How come this tablet wants to be screen layout size large? I have other tablets with worse resolution that display XLarge.. Our current application only displays in "tablet mode" if this method returns screen layout size XLarge. So, this tablet is displayed in phone mode since it returns size Large. Is there a way around this? Can I get this tablet to return size XLarge so it can be displayed in "tablet mode" (since it is actually a tablet)?
Method Information (https://developer.android.com/reference/android/content/res/Configuration#screenLayout):
screenLayout()
public int screenLayout
Bit mask of overall layout of the screen. Currently there are four fields:
The SCREENLAYOUT_SIZE_MASK bits define the overall size of the screen. They may be one of SCREENLAYOUT_SIZE_SMALL, SCREENLAYOUT_SIZE_NORMAL, SCREENLAYOUT_SIZE_LARGE, or SCREENLAYOUT_SIZE_XLARGE.
The SCREENLAYOUT_LONG_MASK defines whether the screen is wider/taller than normal. They may be one of SCREENLAYOUT_LONG_NO or SCREENLAYOUT_LONG_YES.
The SCREENLAYOUT_LAYOUTDIR_MASK defines whether the screen layout is either LTR or RTL. They may be one of SCREENLAYOUT_LAYOUTDIR_LTR or SCREENLAYOUT_LAYOUTDIR_RTL.
The SCREENLAYOUT_ROUND_MASK defines whether the screen has a rounded shape. They may be one of SCREENLAYOUT_ROUND_NO or SCREENLAYOUT_ROUND_YES.
See Supporting Multiple Screens for more information.
What is the difference between pt and px in CSS? Which one should I use and why?
px ≠ Pixels
All of these answers seem to be incorrect. Contrary to intuition, in CSS the px is not pixels. At least, not in the simple physical sense.
Read this article from the W3C, EM, PX, PT, CM, IN…, about how px is a "magical" unit invented for CSS. The meaning of px varies by hardware and resolution. (That article is fresh, last updated 2014-10.)
My own way of thinking about it: 1 px is the size of a thin line intended by a designer to be barely visible.
To quote that article:
The px unit is the magic unit of CSS. It is not related to the current font and also not related to the absolute units. The px unit is defined to be small but visible, and such that a horizontal 1px wide line can be displayed with sharp edges (no anti-aliasing). What is sharp, small and visible depends on the device and the way it is used: do you hold it close to your eyes, like a mobile phone, at arms length, like a computer monitor, or somewhere in between, like a book? The px is thus not defined as a constant length, but as something that depends on the type of device and its typical use.
To get an idea of the appearance of a px, imagine a CRT computer monitor from the 1990s: the smallest dot it can display measures about 1/100th of an inch (0.25mm) or a little more. The px unit got its name from those screen pixels.
Nowadays there are devices that could in principle display smaller sharp dots (although you might need a magnifier to see them). But documents from the last century that used px in CSS still look the same, no matter what the device. Printers, especially, can display sharp lines with much smaller details than 1px, but even on printers, a 1px line looks very much the same as it would look on a computer monitor. Devices change, but the px always has the same visual appearance.
That article gives some guidance about using pt vs px vs em, to answer this Question.
Here you've got a very detailed explanation of their differences
http://kyleschaeffer.com/development/css-font-size-em-vs-px-vs-pt-vs/
The jist of it (from source)
Pixels are fixed-size units that are used in screen media (i.e. to be read on the computer screen). Pixel stands for "picture element" and as you know, one pixel is one little "square" on your screen.
Points are traditionally used in print media (anything that is to be printed on paper, etc.). One point is equal to 1/72 of an inch. Points are much like pixels, in that they are fixed-size units and cannot scale in size.
Have a look at this excellent article at CSS-Tricks:
px – em – % – pt – keyword
Taken from the article:
pt
The final unit of measurement that it is possible to declare font sizes in is point values (pt). Point values are only for print CSS! A point is a unit of measurement used for real-life ink-on-paper typography. 72pts = one inch. One inch = one real-life inch like-on-a-ruler. Not an inch on a screen, which is totally arbitrary based on resolution.
Just like how pixels are dead-accurate on monitors for font-sizing, point sizes are dead-accurate on paper. For the best cross-browser and cross-platform results while printing pages, set up a print stylesheet and size all fonts with point sizes.
