I'm working on a whiteboard app (JS/HTML) which uses a canvas element wrapped with fabric.js.
I'm aware of certain size limitations with the canvas element, however I'm scratching my head as to why to why my canvas fails to render at all on iOS even at relatively small sizes of 2300 x 1200 pixels.
I've prepared a small demo below. On my iPhone XS this only renders the grey div, no canvas. If I drop the canvas size down to say 1500 x 1200 it works.
This is at odds what this canvas size capability checker tells me which states my phone being capable of a 4096 x 4096 pixel canvas.
// create a wrapper around native canvas element (with id="c")
var canvas = new fabric.Canvas('c');
// create a rectangle object
var rect = new fabric.Rect({
left: 100,
top: 100,
fill: 'red',
width: 60,
height: 60
});
// "add" rectangle onto canvas
canvas.add(rect);
canvas.setBackgroundColor('rgba(255, 73, 64, 0.6)', canvas.renderAll.bind(canvas));
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/4.3.1/fabric.min.js"></script>
<link href="https://cdnjs.cloudflare.com/ajax/libs/tailwindcss/2.0.2/tailwind.min.css" rel="stylesheet"/>
<div class="m-10 bg-gray-400 w-3/4 h-64 overflow-x-auto overflow-y-auto">
<canvas id="c" width='2300' height="1200"></canvas>
</div>
Any pointers much appreciated.
I've now worked out that fabric creates a canvas at twice the configured size on retina screens which means that a configured width of 2300px for the fabric object actually results in a canvas of 4600px width which in turn exceeds the device capabilities.
What I still don't know is how to work around this so that I can create a larger canvas on some iOS devices such as my phone which declares a capability of 4096x 4096px.
The added complexity is that we share the canvas in realtime between different devices so one screen may be retina and one may be standard resolution.
Related
When creating a bubble chart, such as https://www.amcharts.com/demos/bubble-chart/, is it possible to ensure the chart area/grid is square without specifying the chart div width and height? I'm hoping it could be somewhat responsive. No matter what the window size, the chart 's grid is square. It would need to take into consideration any axis labels.
I'm using React/TypeScript. Thanks!
After struggling with amchart settings to no avail, the following solution works. However, seems like there should be away to do in with chart settings.
This article explains how to maintain a specific aspect ratio for images. I simply adopted it for the bubble chart.
<div style={{ position: 'relative', paddingTop: '93%' }}>
<div id={chartId} style={{ position: 'absolute', top: 0, left: 0, height: '100%', width: '100%' }}></div>
</div>
Create a container div with relative positioning and the top padding to the correct aspect ratio
Create the chart div as a child with absolute positioning
Render the page
Take a screenshot, paste it in your favorite image editor
Measure the pixels
Recalculate the top padding
For my chart, which has axis text on the left and bottom, 93% was perfect. Now, no matter the page width or device, the grid is always square. HTH.
I have 2 canvases, one uses HTML attributes width and height to size it, the other uses CSS:
<canvas id="compteur1" width="300" height="300" onmousedown="compteurClick(this.id);"></canvas>
<canvas id="compteur2" style="width: 300px; height: 300px;" onmousedown="compteurClick(this.id);"></canvas>
Compteur1 displays like it should, but not compteur2. The content is drawn using JavaScript on a 300x300 canvas.
Why is there a display difference?
It seems that the width and height attributes determine the width or height of the canvas’s coordinate system, whereas the CSS properties just determine the size of the box in which it will be shown.
This is explained in the HTML specification:
The canvas element has two attributes to control the size of the element’s bitmap: width and height. These attributes, when specified, must have values that are valid non-negative integers. The rules for parsing non-negative integers must be used to obtain their numeric values. If an attribute is missing, or if parsing its value returns an error, then the default value must be used instead. The width attribute defaults to 300, and the height attribute defaults to 150.
To set the width and height on a canvas, you may use:
canvasObject.setAttribute('width', '150');
canvasObject.setAttribute('height', '300');
For <canvas> elements, the CSS rules for width and height set the actual size of the canvas element that will be drawn to the page. On the other hand, the HTML attributes of width and height set the size of the coordinate system or 'grid' that the canvas API will use.
