Raises the quality in order to properly calculate glow for very small objects like twinkling stars. Very high values may be needed (around 50) for small objects, especially when the glow and halo spreads are large.
shader_glow is applied to a scaled-down sample of the image (for best speed). When the glowing objects are small, the quality level should be set high. For scenes where a large portion of the screen is glowing (for example, when a glowing window fills the frame) then the quality should be set low in order to avoid long rendering times.
When the image is rendered, the following lines appear if there is shader glow:
Glow Filter Width = 21
Glow Resolution = 0.638943
If the Glow Resolution is equal to 1.0, then the quality is as high as it can go (the shader glow image is the same size as the output pix file). The quality setting sets the Glow Resolution based on the Glow Filter Width so that render time is roughly constant. This takes advantage of the fact that the blurry glows (large filter size) generally do not require high resolution.
The time to calculate the shader glow generally goes up in proportion to filter_width * filter_width * pix_size * pix_size * glowing pixels. (where pix size = Glow_resolution * output_image_size and glowing_pixels is = pixels with shaderglow divided by pixels without shaderglow.
