pub const NUM_SIZES: usize = 5;Expand description
Blurring is performed while downsampling to the smaller sizes in steps and then upsampling back up to the original resolution. Each level is half the size in both dimensions from the previous. For instance with 5 distinct sizes there is a total of 8 passes going from the largest to the smallest to the largest again:
1 -> 1/2 -> 1/4 -> 1/8 -> 1/16 -> 1/8 -> 1/4 -> 1/2 -> 1 ~~~~ [downsampling] smallest [upsampling]
The textures used for downsampling are re-used when upsampling.
Additionally, instead of clearing them the colors are added together in an attempt to obtain a more concentrated bloom near bright areas rather than a uniform blur. In the example above, the added layers would include 1/8, 1/4, and 1/2. The smallest size is not upsampled to and the original full resolution has no blurring and we are already combining the bloom into the full resolution image in a later step, so they are not included here. The 3 extra layers added in mean the total luminosity of the final blurred bloom image will be 4 times more than the input image. To account for this, we divide the bloom intensity by 4 before applying it.
Nevertheless, we have not fully evaluated how this visually compares to the bloom obtained without adding with the previous layers so there is the potential for further artistic investigation here.
NOTE: This constant includes the full resolution size and it is assumed that there will be at least one smaller image to downsample to and upsample back from (otherwise no blurring would be done). Thus, the minimum valid value is 2 and panicking indexing operations we perform assume this will be at least 2.