What should I use instead of pixels in a LibGDX game?

Question

Recently I have read here: https://xoppa.github.io/blog/pixels/ that I should not use pixels in my game. But Im not sure that I have understood this so I have some questions.

1. Xoppa writes that pixels may look different on different devices but I thought all the time that viewport solves the problem of different screen size and aspect ratio. Was I wrong?

2. How can I draw all assets without using pixels?

3. I have an idea to support all screen ratios and sizes by using ExtendViewport with the biggest screen that I will support. It looks like this:

viewport = new ExtendViewport(1080, 1920, 1440, 1920, camera);

And everything works well on the smartphone during test. Game is prepared for 16:9 screen and if somebody have for example 4:3 screen he will se more background texture.

But I dont know how game will work on weaker devices. Is one viewport (1920x1440) enough? Or I should make more viewports for several sceen sizes for example 1920x1440, 1280x960 and 800x600?

Just I dont understand why I should not use pixels in game if everything works well. Can somebody explain it to me in simple way?

Answer 1

Reason's why I use meters instead of pixels

• using pixel is mostly not recommended because base on my experience, when you are using libgdx box2d body the unit is known as meters, for example you created a Vector2 position = Vector2(1,1); the x and y value is 1 meter, so in that case if you use pixels for example 32 pixel the body value would be 32 meters.
• to minimize the value

To convert from pixels to meters is easy.

float UNIT = 32.0f; // unit of 1 meter is 32 pixels in the given unit
float PIXELS_TO_METERS = 1 / UNIT;

float meterValue = PIXELS_TO_METERS * PIXEL_VALUE

For example, you have a camera and set its width to 800 pixels and height to 480 pixels. Then you just need to multiply it by PIXELS_TO_METERS to get the meter value.

public final static float WIDTH = 800;
public final static float HEIGHT = 480;

// This is the typical pixels value of WIDTH and HEIGHT
OrthographicCamera camera = new OrthographicCamera(WIDTH, HEIGHT);

// Now we applied the pixel to meter conversion.
float FRUSTUM_WIDTH = WIDTH * PIXELS_TO_METERS;
float FRUSTUM_HEIGHT = HEIGHT * PIXELS_TO_METERS;

OrthographicCamera camera = new OrthographicCamera(FRUSTUM_WIDTH, FRUSTUM_HEIGHT);

// or set it directly
OrthographicCamera camera = new OrthographicCamera(25, 15);

Answer 2

It is more convenient. Say you are developing a 2D 4X game, a simplified version of the original civilization games. Your ingame world is divided into a 20x20 map of tiles. Tell me, to place your tiles, would you rather draw a tile at tiles[2][2].draw(20,20); or at tiles[2,2].draw(2,2); to draw a tile at (x,y) -> (2,2) from the origin of your world. This is a negligible difference in this case, but as the coordinates increase in value, you could eventually have to write tiles[2][2].draw(2000,2000);depending on your world size.

This might be a bit arbitrary, so let me give you another example. When designing a UI, would you rather have to guess where each UI element should be drawn pixel-wise, or would you rather divide your viewport into 100 units (a 10x10 map of coordinates) and draw it at 10,10 or 1000,1000. And, no, the viewport will not handle pixel -> device screen adjustments, it will handle world coordinates -> device screen positioning, so using pixels will still mess up your rendering.