For example, consider this (jsfiddle):
var ctx = document.getElementById('canvas1').getContext('2d');
ctx.fillStyle = "red";
ctx.fillRect(10, 10, 30, 30);
var ctx2 = document.getElementById('canvas2').getContext('2d');
ctx2.fillStyle = "red";
ctx2.fillRect(10, 10, 30, 30);
canvas {
border: 1px solid black;
}
<canvas id="canvas1" style="width: 50px; height: 100px;" height="50" width="100"></canvas>
<canvas id="canvas2" style="width: 100px; height: 100px;" height="50" width="100"></canvas>
Both have had the same thing drawn on them relative to the internal coordinates of the canvas element. But in the second canvas, the red rectangle will be twice as wide because the canvas as a whole is being stretched across a bigger area by the CSS rules.
Note: If the CSS rules for width and/or height aren't specified then the browser will use the HTML attributes to size the element such that 1 unit of these values equals 1px on the page. If these attributes aren't specified then they will default to a width of 300 and a height of 150.
The canvas will be stretched if you set the width and height in your CSS. If you want to dynamically manipulate the dimension of the canvas you have to use JavaScript like so:
canvas = document.getElementById('canv');
canvas.setAttribute('width', '438');
canvas.setAttribute('height', '462');
The browser uses the css width and height, but the canvas element scales based on the canvas width and height. In javascript, read the css width and height and set the canvas width and height to that.
var myCanvas = $('#TheMainCanvas');
myCanvas[0].width = myCanvas.width();
myCanvas[0].height = myCanvas.height();
Shannimal correction
var el = $('#mycanvas');
el.attr('width', parseInt(el.css('width')))
el.attr('height', parseInt(el.css('height')))
Canvas renders image by buffer, so when you specify the width and height HTML attributes the buffer size and length changes, but when you use CSS, the buffer's size is unchanged. Making the image stretched.
Using HTML sizing.
Size of canvas is changed -> buffer size is changed -> rendered
Using CSS sizing
Size of canvas is changed -> rendered
Since the buffer length is kept unchanged, when the context renders the image,
the image is displayed in resized canvas (but rendered in unchanged buffer).
CSS sets the width and height of the canvas element so it affects the coordinate space leaving everything drawn skewed
Here's my way on how to set the width and height with Vanilla JavaScript
canvas.width = numberForWidth
canvas.height = numberForHeight
I believe CSS has much better machinery for specifying the size of the canvas and CSS must decide styling, not JavaScript or HTML. Having said that, setting width and height in HTML is important for working around the issue with canvas.
CSS has !important rule that allows to override other styling rules for the property, including those in HTML. Usually, its usage is frowned upon but here the use is a legitimate hack.
In Rust module for WebAssembly you can do the following:
fn update_buffer(canvas: &HtmlCanvasElement) {
canvas.set_width(canvas.client_width() as u32);
canvas.set_height(canvas.client_height() as u32);
}
//..
#[wasm_bindgen(start)]
pub fn start() -> Result<(), JsValue> {
// ...
let canvas: Rc<_> = document
.query_selector("canvas")
.unwrap()
.unwrap()
.dyn_into::<HtmlCanvasElement>()
.unwrap()
.into();
update_buffer(&canvas);
// ...
// create resizing handler for window
{
let on_resize = Closure::<dyn FnMut(_)>::new(move |_event: Event| {
let canvas = canvas.clone();
// ...
update_buffer(&canvas);
// ...
window.add_event_listener_with_callback("resize", on_resize.as_ref().unchecked_ref())?;
on_resize.forget();
}
}
There we update the canvas buffer once the WASM module is loaded and then whenever the window is resized. We do it by manually specifying width and height of canvas as values of clientWidth and clientHeight. Maybe there are better ways to update the buffer but I believe this solution is better than those suggested by #SamB, #CoderNaveed, #Anthony Gedeon, #Bluerain, #Ben Jackson, #Manolo, #XaviGuardia, #Russel Harkins, and #fermar because
The element is styled by CSS, not HTML.
Unlike elem.style.width & elem.style.height trick used by #Manolo or its JQuery equivalent used by #XaviGuardia, it will work for canvas whose size is specified by usage as flex or grid item.
Unlike the solution by #Russel Harkings, this also handles resizing. Though I like his answer because it is really clean and easy.
WASM is the future! Haha :D
P.S. there's a ton of .unwrap() because Rust explicitly handles possible failures.
P.P.S.
