G.T.A.2 Map Editor

[Carver413]

in newer versions of opengl textures need not be powers of 2 to work. I create many textures on the fly and none of them are powers of 2 and they render fine.

[Rodrigo Robles]

in newer versions of opengl textures need not be powers of 2 to work. I create many textures on the fly and none of them are powers of 2 and they render fine.

I read somewhere that although non power of 2 textures are supported, the power of 2 will get better performance. I would like to know how much better performance...

[Carver413]

I read somewhere that although non power of 2 textures are supported, the power of 2 will get better performance. I would like to know how much better performance...

I read somewhere that opengl actually expands these internally so they end up as power of 2 anyway. the advantage would be in the passing of smaller texture or maybe thats where the slowdown occures. best practice of course would be to try to put them on a single texture and map them properly

[hwnd]

I have old PC with old gfx card ATI Radeon 9550. And i want to support old hw and os starting from Windows 95. Better don't ask why. I love the old stuff and software. I dunno, if nxPascal GL code supports W95, with the latest possible OpenGL dll in it. I will try with my editor. I don't use any shaders or anything in my editor and "biggest" textures are 64x64.
Just the sprites from GTA2 files are different, like 16x78, 2x28 etc. I don't use any texture atlas, they seem to be too complicated for me.

Te DevIL actually seems to have bug or im just not doing enough or doing something wrong but NPOT .bmp files are completely screwed when rendering them with same code. PNG works fine. I havent tried the pure pixels from pointer. Will do this later, hopefully it will work.

[phibermon]

NPOT : No need to re-scale the image or anything like that in order to support NPOT textures, just simply create an image which snaps to the next largest power of two size on both axis, then load your image data into the 0,0 corner and then rescale your texture co-ordinates by the ratio of the new NPOT image size to the Original image size. You waste some texture memory but it's quicker to load the textures (As you don't need to scale them). If all the GTA2 textures are loaded on map startup and nothing is streamed during gameplay, you may as well rescale like you are in order to save wasting memory.

EDIT : totally ignore that, if you're scaling the images for POT anyway then you won't use any more GPU memory using the method I suggested. it'll be quicker than scaling and you won't have a DevIL (or other image lib) dependancy.

A Texture atlas would let you save memory and would also be faster when rendering (less texture switching) it's really easy, for the first image you create the biggest texture you can for your hardware (256x256 should be fine for example) and load it into the top corner, then return that images GL_ID and the texture coords that are used. Then for each sucessive image you 'search' your available space in your 'texture atlas' for a clear spot that your image will fit in (so look at the dimensions of existing images, itterating along X and Y until you've found some free space) then copy your image data there, then return the coords that were found for use for the new reference.

If your search doesn't find a space big enough for the image due to all the other images, you just create another big texture in GL and start the process all over again.

The end result is a handfull of big textures with all your small textures splattered across them and all your material/texture references are to these images and coord offsets to the actual image data you want.

There's all kinds of ways of doing it, different optimizations to use etc but the basic principal is sound. Look at light-map construction in a BSP map loader for an example, you can also read up on the design of ID Software's mega-texturing implementation in RAGE. Essentially the same technique but creates super large images in system memory, portions of which are copied to GPU memory when needed. RAGE (tech 5 or whatever) has algorithms (at map compile stage) that try to group required textures together in the mega-texture so when the 'atlas' portion is copied to a normal texture you're using most of the sub-textures for the on-screen geometry. They probably use visbility determination, portals etc as part of the algorithm to optimize the grouping of sub-textures.

[hwnd]

Thank your for your reply. Yes i got 2 good examples actually which create opengl texture from npot bitmaps, one is that DevIL and one is with SDL. They load texture fine but biggest problem for me now is rendering quad which has the newly created texture centered exactly on the quad.

I even did a simple example with crosshair on screen and rotated the quad on center and then i discovered that texture is not actually centered on the quad.

The quad itself was "perfect", npot texture was also OK but texture had offset on the quad. But in my case the npot texture must be exactly centered on the quad.

So have discovered that im unable to center the texture on quad. As you said: "rescale your texture co-ordinates by the ratio of the new NPOT image size to the Original image size"

I don't care about memory atm, i need to make it work first.

Im now even unable to find the example i wanted to show you, how the texture is not centered.
I was so disappointed. I thought i got it finally working but no, again some bug or problem.

But i would like to make it work. I will at least learn something from it.
I will try to find the example i made and post a screenshot later.


EDIT
It should be like in image B, but atm its like A. Which is bad!
It should be centered perfectly like in image B.
Original texture size is 32x18





By ratio you mean in this case 32 / 32 and 18 / 32 ?

