I'm working on a drawing application which requires high levels of accuracy, and I'm wondering which of the major browser platforms (including the HTML Canvas element, and Flash) give the best sub-pixel layout accuracy, both for drawn elements (rectangles in the Canvas or Flash, absolutely positioned DIVs in the browser), and for text.
There are a number of posts related to this, both on this site and others, (see list at bottom), but many are quite old, and none summarises the current situation.
My understanding is that Flash has native support for sub-pixel positioning, using twips to position objects to one twentieth of a pixel, and that when the TextLayoutFramework is used, this accuracy also extends to text. There is at least one report, however, that this doesn't work properly in Chrome. Can anyone confirm this?
My understanding of the situation in the browsers is that Firefox 14+ supports sub-pixel positioning for text and drawn elements, both in page layout and within the Canvas, but I haven't been able to ascertain how accurate this is.
I understand Chrome (as of v21) does not support sub-pixel positioning at all.
I understand IE9 doesn't support sub-pixel positioning, but it appears from the MS blog post linked below that IE10 will.
I don't know if there's any Mac/PC variance in this, and I don't know also if the accuracy of Flash varies between platforms and/or browsers.
I understand a summary question like this may provoke some debate, but I believe this is specific enough for people to provide useful answers, and hope that this thread can be a reference for the state of positioning accuracy up to now.
Some references:
http://blogs.msdn.com/b/ie/archive/2012/02/17/sub-pixel-rendering-and-the-css-object-model.aspx
Sub-pixel rendering in Chrome Canvas
http://johnblackburne.blogspot.co.uk/2011/11/twips.html
http://ejohn.org/blog/sub-pixel-problems-in-css/
Sub Pixel CSS positioning
https://productforums.google.com/forum/?fromgroups=#!topic/chrome/pRt3tiVIkSI
Currently, you can expect the best rounding and sub-pixel support to come from Mozilla with IE as the runner up. IE might end up being more fine tuned, but their release cycles are so long that Mozilla is likely to stay ahead of them.
As far as doing sub-pixel layout, you may be chasing a wisp, because the sub-pixel advantage improves anti-aliasing issues, not screen location accuracy. Your image will never be more accurate than 1 pixel from the true position, regardless of sub-pixel support.
The reason why some browsers don't zoom properly has nothing to do with sub-pixel support, it is because they are not remembering the exact position and rounding correctly. In other words, they are prematurely rounding the position and that causes the image to be mis-aligned.
Short answer:
No. It is NOT possible/documented.
And even if determined experimentally, it is NOT guaranteed to remain the same in future.
Long answer:
At sub-pixel accuracies, there is a lot of variance among Browsers/OS/HW about how the input is captured/rendered. With h/w acceleration being enabled on most modern browsers, there are a large number variations in rendering across different PCs running different browsers on different operating systems. So much so that, it is possible to even identify every unique user by the slightly different variations in the rendered output of a common sample.
Rather than worrying about the discrepancies in the underlying frameworks, How about designing the UI of your drawing application to be independent of those problems. Couple of methods i can think of right now are:
Allow editing the image at zoomed/magnified levels.
Design a snap-to-grid method for elements.
Update:
The "zoom" operation would your custom implementation and NOT a feature of the underlying frameworks. So if you need sub-pixel accuracy to the order of 1/10th of a pixel, one would need to have a 10x_zoom() implemented as part of you web-app which would render the data from
1st pixel --> 10x10pixels at (0,0),
2nd pixel --> 10x10pixels starting from (11,11).
This way one would have a very magnified view of the data, but the framework is blissfully unaware of all this and renders accurate to the onscreen-pixel(which in our case now is 1/10th of the image pixel).
Also an important thing to note that this operation would consume a lot of memory if done for the entire image at once. Hence doing this for ONLY the visible part of the image in a "zoom-window" would be faster and a less memory intensive process.
Once implemented in your drawing web-app the sub-pixel inaccuracies in the frameworks might not turn out to be a problem for the user as he can always switch into these modes and provide accurate input.
Setup:
I have a simple box with rounded corners, that has a header and expands according to the amount of text, as discussed in Dan Cederholm's Bullet Proof Web Design (ISBN 0-321-34693-9).
Works great, EXCEPT when zooming in Google Chrome. Then the right margin of the box disappears.
It works in IE and FireFox without problems.
Example:
Example in jsFiddle
In chrome, it fails at zoom 110% and other zooms too. No problems in IE or FireFox.
