Re: Mipmap filtering

[Frank C <li...@si...>]

NOTE: I tired to send this to the list earlier but ran into some list  
troubles - I've already sent Joe some changes that implement mipmapping  
and filtering as discussed below. I apologize if this is a duplicate  
message!

On 2-Jun-04, at 10:53 PM, Joseph J. Strout wrote:

> OK, let's talk about this issue:
>
>> 1. Proper mipmap filtering  
>> <http://sourceforge.net/tracker/index.php? 
>> func=detail&aid=905678&group_id=45158&atid=442052>. There are several  
>> ideas in this request, but the most important one is to automatically  
>> generate mipmaps from a Pixmap texture, just as QD3D 1.6 does.  (And  
>> then of course if you don't want mipmaps generated for you, you can  
>> use a MipMap texture instead.)
>
> My understanding is that in QD3D 1.6, when you use a PixmapTexture,  
> mipmaps are generated under the hood for you, and the renderer then  
> selects the one most suited to the object's usage in the scene.
> ...
> That suggests that maybe the renderer code is the right place to look  
> -- perhaps IRTexture.c?  Perhaps modify ir_texture_convert_pixmap so  
> that it generates an OpenGL mipmap set, as ir_texture_convert_mipmap  
> does?  If we do it here, is all that scaling and conversion going to  
> happen on every frame, or just once for each time the texture is  
> edited?  And if there are multiple objects sharing the same texture,  
> will it happen just once for the whole lot?

Easiest way is to replace the glTexImage2D call with a call to  
gluBuild2DMipmaps and they'll be created auto-magically. You can  
minimize them manually and call glTexImage2D multiple times as well,  
which is often preferred since the result will be more predictable  
regardless of OS, hardware, or OGL implementation. A custom algorithm  
can also be tweaked to give better results than gluBuild2DMipmaps.

Creating the mipmaps is only the first step however. The  
cachedTexture->qualityFilter settings in the ir_texture_set_state  
function have to be changed to take advantage of mipmaps. This can be  
done in a couple ways, though I'd recommend the following:

Create a new private struct:

typedef struct TQ3QualityFilter {
	GLuint					magFilter;
	GLuint					minFilter;
} TQ3QualityFilter;

Then replace the qualityFilter member of the TQ3CachedTexture struct  
with TQ3QualityFilter and modify the affected routines accordingly;  
ir_texture_convert_rave_filter, ir_texture_set_state,  
IRRenderer_Texture_Rebuild, and ir_texture_cache_add.

The actual values of the mag/min filters would follow the  
recommendations outlined in the bug report.

I've actually gone ahead and did this on a local copy and it seems to  
work just fine (currently using gluBuild2DMipmaps).

Frank.