Do anyone know any algorithm which would calculate automatically kerning of characters based on glyph shapes when user types text?
I don't mean trivial calculation of advance widths or similar, I mean analyzing the shape of glyphs to estimate the visually optimal distance between characters. For example if we lay out three characters sequentially in a line, the middle character should SEEM to be in the center of the line despite of the character's shapes. An example enlightens the kerning-on-the-fly functionality:
An example of kerning-on-the-fly can be seen from below snapshot:
In the above image a seems to be too right. It should be shifted a certain amount towards T so that it seems to be in the middle of T and g. The algorithm should examine the shapes of T and a (and possibly other letters also) and decide how much a have to be shifted to the left. This certain amount is the thing that the algorithm should calculate - WITHOUT EXAMINING THE POSSIBLE KERNING PAIRS OF THE FONT.
I'm thinking of coding a javascript (+svg+html) program that uses hand drawn fonts and many of them lacks kerning pairs. The textfields will be editable and can include text of multiple fonts. I think that kerning-on-the-fly could be one way to ensure mean text flow in this case.
EDIT: One starting point to this could be to use svg font, so it's easy to get path values. In svg font the path is defined this way:
<glyph glyph-name="T" unicode="T" horiz-adv-x="1251" d="M531 0v1293h
-483v173h1162v-173h-485v-1293h-194z"/>
<glyph glyph-name="a" unicode="a" horiz-adv-x="1139" d="M828 131q-100 -85
-192.5 -120t-198.5 -35q-175 0 -269 85.5t-94 218.5q0 78 35.5 142.5t93
103.5t129.5 59q53 14 160 27q218 26 321 62q1 37 1 47q0 110 -51 155q-69 61
-205 61q-127 0 -187.5 -44.5t-89.5 -157.5l-176 24q24 113 79 182.5t159
107t241 37.5 q136 0 221 -32t125 -80.5t56 -122.5q9 -46 9 -166v-240q0
-251 11.5 -317.5t45.5 -127.5h-188q-28 56 -36 131zM813 533q-98 -40 -294
-68q-111 -16 -157 -36t-71 -58.5t-25 -85.5q0 -72 54.5 -120t159.5 -48q104
0 185 45.5t119 124.5q29 61 29 180v66z"/>
The algorithm (or javascript code) should examine those paths some way and determine the optimal distance between them.
Here's an idea for how to find the kerning automatically.
For each glyph, find the convex hull of the glyph, i.e. the smallest convex shape with encloses the glyph (Convex means that if two points $a$,$b$ lie inside the shape, then the line connecting $a$ and $b$ also lies inside the shape).
Then define the distance between two glyphs $g_1$,$g_2$ the geometric distance between their convex hulls $H(g_1),H(g_2)$, i.e. $d(g_1,g_2) = \text{min }\{\||a-b||:a \in H(g_1), b \in H(g_2)\}$.
The kerning is then obtained by moving $g_2$ to the right until $d(g_1,g_2) = d$, where $d$ is some percentage of the font size or so.