Questions:
Any ideas what is causing this?
In general, what makes layouts zoom-sensitive (if any such general rule exists...)?
Is Dan Cederholm's book really bullet proof...?
How far back do you need to be compatible?
I mean, if you can drop IE7/8 you should be using css3 rounded corners. If you need to support IE8/7 you should definitely considder using graceful degradation in this case. It is probably not worth the time and effort to strive for perfection everywhere. That is simply a goal which cannot be met when browsers will never get updated again.
1) What may be causing this
That is a fairly broad question, I couldn't reproduce the problem, or really find one in Chrome 20 (beta) so I will just list a things that can mess it up.
General browser rounding errors, browsers aren't precise, weren't designed to be precise sub-pixel
Mixing px values with other values, different roudings make values add up differently..
Positioning of in-flow elements which get influenced by other in-flow elements on the page (these are hard to track down usually)
Parent element properties (parents with overflow hidden, fixed sizes, for example, I think this might be the problem here in the jsfiddle)
Bugs in browsers
Combination of the above
In this case jsfiddle has a crapload of containers and frames (with overflows set to hidden, fixed heights/widths, px based) etc on the page, even in 'full screen' view. So if you really want to make sure, make a html file on your own pc open/test with that.
2) In general, what makes layouts zoom-sensitive (if any such general rule exists...)?
In todays browsers this may not be all that relevant because zoom functionality is often very advanced and can even scale full-px based layouts without much problems. The only real problem browser which is still used today is IE7. The zoom capability of IE7 is atrocious, and for that reason you should only use % or em based values for text.
The only 'official' related guidelines can be found in WCAG 2.0, the w3 accessibility guidelines/techniques writeup:
http://www.w3.org/TR/WCAG20-TECHS/G142.html
So browsers can scale, modern ones have no problem here, but weren't designed to be accurate, it's also an impossible task with mixed units (em, %, px).
3) Is Dan Cederholm's book really bullet proof...?
Before I start here, I haven't read the book... I never read a CSS book (plenty other resources) in my life, but my first and foremost skill is dreaming it.
Let's start with "What is bulletproof?". Bulletproof in web-design means it will work, everywhere, and will not break, anywhere. This alone should give you a clue.
It might have very well been bulletproof when he wrote that book, but the web is a dynamic place, and even if I take the latest announcement blogpost for the book it dates from December last year. Since then at least 3 new Chrome versions came out (rough estimation) and even more Firefox versions. Microsoft sat on his ass that this time (we would've been in big trouble if they decided to do rapid release schedules).
Things changed, new bugs have definitely been introduced since then.
Regardless of what is breaking it, nothing is ever bullet proof, just very, very close to what you want to always happen, with slight variations between browsers.
That doesn't mean it is a terrible book, looking at his CV he's definitely and a guru on web-design, so he's probably right about a lot of things in that field. I just hope he explains why things are done in a certain way, because that makes you a lot wiser than just learning to do things.
A: "You always use EMs for text! EMs are annoying! Why do you do that anyway?!"
B: "I dunno, read somewhere I should..."
A: "Lets just use pixels! Pixels always work."
B: "Hmmm ok."
You just lost IE7 support. (whether that's a bad thing, is another discussion)
First of all, you're using a background-image, something I would have loved you to have mentioned.
1) So yah, as mentioned in the comments below your post, it's just rounding errors of the div, which crops the background-image.
2) I have no sources sadly, but in my experience, objects using text as a measurement are zoom-sensitive, pictures sometimes not zooming relative to everything else, and content with a predetermined 'set' size (such as textareas, radios buttons, etc).
3) Nothing is bullet proof, especially with something as ever-changing as the web that also behaves differently on different browsers. Hazards of the trade.
Is it possible to achieve Retina-quality CSS masking using -webkit-mask-box-image? In this particular case, I am trying to round the corners of an element (border-radius is not performant enough):
.element {
-webkit-mask-box-image: url('mask.png') 12 12 12 12 stretch stretch;
}
The mask image is twice the size that it needs to be (6 is used in place of 12 for non-retina screens).
The mask is correctly positioned, but the corner rounding is not Retina-smooth.
I see three solutions, here:
Suck it up and deal with border-radius, because you can't be getting that much lag on modern machines. Plus, only Safari and Chrome (and minor webkit-based browsers like RockMelt,
Yandex, et cetera) use -webkit-mask, so unless you're making a Chrome app, you're losing a lot of your audience (currently about 54.25%) to browser incompatibility, not to mention that it requires the user to download an image just to see rounded corners.
