[freetype2] anuj-distance-field 4690b0d 20/95: * src/sdf/ftsdf.c (cube_root, arc_cos): Added a few math functions.

[Anuj Verma]

branch: anuj-distance-field
commit 4690b0d421315113b9f35f3b231da2836a93a9d1
Author: Anuj Verma <anujv@iitbhilai.ac.in>
Commit: Anuj Verma <anujv@iitbhilai.ac.in>

    * src/sdf/ftsdf.c (cube_root, arc_cos): Added a few math functions.
---
 [GSoC]ChangeLog |  5 +++++
 src/sdf/ftsdf.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/[GSoC]ChangeLog b/[GSoC]ChangeLog
index 60258af..22c1fe1 100644
--- a/[GSoC]ChangeLog
+++ b/[GSoC]ChangeLog
@@ -1,5 +1,10 @@
 2020-06-30  Anuj Verma  <anujv@iitbhilai.ac.in>
 
+       * src/sdf/ftsdf.c (cube_root, arc_cos): Added a few
+         essential math functions.
+
+2020-06-30  Anuj Verma  <anujv@iitbhilai.ac.in>
+
        [sdf] Fixed compilation under gnumake.
 
        * src/sdf/rules.mk (DRV_OBJ_ => DRV_OBJS_): Fixed varialbe
diff --git a/src/sdf/ftsdf.c b/src/sdf/ftsdf.c
index 2f676be..6ee6bcc 100644
--- a/src/sdf/ftsdf.c
+++ b/src/sdf/ftsdf.c
@@ -2,6 +2,7 @@
 #include <freetype/internal/ftobjs.h>
 #include <freetype/internal/ftdebug.h>
 #include <freetype/ftlist.h>
+#include <freetype/fttrigon.h>
 #include "ftsdf.h"
 
 #include "ftsdferrs.h"
@@ -624,6 +625,57 @@
     return q;
   }
 
+  /* This function uses newton's iteration to find */
+  /* cube root of a fixed point integer.           */
+  static FT_Fixed
+  cube_root( FT_Fixed  val )
+  {
+    /* [IMPORTANT]: This function is not good as it may */
+    /* not break, so use a lookup table instead.        */
+
+    FT_Int  v, g, c;
+
+
+    if ( val == 0 ||
+         val == -FT_INT_16D16( 1 ) ||
+         val ==  FT_INT_16D16( 1 ) )
+      return val;
+
+    v = val < 0 ? -val : val;
+    g = square_root( v );
+    c = 0;
+
+    while ( 1 )
+    {
+      c = FT_MulFix( FT_MulFix( g, g ), g ) - v;
+      c = FT_DivFix( c, 3 * FT_MulFix( g, g ) );
+
+      g -= c;
+
+      if ( ( c < 0 ? -c : c ) < 30 )
+        break;
+    }
+
+    return val < 0 ? -g : g;
+  }
+
+  /* returns cos inverse of a value */
+  static FT_Fixed
+  arc_cos( FT_Fixed  val )
+  {
+    FT_Fixed  p, b = val;
+    FT_Fixed  one  = FT_INT_16D16( 1 );
+
+
+    if ( b >  one ) b =  one;
+    if ( b < -one ) b = -one;
+
+    p = one - FT_MulFix( b, b );
+    p = square_root( p );
+
+    return FT_Atan2( b, p );
+  }
+
   /*************************************************************************/
   /*************************************************************************/
   /**                                                                     **/