A bloom effect makes the bright area of image has a 'hazy' around. To achieve bloom effect, you need:
1. Bright-pass image to produce the bright pattern.
use the bright_pass.fx shader to filter out bright area to a texture ( 256 x 256 size is suitable).
2. Blurring the bright pattern and down scale it.
use the blur_4x_tex.fx or blur_2x2.fx shader to blur &
down-scale bright pattern to a small texture (64 x 64 size is suitable).
A example flow path:
blur_2x2_256.fx ( output to 128 x 128 image ) blur_2x2_128.fx ( output to 64 x 64 image ) blur_2x2_64.fx ( output to 64 x 64 image ) more blurring if needed...
3. Combine the original scene image and the final bright pattern.
use the present_bloom.fx shader cover bright pattern to the original scene image.