From: Mikko Rasa <tdb@tdb.fi>
Date: Fri, 4 May 2018 19:15:07 +0000 (+0300)
Subject: Improve distance field accuracy
X-Git-Url: http://git.tdb.fi/?p=ttf2png.git;a=commitdiff_plain;h=1fb6f37cfa76c47b65331b6fe8217f8973f35885

Improve distance field accuracy

A better initial guess allows the square root function to deal with
larger numbers.
---

diff --git a/ttf2png.c b/ttf2png.c
index 5e6e351..bf9f8d2 100644
--- a/ttf2png.c
+++ b/ttf2png.c
@@ -694,15 +694,9 @@ int copy_bitmap(const FT_Bitmap *bmp, Image *image)
 
 unsigned sqrti(unsigned num)
 {
-	unsigned result = num;
-	while(result*result>num)
-	{
-		unsigned diff = result*result-num;
-		if(diff<result)
-			break;
-
-		result -= (diff+result)/(result*2);
-	}
+	unsigned result = (num>0xFFFF ? 0xFFFF : 0x100);
+	while(result && result*result>=result+num)
+		result -= (result*result+result-num)/(result*2);
 
 	return result;
 }
@@ -740,7 +734,7 @@ unsigned find_distance_to_edge(const Image *image, int origin_x, int origin_y, u
 		}
 	}
 
-	return sqrti(closest)*0x7F/range;
+	return sqrti(closest*0x3F01)/range;
 }
 
 int create_distance_field(const FT_Bitmap *bmp, Image *image, unsigned scale, unsigned margin)