im throughoutly confused by dips on Android.
I understand from the reference that the base for dp values is 160.
So, shouldn't 80dp in width equals a view with a width of 50% of the screen ?
On my Nexus One the width in dp is something around 300dp as it seems.
What am i missing here ?
thx in advance
"dp" == "Density-independent Pixels" (This is also why it was earlier called "dip", though I prefer to use "dp" these days.)
Think of it like other units -- "in" (inches), "mm" (millimeters), etc. It allows you to provide a size that is scaled based on the density of the screen.
We define mdpi to be the base density, so "10dp" on an mdpi screen will result in exactly 10 pixels. On an hdpi screen it will result in 15 pixels, because hdpi is 1.5*mdpi.
Note that though the constants for various densities are similar to DPI (mdpi is 160, etc), density is not exactly DPI. It is an abstract scaling factor that adjusts for screen dpi, but does not try to exactly reflect it. (You would use "in", "mm", etc for exact sizes but 99.9% that is not what you want so stick with "dp".) This greatly simplifies life for everyone because you don't need to deal with many Android devices having a slightly different amount of space for its UI because they each of slight different screen DPIs. Also, device manufacturers can select the density of their device to achieve a desired UI -- for example the Samsung Tab uses a density that is a fair amount larger than the actual DPI, resulting in an overall larger UI.
160 dots per inch. So 80dp would be 1/2 an inch, roughly.
I don't understand your question completely but I suggest you take a look at this, if you haven't already.
http://developer.android.com/guide/practices/screens_support.html
pixels = dps * (density / 160)
Density independent pixels (short: dp) are a virtual pixel unit that will be determined at the runtime of your application.
Formala:
1 dp = 1 Pixel on 160 dpi screen.
So 160 dpi is the baseline density for the system.
The conversion of dp units to screen pixels are quite simple.
Actual device pixels (px) = dp (1) * (dpi (of the device) / 160(baseline) )
For the sake of simplicity: px = dp * (dpi / 160)
Example:
If a 240 dpi device starts your app, then 1 dp equals to 1,5 actual device pixels.
Conclusion:
Dp automatically handles any scaling to bigger or smaller devices. The times where you hardcode the pixels are over. DP ensures the proper scaling on different screen densities.
Related
I know this might be a silly question but I have really gone through so many materiel and links but still not quite understand it. In the "Supporting Multiple Screens" section of Android Develop Doc, it introduces dp like this:
Density-independent pixel (dp)
A virtual pixel unit that you should use when defining UI layout, to express layout dimensions or position in a density-independent way. The density-independent pixel is equivalent to one physical pixel on a 160 dpi screen, which is the baseline density assumed by the system for a "medium" density screen. At runtime, the system transparently handles any scaling of the dp units, as necessary, based on the actual density of the screen in use. The conversion of dp units to screen pixels is simple: px = dp * (dpi / 160). For example, on a 240 dpi screen, 1 dp equals 1.5 physical pixels. You should always use dp units when defining your application's UI, to ensure proper display of your UI on screens with different densities.
Basically I understand the fact that screen with higher dpi would have more pixels in a single physical inch, which means a dp in such a screen would equal more physical pixels(px).
But according to the above conversion equation (in bold font), in a screen with higher dpi (e.g. 240 dpi screen) , a px = (240 / 160) * dp = 1.5dp. This seems to mean that in higher dpi screen a px would equal more dp. This looks in conflict with my previous understanding.
So, please, could anyone help me to figure this tricky issue out. Thank you a lot, really.
You are looking at the wrong place in the formula. To see how many dp equals one px in different density, lets rearrange the formula:
px = dp * (dpi/160)
dp = px / (dpi/160)
Now for 1px, in mdpi devices:
dp = 1 / (160/160) = 1dp
In hdpi devices:
dp = 1 / (240/160) = 0.666666667dp
You can see that 1px equals less dp in higher density devices
I'm asking this question after much reading. I've always heard that dpi is for printers, but when it comes to screen now, they are also talking about dpi. Are they referring to ppi?
