Decided to have uiBox implementations be per-OS and switched to using GtkBox on GTK+. This has the advantage that a) all uiControls on GTK+ now use exactly one GtkWidget so we don't need container, and b) we can use Auto Layout on OS X. Only more work will decide if we keep this system..

redo/unix/box.c

@@ -0,0 +1,147 @@
+// 7 april 2015
+#include "out/ui.h"
+#include "uipriv.h"
+
+struct box {
+	uiBox b;
+	GtkWidget *widget;
+	GtkBox *box;
+	void (*baseCommitDestroy)(uiControl *);
+	// TODO switch to GArray
+	struct ptrArray *controls;
+	int vertical;
+	int padded;
+};
+
+struct boxControl {
+	uiControl *c;
+	int stretchy;
+};
+
+uiDefineControlType(uiBox, uiTypeBox, struct box)
+
+static void boxCommitDestroy(uiControl *c)
+{
+	struct box *b = (struct box *) c;
+	struct boxControl *bc;
+
+	// don't chain up to base here; we need to destroy children ourselves first
+	while (b->controls->len != 0) {
+		bc = ptrArrayIndex(b->controls, struct boxControl *, 0);
+		uiControlSetParent(bc->c, NULL);
+		uiControlDestroy(bc->c);
+		ptrArrayDelete(b->controls, 0);
+		uiFree(bc);
+	}
+	ptrArrayDestroy(b->controls);
+	// NOW we can chain up to base
+	(*(b->baseCommitDestroy))(uiControl(b));
+}
+
+static uintptr_t boxHandle(uiControl *c)
+{
+	struct box *b = (struct box *) c;
+
+	return (uintptr_t) (b->widget);
+}
+
+static void boxContainerUpdateState(uiControl *c)
+{
+	struct box *b = (struct box *) c;
+	struct boxControl *bc;
+	uintmax_t i;
+
+	for (i = 0; i < b->controls->len; i++) {
+		bc = ptrArrayIndex(b->controls, struct boxControl *, i);
+		uiControlUpdateState(bc->c);
+	}
+}
+
+static void boxAppend(uiBox *ss, uiControl *c, int stretchy)
+{
+	struct box *b = (struct box *) ss;
+	struct boxControl *bc;
+	uintmax_t i;
+
+	bc = uiNew(struct boxControl);
+	bc->c = c;
+	bc->stretchy = stretchy;
+	uiControlSetParent(bc->c, uiControl(b));
+	ptrArrayAppend(b->controls, bc);
+	uiControlQueueResize(uiControl(b));
+	// TODO stretchy
+	// TODO when adding boxInsertAt(), we use gtk_box_reorder_child()
+}
+
+static void boxDelete(uiBox *ss, uintmax_t index)
+{
+	struct box *b = (struct box *) ss;
+	struct boxControl *bc;
+	uiControl *removed;
+
+	bc = ptrArrayIndex(b->controls, struct boxControl *, index);
+	removed = bc->c;
+	ptrArrayDelete(b->controls, index);
+	uiControlSetParent(removed, NULL);
+	uiFree(bc);
+	uiControlQueueResize(uiControl(b));
+}
+
+static int boxPadded(uiBox *ss)
+{
+	struct box *b = (struct box *) ss;
+
+	return b->padded;
+}
+
+static void boxSetPadded(uiBox *ss, int padded)
+{
+	struct box *b = (struct box *) ss;
+
+	b->padded = padded;
+	if (b->padded)
+		if (b->vertical)
+			gtk_box_set_spacing(b->box, gtkYPadding);
+		else
+			gtk_box_set_spacing(b->box, gtkXPadding);
+	else
+		gtk_box_set_spacing(b->box, 0);
+	uiControlQueueResize(uiControl(b));
+}
+
+uiBox *finishNewBox(GtkOrientation orientation)
+{
+	struct box *b;
+
+	b = (struct box *) uiNewControl(uiTypeBox());
+
+	b->widget = gtk_box_new(orientation, 0);
+	b->box = GTK_BOX(b->widget);
+	uiUnixMakeSingleWidgetControl(uiControl(b), b->widget);
+
+	b->controls = newPtrArray();
+
+	b->vertical = orientation == GTK_ORIENTATION_VERTICAL;
+
+	uiControl(b)->Handle = boxHandle;
+	b->baseCommitDestroy = uiControl(b)->CommitDestroy;
+	uiControl(b)->CommitDestroy = boxCommitDestroy;
+	uiControl(b)->ContainerUpdateState = boxContainerUpdateState;
+
+	uiBox(b)->Append = boxAppend;
+	uiBox(b)->Delete = boxDelete;
+	uiBox(b)->Padded = boxPadded;
+	uiBox(b)->SetPadded = boxSetPadded;
+
+	return uiBox(b);
+}
+
+uiBox *uiNewHorizontalBox(void)
+{
+	return finishNewBox(GTK_ORIENTATION_HORIZONTAL);
+}
+
+uiBox *uiNewVerticalBox(void)
+{
+	return finishNewBox(GTK_ORIENTATION_VERTICAL);
+}