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Add constraints

A constraint fixes a relationship between geometric values. It's different from the initial values the GUI wrote when you drew the rectangles: a constraint determines a value, while an initial value only positions something that is otherwise free.

Inset the inner rectangle​

Press D for the Dimension tool. Click the matching edge on each rectangle, then click where the label should go. Type 50. and press Enter.

Do the same for the other three sides.

Floats need a decimal point

50 is an Int; 50. is a Float. Coordinates and dimensions are floats.

In source, the four dimensions amount to:

eq(inner.x0, outer.x0 + 50.);
eq(inner.y0, outer.y0 + 50.);
eq(inner.x1, outer.x1 - 50.);
eq(inner.y1, outer.y1 - 50.);

Make width and height parameters​

Give the cell two arguments and constrain the outer rectangle to them:

cell inset_rect(w: Float, h: Float) {
    let outer = rect("met1", x0=0., y0=0.);
    eq(outer.w, w);
    eq(outer.h, h);

    let inner = rect("met2");
    eq(inner.x0, outer.x0 + 50.);
    eq(inner.y0, outer.y0 + 50.);
    eq(inner.x1, outer.x1 - 50.);
    eq(inner.y1, outer.y1 - 50.);
}

The cell now takes two arguments, so inset_rect() no longer compiles. Press O and open inset_rect(200., 200.).

Reading the canvas​

  • A solid edge is fixed by constraints.
  • A dashed edge still depends on an initial value.
  • Dragging a dashed edge updates its *i argument in the source.
  • An initial value never overrides a constraint.

Constraints and fallback values covers the model in more depth.