Webkit uses image smoothing within its scaling algorithm, so simply provide a gigantic mask image and let it do its one-time scaling on load. This has the inherent downside of taking much longer to download and some time after to scale, but, again, it's a one-time thing until the cache clears.
Instead of using a PNG, use an SVG. The whole point of Scalable Vector Graphics is that they're infinitely scalable and don't lose quality at any resolution or size. For more on how to make a SVG file, see http://www.w3.org/Graphics/SVG/
Let me start off by stating that I realize the arguments against doing CSS Sprites for large images. I even asked a question about why that could be considered a bad idea (and added an answer of my own). Now that we've had that talk...
I'm going to be making a large CSS Sprite-map. For the process of making this sprite-map, it behooves me to know what (if any) limit exists for the height and/or width of a sprite image in order for browsers to properly process it.
The ultimate reason behind this question is a debate over whether to lay out the sprite images in a grid or in a single row/column. For example: is it necessary or beneficial to do 4000 x 3000 instead of 400 x 30000?
Edit: The sticking point here isn't about what size images can be, but rather what size browsers can process for sprites. Given the lack of detail thus far, I'm moving forward with generating the single-large-column sprite. I'll post details of my experiences as an answer once that is complete.
Sometimes it's more of a matter of download time. Since browsers can use multiple connections to download files, a huge image can take longer to download than a few smaller ones.
If your image is so big that it's slowing down page load maybe it's time to consider several smaller sprite images.
Direct-X 9 has a size limit if 4096 pixels, so any Internet Explorer filters applied to these elements will crop them at 4096 pixels.
See: IE display transparency bug on height > 4096px?
In practice, this seems to work with no problems in Firefox 5+, Chrome, and IE7+ for a sprite image of 400x16560.
The potential issues of IE's directx rendering engine failing on images over 4096px do not create problems in IE7 or beyond; we have no method or need to test IE6 for our current project.
The one place that we experienced problems with really large spritemaps is on mobile platforms. Android devices handle them reasonably well, but iOS devices break down pretty badly, and in a strange way: They shrink the image down to fit within the dimensions they accept. So our CSS works perfectly for a small spritemap, but with no changes except increasing the physical dimensions of the spritemap image, the sprited images begin to show four times as much of the spritemap in the same html entity, with exactly the same CSS.
There is a limit in version 1.0 that is upgraded in v1.1 But still there is a limit for dimensions:
In accord with version 1.1, the scope of the 31-bit limit on chunk
lengths and image dimensions has been extended to apply to all
four-byte unsigned integers. The value -231 is not allowed in signed
integers.
Source
A funny limit is IE6.0 fails to display PNG images of 4097 or 4098 bytes in size!
But these limits are very huge in compare to what we're using in web pages.
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Is it bad in terms of compatibility to use pixel numbers in CSS instead of percentages? How about lower resolutions? Is it okay to work with them in ranges of 1-100?
All of the measurements have their own purposes:
Use pixels for pixel-based things, like borders. You probably don't want a border that ends up being 1.3422 pixels wide.
Use text-centric measures (em, ex) for text-based things, like content areas, labels, and input boxes. It's an easy way to make sure you have room for text of a certain length and width.
Use percents for window-based things, like columns.
There are exceptions, of course. For example, you might want to specify a minimum column width in pixels. But follow the above and your pages will scale well. ALWAYS zoom in and out on your pages to see how they work with different font sizes and browser shapes -- don't get surprised later.
This is a difficult question, because the answer mostly depends on your situation.
Pixels are not that bad, I mostly use them too. (Sometimes even for font sizes.)
I usually fix the outer block element of the layout by a given size (pixels with fixed-width layouts, and percentages with fluid layouts), and on the inside elements I usually set percentages whenever possible.
There are some elements which simply can't be styled with percentages or ems, especially the more fancy stuff coming from graphical designers who don't understand such principles.
For example: if you have a column on your site with a simple style, you can set its width to a percentage easily, but if it has a background image with a specific width that is not designed with scaling in mind, it only looks good with a fixed-width. In such cases, you'll have to ensure that the rest of the page occupies the remaining width correctly.
Note that you can use pixels with percentages together.
For example, this is a snippet from one of my latest web apps:
min-width: 800px;
width: 80%;
max-width: 1500px;
The choice also depends on what design or layout you would like to achieve.
