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noshel

[Android - 2D] How to work with different screen sizes

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Hi all!

Im having doubts on how to work with different screen sizes. Im giving the left top corner to (0,0), and for the right bottom corner i give (screen_width, screen_height). In this way i always know the size of the screen, and keep the aspect ratio of the objects i draw. But what happens when it try it on a smaller/higher screen? well, i keep having the aspect ratio, but have a look to this example:

Screen 1 (landscape):
width = 800
height = 400

I draw an object in (780,380), just in the right bottom corner. See screen 2 example:

Screen 2 (landscape)
width = 600
height = 300

They have same aspect ratio, but if in my code i draw something on (780,380), i some screens it would be visible, and in others it wont. Im thinking in converting coordinates, for example (600*780)/800 = 585, so i have the corresponding coordinates for both screens. But i dont know if this keep the acpect ratio, and i should apply it just not to coordinates, also for object dimensions.

Here is how i setup ortho view:

[code]
public void seUpOrthoProjection(int w, int h)
{
float[] c_matrix = new float[16];
float[] p_matrix = new float[16];

engine.setScreenWidth(w);
engine.setScreenHeight(h);

setUpViewPort(w,h);

Matrix.orthoM(p_matrix, 0, 0, w, h, 0, -1.0f, 1.0f);
Matrix.setLookAtM(c_matrix, 0, 0, 0, 1, 0f, 0f, 0f, 0f, 1.0f, 0.0f);

engine.setProjectionMatrix(p_matrix);
engine.setCameraMatrix(c_matrix);
}
[/code]


Maybe this is a stupid question, but i dont know what is the way to work with it.

Thanks in advance!

Regards

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When targeting PC with 2D, I use several hacks that calculate the available screen space for each component on the screen. ie for my map/terrain, I calculate the percentage of the screen I want to use, and tell the camera to only render what will fit in that space. I've only messed with mobile development slightly, so I'm not sure if the same hacks I use would be justifiable with the lack of processing power.

I do recall, reading that android sdk will scale everything to fit to the screen though. ie, if what you're rendering takes up 1024x768, but your phone only does 720x320. It will stretch/squish the screen to fit the smaller size. So you could pick your target size, ie you could say I want to target the droid 2, and do everything at it's size. Then on all other phones your game will just have to fit the appropriate size. Might look slightly off, but with so much variety out there it's going to be a given that someone isn't going to have the screen space you need. Same on the PC, I render everything to a seperate texture and then stretch/squish that to fit the actual size of the screen, adjusting for different ratios.

Another thing I like to use, is anchor points. Every time I create my render device or re size it. I build a table of screen positions like a grid, that are at every 10% of the screen. ie if my screen was 100x100 pixel. anchor point 1x1 would be at 10x10. I use this heavily in my widget and ui classes to be able to position elements along the edges of the screen.

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[quote name='freeworld' timestamp='1317597704' post='4868423']
I do recall, reading that android sdk will scale everything to fit to the screen though. ie, if what you're rendering takes up 1024x768, but your phone only does 720x320. It will stretch/squish the screen to fit the smaller size. So you could pick your target size, ie you could say I want to target the droid 2, and do everything at it's size.
[/quote]

Yeah thats true, but the problem its about ratio. If i work agaisnt Nexus One, which has aspect ratio 1.333 (i think its was), but then i run my game on a Cell phone with (no matter resolution) aspect ratio 1.5, the view will fit into the screen but out of proportion.

[quote name='freeworld' timestamp='1317597704' post='4868423']
... then stretch/squish that to fit the actual size of the screen, adjusting for different ratios.
[/quote]

Thats what i dont know how to work with. Do i have to convert all my coordinates/sizes? but when? when the user just define the object? in render time? apply opengl glScale?

Thank you for your answer :)

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[quote name='noshel' timestamp='1317652235' post='4868561']
[quote name='freeworld' timestamp='1317597704' post='4868423']
I do recall, reading that android sdk will scale everything to fit to the screen though. ie, if what you're rendering takes up 1024x768, but your phone only does 720x320. It will stretch/squish the screen to fit the smaller size. So you could pick your target size, ie you could say I want to target the droid 2, and do everything at it's size.
[/quote]

Yeah thats true, but the problem its about ratio. If i work agaisnt Nexus One, which has aspect ratio 1.333 (i think its was), but then i run my game on a Cell phone with (no matter resolution) aspect ratio 1.5, the view will fit into the screen but out of proportion.

[quote name='freeworld' timestamp='1317597704' post='4868423']
... then stretch/squish that to fit the actual size of the screen, adjusting for different ratios.
[/quote]

Thats what i dont know how to work with. Do i have to convert all my coordinates/sizes? but when? when the user just define the object? in render time? apply opengl glScale?

Thank you for your answer :)
[/quote]

You have to recalculate the ratio when the Renderer starts up and any time the screen changes. You only need to change the glViewport's ratio, not the individual sprites or anything. Android's GLSurfaceView.Renderer has a function for this where you can calculate it:

[code]
onSurfaceChanged(GL10 gl, int width, int height)
[/code]

It gets called at startup and any time the screen changes.

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What you can do is render you scene into an render to texture. Then create a screen aligned quad that will be the desired size you want and then apply the texture onto that quad. That way any stretching will be done automatically by the hardware.

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