I am running firefox 3.5.6.
I want to display an image on a canvas and draw a couple lines on it. It needs to display properly in firefox and internet explorer (using excanvas).
Here is what I am getting:
The top image is what I see in IE8, the bottom is what I see in firefox.
IE seems to be a bit messed up as far as the canvas is the wrong size but firefox is going crazy! What gives with this aspect ratio? Why does the second half of my arc not appear?
Also, some times firefox just flat out doesn't show anything.
Here is my code by the way.
Aspect ratio problem
If you don't set a width on the canvas element, it defaults to 300x150. In your CSS, you set the style to 94x120, so it scales the image to that size. To fix it, you need to either set the width and height in the HTML, or with JavaScript.
In HTML:
<canvas id="c" width="94" height="120">Ugh, this just ain't gonna work</canvas>
In JavaScript (with jQuery):
$('canvas').attr('width', '94').attr('height', '120');
Internet Explorer's incorrect size
Adding the size to the canvas element should fix this problem too. Since IE is using VML instead of a canvas to render the image, the CSS rule for canvas won't apply. excanvas should see the specified size and apply it in IE.
Missing the second half of the arc
The simpleArc function doesn't work in Firefox when the amplitude is negative. The problem is that a negative amplitude results in a negative radius for the arc, which is illegal according to the canvas spec. It should actually throw an INDEX_SIZE_ERR exception, but Firefox just seems to ignore the call.
There are two possible solutions (basically; there are several ways you could accomplish either): when you pass a negative amplitude, either calculate the parameters for the arc taking into account the negative radius (with a different center point and angles, etc.), or change the sign and use transformations to rotate the arc. I implemented the second solution like this:
ctx.simpleArc = function(x,y, length, amplitude) {
var rotate = false;
// Check whether we need to rotate the image
if (amplitude < 0) {
rotate = true;
amplitude = -amplitude;
}
var radius = amplitude/2+ length*length/(8*amplitude);
var outerAngle = Math.asin((radius-amplitude)/radius);
var innerAngle = Math.PI - 2*outerAngle;
// The translate/rotate/translate steps could be combined into one matrix
// transformation, but I think this is clearer and less error-prone.
if (rotate) {
this.save(); // So we can easily undo the transformation
this.translate(x + length, y);
this.rotate(Math.PI);
this.translate(-length, -y);
}
this.arc(x+length/2, y+(radius-amplitude), radius, -(outerAngle+innerAngle), -outerAngle, false);
// Reset the transformation matrix to its original value
if (rotate) {
this.restore();
}
return this;
}
Firefox not showing anything
In your code, you create the image and set the source, but it may not be loaded before the rest of the code get's executed. The image loads asynchronously, and when you draw the image onto the canvas, it doesn't wait for it to finish. You will need to call the code that uses the image from an onload event.
var img = $('<img>');
img[0].onload = function() {
ctx.drawImage(img[0], 0, 0);
ctx.strokeStyle = "blue";
ctx.simpleStroke(function(ctx) { ctx.simpleArc(0, 70, img_w/2, 3)});
ctx.simpleStroke(function(ctx) { ctx.simpleArc(img_w / 2, 70, img_w/2, -3)});
};
// I moved this so it happens after you set the `onload` event, because I
// think IE won't call `onload` if it happens to already be loaded.
img.attr('src', 'shortcylinder.png');
You could also pre-load all the images you will need instead of creating them when you need them. You would still need to prevent the code from running until all the images are loaded.
I've recently noticed that using style to define width & height for canvas elements caused an issue like this. Taking from an earlier example
This works in FF 9.0.1 Mac
<canvas id="c" width="94" height="120">Ugh, this just ain't gonna work</canvas>
vs.
This had similar display issues as your example, in FF 9.0.1 Mac
<canvas id="c" style="width:94;height:120;">Ugh, this just ain't gonna work</canvas>
Maybe that's it?
Related
Context:
I'm working on a project to render a map into a HTML Canvas, this map is based on a jittered points and voronoi diagrams. Because of this technique I need to use ctx.scale (both values, width and height are set to 8). Once the map is generated in the canvas, I read each pixel looking for a specific color set, which will then became a 3D map.
Problem:
Everything 'works' fine, except that the canvas shapes gets somehow anti-aliased, and that obviously creates a huge problem since some of the colors I read from the pixels won't match my colorset.
