# OpenGL manual mipmap creation

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I have the following proglem: Until now i created mipmaps using gluBuild2DMipmaps which worked like a charm. But now i wanted to use s3tc compressed textures using this [http://www.opengl.org/registry/specs/EXT/texture_compression_s3tc.txt] extension. I have all the Mipmaps precalculated in DDS files, and when i open those in ATI's compressionator it reads the mipmaps correctly, so obviously no problem here. I am loading the mipmaps using DevIL, which seems to work - it tells me the right number of mipmaps, and if i load any of the mipmap levels as a single texture (without mipmaps), it works - i can see the texture correctly in the gDebugger which also reports the size correctly for the compressed texture. Now the problem is: i can't get mipmaps to work. The code i use to create them:
int mipmaps = ilGetInteger(IL_NUM_MIPMAPS);
for(int i=0; i<mipmaps; i++)
{
// reset mipmap level to main image, otherwise the counter (i) is relative from the last mipmap level.
ilBindImage(imageName);
ilActiveMipmap(i);
int width =  ilGetInteger(IL_IMAGE_WIDTH);
int height = ilGetInteger(IL_IMAGE_HEIGHT);
int size = ilGetDXTCData(NULL,0,dxtcMode);
ILubyte* buffer = new ILubyte[size];
ilGetDXTCData(buffer,size,dxtcMode);
glCompressedTexImage2D(GL_TEXTURE_2D, i, dxtcILtoGL[dxtcMode], width, height, 0, size, buffer);
delete[] buffer;
}
dxtcMode is one of the supported DevIL compression modes (also read from DevIL, so it's the correct one for each image): * IL_DXT1 * IL_DXT1a * IL_DXT3 * IL_DXT5 and dxtcILtoGL is a map mapping from the DevIL modes to the GL modes: * GL_COMPRESSED_RGB_S3TC_DXT1_EXT * GL_COMPRESSED_RGBA_S3TC_DXT1_EXT * GL_COMPRESSED_RGBA_S3TC_DXT3_EXT * GL_COMPRESSED_RGBA_S3TC_DXT5_EXT When i debug this code in gDebugger, it seems to work correctly, also the texture is created and its size grows with each mipmap. But ingame i can't see any textures as long as mipmapping is enabled. if i disable mipmaps (
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
) everything works. I think i can exclude DevIL as an error source, because as said, if i do something like
ilActiveMipmap(3);
int width =  ilGetInteger(IL_IMAGE_WIDTH);
int height = ilGetInteger(IL_IMAGE_HEIGHT);
int size = ilGetDXTCData(NULL,0,dxtcMode);
ILubyte* buffer = new ILubyte[size];
ilGetDXTCData(buffer,size,dxtcMode);
glCompressedTexImage2D(GL_TEXTURE_2D, 0, dxtcILtoGL[dxtcMode], width, height, 0, size, buffer);
delete[] buffer;
without the for loop, it works (without mipmaps of course). The *exact* same thing happens by the way when i do the texture uploading without the compression (again everything seems to be ok in gDebugger, but ingame i only see textures if i disable mipmapping):
int mipmaps = ilGetInteger(IL_NUM_MIPMAPS);
for(int i=0; i<mipmaps; i++)
{
ilBindImage(imageName);
ilActiveMipmap(i);
glTexImage2D(GL_TEXTURE_2D, i, ilGetInteger(IL_IMAGE_BPP), ilGetInteger(IL_IMAGE_WIDTH), ilGetInteger(IL_IMAGE_HEIGHT), 0, ilGetInteger(IL_IMAGE_FORMAT),GL_UNSIGNED_BYTE,ilGetData());
}
The posted code snippet is at exactly the same location in my code where gluBuild2DMipmaps was before. in fact there's only an if switching between compressed and uncompressed textures, uncompressed ones are still generated with gluBuild2DMipmaps (and mipmapping still works with those). At last, the gluBuild2DMipmaps code i use to create mipmaps (which works):
gluBuild2DMipmaps(GL_TEXTURE_2D, ilGetInteger(IL_IMAGE_BPP), ilGetInteger(IL_IMAGE_WIDTH), ilGetInteger(IL_IMAGE_HEIGHT), ilGetInteger(IL_IMAGE_FORMAT), GL_UNSIGNED_BYTE, ilGetData());
pontomedon [Edited by - pontomedon on June 22, 2009 4:32:20 AM]

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Or just use glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);

http://www.opengl.org/wiki/Texture_Mapping

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yeah *looks* great but it seems the mipmaps created that way are not compressed. gDebugger reports the texture to be more than double in size than the one with all the mipmaps uploaded manually. And if i wouldn't need compression i could as well use gluBuild2DMipmaps :(

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You should let the gDeguffer guys know because they probably have a bug.

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I would assume if you call glGetPixels or whatever, you can see if the data comes back compressed? Although I dont know if it by default will give convert compressed and give you the uncompressed RGB values. You could try it with a non-mip map texture and see. If so , check the other ones.

But as the other guy said, each texture has a format, so it would know all the offsets for each compressed piece of data. I doubt it would hold 2 types of data because it would have to switch algorithm offsets.

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Got it working!
Even if auto generated mipmaps were saved in the correct compression format, i was reluctant to use them because they're deprecated... (and also because I seem to be too stubborn not to get my original idea to work ;-))

glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, mipmaps-1);

Seems OpenGL somehow considered my texture as incomplete although i uploaded all the mipmap levels. The -1 is because mipmaps contains the number of leves and i need the index of the max level.

Anyway thank you for your help!

pontomedon

P.S.: for others who have similar problems in the future: There i got the idea from.

EDIT: LOOOOL
I know why OpenGL was thinking that the texture was incomplete: ilGetInteger(IL_NUM_MIPMAPS); actually returns the number of *MipMap* levels, not the total number of layers. so since the for loop was going from 0 to mipmaps I always missed the last mipmap level (1x1). letting the loop go to mipmaps+1 the GL_TEXTURE_MAX_LEVEL property is not necessary...

what a dumb mistake...

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Quote:
 Original post by dpadam450I would assume if you call glGetPixels or whatever, you can see if the data comes back compressed?

Yes, glGetTexImage will uncompress compressed texture. To check if texture is compressed you call glGetTexLevelParameter with GL_TEXTURE_COMPRESSED pname. If you want to get back compressed image, you should use glGetCompressedTexImage function.

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Quote:
 Original post by pontomedonGot it working!Even if auto generated mipmaps were saved in the correct compression format, i was reluctant to use them because they're deprecated... (and also because I seem to be too stubborn not to get my original idea to work ;-))

Yes, but glGenerateMipmap(GLenum target) hasn't been deprecated.

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