   Bloom: downsample&blur in same pass?
  On http://prideout.net/archive/bloom/index.php site I saw this:It says fewer samples for the Gaussian can be used by sampling between texels to take advantage of the linear texture filtering.Based on this, for each reduction level my first pass fragment shader creates the reduced texture by half using a simple copy outCol = vec4(vec3(texture(tex, tc)), 1.0); and linear filtering for tex (actually combined with bright-pass for the first time), then I do horiziontal and vertical passes with outCol = coef[0] * texture(tex, tc - vec2(offx, offy)) + coef[1] * texture(tex, tc) + coef[2] * texture(tex, tc + vec2(offx, offy));  In these tc = inPos * 0.5 + 0.5; in the vertex shader and the offsets are 1.2, 0 and 0, 1.2 for the two blur passes (got the 1.2 from the source of the image above).If I combine the reduction and first filtering passes into one, would I still get the same results, or would I need to sample 5 locations?  I'm thinking that it wouldn't be the same since the reduction pass does one linear filtering, then a second one when I read at offset 1.2, so that gets contributions from 4 texels instead of 2.  But I'm assuming that 5 sample locations with one less pass should faster (yes/no?) so I want to ask how to calculate the offsets for that case, as well as what coefficients to use.   
  It's not the same as you're not covering the same area. It's also a misnomer to try and combine these separable passes into one.To do it properly in one hit, you'd need to sample a 5x5 block = 25 samples. To do it in two passes, you sample 5 locations twice = 10 samples for the same result. It's faster to do it separately anyway.   ;  Yes, but my issue is the offset computation.In the tutorial code, my best guess for the offsets of 1.2 texels is that it's linearly interpolated based on the weights, which are themselves summed.So weights 1 4 6 4 1 (and normalized) sampled at -2 -1 0 1 2 texel offsets becomes 5 6 5 (and normalized) sampled at -1.2 0 1.2 which is a good approximation.So looking at more samples, starting with 1 8 28 56 70 56 28 8 1 (and normalized) sampled at texel offsets of integral positions in [-4, 4], using the optimization he suggests, I would use 9 84 70 84 9 (and normalized) sampled at -3.11 -1.5 0 1.5 3.11 texel offsets (keeping in mind texel size would be half before now that I'd be combining the reduction pass).Does my arithmetic look right?   