Now, what is really resolution, for me its the the number of pixels each dimension can display, e.g. 800x600 means 800 pixesl on width and 600 pixels on the height, but at some places I'm seeing that they are referring to resolution as dpi.
I'm trying to understand this concept well because its very important in Android, like in this article,
For example, say an icon is intended to be 0.5x0.5 in when rendered on a screen. Next, the image must be created at the largest density supported, or as a scalable vector graphic. Best practice is to support the maximum density, which currently is xxhdpi at 480 dpi. At 480 dpi, a 0.5x0.5 in image converts to 240x240 px.
So it is referring dpi as ppi actually if I understand?
So far what I've understood is that different pixels may render different number of pixels. This is why we don't use pixels as measurement unit. Instead we use dp, where a dp is one pixel on 160 dpi device (again the confusion about dpi & ppi)
Can someone clear this big confusion or direct me to an article that may clear it
Mate, Resolution being 800 X 600 implies that the screen has 480,000 pixel points that will be used to render the screen(This is often confused with the dimensions of the display). DPI or PPI means dots/points per inch, this is the measure of the density of the screen.
So just given the Resolution, one can not determine the actual length of the display unless the density parameter is also available. So a 800 X 600 resolution has 480,000 Pixel points & a let this device has a density of 480 dpi.
So the Width of the screen
= No of pixel points along its width/Density
= 800/480
= 1.67 inches
Similarly,
Height = 600/480
=1.25 inches
and if 800X600 resolution device has density of 160 dpi, its dimensions will vary drastically. Following calculations calculate Height/Width of 800X600 on 160 dpi. Compare these two values with above 480 dpi calculations.
the Width of the screen
= No of pixel points along its width/Density
= 800/160
= 5.0 inches
Similarly,
Height = 600/160
=3.75 inches
This is the very reason that scaling images to best fit the screen is such a complex issue on frafmented android environment.However, I love android!
Hope this helps!
and any one who has some thing to add/delete.modify to this answer is most welcome.
dpi (dots per inch) == ppi (pixels per inch)
You are also talking about the DisplayMetrics.density, which gives you the multiplier for the dp unit of measurement.
There's also DisplayMetrics.scaledDensity which also takes into account text size user chose.
To put it plainly, dp unit is intended to give you some security about size of your objects on screen. 160dp should represent one inch on any screen. In order to achieve that, you have to multiply your dimension by DisplayMetrics.density or DisplayMetrics.scaledDensity.
That is, if you're doing that in code. For Layouts, you can just enter a View's dimensions in dp and have Android framework take care of that for you.
I am new to android. I read about DP but m still confused. In one definition it says-
dp (density-independent pixels): An abstract unit based on the density of the screen. On a display with 160 dots per inch, 1dp = 1px.
does it mean- 160 dots=1 dp = 1 px (each dot is 1 pixel , right?)
OR 1 dp = 1 dot(pixel) among the 160 dots
Pleas clarify
density-independent pixels is a virtual pixel unit that you should use when defining UI layout, to express layout dimensions or position in a density-independent way.
The density-independent pixel is equivalent to one physical pixel on a 160 dpi screen, which is the baseline density assumed by the system for a "medium" density screen. At runtime, the system transparently handles any scaling of the dp units, as necessary, based on the actual density of the screen in use. The conversion of dp units to screen pixels is simple:
px = dp * (dpi / 160)
For example, on a 240 dpi screen, 1 dp equals 1.5 physical pixels. You should always use dp units when defining your application's UI, to ensure proper display of your UI on screens with different densities.
For 160 dpi screen 1 dp equals 1 px.
Refer to this blog and this answer.
The android documentation say -
The density-independent pixel is equivalent to one physical pixel on a 160 dpi screen, the baseline density assumed by the platform (as described later in this document). At run time, the platform transparently handles any scaling of the dp units needed, based on the actual density of the screen in use. The conversion of dp units to screen pixels is simple: pixels = dps * (density / 160). For example, on 240 dpi screen, 1 dp would equal 1.5 physical pixels. Using dp units to define your application’s UI is highly recommended, as a way of ensuring proper display of your UI on different screens.
you may take a look at the supporting multiple screens. you may also take a look at this question.