For good measure, the reason we don't use point sizes for screen display (other than it being absurd), is that the cross-browser results are drastically different:
px
If you need fine-grained control, sizing fonts in pixel values (px) is an excellent choice (it's my favorite). On a computer screen, it doesn't get any more accurate than a single pixel. With sizing fonts in pixels, you are literally telling browsers to render the letters exactly that number of pixels in height:
Windows, Mac, aliased, anti-aliased, cross-browsers, doesn't matter, a font set at 14px will be 14px tall. But that isn't to say there won't still be some variation. In a quick test below, the results were slightly more consistent than with keywords but not identical:
Due to the nature of pixel values, they do not cascade. If a parent element has an 18px pixel size and the child is 16px, the child will be 16px. However, font-sizing settings can be using in combination. For example, if the parent was set to 16px and the child was set to larger, the child would indeed come out larger than the parent. A quick test showed me this:
"Larger" bumped the 16px of the parent into 20px, a 25% increase.
Pixels have gotten a bad wrap in the past for accessibility and usability concerns. In IE 6 and below, font-sizes set in pixels cannot be resized by the user. That means that us hip young healthy designers can set type in 12px and read it on the screen just fine, but when folks a little longer in the tooth go to bump up the size so they can read it, they are unable to. This is really IE 6's fault, not ours, but we gots what we gots and we have to deal with it.
Setting font-size in pixels is the most accurate (and I find the most satisfying) method, but do take into consideration the number of visitors still using IE 6 on your site and their accessibility needs. We are right on the bleeding edge of not needing to care about this anymore.
A pt is 1/72th of an inch and is a useless measure for anything that is rendered on a device which doesn't calculate the DPI correctly. This makes it a reasonable choice for printing and a dreadful choice for use on screen.
A px is a pixel, which will map on to a screen pixel in most cases.
CSS provides a bunch of other units, and which one you should choose depends on what you are setting the size of.
A pixel is great if you need to size something to match an image, or if you want a thin border.
Percentages are great for font sizes as, if you use them consistently, you get font sizes proportional to the user's preference.
Ems are great when you want an element to size itself based on the font size (so a paragraph might get wider if the font size is larger)
… and so on.
pt is a derivation (abbreviation) of "point" which historically was used in print type faces where the size was commonly "measured" in "points" where 1 point has an approximate measurement of 1/72 of an inch, and thus a 72 point font would be 1 inch in size.
EDIT: Note to clarify
There are approximately 72 (72.272) points in one inch or 2.54 cm. The point was first established by the Milanese typographer, Francesco Torniella da Novara ( c. 1490 – 1589) in his 1517 alphabet, L'Alfabeto. (you can search for various references to those)
px is an abbreviation for "pixel" which is a simple "dot" on either a screen or a dot matrix printer or other printer or device which renders in a dot fashion - as opposed to old typewriters which had a fixed size, solid striker which left an imprint of the character by pressing on a ribbon, thus leaving an image of a fixed size.
Closely related to point are the terms "uppercase" and "lowercase" which historically had to do with the selection of the fixed typographical characters where the "capital" characters where placed in a box (case) above the non-capitalized characters which were place in a box below, and thus the "lower" case.
There were different boxes (cases) for different typographical fonts and sizes, but still and "upper" and "lower" case for each of those.
Another term is the "pica" which is a measure of one character in the font, thus a pica is 1/6 of an inch or 12 point units of measure (12/72) of measure.
Strickly speaking the measurement is on computers 4.233mm or 0.166in whereas the old point (American) is 1/72.27 of an inch and French is 4.512mm (0.177in.). Thus my statement of "approximate" regarding the measurements.
Further, typewriters as used in offices, had either and "Elite" or a "Pica" size where the size was 10 and 12 characters per inch respectively.
Additionally, the "point", prior to standardization was based on the metal typographers "foot" size, the size of the basic footprint of one character, and varied somewhat in size.
Note that a typographical "foot" was originally from a deceased printers actual foot. A typographic foot contains 72 picas or 864 points.
As to CSS use, I prefer to use EM rather than px or pt, thus gaining the advantage of scaling without loss of relative location and size.
EDIT: Just for completeness you can think of EM (em) as an element of measure of one font height, thus 1em for a 12pt font would be the height of that font and 2em would be twice that height. Note that for a 12px font, 2em is 24 pixels. SO 10px is typically 0.63em of a standard font as "most" browsers base on 16px = 1em as a standard font size.
Yes, "px" means "pixel"
Now that I said it, I can already hear an army of clairvoyants approaching, with "px has nothing to do with pixels" on their banners. They're so proud of knowing better that they look up every comment containing the original truth and explain in detail that it's false, incorrect, misleading, etc.
And yes they have a point - a very specific point in time, actually, called iPhone 4.
Here's what happened.
The peaceful days
Before Retina displays, one pixel was one pixel. Because that's how it should be, according to human logic. You put a single pixel line on the screen, you magnify the hell out of it, and there you go: it's exactly ONE PIXEL wide. On many hardwares, modern ones included, this is still the case, so it's everything but "incorrect" to say 1px = 1 pixel.
