Remove dotted circle for ാം rendering

This has been a recurrent issue for the users. While browser and most
modern applications use recent shaping engines that remove the dotted circle,
applications like libreoffice has this issue unresolved for long time.

Here, remove the dotted circle if followed by aa sign and anuswara. This
rule will be picked up only if shaping engines had not removed the dotted
circle.

sources/glyphs/ാം.mp

@@ -0,0 +1,37 @@
+input glyph;
+beginglyph;
+slant_ := tand(-8);
+height_correction :=  thick/4;
+z0=(0, m/2);
+z1=(x0 + mw/3, m - height_correction);
+z2=(x1 + mw/3, y0);
+z3=(x2 - mw/3,  height_correction);
+paths[0] = z0 .. z1.. z2 .. z3 ..  cycle;
+paths[0] := paths[0] xyscaled(1,1) slanted slant_;
+paths[0]:= paths[0] shifted (-slant_*m/2, 0);
+paths[0]:= subpath(.3, 2.9) of paths[0]   ..  {dir 120}(x0, y0 - m/4);
+
+pen_stroke(
+    nib(thinnib)(2)
+    nib(terminalnib rotated terminalangle 0 of paths[0])(0)
+    nib(terminalnib rotated terminalangle infinity of paths[0])(infinity)
+)(paths[0])(strokes[0]);
+
+clearxy;
+z0=(0, (y1+y3)/2);
+z1=((x2+x0)/2, m/2);
+z2=(x0+mw/2.25 , y0);
+z3=(x1, 0);
+z4=(x0, y0);
+
+paths[1] = z0{dir 90}..z1{dir 4}..z2{dir 266}..z3{dir 184}..{dir 90}z0;
+paths[1] := reverse paths[1];
+paths[1] := paths[1] shifted (xpart(point 2 of paths[0]) + 2thick,0);
+
+pen_stroke(
+    nib(thicknib)(1, 3)
+    nib(thinnib)(0, 2, 4)
+)(paths[1])(strokes[1]);
+
+
+endglyph;

sources/glyphs/◌.mp

@@ -0,0 +1,19 @@
+input glyph;
+beginglyph;
+
+clearxy;
+z0=(0, (y1+y3)/2);
+z1=((x2+x0)/2, m);
+z2=(x0+mw , y0);
+z3=(x1, 0);
+z4=(x0, y0);
+
+path fpath; fpath:= z0{dir 90}..z1{dir 4}..z2{dir 266}..z3{dir 184}..{dir 90}z0;
+soften:=0;
+for j=0 upto 3:
+    paths[j] := subpath(j, j + .5) of fpath;
+    pen_stroke( cut(thinnib, rel 90)(0,1, 2))(paths[j])(strokes[j]);
+endfor;
+
+
+endglyph;

tools/malayalamfont.py

@@ -268,6 +268,23 @@ def build_cons_ra_substitutions(self):
         routine = Routine(rules=rules, name=name, languages=LANGUAGE_MALAYALAM)
         self.fontFeatures.addFeature(feature, [routine])
 
+    def build_aam_sign(self):
+        """
+        Remove dotted circle from aam sign 'ാം'
+        """
+        feature = "akhn"
+        name = "remove_dotted_circle"
+
+        ligature_glyph_name = SVGGlyph.get_glyph_name("ാം")
+        sub = Substitution(
+            [[SVGGlyph.get_glyph_name("◌")], [SVGGlyph.get_glyph_name("ാ")], [SVGGlyph.get_glyph_name("ം")]],
+            replacement=[[ligature_glyph_name]],
+        )
+        rules = [sub]
+
+        routine = Routine(rules=rules, name=name, languages=LANGUAGE_MALAYALAM)
+        self.fontFeatures.addFeature(feature, [routine])
+
     def build_cons_conj_vowel_signs(self):
         feature = "psts"
         name = "psts_vowel_signs"
@@ -553,6 +570,7 @@ def buildFeatures(self):
         self.build_ra_sign()
         self.build_cons_ra_substitutions()
         self.build_cons_conj_vowel_signs()
+        self.build_aam_sign()
         self.build_kern()
         self.build_gpos()
         self.build_gdef()

tools/svgglyph.py

@@ -49,6 +49,7 @@
     "dotlessj": 0x0237,
     "jcaron": 0x01F0,
     "notdef": 0,
+    "uni25CC": 0x25CC,
 }
 UV2AGL_EXTRA = {
     0x0326: "commaaccent",