Drawing a tiled map

OpenGL Development
#1

Hi,
What’s the best way of drawing a scrolling tiled map in LWJGL (OpenGL)?

Should I use the bitmap methods?
Should I use one textured rectangle per tile?
Should I use one large textured rectangle and draw the tiles to its texture?

  • The tiled map is going to be scrolled.
  • It can be a quite large map.
  • Separate tiles can be animated.

Are there any examples?

#2
  • Sprites are best done with textured quads, the bitmap drawing methods are far too slow and unflexible.
  • Sprite animation then means just switching which texture you’re using
  • Sort your drawing by texture to minimise texture binds
  • Further improve the above by packing multiple sprites/tiles into one larger texture
#3

Thanks for you answer.

But my question wasn’t really about sprites. It was about using a tiled map as a background.
I want to build up my level backgrounds using tiles.

Any ideas of that issue?

#4

Tiles are sprites, just a somewhat special case as they don’t usually move and are the same dimensions.

#5

You are, of course correct. Tiles are in most ways identical to sprites. :slight_smile:
And when I re-read your tips with that in mind it all made sense.
I’m just sort of stuck in the Java2D thinking. sorry

I also found a nice little example on how to make tiled maps in OpenGL which made it even more clear.

A question though: How expensive is a texture binding? Do I save a lot of time by trying to minimize the number of bindings?

#6

Texture binding is the most expensive operation in OpenGL. Always sort where possible. Tilemaps are great though because lots of little tiles fit on one big texture.

Cas :slight_smile:

#7

What do you mean by “…lots of little tiles fit on one big texture…”?
Should I load one texture that contains all tiles?
… or should I draw the level map to a texture and then just draw one rectangle which is bind to that texture?

Sorry if the questions are rather stupid but I’m just starting to dig in to OpenGL .

#8

Wow, thats about the most inefficient way of doing a tile map in OpenGL ever. :o

  • Always try and avoid immediate mode (glBegin(*) etc.) unless you’re doing really simple stuff.
  • It uses glBegin/end in a really tight loop, which is horrible. At the very least you could move the glBegin outside the loop (except that this breaks its method of texturing)
  • It doesn’t sort by texture, so you get a bind per tile (ouch!).
  • One texture which contains all tiles is the way to go. Then just tinker with the texture coords to get the correct tile out of it.
#9

Allright, this I can understand (I think). :wink:

So what you do is this…

  1. bind your one-large-texture-containing-all-tiles
  2. draw all visible tiles but change the texture coords for each tile so that the correct tile is drawn.

Do I need to sort the drawing order when using this tech as well or is the tinkering with texture coords unexpensive?

Are there any examples out there using this technique?

#10

Only if you can’t fit all tiles on one texture. Then you still need to sort or you might end up switching between two textures wich is just as bad.

#11

These days you can aim for a 1024x1024 tile texture, and if your tiles are, say, 32x32, that’s a total of 1024 different tiles just in one texture! Even in the rare occasion you need to swap textures, your tile textures only take up 3MB of VRAM, so you’re likely to be able to fit at least 2 in VRAM at a time (that’s the main cost - uploading a texture if it isn’t in the VRAM cache). So if you had, say, 2048 different tiles in your game (I’d be impressed if you did!), you’d have at most just two texture binds per frame to draw the lot if you sorted them correctly.

Cas :slight_smile:

#12

Thanks for all you help!

Next thing I must learn i how to configure the viewport and other things to get the graphics pixel aligned.

But I think I did see some thread about this matter? Or maybe you guys have a good snipplet just waiting to get posted as a response to this question? :wink:

#13

The default LWJGL display is already setup with opengl units corresponding to pixels. If you need to do it manually you need a glOrtho call, IIRC: glOrtho(0, 0, width, height, -z, +z);

#14

Hello,

Here is some code for drawing a scrolling tiled map. I used it in my “Keith Goes Painting” game, I hope you find it usefull.

I found that using a single texture, with all your tiles on, led to some texel bleeding from neighbouring tiles.
I fixed that problem by reducing the floating point resolution that the map could be drawn at, using this code:

        displayPosX -= displayPosX%0.1f;
        displayPosY -= displayPosY%0.1f;

I then called the map drawer stuff in the attached file.