Develop Reference

High res images on low pixel density screens

Regarding Android's call to provide multiple versions of a bitmap/image, why can't only the highest resolution image be used?
E.g if the xxhdpi image is available - will that be able to scale down to all lower density versions or will it just mean it will scale bigger than the allocated size (View)?
PS: If I'm using a background image, does scaling matter? E.g. should I still provide multiple versions of 1 image to fit different pixel densities?

Usually image scaling operation is resourceful and the outcome might be worse than using pre-scaled image.

It has already been answered several times, but I will answer it again. Btw I'm not myself a big pro in Android, but I will try to answer in the best way possible.
Automatic scaling is a thing in Android, but using that is a waste of resource, we already know that using a PNG Graphic asset is a waste of CPU/GPU power when we can use XML for basic designs (which uses less resources), so why waste more power for downscaling it (which increases app opening time and makes it laggy), simply creating multiple sized images for different display sizes is the best option.
A simple and convenient option is to use a free software like Adobe XD which supports export into different sizes.
Simple answer: Avoid using PNG(or other image format), but when you don't have other options do create multiple sizes to save resources.

Better way for Andengine screen size?

I understand that Andengine gives us option to scale our scene to any size screen that the user may have.
My question is if it would be better to develop for a larger resolution, say 1280/800 and scale it down for smaller screens OR to go for smaller resolution, say 800/480 and scale it up on bigger screens?
I did try to test this in a sample game by developing it for 1280/800 and scaling down (by ratioResolutionPolicy) to 800/480, and the results weren't satisfactory, there was stutter every here and there the framerate on the debugger though showed 60+. Is it bad programming on my part or does it have to do with the scaling down of the pixels, should I develop for smaller screen and scale it up?

I guess it depends on what kind of graphics you are using.
Say, for example, you want to create something in a retro-gameboy-pixel style, then it makes more sense to use small images and develop for a small resolution (like 480x320). Pixel graphics can be scaled up without loosing quality, but not down (then the pixels loose form).
But if you want high resolution graphics you are most likely better of developing the whole thing for a big resolution and let the AndEngine scale it down.
In both cases the quality of the pictures also depends on the TextureOption of your TextureAtlases as well.
Anyway, I can imagine that neither scaling down, nor scaling up is more efficient. Scaling is done by openGL and should go quite quickly. The downside of using big resolutions though, is that the device has to hold huge images in it's memory and the of course processing big images always takes more time than processing small images. So maybe the best way is to develop for middle-size devices (e.g. 960x640) ?
I know this isn't much help, unfortunately it is a lot of try and error to get the best results for your specific requirements.
christoph

To achieve good result on all type of android device you have two ways to follow from my perspective.
First, you have to develop and use two graphics to handle all the type of devices. For example one with resolution 1024x600 and other with 480x320. Based on device current resolution you have to load specific one type of graphics.
Second, you choose any single resolution that best suits to you and have great share in the market. Develop and use graphics only for that resolution. For other resolution scale that graphics based on aspect ratio. For this you have to create super class of sprite and change value of x,y,height and with based on aspect ratio calculate.
This was my experience that I share with you. If you have any doubt then feel free to ask it.

android developers - what do you need from the designer?

i am NOT an android developer and im trying to understand what they need in terms of graphical resources to make an app that functions across many android devices.
i have (tried to) read this page http://developer.android.com/guide/practices/screens_support.html , but find it somewhat bewildering. they talk as if screen density is the important thing "Supply alternative bitmap drawables for different screen densities" but then, if you dont know the size of the screen, you cant really think in terms of layout. is the idea to make buttons and logos that are the same size on all screens with the same density, such that on a large screen there is just a bunch of space, and on the small screen its all packed in tight? i dont understand how just thinking in pixel density gets me any closer to knowing what to provide.
are you supposed to create resources for every screen size AND pixel density? say it aint so.
anyway can somebody tell me... if you were developing an app what do you need for graphics? is it possible to provide graphics that are large and just let them scale down? is it inevitable that the devloper will have to mess with the graphics himself anyway? or can he be provided with sets of png files of certain sizes that will be ready to use?
thanks!

Here's what we do at my work place. Suppose we get a desing for the app. We make our designer create 3 psds versions for the same desing. the 3 psd's are for the 3 ranges of desnity. The size used for the psd are
240*320 (Low Density)
320*480 (Medium Density)
480*800 (High Density)
Most of the time when I write layouts, I use wrap_content which means a view must take the size of the content it wraps. Which works most of the time as I have a density specific version of the design so the image i use as background should be suitable. The thing to note is that, in android you can can put the 3 sizes of the same image in different folders such as drawable/ldpi, drawable/hdpi.
Eg: you have a bg.png and have a version for large phones and a version for small phones. You put the big bg.png into hdpi folder and the small png in the ldpi folder. Android will automatically select the appropriate image based on the phone density. But you need to make sure the file name is the same.
There are cases where you need to resize you background images without makeing the image looking too scaled. For this android uses the draw9patch tool. With this tool you can specify areas which can scale and areas that shouldn't scale.