For a fixed-width layout, pixel values are fine. If a designer gives you a Photoshop image that contains really fancy stuff which would be extremely complicated to even think about how it would resize, you should definitely go for this.
If your layout needs to be dynamic, you should use percentages to make sure that it expands as the resolution changes, and you can use the above code snippet to make it look better in scenarios where it would otherwise look insane.
Some layouts (eg. imagine if StackOverflow would take up all the space) would look pretty ugly on a width of eg. 1920 pixels - the line widths would be so insanely high that it would be extremely unconvenient to read.
This is what max-width is for. Even in some dynamic layouts, you'll have to limit the maximal width of your site to maximize usability and readability.
And also take into consideration the smaller screens.
It is true that noone uses a 800×600 desktop anymore, but many people browse the web with mobile devices which have even smaller resolution.
This is what min-width is for: to make your dynamically expanded layout look less crowded on smaller resoultions.
I hope this helps.
EDIT:
The Smashing Book has some very nice thoughts about the subject.
EDIT 2:
I don't want my post to sound like I want you to force pixel-based sizing on your visitors.
(Apparently, some people in the comments misunderstood me in such a way.)
To clear it up:
I believe that the ideal layout is one that adjusts well to any possible resolution or setting.
However, we can't always do everything perfectly. Time/resources and the target audience are the key to determine if your site requires that advanced functionality or not.
I'm suggesting that you use the right thing for the given job.
If you are developing a site which will have a significant percentage of visitors who require more advanced adjustments to the site, it may be well worth it.
(Of course, sometimes we just do it for ourselves to have the feeling of doing things the right way, but is is not always a financially sound decision.)
Still, you should do the proper research about what sort of site will be it, who will be the visitors, and such stuff, before deciding about layouts, and whether it is worth the time to make them fluid or more dynamic.
Font sizes
I think you must first understand the issues that exist with working with pixels in CSS:
Zoom in older browsers is broken. For example, IE6 and IE7 do not resize text when zooming. Line-height can be quirky too. These problems do not exist in modern browsers, but they are a reason why many shy away from using pixels for font sizes.
Everybody will see text the same size if you specify the font size in pixels. Browsers have a default size of 16px for paragraphs, so if you only use em and other relative sizes, you will respect the decision of users who change this. This is especially important on text heavy sites, especially if there are more older users. On the other hand, if the design of a site is important I think it is possible and justifiable to use px to specify font sizes without breaking usability.
In the end, you need to make the decision yourself, and it does depend on the exact circumstances, but I think that specifying font sizes in pixels is okay.
By the way, when working with em to specify font size it is a good idea to set the body to font-size: 62.5%. This means the base font size is 10px, so 1em is 10px, 1.6em is 16px and so on, making it easier to think in pixels while designing using ems. I still find it frustrating to work like this, especially when the values of ems cascade. There are some very handy sites like PXtoEM.com that help with this.
Layout issues
The screen is a pixel based layout, so pixels are an intuitive choice for many things. The main issue here is that different users have different screen sizes. As others have pointed out, using min-width and max-width in pixels along with width in percent is a helpful way to respect the size of the screen, while preventing your site to be unreasonably squished or stretched on very small and very large windows.
However, I would generally avoid this approach in favour of CSS media queries. You can then use fixed width chunks and make the layout wider (amongst other things) as the screen size increases. However, CSS media queries, like all cool web technologies, suffers from lack of browser support. Most notably, IE8 and earlier do not support them, although there are JavaScript fixes. On the other hand, the iPhone and other handheld devices do support them, and I would strongly recommend them if you want your site to look nice on these devices.
I think fixed width grids are fine. Fixed width grid systems like 960 Grid System
are popular enough in their own right, and there are so many other sites that have a fixed width, that I doubt you would hear many complaints if you did this. Handheld devices that do not have large screens are an issue, but this is where CSS media queries should be used, so it is possible to specify everything in pixels and have your site looking beautiful on the desktop and on the iPhone.
Conclusion
Ultimately, everything depends on who your users are, what you need to support, and what you want your site to look like, but there is nothing inherently wrong with using pixels in CSS.
That depends on what you are styling. For columns for example, the width should probably depend on the text size to ensure that it will look optimal on multiple resolutions/screens. If you want to divide your page in two parts, you should use percentages. But if you want a 1px border between these two parts, independent of the resolution, use pixels.
Basically it depends on who's hiring you and consequently the audience of your work.