I am a bit worried by what I read here, which kind-of implies that there is no reliable formula to compute px based on dp and screen density (and vice versa):
dp :
Density-independent Pixels - An abstract unit that is based on the physical density of the screen. These units are relative to a 160 dpi (dots per inch) screen, on which 1dp is roughly equal to 1px. When running on a higher density screen, the number of pixels used to draw 1dp is scaled up by a factor appropriate for the screen's dpi. Likewise, when on a lower density screen, the number of pixels used for 1dp is scaled down. The ratio of dp-to-pixel will change with the screen density, but not necessarily in direct proportion. Using dp units (instead of px units) is a simple solution to making the view dimensions in your layout resize properly for different screen densities. In other words, it provides consistency for the real-world sizes of your UI elements across different devices.
I thought we could always use the following formula (explained here) :
px = dp * (dpi / 160)
However, the testimony in this question seems to highlight a case where specifying sizes in dp does not guarantee a fixed perceived size across devices.
What is the real meaning of the sentence in bold ?
Do we need to use mm in order to be sure to keep the same perceived size ??
I thought we could always use the following formula (explained here) : px = dp * (dpi / 160)
This formula can always be used to convert between pixels and dp. Just make sure you use DisplayMetrics.densityDpi as the value for dpi in the formula.
However, the testimony in this question seems to highlight a case where specifying sizes in dp does not guarantee a fixed perceived size across devices.
Yes it is true that a certain dp does not guarantee a fixed perceived size across devices. It does however guarantee a similar perceived size across devices. The reason for this is that on some devices densityDpi (the density bucket) is different than the physical dpi of the device. Please see my answer to the question you linked for more details.
The ratio of dp-to-pixel will change with the screen density, but not necessarily in direct proportion
Here I think they mean the actual physical screen density when they say "screen density" and not which density bucket the phone belongs to.
For example a device with a physical dpi of 270 will belong to the "high" (240) density bucket and have a dp-to-pixel ratio of 240/160 = 1.5
Another device with a physical dpi of 290 will belong to the "xhigh" (320) density bucket and have a dp-to-pixel ratio of 320/160 = 2
When you compare these devices with each other the physical screen density has increased by 7% (270 -> 290) while the dp-to-pixel ratio has increased by 33% (1.5 -> 2) so it's not a direct proportion between them.
Do we need to use mm in order to be sure to keep the same perceived size ??
If it's important that the preceived size is as similar as possible between devices you have to use mm or inch. However this have some drawbacks as I mention in the question you linked.
It is also important to keep in mind that there are some devices where the mm and inch units are broken, for more information on this see the question Why Lint shows warning when using in (inch) or mm (millimeter) units as dimension?
What is the formula for converting regular pixels to DIP?
Assuming I have a photoshop document with a design in it that was intended for the Galaxy Tab (for example) which is 600x1024 actual pixels.
What is the ratio between those and the DIP? I'm unclear on how Android translates this.
I want to use DIP (rather than pixels) so that it scales to look "ok" on other devices, but my primary concern is to get it pixel perfect in this resolution and my aim is to measure the position of an element in photoshop and then get an exact translation as to what the DIP needs to be for it to lay out identically on the Tab.
Their formula is somewhere in the docs:
truePixels = DIPs * (device DPI / 160)
Ah, there it is:
The density-independent pixel is
equivalent to one physical pixel on a
160 dpi screen, which is the baseline
density assumed by the system for a
"medium" density screen. At runtime,
the system transparently handles any
scaling of the dp units, as necessary,
based on the actual density of the
screen in use. The conversion of dp
units to screen pixels is simple: px =
dp * (dpi / 160). For example, on a
240 dpi screen, 1 dp equals 1.5
physical pixels. You should always use
dp units when defining your
application's UI, to ensure proper
display of your UI on screens with
different densities.
Taken from here.