Develop Reference

HTML Canvas not drawing extreme points

For some reason, HTML canvas isn't drawing a line between extreme points. Same goes with SVG. I am trying to run the following simple snippet:
As you see, the point with 10^9 draws fine but the one with 10^10 does not. Is there a particular reason? Am I missing something here? Or can I please be pointed to a reference link? I did search but couldn't find a relevant answer.
var ctx = document.getElementById('canvas').getContext('2d');
// draws
//ctx.moveTo(10, -1000000000);
// does not draw
ctx.moveTo(10, -10000000000);
ctx.lineTo(200, 100);
ctx.stroke();
<canvas width="500" height="500" id="canvas"></canvas>
Here's a fiddle if that helps: https://jsfiddle.net/qov72ag4/

JS building up a city map

Alright so I got this issue.
I am currently making a City Map (village) for my game, but the problem is building placing. How do I achieve this?
Now im taking for example Ikariams map as an example, testing grounds. Now this is the map itself
http://www.mmoreviews.com/imgs/Ikariam-shot-1.jpg
Now how do I place the buildings in? Getting coordinates of where the building should be and then just fit in the building.png into it or?

A good solution for that is using the HTML5 Canvas element. That allows you to have a background image and draw other images on it. Drawing lines, circles is quite simple as well (that can be animated with javaScript).
You need the canvas itself:
<canvas id="canvas" width="800" height="600">
</canvas>
Some CSS:
canvas{
background-image: url('village.jpg');
}
And some lines in your <script>
var canvas = document.getElementById("canvas");
var map = canvas.getContext("2d"); //main object to draw
var house=new Image();
house.src='house.jpg';
house.onload=function(){
map.drawImage(house, 80,80); //actually drawing and giving coordinates
}
Hope it is helpful.

Clipping multiple images in HTML5 canvas

I am working on HTML5 canvas with image manipulation. In my canvas I have number of images. When I want to clip the images individually. But when I clip one image by creating a shape and use clip() function, it is working fine. But the problem arise when I try to clip another image using the same method. As the canvas stored the previous shape it will concatenate with the new one and clip the second image accordingly. I want destroy the previous shape. Please note that I can't use the clearRect() to clear the canvas as my previous clipped image is there.
Please ref the link :
Demo Problem
In the link drag the image into canvas predefined layer and drag the image around. You can clearly see that the image got clipped properly if it try to go out of the border.
Now drag another image into the canvas in a different box. Now you can see the clipping is not functioning properly.
Here what I have done in the script :
JS Script
Here the JSFiddle Link
JSFiddle Link
Can you help me to fix this issue?
It will be helpful if you find another way to clear the previous shape.
Thanks in advance.

I have fix the issue by own. The canvas doesn't provide the multiple image clip option. So if you want to clip multiple image in your canvas you have to use your own clip function. Just clear the area by clearRect() of the canvas outside your selection. Iterate this process for each image and you are done !
Solution Link :
Solution Demo
JS Script Link :
JS Script
Thanks.

The best solution I could find is to use a hidden canvas, and draw to that, then use the putImageData method onto your main canvas.
var c = document.getElementById("myCanvas");
var ctemp = document.getElementById("myCanvasTemp");
var ctx = c.getContext("2d");
var ctxTemp = ctemp.getContext("2d");
ctxTemp.fillStyle = "red";
ctxTemp.fillRect(10, 10, 50, 50);
ctxTemp.fillStyle = "blue";
ctxTemp.fillRect(20, 20, 50, 50);
function copy() {
var imgData = ctxTemp.getImageData(10, 20, 50, 10);
ctx.putImageData(imgData, 10, 10);
}
<canvas id="myCanvas" width="300" height="150" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>
<canvas id="myCanvasTemp" width="300" height="150" style="display:none;">
Your browser does not support the HTML5 canvas tag.</canvas>
<br /><br />
<br />
<button onclick="copy()">Copy</button>

How can I generate an image based on text and CSS?

I'm developing a web app. It generates signatures for a game, with information from its API.
I'll need to store the images with a script that gathers the information and turns it into an image.
Do you know a way to turn text + CSS into an image?

Yes this can be done, what you want to do is draw the text on a canvas, and then save the canvas. you do not need to have the canvas show, you can hide it like any other html element, just add it, draw the text on it, and save it.
Here is a link on a library that saves:
https://github.com/hongru/canvas2image
Some sample code drawing text on canvas:
<canvas id="myCanvas" width="200" 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");
ctx.font="30px Arial";
ctx.fillText("Your Text",10,50);
// save img
Canvas2Image.saveAsImage(c, 200, 100, 'png');
</script>

Why aren't canvas lines visible?

I am building up to a rotating hypercube on an HTML5 Canvas, but before that goal I am reaching a basic difficulty with the Canvas. I have a white/uncolored canvas, and I am trying to draw lines after setting fillStyle and strokeStyle to '#000000', and I have not yet succeeded at getting any pixel on the canvas to appear other than white.
The canvas is at http://blajeny.com/tesseract.html , and the JavaScript which is part math and part old-fashioned JavaScript, is at http://blajeny.com/js/tesseract.js . The log says that it is drawing lines on the canvas, some of which should intersect the 500x500 canvas and some of which should lie completely inside the canvas, but all I can see is pure white.
The math side of it needs work in terms of projection from a higher- to a lower-dimensional surface. However the difficulty I am trying to address now is a basic HTML5 canvas issue in that I am setting a color, moving to and drawing a line to coordinates some of which overlap and some of which are within the 500x500 canvas, and not seeing anything turn black. (The JavaScript console logs the lines I am trying to draw.)
How can I get the lines I am trying to draw to show up?

You need to let canvas know when you start and stop drawing using context.beginPath() and context.stroke()/context.fill(). Here's code and a Fiddle: http://jsfiddle.net/m1erickson/Jw8XU/
<!DOCTYPE HTML>
<html>
<head>
<style>
canvas{border:1px solid red;}
</style>
</head>
<body>
<canvas id="canvas" width="300" height="300"></canvas>
<script>
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
ctx.beginPath();
ctx.moveTo(50, 75);
ctx.lineTo(150, 150);
ctx.stroke();
</script>
</body>
</html>