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Constraints and fallback values

Argon has two ways to give a coordinate a value. A constraint fixes it. An initial value only says where it starts, and the GUI can move it.

Equality constraints​

eq(left, right) makes two linear float expressions equal:

eq(inner.x0, outer.x0 + inset);
eq(inner.y0, outer.y0 + inset);
eq(inner.x1, outer.x1 - inset);
eq(inner.y1, outer.y1 - inset);

Either side can mix cell parameters, literals, and geometry fields, as long as the result is linear.

Free values​

float() creates a new solver variable with no value yet:

let center = float();
eq(center, (bounds.x0 + bounds.x1) / 2.);

Initial values​

Keyword arguments ending in i, such as x0i, y1i, widthi, or x2i, are initial values. The GUI uses them for any coordinate that no constraint determines:

let shape = rect("met1", x0i=20., y0i=30., x1i=120., y1i=90.);
  • Dashed edges are under-constrained.
  • Dragging an under-constrained shape updates its initial values.
  • Adding a constraint turns the edge solid.
  • An initial value never overrides a constraint.

You don't need to write initial values by hand. The first time you drag a shape, the GUI adds any that are missing.

Dimensions​

The Dimension tool writes dimension calls, which record both the constraint and where its label sits. Create them from the canvas; their arguments are tedious to write by hand.