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OpenGL Wow this is a good one, stumped

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When I render my horizon map that I calculate in my engine all of a sudden its smeared. I don't know what I would have changed to make this happen but it wasn't doing this a few hours ago. So when I save out the data that I send to OpenGL the image is fine and not smeared or zoomed in. I am not sure what would be causing this. Any ideas would be great. As of now I have no idea what I would post for code...

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how is it "smeared"? Maybe a screenshot of how it's supposed to look, and then how it's smeared and a little more detail on exactly what you're doing.

You say you calculate it in your engine (I imagine you don't load it so there is no file to corrupt) how do you go about doing this?

We need more info. (Well, I do, maybe some other people don't.)

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Ok, here is the messy image

http://img86.imageshack.us/img86/7921/untitled1copy0fu.jpg

and the one I save out to a file just before I upload it to OpenGL. And no on the repeating the texture coords.

http://img103.imageshack.us/img103/3844/map1296horizonmap8qt.jpg

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May I suggest checking to make sure it's being attached to the proper verts at the proper texture coords? It looks to me like the texture is loading fine, but that the texture coordinates are wrong.

Maybe make a grid with easy to read numbers on it and try to load that in and see how it's distorted to give you a quick visual before looking at it in code. After checking the code, run the debugger over it, make sure the values are created properly and then if for some reason it looks like the code doesn't match the debug try rebuilding your project (maybe you're running off an old build, it happens sometimes.)

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Quote:
Original post by M2tM
May I suggest checking to make sure it's being attached to the proper verts at the proper texture coords? It looks to me like the texture is loading fine, but that the texture coordinates are wrong.

Maybe make a grid with easy to read numbers on it and try to load that in and see how it's distorted to give you a quick visual before looking at it in code.


Can't be the thing render just fine a few hours ago, and I haven't changed the texture coordinates for it... Thats why I am stumped... ;(

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If you're in Visual Studio try cleaning your solution and rebuilding. If truly nothing has changed, that might be the issue. I definitly suggest running the debugger over the values to make sure it is what you think it should be. Obviously something isn't working, don't dwell on the fact that it used to work. Focus on solving the problem through debugging and clear thinking. Try rebooting your computer if all else fails. Who knows what it could be without the project file?

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Quote:
Original post by M2tM
If you're in Visual Studio try cleaning your solution and rebuilding. If truly nothing has changed, that might be the issue. I definitly suggest running the debugger over the values to make sure it is what you think it should be. Obviously something isn't working, don't dwell on the fact that it used to work. Focus on solving the problem through debugging and clear thinking. Try rebooting your computer if all else fails. Who knows what it could be without the project file?


Thanks for the ideas, but tried most of them so far... One thing I have noticed is that my app is taking 115megs to run in the task manager?? Do I need to tell the compiler to allocate more RAM for the app? Just wondering...

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Quote:
Original post by MARS_999

Thanks for the ideas, but tried most of them so far... One thing I have noticed is that my app is taking 115megs to run in the task manager?? Do I need to tell the compiler to allocate more RAM for the app? Just wondering...


Tell the compiler to allocate more ram?? What language are you using.

If you use C/C++ check for uninitialized variables and/or buffer overflows. just a thought.

I would sugest you, to start using revision control (svn, cvs,..), so that you can see what you changed in the last couple of versions. Its a good feeling to know you can restore past versions at will :)

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Odds are your packing alignment (set via glPixelStore) is incorrect. The default for GL_UNPACK_ALIGNMENT is 4.

The "horizon map" image you linked to is 129x129, so if you unpacked it into 24-bit RGB, your row size (or stride) would be 129x3 = 387 bytes, but since OpenGL is expecting a row alignment of 4, glTexImage2D would actually transfer 388 bytes (387 bytes read, 1 byte skipped).

This is why your texture has black pixels on the left-hand side -- OpenGL is skipping parts of your texture data and eventually is reading data from unallocated memory. Power-of-two (and many other) sized textures do not exhibit this problem because the width of the texture times 3 "just happens" to also be aligned to 4.

Either set GL_UNPACK_ALIGNMENT to 1 before calling glTexImage2D, or unpack your texture so each row is aligned to 4 bytes in memory.

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Quote:
Original post by bpoint
Odds are your packing alignment (set via glPixelStore) is incorrect. The default for GL_UNPACK_ALIGNMENT is 4.

The "horizon map" image you linked to is 129x129, so if you unpacked it into 24-bit RGB, your row size (or stride) would be 129x3 = 387 bytes, but since OpenGL is expecting a row alignment of 4, glTexImage2D would actually transfer 388 bytes (387 bytes read, 1 byte skipped).

This is why your texture has black pixels on the left-hand side -- OpenGL is skipping parts of your texture data and eventually is reading data from unallocated memory. Power-of-two (and many other) sized textures do not exhibit this problem because the width of the texture times 3 "just happens" to also be aligned to 4.

Either set GL_UNPACK_ALIGNMENT to 1 before calling glTexImage2D, or unpack your texture so each row is aligned to 4 bytes in memory.


Ok, that makes sense. I will try it when I get home. I will let you know. Thanks

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Hey thanks a million bponit that was it! Now I don't understand why its been working all along and now it failed today? I haven't touched the code that deals with that texture in a long time... I am on a 7800GT so NONPOT isn't an issue I thought? due to the 7800GT being OpenGL2.0 compliant... I am also using mipmapping so that should have clipped it to 128x128? or with GL2.0 does it leave it at 129x129? Thanks again!

Oh and BTW I am using GL_LUMINANCE8

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The way NPOT textures are stored in memory and the way they are rendered are two completely different things. Actually, I really shouldn't have mentioned that because it's not what the problem is here -- it's just that a width of 129 is not a multiple of 4. Power-of-two sized textures just "happen" to be multiples of 4, so they don't exhibit this issue.

For example, a 24-bit RGB texture with a width of 48 (48x3 = 144) is still divisible by 4, so the standard GL_UNPACK_ALIGNMENT of 4 would not have any problem transferring it from main memory to video memory, even though it is a NPOT texture.

Since you are using GL_LUMINANCE8, glTexImage2D would instead read 129 bytes and skip 3 bytes for each row in the texture.

Edit: Just an addition -- this unpacking is identical to the way BMPs store their bitmap data. BMPs also use 4 bytes alignment per row, so regardless of the width of the image (NPOT or not), the texture would be transferred without problems.

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Quote:
Original post by bpoint
The way NPOT textures are stored in memory and the way they are rendered are two completely different things. Actually, I really shouldn't have mentioned that because it's not what the problem is here -- it's just that a width of 129 is not a multiple of 4. Power-of-two sized textures just "happen" to be multiples of 4, so they don't exhibit this issue.

For example, a 24-bit RGB texture with a width of 48 (48x3 = 144) is still divisible by 4, so the standard GL_UNPACK_ALIGNMENT of 4 would not have any problem transferring it from main memory to video memory, even though it is a NPOT texture.

Since you are using GL_LUMINANCE8, glTexImage2D would instead read 129 bytes and skip 3 bytes for each row in the texture.


So byte alignment matters with NONPOT textures that don't align to a value thats divisable by 4 and I need to be aware of it on all NONPOT textures.
If so I gotcha. :)

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Technically, alignment matters for _all_ transfers, NPOT or not.

But what you've said is basically right, yes. :)

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