Made the kerning a float, this give a little more of tweak.

0.5 is the default value now, the range are from -5.0 to 5.0.
Note that we allow negative value, but the current draw code
always check for overlap characters.

source/blender/blenfont/BLF_api.h

@@ -85,7 +85,7 @@ float BLF_height_default(char *str);
 void BLF_rotation(float angle);
 void BLF_clipping(float xmin, float ymin, float xmax, float ymax);
 void BLF_blur(int size);
-void BLF_kerning(int space);
+void BLF_kerning(float space);
 
 void BLF_enable(int option);
 void BLF_disable(int option);

source/blender/blenfont/intern/blf.c

@@ -492,7 +492,7 @@ void BLF_mode(int mode)
 		font->mode= mode;
 }
 
-void BLF_kerning(int space)
+void BLF_kerning(float space)
 {
 	FontBLF *font;
 

source/blender/blenfont/intern/blf_font.c

@@ -100,7 +100,7 @@ void blf_font_draw(FontBLF *font, char *str)
 	GlyphBLF *g, *g_prev;
 	FT_Vector delta;
 	FT_UInt glyph_index, g_prev_index;
-	int pen_x, pen_y, old_pen_x;
+	float pen_x, pen_y, old_pen_x;
 	int i, has_kerning;
 
 	if (!font->glyph_cache)
@@ -159,7 +159,7 @@ void blf_font_draw(FontBLF *font, char *str)
 		}
 
 		/* do not return this loop if clipped, we want every character tested */
-		blf_glyph_render(font, g, (float)pen_x, (float)pen_y);
+		blf_glyph_render(font, g, pen_x, pen_y);
 
 		pen_x += g->advance;
 		g_prev= g;
@@ -321,7 +321,7 @@ void blf_font_fill(FontBLF *font)
 	font->flags= BLF_USER_KERNING;
 	font->dpi= 0;
 	font->size= 0;
-	font->kerning= 0;
+	font->kerning= 0.0f;
 	font->cache.first= NULL;
 	font->cache.last= NULL;
 	font->glyph_cache= NULL;

source/blender/blenfont/intern/blf_internal_types.h

@@ -168,7 +168,7 @@ typedef struct FontBLF {
 	int size;
 
 	/* kerning space, user setting. */
-	int kerning;
+	float kerning;
 
 	/* max texture size. */
 	int max_tex_size;

source/blender/editors/interface/interface_style.c

@@ -91,7 +91,7 @@ static uiStyle *ui_style_new(ListBase *styles, const char *name)
 	
 	style->paneltitle.uifont_id= UIFONT_DEFAULT;
 	style->paneltitle.points= 13;
-	style->paneltitle.kerning= 1;
+	style->paneltitle.kerning= 0.5;
 	style->paneltitle.shadow= 5;
 	style->paneltitle.shadx= 2;
 	style->paneltitle.shady= -2;
@@ -100,7 +100,7 @@ static uiStyle *ui_style_new(ListBase *styles, const char *name)
 	
 	style->grouplabel.uifont_id= UIFONT_DEFAULT;
 	style->grouplabel.points= 12;
-	style->grouplabel.kerning= 1;
+	style->grouplabel.kerning= 0.5;
 	style->grouplabel.shadow= 3;
 	style->grouplabel.shadx= 1;
 	style->grouplabel.shady= -1;
@@ -108,7 +108,7 @@ static uiStyle *ui_style_new(ListBase *styles, const char *name)
 	
 	style->widgetlabel.uifont_id= UIFONT_DEFAULT;
 	style->widgetlabel.points= 11;
-	style->widgetlabel.kerning= 1;
+	style->widgetlabel.kerning= 0.5;
 	style->widgetlabel.shadow= 3;
 	style->widgetlabel.shadx= 1;
 	style->widgetlabel.shady= -1;
@@ -117,7 +117,7 @@ static uiStyle *ui_style_new(ListBase *styles, const char *name)
 	
 	style->widget.uifont_id= UIFONT_DEFAULT;
 	style->widget.points= 11;
-	style->widget.kerning= 1;
+	style->widget.kerning= 0.5;
 	style->widget.shadowalpha= 0.25f;
 
 	style->columnspace= 5;

source/blender/makesdna/DNA_userdef_types.h

@@ -66,8 +66,8 @@ typedef struct uiFont {
 typedef struct uiFontStyle {
 	short uifont_id;		/* saved in file, 0 is default */
 	short points;			/* actual size depends on 'global' dpi */
-	short kerning;			/* kerning space between characters. */
-	char pad[6];
+	float kerning;			/* kerning space between characters. */
+	float pad;
 	short italic, bold;		/* style hint */
 	short shadow;			/* value is amount of pixels blur */
 	short shadx, shady;		/* shadow offset in pixels */

source/blender/makesrna/intern/rna_userdef.c

@@ -137,8 +137,8 @@ static void rna_def_userdef_theme_ui_font_style(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Points", "");
 	RNA_def_property_update(prop, NC_WINDOW, NULL);
 
-	prop= RNA_def_property(srna, "kerning", PROP_INT, PROP_NONE);
-	RNA_def_property_range(prop, -5, 5);
+	prop= RNA_def_property(srna, "kerning", PROP_FLOAT, PROP_NONE);
+	RNA_def_property_range(prop, -5.0, 5.0);
 	RNA_def_property_ui_text(prop, "Kerning", "");
 	RNA_def_property_update(prop, NC_WINDOW, NULL);