Since next POT for 32 is 32 (unchanged in this case) and for 18 it's 32.


Here is the way im doing atm:

 
var texTop, texbottom, texleft, texright:single;
w,h:Single;


  texTop:=0; // This shouldnt be 0 i think, must be calculated?
  texleft:=0; // This shouldnt be 0 i think, must be calculated?
  texbottom:=th /getnextpot(th);
  texright:=tw / getnextpot(tw);


  w:=tw/64;
  h:=th/64;





glBegin( GL_QUADS );
         // Top-left vertex (corner)
         glTexCoord2f( texLeft,    texTop ); glVertex3f( -w/2, -h/2, 0 );

         // Bottom-left vertex (corner)
         glTexCoord2f( texRight,    texTop); glVertex3f( w/2, -h/2, 0 );

         // Bottom-right vertex (corner)
         glTexCoord2f(  texRight, texBottom); glVertex3f( w/2, h/2, 0 );

         // Top-right vertex (corner)
         glTexCoord2f(texLeft, texBottom); glVertex3f( -w/2, h/2, 0 );

   glEnd();

If i modify either texTop and / or texLeft then i can move texture to center.
But then it looks pretty bad, like squeezed together a bit or something.

"tw" and "th" are NPOT image width and height, assigned on image loading!
In this case they contain: 32 and 18.

This code causes things look like in image A.

I divide by 64 because every tile in GTA2 is 64x64. Main gfx. Every object like this roadblock is placed on the tiles of size 64x64.

It seems everything should be calculated. But whats the correct math?
I will try to find some example on net.

Texture centering is the only problem atm.

[phibermon]

Ok, that should actually work, your understanding is correct. however if you're getting A with that exact code then there's somthing else at play here, whilst implementing this solution I assume you turned off the image scaling you previously implemented?

Step thru it with your debugger, Ensure that just before your GL_QUADS call that texbottom and texright are what they are supposed to be, in this example texbottom should be 1 and texright should be 0.56.

I can assure you that an image of 18x32, stored in a GL texture of 32x32 (none scaled, origin at 0,0) rendered with tex coords (0,0) (0.56,1.0) would be mapped onto your quad of any size. if your source image was red with a 1 pixel blue border, you'd see that blue border tight against every quad edge.

(A) is exactly what you'd get if you loaded a 18x32 image into a 32x32 texture and rendered with tex coords of (0,0)(1,1) you'd have a 'gap' along one side where the X coord of 1 (Which should be 0.56) is causing the unused part of the texture to be rendered, 'squashing' the original texture (not offset as it appears) so that it's mapped across 0.44 of the width of the quad.

Debug this exact example, ensure that texright=0.56, if it's right then that is very strange indeed, let me know and I'll do my best to help, if needed I'll make you a GL1.x example you can use as a reference

[SilverWarior]

Here is the way im doing atm:

 
var texTop, texbottom, texleft, texright:single;
w,h:Single;


  texTop:=0; // This shouldnt be 0 i think, must be calculated?
  texleft:=0; // This shouldnt be 0 i think, must be calculated?
  texbottom:=th /getnextpot(th);
  texright:=tw / getnextpot(tw);


  w:=tw/64;
  h:=th/64;





glBegin( GL_QUADS );
         // Top-left vertex (corner)
         glTexCoord2f( texLeft,    texTop ); glVertex3f( -w/2, -h/2, 0 );

         // Bottom-left vertex (corner)
         glTexCoord2f( texRight,    texTop); glVertex3f( w/2, -h/2, 0 );

         // Bottom-right vertex (corner)
         glTexCoord2f(  texRight, texBottom); glVertex3f( w/2, h/2, 0 );

         // Top-right vertex (corner)
         glTexCoord2f(texLeft, texBottom); glVertex3f( -w/2, h/2, 0 );

   glEnd();

If i modify either texTop and / or texLeft then i can move texture to center.
But then it looks pretty bad, like squeezed together a bit or something.

The problem of this code you had is that you have only been moving texTop and/or texLeft but not texBottom and/or texRight. So instead of moving texture you have actually been scaling it.
You should have changed your code like this:

 
  texTop:=0; // This shouldnt be 0 i think, must be calculated?
  texleft:=0; // This shouldnt be 0 i think, must be calculated?
  texbottom:=textTop + (th /getnextpot(th)); //Bottom edge is always position of top edge + height
  texright:=texLeft + (tw / getnextpot(tw)); //Right edge is always position of left edge + width