So far this is how my canvas setup looks like:
const dpr = window.devicePixelRatio | 1
const ctx = mapCanvas.getContext('2d')
ctx.save()
ctx.scale((mapCanvas.width / CONFIG.RESOLUTION) *dpr, (mapCanvas.Height / CONFIG.RESOLUTION) *dpr)
ctx.lineWidth = 0.5
ctx.globalCompositeOperation = 'source-over'
ctx.imageSmoothingEnabled = false
As for globalCompositeOperation I tried almost all options that made some sense, but the results still the same.
I also added on the CSS side the following:
image-rendering: pixelated;
But also tried crisp-edges.
Long story short, I read more articles / tutorial than I wished, spent 3 hours trying to get around it, but no matter what I do I can't see how am I going to fix it.
Can anybody give a little help?
Thanks in advance.
TF
So we all know the issue with shapes being drawn with a slightly blurred stroke. I was able to fix it without further problems when using plain js and canvas with following methods:
context.sRect=function(x,y,w,h){
x=parseInt(x)+0.50;
y=parseInt(y)+0.50;
this.strokeRect(x,y,w,h);
}
context.fRect=function(x,y,w,h){
x=parseInt(x);
y=parseInt(y);
context.fillRect(x,y,w,h);
}
However, when using easeljs stage, these methods dont have any impact at all and the shapes stay blurred. I also tried offsetting x and y as well as width and height by -.5 when using drawRect(); That didnt work either. The last thing I tried was setting stage.regX and stage.regY to -.5 which did change the output but only to an altered blur (slightly more blurry).
Did I miss something?
PS: I need the canvas to always have the same width and height (200 * 200) but at the same time always fill the screen. I accomplish this by always setting canvas.width/height to 200 and the css of canvas to 100%.
Simple answer: you can't.
When you use CSS to scale a canvas, you can think of it as scaling each pixel on the canvas individually. Because of this, you are going to need to counteract the antialiasing of the browser itself.
To accurately counteract antialiasing in raster graphics, you always need more space than the container, simply because of the quantisation of information in pixels. If you do want your canvas to hold a fixed amount of information (200x200 pixels), this is not possible.
What you can still do is use that canvas as the model, but not the view ;)
If I did not want antialiasing of a fix-sized canvas over a variable space, I'd create another canvas whose size won't depend on the css, but on js events (look into window resize event listener and window.innerWidth, window.innerHeight), then draw the "model" original canvas on it while disabling ctx.imageSmoothingEnabled (= false), so that you'll get the needed result.
Here's a minimal example:
var canvasModel = document.createElement( 'canvas' ), // your current canvas
canvas = document.getElementById( 'view-canvas' ), // displaying on the screen
ctxModel = canvasModel.getContext( '2d' ),
ctx = canvas.getContext( '2d' );
ctx.imageSmoothingEnabled = false;
// all of your stuff that you're currently doing goes here
...
// every time you update the 200x200 canvas, you do this:
ctx.drawImage( canvasModel, 0, 0, w, h );
I am working on a big project where exercises in Canvas are created through JSON-data and CreateJS. The purpose of having it in HTML 5 is to not have to use a separate app for your phone, you can always use the website.
Everything works fine, however in mobile the Canvas is rescaled to full screen. This is done through checking the screen size, and if it's small enough to be mobile the canvas is scaled through this code:
// browser viewport size
var w = window.innerWidth;
var h = window.innerHeight;
// stage dimensions
var ow = canvasWidth;
var oh = canvasHeight;
// keep aspect ratio
var scale = Math.min(w / ow, h / oh);
stage.scaleX = scale;
stage.scaleY = scale;
// adjust canvas size
stage.canvas.width = ow * scale;
stage.canvas.height = oh * scale;
This works great for most of the exercises, like quizzes and such, where all you have to do is click on a button. However we also have some drag and drop-exercises, and an exercise where you can color a drawing. These of course rely on the mouse coordinates to work properly. The problem is, when the canvas is scaled the mouse coordinates are not. So when you drag an item or try to draw, there is an offset happening. So your drawing appears way left of your click, and when picking up a draggable object it doesn't quite follow your click correctly.
Had I made the code from the beginning I'm fairly sure how I would have recalculated the coordinates, but since they are calculated by CreateJS I don't really know how I should go about this.
This was reported as a problem by someone about a year ago here, where this solution was suggested:
I was able to work around this by adding a top-level container and attaching my Bitmaps to that and scaling it.
The whole exercise is inside a container which I have tried to scale but to no avail. I have also tried sending the scale as a parameter to the parts of the exercise created (for example the menu, background images and such) and not scale it all together, and it seems to work okay since then I can exclude the drawing layer. But since it is a large project and many different exercises and parts to be scaled it would take quite some time to implement, and I'm not sure it's a viable solution.
