Solve HTML Canvas image-rendering DOWNGRADE issue - javascript

These days, while trying to render some graphics in a HTML page with canvas, I fot the following issue: The canvas element is downgrading my images while rendering, after some time.
Here's the issue visualized:
Image to render (32x32)
Rendering at first instance (with browser zoom)
How the image gets after some moves (by keyboard events), randomly
Note 1: I'm not resizing the image!
Note 2: The function responsible to draw is being called every 10 miliseconds
Note 3: I'm using image-rendering: pixelated for canvas in CSS
Note 4: Here's the function responsible for drawing it:
function draw_player(x,y,w,h,state){
if(state>2){ctx.drawImage(player_sprite_jump, x,y, w,h)}
if(state<=1){ctx.drawImage(player_sprite_left, x,y, w,h)}
if(state===2){ctx.drawImage(player_sprite_right, x,y, w,h)}
}
(w and h are, again, 32, I'm not resizing the image anywhere!)
Note 5: I'm using HTML, CSS and only vanilla JS
If any other info is needed, I would like to contribute.
PLEASE HELP!

Basically, it was happening by imageSmoothingEnabled, that is set 'true' by default
It tries to smooth the image, and removes pixels's sharpness!
Resolution: ctx.imageSmoothingEnabled = false;

Related

Apply frame image on top of Fabric JS Canvas

I am using Fabric JS to allow the user to have an interactive experience on my React app. Is it possible to apply a frame around a Fabric JS that is taken from an image? For instance, if the canvas is 400x400 px I can resize an image of a frame that is transparent in the middle to 410x410px and apply it on top of the canvas for the user to see? I have attached two images for reference.
Edit: This is the code I am using for zooming in
const zoomIn = useCallback(() => {
// Get original height of canvas
const canvasDimensions = getInitialCanvasSize()
let zoom = HTML5Canvas.getZoom()
zoom += 0.2
if (zoom >= 2) zoom = 2
HTML5Canvas.setZoom(zoom)
HTML5Canvas.setWidth(canvasDimensions.width * HTML5Canvas.getZoom());
HTML5Canvas.setHeight(canvasDimensions.height * HTML5Canvas.getZoom());
}, [HTML5Canvas])
There is no option for canvas's border in fabricjs canvas docs
But you can still achieve this easily using following steps.
PART 1: Creating the Illusion of border
CSS Method
First one can easily create CSS border around the canvas.
Best way to do this is to create div around canvas, as fabricjs split canvas in 2 while running.
You can create slider to control width and color/image for div's border.
This will looks like exactly your second image with customization.
OR
Another Canvas Method
Behind current canvas put this second canvas and control its width and image.
I don't recommend this one, as this will make it more complex to implement.
PART 2: Making Illusion real
If you used CSS METHOD
Now you get what your canvas looks like. You have width of border, image/color of border.
Steps:
Create new canvas (lets' call it 2nd Canvas) of 410px if canvas's width 400px with border of 5px.
Export main canvas as image and put it over 2nd Canvas. And now you can export this as final image.
For 2nd step check my answer on this stack
If you used Another Canvas Method
Directly follow above 2nd step
Export main canvas as image and put it over 2nd Canvas. And now you can export this as final image.
For 2nd step check my answer on this stack

How to make a 'Flash' effect over a Sprite in Phaser.js?

