Two drawings of a mouth with the same three points: a frown and a smile. Any mix of the two is a mouth too. The mix is two weights that add up to 1, and the drawing is each point at its weighted average.
Click frown and smile in the panel to drive the blend. Then grab a corner of the mouth and pull it up or down. The engine finds the weights that bring the corner closest to your cursor; the other two points come along.
Two examples make a line segment of blends. Pull past either end and the mouth stops there: there's no blend beyond 100% smile.
The state in a line segment.
| 1.000 | ||
| 0.000 |
Drag a point, or the dot on the map. Shift-click pins a point. The buttons drive to an example.
The readout says J is 2×1, tall: you asked for two numbers (the corner's x and y) and there's one free number (how much smile). You can't always get both, so the solver gets as close as it can.