Is there a good and easy way to rescale the mouse coordinates along with the canvas size in CreateJS? I have found pure Javascript examples here on SO, but nothing for CreateJS in particular.
Continued searching and finally stumbled upon this, which I hadn't seen before:
EaselJS - dragging children of scaled parent. It was exactly what I was looking for. I needed to change the coordinates I drew with this:
var coords = e.target.globalToLocal(e.stageX, e.stageY);
Then I could use the coords.x and coords.y instead of directly using e.stageX and e.stageY like before.
For a Project I want to take the content of a canvas (Called SAVE_CV) and display it in another, smaller canvas.
Some things that I am aware of so far that could be causing me problems: resizing a canvas clears its content, the JS-size of a canvas is different from the CSS-size.
I want the smaller canvas to be 500px wide and appropriately high.
function restoreTaggingCV() {
var cv = document.getElementById( 'taggingCV' );
var ctx = cv.getContext( "2d" );
var styleHeight = SAVE_CV.height * 500 / SAVE_CV.width;
ctx.drawImage(SAVE_CV, 0, 0, cv.width, cv.height);
}
This is my Code so far. Whenever I try to resize the smaller canvas appropriately it only gives me a blank canvas with nothing in it. I tried to set the size with "cv.height = X" and "cv.style.height = styleHeight + 'px'" but neither worked. Also I would love to set the width of the canvas using CSS.
Appreciate any help.
EDIT
I want the image in a picture because later I want the user to mark areas in the smaller version which I then want to use to create individual imaged from the big version. I want to visualise thise area to the user. I probably could do all this by using an image and putting divs over it or something but I just fell more comfident using a canvas since I am pritty new to HTML and CSS.
Try using the CanvasRenderingContext2d.prototype.scale method. It sets the scale factor of the canvas and renders anything in the current state with it's dimensions multiplied by the factor.
So before you use the drawImage function, you scale the context appropriately (in this case, down). For example:
context.save();
context.scale(0.5, 0.5);
context.drawImage(canvas, 0, 0);
context.restore();
This would render the canvas on the context at 0.5 times it's current size. See in this fiddle how I used it to mirror a larger canvas onto a smaller, separate one.
Canvas objects don't like to be resised. After drawing Your image simply convert it toDataURL() and set as image source. They You may resize image as you want.
$img.attr('src',canvas.toDataURL());
I'm trying to accomplish an effect similar to what you might see on the cartoon Chowder (example link) , where shapes serve as masking layers for a texture underneath that stays static. I've begun playing around with this idea by creating a render loop that clears the canvas, saves it's state, then draws a rectangular clipping region, followed by drawing the background texture that occupies the entire width and height of the canvas.
Here's the draw function:
function draw()
{
context.clearRect(0,0, 640, 480);
context.save();
x += velocityX;
y += velocityY;
context.rect(x, y, 40, 40);
context.clip();
context.drawImage(image, 0,0, 640, 480);
context.restore();
}
Basically it just runs at 60 frames per second, updating the position of the rectangle and clipping a background image inside the clipping region. (I know the code isn't structured perfectly, but I was just experimenting to see if this effect was even possible on the canvas).
http://jsfiddle.net/JERje/86/
The problem I seem to be having is that the clipping area from the previous iteration of the loop hangs around creating the weird effect that you see in the fiddle above. I've tried reordering everything in the draw() step of the loop, but the only thing that seems to work is the canvas.width = canvas.width trick for clearing the screen. I'd like to avoid this method of clearing the screen, since it doesn't seem to work in IE, and it also destroys the canvas state. clearRect() should work to clear the screen. What am I doing wrong?
You're using the same HTML5 Canvas paperback I am aren't you.
If you set up an adhoc canvas as I did on your jsfiddle like so:
var newCanvas = document.createElement('canvas');
newCanvas.getContext("2d").drawImage(image,0,0);
A function such as this would be able to hack a section out of that canvas:
context.putImageData(newCanvas.getContext("2d").getImageData(x,y,40,40),x,y);
Thus giving you the chowder effect. Good show man, good luck. Pst me if it doesn't work
EDIT: However this solution will ignore some context scaling transformations. Just be smart about how you handle scale on your own (and you really should be anyways if you want the true "chowder" effect)
So, feel pretty dumb about this, but apparently when you call rect() you also have to make sure to call closePath afterwards in order to close the clipping area. Glad I figured it out finally, now on to adding multiple layers!
Here's the working fiddle: http://jsfiddle.net/JERje/129/