#28 TBitmap_BoxBlurRect/Ellipse get slower with a large radius

[Thomas Mueller]

BoxBlurLine in src/u_dzGraphicsUtils.pas (added in revision #2377 for [features:#26]) builds the starting sum of every line with a loop from -Radius to Radius, so each line costs 2 * Radius + 1 steps before the running sum starts. The doc comment of TBitmap_BoxBlurRect says the time does not depend on the radius; that only holds while the radius is small compared to the area.

Measured on Delphi 12 Win32, blurring a whole 200x200 bitmap: 0 / 31 / 406 / 844 / 2172 ms for Radius = 5 / 100 / 1000 / 10000 / 65535.

The results are correct. Fix: compute the starting sum from the clamped ends, (Radius + 1) times the first value, plus the values 1 to Min(Radius, Count - 1), plus the repeated last value for the positions beyond the end. That is the same sum, so the results do not change.

Found by a review of revision #2377 for a sync.

[Thomas Mueller]

Fixed in revision #2378.