{
let on_resize = Closure::<dyn FnMut(_)>::new(move |_event: Event| {
let canvas = canvas.clone();
// ...
update_buffer(&canvas);
// ...
window.add_event_listener_with_callback("resize", on_resize.as_ref().unchecked_ref())?;
on_resize.forget();
}
can be done much cleaner with better libraries. E.g.
add_resize_handler(&window, move |e: ResizeEvent| {
let canvas = canvas.clone();
// ...
update_buffer(&canvas);
})
If you want a dynamic behaviour based on, e.g. CSS media queries, don't use canvas width and height attributes. Use CSS rules and then, before getting the canvas rendering context, assign to width and height attributes the CSS width and height styles:
var elem = document.getElementById("mycanvas");
elem.width = elem.style.width;
elem.height = elem.style.height;
var ctx1 = elem.getContext("2d");
...
I have a 1242 X 450 image, which I’d like to display on a 1x 2x and 3x devices. The current code, which I have, works fine for 3x devices but I see that the edge of the image gets cropped on a 2x device and possible on a 1x device too.
In code I am setting width to 414 and height to 150 (because 1242 X 450 /3x)
Is there any way I can fix it?
The image is inside a list view
<View style={styles.row}>
<Image
style={styles.featureImage}
source={{
uri: this.props.image_src
}}/>
</View>
const styles = StyleSheet.create({
row: {
alignItems: 'center',
backgroundColor: 'lightgrey',
flexDirection: 'row',
margin: 6,
},
featureImage: {
height: 150,
width: 414
}
});
You don't need to deal with image's size. You just give width and height property properly.
import Platform and get width and height of device.https://facebook.github.io/react-native/docs/dimensions.html
var {scrHeight, scrwidth} = Dimensions.get('window');
define an image container style
imageContainer = {
width:scrwidth/5,
height:scrHeight/5,
}
define image style and use resizeMode for image
resizeMode enum('cover', 'contain', 'stretch', 'repeat', 'center')
imageStyle={
flex:1,
}
<View style={styles.imageContainer }>
<Image style={styles.imageStyle} resizeMode={'contain'}>
</Image>
</View>
No matter how big the image is it will cover screenWidth/5 X screenHeight/5.
If your image has high resolution and device is not the image will be compressed in the contrary case it will be stretched. Both case especially second one if there is a big difference between image resolution and area which is left for image you will have bad image vision in your app. To avoid this situation you can add different sizes of the same image.
add
└── img
├── apple#1x.png 100x100 (resolutions are random)
└── apple#2x.png 150x150
apple#3x.png 175x175
https://facebook.github.io/react-native/docs/images.html
If you do so proper image will be chosen by react automatically. Images are chosen according to dpi of device. If your device has nice resolution you get bigger image if not so smaller image. This situation mostly works except devices having big sizes and low resolutions( some android tablets). In this case according to dpi image will be probably smallest image so there will be a bad quality.
I am developing an application on react-native. I have made a UI which works fine on iPhone 6 but not working fine on iPhone 5 or lower versions.
How should I fix this ?
You need to think about proportion when building your UI.
1, Use percentage(%) for width and aspectRatio for height, or vice versa.
container: {
width: "100%",
aspectRatio: 10 / 3, //height will be "30%" of your width
}
2, Use flex for the jobs percentage can't do. For example, if you have arbitrary size of items in a list and you want them to share equal sizes. Assign each of them with flex: 1
3, Use rem from EStyleSheet instead of pixels. rem is a scale fator. For example, if your rem is 2 and your “11rem” will become “11*2” = “22”. If we make rem proportion to the screen sizes, your UI will scale with any screen sizes.
//we define rem equals to the entireScreenWidth / 380
const entireScreenWidth = Dimensions.get('window').width;
EStyleSheet.build({$rem: entireScreenWidth / 380});
//how to use rem
container: {
width: "100%",
aspectRatio: 10 / 3, //height will be "30%"
padding: "8rem", //it'll scale depend on the screen sizes.
}
4, Use scrollView for contents that could potentially scale out of the boxes. For example, a TextView
5, Every time you think about using pixels, consider use rem in method 3.
For a detailed explanation, you can read the article here. 7 Tips to Develop React Native UIs For All Screen Sizes
Have you designed the app using fixed widths and heights? You should definitely use the capabilities of flexbox and try to avoid settings fixed sizes as much as possible. The flex property can be used to define how much space a <View /> should use releative to others, and the other properties on that page can be used to lay out elements in a flexible way that should give the desired results on a range of different screen sizes.
