corner of a 400x400 canvas, or any specific region of an existing canvas.
Same question to scale the existing canvas content...
I know getImageData/putImageData provide a potential to transform the pixel array, but it's just too slow and inefficient.
It's pretty easy to do with a temp canvas.
Live Demo
Live Demo Animated (just for the heck of it)
The above example draws 2 boxes, then rotates and scales from 0,0 to 200,200
var canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d");
canvas.width = canvas.height = 400;
// fill the canvas black, and draw 2 boxes
ctx.fillStyle = "#000";
ctx.fillRect(0,0,400,400);
ctx.fillStyle = "rgb(255,0,0)";
ctx.fillRect(10,10,190,190);
ctx.fillStyle = "rgb(255,255,0)";
ctx.fillRect(250,250,90,90);
// Create a temp canvas to store our data (because we need to clear the other box after rotation.
var tempCanvas = document.createElement("canvas"),
tempCtx = tempCanvas.getContext("2d");
tempCanvas.width = canvas.width;
tempCanvas.height = canvas.height;
// put our data onto the temp canvas
tempCtx.drawImage(canvas,0,0,canvas.width,canvas.height);
// Append for debugging purposes, just to show what the canvas did look like before the transforms.
document.body.appendChild(tempCanvas);
// Now clear the portion to rotate.
ctx.fillStyle = "#000";
ctx.fillRect(0,0,200,200);
ctx.save();
// Translate (190/2 is half of the box we drew)
ctx.translate(190/2, 0);
// Scale
ctx.scale(0.5,0.5);
// Rotate it
ctx.rotate(45*Math.PI/180);
// Finally draw the image data from the temp canvas.
ctx.drawImage(tempCanvas,0,0,200,200,10,10,190,190);
ctx.restore();
If you first want to draw on a canvas and then rotate it for use on e.g. corners, you can to that when you "clone" the canvas or by using CSS.
Examples
Get the first canvas element:
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
draw on it:
ctx.fillStyle = 'blue';
ctx.fillRect(0,0, 25, 5);
ctx.fill();
ctx.fillStyle = 'red';
ctx.fillRect(25, 0, 25, 5);
ctx.fill();
clone it to another canvas (that is rotated by CSS):
var ctx2 = document.getElementById("canvas2").getContext("2d");
ctx2.drawImage(canvas, 0,0);
or rotate the canvas while you "clone" it:
var ctx3 = document.getElementById("canvas3").getContext("2d");
ctx3.rotate(Math.PI/2);
ctx3.translate(0,-50);
ctx3.drawImage(canvas, 0,0);
here is the CSS for rotating it:
#canvas2 {
-webkit-transform:rotate(90deg);
-moz-transform:rotate(90deg);
-o-transform:rotate(90deg);
-ms-transform:rotate(90deg);
}
Here is the full example:
<!DOCTYPE html>
<html>
<head>
<script>
window.onload = function() {
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
ctx.fillStyle = 'blue';
ctx.fillRect(0,0, 25, 5);
ctx.fill();
ctx.fillStyle = 'red';
ctx.fillRect(25, 0, 25, 5);
ctx.fill();
var ctx2 = document.getElementById("canvas2").getContext("2d");
ctx2.drawImage(canvas, 0,0);
var ctx3 = document.getElementById("canvas3").getContext("2d");
ctx3.rotate(Math.PI/2);
ctx3.translate(0,-50);
ctx3.drawImage(canvas, 0,0);
}
</script>
<style>
#canvas2 {
-webkit-transform:rotate(90deg);
-moz-transform:rotate(90deg);
-o-transform:rotate(90deg);
-ms-transform:rotate(90deg);
}
</style>
</head>
<body>
<canvas id="canvas" width="50" height="50"></canvas>
<canvas id="canvas2" width="50" height="50"></canvas>
<canvas id="canvas3" width="50" height="50"></canvas>
</body>
</html>