OpenGL Mipmapping: how does OpenGL decide on map level?
- by Droozle
Hi,
I am having trouble implementing mipmapping in OpenGL. I am using OpenFrameworks and have modified the ofTexture class to support the creation and rendering of mipmaps.
The following code is the original texture creation code from the class (slightly modified for clarity):
glEnable(texData.textureTarget);
glBindTexture(texData.textureTarget, (GLuint)texData.textureID);
glTexSubImage2D(texData.textureTarget, 0, 0, 0, w, h, texData.glType, texData.pixelType, data);
glTexParameteri(texData.textureTarget, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(texData.textureTarget, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glDisable(texData.textureTarget);
This is my version with mipmap support:
glEnable(texData.textureTarget);
glBindTexture(texData.textureTarget, (GLuint)texData.textureID);
gluBuild2DMipmaps(texData.textureTarget, texData.glTypeInternal, w, h, texData.glType, texData.pixelType, data);
glTexParameteri(texData.textureTarget, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri(texData.textureTarget, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glDisable(texData.textureTarget);
The code does not generate errors (gluBuild2DMipmaps returns '0') and the textures are rendered without problems. However, I do not see any difference.
The scene I render consists of "flat, square tiles" at z=0. It's basically a 2D scene. I zoom in and out by using "glScale()" before drawing the tiles. When I zoom out, the pixels of the tile textures start to "dance", indicating (as far as I can tell) unfiltered texture look-up. See: http://www.youtube.com/watch?v=b_As2Np3m8A at 25s.
My question is: since I do not move the camera position, but only use scaling of the whole scene, does this mean OpenGL can not decide on the appropriate mipmap level and uses the full texture size (level 0)?
Paul