But.
Back then, one day, iPhone 3 was followed by iPhone 4, doubling the resolution in both X and Y, and the developers of Safari worried that all webpages will look ricidulous, especially because many web developers relied on the steady 320x480 resolution. So just creating a 640x960 pixel area would have killed most of the sites. And at this point, someone had the billion-dollar idea to introduce a magical beast: a CSS feature called -webkit-min-device-pixel-ratio - on iPhone 3 it was 1, and on iPhone 4 it was set to 2 by default. Meaning "1 CSS pixel now means 2 screen pixels". A very ugly hack to keep websites look somewhat intact - it worked at that time, with the very small cost of some images looking a bit blurry, but in the long run it caused this worldwide misunderstanding of poor old px who actually did nothing wrong.
So then: pt or px?
On screens, use px because on many-many displays it will mean ONE PIXEL. The biggest advantage of using pixels is they look crispy; even if 1px means 2 or 3 physical picture elements, whatever you draw will start at the boundary, not somewhere-in-between. This is very important. Watch any browser animation that includes text, especially size transitions: when you increase a div to double size, but slowly. You'll see how your browser recalculates its pixels and redraws the font when the animation is done. There's a temporary image of the area which is a little blurry - to make the animation itself smoother -, and then, after reaching its final state, a more exact image is calculated. See this CodePen.
1px is always an integer multiplication of hardware pixels; that is, unless your operating system is being smart like resizing your whole desktop to sqrt(2) x PI. Or just 125%, yes, hello Windows on tiny laptops. But anyway - with px, you have the highest chance to align your things with the physical grid.
What about pt? The funny thing about pt is it's actually translated to px, so it's just a worse way to specify pixel sizes. Here's a calculator. Points (since they come from the print world) start to make sense when you print something, but today there are better alternatives, depending on what you need - so tbh, points are almost never needed.
TL;DR
For screens, use px whenever possible.
I would like to create a adaptive UI for both mobile and tablet devices. I would like to know for example for mobile devices if I give android:textsize="2dp then how much I should give for tablet devices. I know I should give them in values-w820dp and appropriate folder but how to calculate the difference of this dp. I couldn't find any resource for this. Help me out.
(1) For most text, it's best to size it in sp units so it scales automatically relative to the user's text-size preference. Folks with lesser vision can pick larger text and then be able to read your app without eyestrain.
(2) If you need some text to appear in a fixed size, e.g. a big headline, then use dp units so it scales automatically relative to the screen's pixel density. (Pixel density is independent of the overall screen size. It's a high vs. low density thing, not a phone vs. tablet thing.)
But don't use size 2dp! That'd be unreadably tiny -- the height of 2 physical pixels of a 160 dpi screen.
(3) If you need some text that uses approximately a fixed proportion of the screen size, then it makes sense to either define screen-size-dependent parameters, e.g. in values-w820dp, or to size it in code.
(4) If you need some text in a fixed number of pixels tall even when the pixels are really tiny, e.g. to draw into a raster image, then use px units.
See Supporting Multiple Screens - best practices.
There are no strict rules here. You can have android:textsize="2dp on your tablet as well if you wish so. You can have a look at the following android developer page which tells how to support tablets and contains chapter called: 5. Adjust Font Sizes and Touch Targets
I developed my app on a Samsung GT-P7510 (10.1" WXGA 1280x800 pixels). When I download to the Nexus 7 (7" 1280x800 pixels) the buttons that I use appear to be about the same physical size. The Nexus buttons are about 95% of the Samsung buttons. The rest of the screen seems to work OK- the text is in the right location and is proportionately smaller because that is defined in terms of screen height.
All my button sizes are defined using "dp" settings in the XML layout files. I would have expected that with the same pixel ratio the buttons would scale. I am obviously misunderstanding this. What setting would I use to get the buttons to scale?
Why do you think Android should scale your app without anything that you tell it to do?
"dp" simply makes things look the same across devices with different densities (higher density makes use of more pixels) . It won't make things larger or smaller, and it's a good thing since you don't want text to be either huge or too small to be able to read.
For text, BTW, it's usually better to use "sp" so that the user might be able to change its size (because people might have eyes problems to read small letters).
If you wish to scale things, you can either create your own mechanism (like this one) or use openGL .
Is there a performance impact, especially with regard to battery performance, if we switch from the default black theme of android to white or another colour?
If the screen is LCD white light consumes less power than the black.
What Chimmy said, plus for AMOLED displays black uses less power as far as I know. The Nexus One is AMOLED and Samsung Galaxy S is Super AMOLED.