I'm creating an Rpg in Phaser, and I'm trying to make a Flash effect happen over a Sprite -that means turning the Sprite all white for a moment and then returning to its original color-.
So my question is: what's the best way of achieving this effect?. I've tried two solutions so far, but i'm missing something:
Solution 1:
I tried tweening the tint parameter of the sprite, like this:
this.game.add.tween(enemy).to({
tint: 0xffffff,
}, 100, Phaser.Easing.Exponential.Out, true, 0, 0, true);
But it doesn't work since setting the tint to 0xffffff is the same as setting it to its default color.
Solution 2:
My second possible solution is adding a white square that has the same size of the sprite, and using the actual sprite as a mask for the square:
var flash = this.game.add.graphics(0, 0);
flash.beginFill(0xffffff);
flash.drawRect(enemy.x, enemy.y, enemy.width, enemy.height);
flash.endFill();
flash.mask = enemy // enemy is my Sprite
/* .. code for tweening the flash */
The problem with this solution is that the mask needs to be a PIXI.Graphics object; and I'm using a Sprite object.
So please, any guidance would be appreciated.
In the version of Pixi that Phaser 2.2.2 uses there is a 'tintCache' which basically rounds the tint value, then caches the result. This means you can't do subtle tint ramping like you're trying to do with a tween. We removed this in Phaser 2.3, so it will be available from then, but as of now it's still in dev.
Also you can tint to a 'near white' colour - only 0xffffff precisely resets the tint. But a value very close to that would still be set ok and probably have the desired result.
If you're using WebGL I would still use a tint with 'as near as white as possible' colour values and tween them. You could disable the tint cache for yourself by copying that part of the changed code from the Phaser dev branch.
In Canvas mode it's expensive though as it has to recalculate the pixels every single time you update it.
If you need to worry about Canvas performance then honestly I would create a new PNG that matches your sprite, colour it in all-white and display it over the top of your main sprite as needed and alpha it out. It's less than ideal because of the extra assets required, but it would be the fastest in canvas mode for sure. All depends on your game though is that's acceptable or not.
Edit: Also occurred to me that you could probably achieve what you need by using a blend mode too, such as lighten. You'd duplicate your main sprite, set the blend mode on it, display it over the top of your sprite and fade it out. This would work fine in Canvas at least.
You can use a ColorMatrixFilter on the Sprite. In Phaser, you may have to manually load in the PIXI script first:
game.load.script('filter', 'js/filters/ColorMatrixFilter.js');
Use this for white:
var filter = new PIXI.ColorMatrixFilter();
filter.matrix = [1,1,1,1,1,1,1,1,1,1,1,1,0,0,0,1];
this.game.filter = [filter];
You can also tween the matrix values if you want a smooth transition.

html5 canvas filltext disappears with sketch.js

I have a problem with the HTML5 canvas element. I use sketch.js so the client can make drawings in a webpage. One of the clients requirement is that he can add 'stamps' with numbers. So I made some modifications to the JS to make this possible. And it works, its possible to add stamps. But when the user switches back to the pen tool and starts drawing again, the numbers dissappears.
I add the stamps using fillText()
$.sketch.tools.text = {
onEvent: function(e) {
switch (e.type) {
case 'mousedown':
case 'touchstart':
this.context.font="16px Verdana";
this.context.fillText(this.stamp, e.pageX - this.canvas.offset().left, e.pageY - this.canvas.offset().top);
break;
}
return true;
},
draw: function(action) {
return true;
}
};
See a demo here:
http://jsfiddle.net/brixion/m5dpwvx5/2/
Hopefully somebody can help me
sketchJS clears and redraws the canvas frequently as determined by its source code. For example each new drawing action by the user will clear & redraw the canvas.
Your this.context.fillText code temporarily "borrows" the sketchJS canvas and draws your text on the canvas. Your text disappears when sketchJS internally decides it need to clear the canvas.
sketchJS does not currently support text, so if you want to permanently put text onto the canvas without having sketchJS erase your text, you will have to modify the source to add the fillText capability.
Alternatively, a workaround might be to add an html canvas element on top-of-and-overlapping your sketchJS canvas (like an html canvas "layer" over your sketchJS canvas). Then draw your text onto the top canvas. This way SketchJS won't erase your desired text.
Note: You must prevent the overlaying canvas from intercepting mouse events. You can do this by setting pointer-events:none; on the top canvas. Here's a link about pointer-events: https://developer.mozilla.org/en-US/docs/Web/CSS/pointer-events

Drawing a Canvas into a smaller Canvas not working

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());

drawImage on canvas has weird aspect ratio in firefox and other problems

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?

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