Sometimes, you may also need a <ScrollView />.
When you do need fixed sizes, you could use Dimensions.get('window').
You need to calculate sizes dynamically, relying on screen size.
import { Dimensions, StyleSheet } from 'react-native'
[...]
const { width, height } = Dimensions.get('window')
[...]
const styles = StyleSheet.create({
container: {
flex: 1.
flexDirection: 'column',
},
myView: {
width: width * 0.8, // 80% of screen's width
height: height * 0.2 // 20% of screen's height
}
})
If you are using TabbarIOS, remember that Dimensions.get('window') gives you the whole screen's height, this means that you'll have to take in account that the tabbar has fixed-height of 56.
So for example, when using TabbarIOS:
const WIDTH = Dimensions.get('window').width,
HEIGHT = Dimensions.get('window').height - 56
Then use WIDTH and HEIGHT as above.
I am working on a game using EaselJS, and I am still trying the functions provided by this great library.
What I may need is Alphamaskfilter class & Spritesheet class.
Currently, I have a canvas like this:
<canvas id = 'container3' width = 320px; height = 480px;
style = 'outline: 2px solid; margin-right: 10px;float:left;'></canvas>
and in my script, I have draw a rect with blue color:
var ctx3 = document.getElementById('container3').getContext('2d');
ctx3.beginPath();
ctx3.rect(0,0,320,480);
ctx3.fillStyle = 'blue';
ctx3.fill();
So now I have a blue color 320*480 canvas. And now I have a sprite sheet to animate on it,
here is the sprite and code I wrote:
http://i.imgur.com/XumDvic.png
PS: the sprite frame is 200*200 FYI.
stage = new createjs.Stage(document.getElementById('container3'));
var test = new Image();
test.src = 'trans_blackball.png';
test.onload = function(){
var sprite = new createjs.SpriteSheet({
images: [test],
frames: {width: 200, height: 200},
animations: {
born: [0,3,0]
}
});
var animation = new createjs.BitmapAnimation(sprite);
animation.gotoAndPlay("born");
animation.x = 10;
animation.y = 10;
animation.currentFrame = 0;
stage.addChild(animation);
createjs.Ticker.addListener(window);
createjs.Ticker.useRAF = true;
createjs.Ticker.setFPS(10);
}
function tick(){
stage.update();
}
Okay, my question is: I expect an animation of an enlarging black circle on a blue background(rect), but what I got is firstly the canvas is blue, but for a certain mini-second after, the whole canvas became white, and the animation is running on the white background, what is the reason of this and how can I solve it?
Here is two points that may help:
I am working with chrome, and I check with F12 & console, the fillStyle of the canvas is still blue even it appears white after the sprite animation start
If I set the canvas background property to blue instead of drawing a blue rect on it, everything's fine!!
<canvas id = 'container3' width = 320px; height = 480px;
style = 'background: blue; outline: 2px solid; margin-right:
10px;float:left;'></canvas>
but clearly this is not what I want...
The problem can be solved as well by not using native canvas rect but use EaselJS's Shape to draw the rect:
var shape = new createjs.Shape();
shape.graphics.beginFill("#ff0000").drawRect(0, 0, 320, 480);
stage.addChild(shape);
But I still wanna know why the native rect drawing code is not working...
Please bare my bad english and thanks for reading and any attempt to help...I can elaborate more if there is anything unclear in the situation..thanks!
createjs.Stage.update() will clear the canvas-contents by default before rendering the new frame.
The reason for this is one the one hand the technical behaviour of canvas, the canvas is basically just an image of pixels, you cannot have real 'layers' and say "I just want to remove/update this one object" - you just can modify the flattened pixels of the frame or remove everything and redraw it(which is safer, easier to achieve, and actually fast enough performance-whise. And on the other hand, it makes sense to make consistent use of a framework like EaselJS, and not do some parts with the framework and some parts without it, this would result in a big mess at the end.
So, the right solution is to go with 3.
You can set myStage.autoClear = false; to prevent the Stage from autoClearing the canvas on every update() but I don't think this will suit your needs in this case.
I would recommend instead using the EaselJS Shape class to make your blue box. If it part of the EaselJS display list, it will be drawn with the other content.
javascript
var shape = new createjs.Shape();
shape.graphics.beginFill("blue").drawRect(0,0,320,480);
stage.addChild(shape);