I think I've figured out a way for you to do a fast blur, of any blur strength.
1. Render the scene you want at a large size. Say 256x256.
2. Copy this to a texture.
3. Render this texture on a polygon of a smaller size, say 16x16.
4. Copy that to a texture.
5. Use that texture as the blurred version.
This should work because the texture will have mipmaps generarted automatically for it, and rendering the larger texture on the smaller polygon will allow you to grab one of those mipmaps.
Oh, and actually, in both cases the polygon is the same size. It fills the window. You just need to change the viewport size from 256x256 to 16x16.
AND, if you're really clever, you can probably stick several of these textures side by side and render them all at once, but I don't know if that would actually be faster or not, and it would certainly be less generalized and usable in all situations where you need a blurred texture.
1. Render the scene you want at a large size. Say 256x256.
2. Copy this to a texture.
3. Render this texture on a polygon of a smaller size, say 16x16.
4. Copy that to a texture.
5. Use that texture as the blurred version.
This should work because the texture will have mipmaps generarted automatically for it, and rendering the larger texture on the smaller polygon will allow you to grab one of those mipmaps.
Oh, and actually, in both cases the polygon is the same size. It fills the window. You just need to change the viewport size from 256x256 to 16x16.
AND, if you're really clever, you can probably stick several of these textures side by side and render them all at once, but I don't know if that would actually be faster or not, and it would certainly be less generalized and usable in all situations where you need a blurred texture.