9 Patch png's are your friend. Read up on them here:
http://developer.android.com/guide/topics/resources/drawable-resource.html#NinePatch
and here:
http://developer.android.com/guide/developing/tools/draw9patch.html
Those are your best bet for any kind of graphic that will stretch nicely (i.e. not gradients, they will come out slightly pixelated on some screens probably) The power of these types of images is that you can tell the system which pixels to repeat if it needs to stretch the graphic. This means that stretching can be done without loss of image quality (again depending on your image and how you choose to make the nine patch. The "show bad patches" button in the draw9patch program will show you potential problems. Hint: keep your repeatable pixels down to 1 on left and 1 on top and you'll have no problems with bad patches) Any graphics that can be made in to 9 patches will only need 1 size since the system can effectively make it whatever size it needs.
are you supposed to create resources for every screen size AND pixel density?
You may if you like. This would ensure that the application will look great across all devices. I understand that this is not feasible for all projects though. In general if you make separate resources for the different densities you'll get something that looks acceptable on most of the devices out there. All of the devices are classified as ldpi, mdpi, or hdpi (there may be an "extra high" level now too, I am not certain off the top of my head) So if you supply graphics for those 3 densities then the system will know where the device falls under and will pull the correct graphics.
is it possible to provide graphics that are large and just let them scale down?
Yes the system will scale down your graphics if needbe. But be aware there are consequences with this approach. First every time the system hast to scale a graphic up or down it is going to taking up CPU and memory to do so. This may not be an issue if you have relatively few things to scale, but if you have many it could cause noticeable lag time during on the lower power phones. Second, To my knowledge all of the graphics in android are raster, which means if you are letting the system scale something up or down image quality is going to decrease some. Again depending on the specific images this may be more or less noticeable on the actually device at runtime.
My best advice is supply them with resources of a few different sizes and run the app on as many different devices as you can. Once you see how your different resources look on the devices of different sizes you'll have a much better feel for which ones you need to supply to get the UI looking as consistent as possible across the largest swath of screen sizes and densities.

From .psd to screen

I have a client that gave me a .psd file that contains the entire screen of an Activity with all the graphics. The resolution is 480x800. The client wants the application to look identical to the one in the .psd file. The problem is that different devices have different resolutions and sizes. I know that the density is what really matters but how can I scale the graphics to look the same on all the devices? For example, I exported all the layers and recreated the screen in Android but, for some reason, the screen looks more crowded on a Nexus One (480x800).
One idea would be to create 9 patch images from the graphics and use for ImageViews android:background instead of android:src right?
Isn't it better to have a 320x480 resolution for the graphics? Or do I need for both resolutions? Also, I have to consider the height of the status bar which I understood it is 25dip but I am not certain about this.
So, to summarize, I am interested to find out what is the best way for a client to give you the mockups and graphics so that it is easy for the developer to implement according to the specifications.

That's something that's not easy to solve. Think of a webdesigner, one can't know all the possible resolutions and settings of every browser so he has to scale things accordingly.
In my opinion there are only three approaches here.
First: Let him state what devices he wants to support and only support those devices. Extract the layers with the size of the device with the highest resolution and scale them down on other devices.
E.g. If you have to support two devices with 480x800(2) and 240x300(1), export all images to be 480x800 and scale them down accordingly. Don't write a single application for every device.
Second: Export the graphics with the highest resolution possible and scale them down on all devices relative to the device being used. Imagine, again, a webdesigner. All he does is define margins, paddings, etc. and it will look nice in almost any browser. You should do the same and resize your elements on demand.
Third: Make the application fixed, e.g. define a size of 200x200 for your whole application and just fill everything larger than the screen with a certain color, e.g. black. This happens a lot with java ME applications, they look great on the hardware they were made for and are still playable on hardware that is beyond their time though they look pretty ugly.
Hope this helps,
Robin.

How big can I make an Android application's canvas in terms of pixels?

I've determined an estimate of the size of my Android emulator's screen in pixels, although I think its resolution can be changed to other numbers. Quite frankly though that doesn't eliminate the general problem of not knowing how many pixels on each axis I have to work with on my Android applications in general.
The main problem I'm trying to solve is this: How do I make sure I don't use a faulty resolution on Android applications if I want to keep things' sizes constant (so that if the application screen shrinks, for instances, objects will still show up just as big - there just won't be as many of them being shown) if I wish to do this with a single universal resolution for each program? Failing that, how do I make sure everything's alright if I try to do everything the same way with maybe a few different pre-set resolutions?
Mainly it seems like a relevant question that must be answered before I can come across a complete answer for the general problem is how big can I always make my application in pixels, NOT regarding if and when a user resizes the application's screen to something smaller than the maximum size permitted by the phone and its operating system.
I really want to try to keep this simple. If I were doing this for a modern desktop, for instance, I know that if I design the application with a 800x600 canvas, the user can still shrink the application to the point they're not doing themselves any favors, but at least I can basically count on it working right and not being too big for the monitor or something. Is there such a magic resolution for Android, assuming that I'm designing for API levels 3+ (Android 1.5+)?
Thanks

Hmm, I suggest you read this: Supporting Multiple Screens. That gives a wealth of information on how to handle different screen sizes. In particular, read about its concept of density independent pixels versus absolute pixels. Density independent pixels are essentially pixel sizes that the system automatically scales for you depending on the screen size you're working on. It considers the 'standard' screen as that of the G1, Hero or similar devices, i.e. 480x320 pixels with a density of 160dpi. If the screen you're working with is bigger than that, i.e. the Droid or Nexus One, it adjusts all density independent pixel sizes by 50%.
Alternatively, if you're really talking about canvases, as in, Canvas for animations etc, you can just call canvas.getWidth() and canvas.getHeight().