Blur filter

Best practices:

• Scale down before applying filter to increase blur radius
• Separate into horizontal + vertical passes to reduce number of texture lookups
• Use hardware filtering to reduce number of texture lookups
• Make sure blending happens in linear RGB to avoid darkening

See also

• https://www.codeproject.com/Articles/839187/An-investigation-of-fast-real-time-GPU-based-image
• https://iquilezles.org/www/articles/gamma/gamma.htm