For institutional purposes (where content should prevail over the shape, like a goverment project), you better work with .em or %, they are harder to control, but they will be really user friendly in terms of accessibility.
If we talk about corporative Websites (Where shape is the deal) pixel will be a more accurate tool to fulfill your customer expectation regarding his brand.
A liquid interface (%, .em) is always a good stuff when it is smartly done, but don't forget to check your design under extreme conditions and be sure that it will be stable.
If you work with pixels, you will have absolute control over the final look of your site, but you will have to assume the impossibility for some user's to operate with it efficiently.
Best option: rather than designing a Website compatible for all platforms (what will result in a multi-deficiency design) suggest your customers special versions of the site adapted for every demand, what is a better practice and a better business for a designer too...
I would say avoid it if possible except for in certain cases.
For instance for a thin border it's ok to just specify 1px.
Also for max- and min- style attributes it is ok. But then make the non-max/min attribute be a percentage if possible.
This really is a good question which I have asked many times before. Not being a hardcore web designer (I'm more on the development side) I've usually asked the designers I work with about their opinions, and here is what I have distilled:
Using percentages vs pixels for sizing elements and so on is really a matter of personal taste or the requirements in each specific case. If you need it to scale, or it will scale well, use percentages. If not, use pixels. People here have used the examples of major columns in a page maybe needing to be fluid but borders may well need the precision of a pixel measurement.
Obviously sizing images is pretty much tied to their resolution and pixel units, so I always use them in this case.
However, using em sizing versus pixel or even point sizing for text is a whole different kettle of fish. Most of the guys I work with have a base reset style for font sizes which brings the size of 1em down to about 12px. They then use ems everywhere else (or as near to everywhere else as is possible) to size text elements, form controls and the like. This is how I operate now too as it seems to work well across a variety of browsers, OSes and DPIs on desktops and laptops. I can't vouch for mobile devices though.
Accessibility is the key though - if you need to make something usable for people with disabilities or work on a variety of devices out the box, even things you may consider old, then scaling will be a requirement. Build it into your model for designing the site from the get-go and you may realise that absolute pixel sizing is not even needed in that case.
For example, an art-heavy design is probably going to be designed at a single scale, but the new educational website for disabled users is going to have to work in a variety of situations.
Just remember, the W3C put a variety of methods for sizing and scaling into their specifications for a reason - flexibility. Do whatever fits best and works well for your audience (as Moustard said earlier).
I'm not a css/html expert but convention I use is to use pixels for the outer containers and percentages for the inner objects.
Another rule of thumb I have with anyone reviewing my layout is a Three Pixel Rule. It is rare that everything will line up exactly within every browser out there. We've agreed the effort outweighs the benefits to move anything three pixels or less.
Do the right thing by default. If a user visits your site with javascript disabled and no preference cookies, you should serve them a web page that is as functional and accessible as possible.
Your default stylesheet should assume nothing about the browser window, and still render a functional page, however hideous, down to 320x320 resolution, and up to unbounded sizes. If photographic fidelity is so important that you can't trust browser scaling, and sometimes it is, then you should use pixel measurements (at least minimums) for elements encapsulating images of fixed size, to make sure that you don't end up with important things being covered up. Specifying minimum widths along with percentages should give you the control you need while giving your users the accessibility they need. Even if accessibility isn't an issue now, it will be later if the site is successful.
When you do know more about the browser window, then it's okay to use fixed widths in alternate stylesheets, if the importance of preserving the design justifies the added work.
If you're targeting a fixed size then pixels are fine. But if you want your layout to look good on various resolutions/screen sizes, then you should stick to more relative measures like percentages. Most folks are targeting the latter.
It is ok if that is what it takes to please your client. Most of the time, you can't balance the amount of space in diverse screen sizes with only percentages. CSS3 media queries helps here but adoption is still problematic.
I prefer pixel in most cases.
For example - default width of content ares: 960px.
In "1024" it will be ok, with small free spaces on the both side of the screen. Put some gradient or background there. In "1280" or "1440" or "1680", or whatever - there will be bigger and bigger gap, but it will look nice.
Yep, for 800 - this site will be ugly. But who cares? Every major players dropped support for 800. There are too few people with this resolution..
There are many various sites, where %% will be much better solution, though.
The building blocks of a screen are pixels. You can't go wrong with fixed pixel sizes. As other posters have mentioned, you can also use percentages or "em"s for a scalable substitute.