add layout constraints and abs/rel units

1 files changed, 34 insertions, 0 deletions

diff --git a/constraint.go b/constraint.go
new file mode 100644
index 0000000..c08e222
--- /dev/null
+++ b/constraint.go
@@ -0,0 +1,34 @@
+package gui
+
+// Constraint imposes a restriction on the size of a widget or layout.
+type Constraint struct {
+	// Dim is the dimension to constrain: width/height.
+	Dim
+
+	// Relation declares whether the constraint is an upper, lower, or exact bound.
+	Relation
+
+	// Length is the target or threshold value.
+	Length
+}
+
+// Dim is a dimension of a widget or layout that can be constrained.
+type Dim int
+
+const (
+	_ Dim = iota
+	Width
+	Height
+)
+
+// Relation is an (in)equality.
+type Relation int
+
+const (
+	_    Relation = iota
+	Eq            // ==
+	Gteq          // >=
+	Gt            // >
+	Lteq          // <=
+	Lt            // <
+)