create lay/strain package

The lay/strain package uses the Cassowary algorithm to solve systems of
layout constraints.

1 files changed, 28 insertions, 0 deletions

diff --git a/lay/strain/constraint.go b/lay/strain/constraint.go
new file mode 100644
index 0000000..44c9e0a
--- /dev/null
+++ b/lay/strain/constraint.go
@@ -0,0 +1,28 @@
+package strain
+
+import (
+	"github.com/lithdew/casso"
+	"golang.org/x/exp/shiny/unit"
+)
+
+// Constraint imposes a restriction on the size of a widget or layout.
+type Constraint struct {
+	// Dimension is the dimension to constrain: width/height.
+	Dimension
+
+	// Relation declares whether the constraint is an upper, lower,
+	// or exact bound.
+	casso.Op
+
+	// Value is the target or threshold value.
+	unit.Value
+}
+
+// Dim is a dimension of a widget or layout that can be constrained.
+type Dimension int
+
+const (
+	_ Dimension = iota
+	Width
+	Height
+)