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Editorial Team
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Asked: 2026-05-31T09:39:39+00:00

I’m writing a little cross platform game engine for iOS, Android and BADA. I

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I’m writing a little cross platform game engine for iOS, Android and BADA. I have a question about setting the perspective to be consistent regardless of screen resolution and ratio.

I have the following set up for my flipped normalized orthographic projection which works fine:

 glViewport(0, 0, mWidth, mHeight);

 glMatrixMode(GL_PROJECTION);

glOrthof(-1.0,                  //LEFT
          1.0,                   //RIGHT
          -1.0 * mHeight / mWidth,  //BOTTOM
          1.0 * mHeight / mWidth,   //TOP
          -2.0,                  //NEAR
          100.0);                //FAR

On my iPhone’s this is fine and I get the desired position of world objects but on some of the Android devices and iPads the position when retaining the correct ratio.

All of the meshes are the right proportions but the position obviously alters so that if something is aligned to the bottom of the screen, when rendered on the iPad the objects will be drawen partly off the screen.

So the question:

Is this correct and I need to place objects relative to the width and height of the viewport?

Or

Is there a method to setting up the orthogonal perspective so that regardless of screen ratio the positioning will remain constant without damaging the perspective of world objects?

I am thinking from what I know and the math I did the second isn’t an option because perspective is defined based on ratio.

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1 Answer

  1. Editorial Team

    The iPad and iPhone screens have different proportions. The iPhone is 3:2 and the iPad is 4:3. Android phones have too wide range of different proportions to list and I wouldn’t really like to comment on Bada. So unless you’re going to show your image in a letterbox or pillarbox, or stretch it so that the aspect ratio changes from device to device, the amount of your internal world that’s visible is going to change between devices.

    At the minute you’ve fixed the left and right parameters while calculating the top and bottom based on the screen proportions. So you’ll get exactly the same amount of your world across the screen on every device but the amount on the vertical will change.

    If your game involves a camera moving in 3d then there’s really not much you can do about it. But since you’re talking about things being aligned to sides of the screen I guess the camera moves in 2d?

    As a general rule, if the camera moves along the vertical then you probably want to keep what you have. Your level layouts that are exactly the width of the screen will be the width of everybody’s screen. Wider devices will be able to see further ahead or behind, but there you go.

    If the camera moves along the horizontal then you probably want to switch to supplying fixed values for top and bottom, and calculating left and right as per the aspect ratio. So I guess that’d be:

    glOrthof(-1.0 * mWidth / mHeight, //LEFT
          1.0 * mWidth / mHeight, //RIGHT
          -1.0 ,                  //BOTTOM
          1.0 ,                   //TOP
          -2.0,                   //NEAR
          100.0);                 //FAR

    In terms of being able to close this all off inside a library, you’ll probably just need to receive a flag as to whether logical viewport width should be fixed and height adapted to the screen or height fixed and width adapted.

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