Add ui::positioner element that helps with positioning a child on screen

libs/ui/include/psemek/ui/positioner.hpp

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <psemek/ui/single_container.hpp>
+#include <psemek/ui/box_shape.hpp>
+
+namespace psemek::ui
+{
+
+	struct positioner
+		: single_container
+	{
+		enum class x_align
+		{
+			left,
+			center,
+			right,
+		};
+
+		enum class y_align
+		{
+			top,
+			center,
+			bottom,
+		};
+
+		struct shape const & shape() const override;
+		void reshape(geom::box<float, 2> const & box) override;
+
+		virtual void set_position(geom::point<float, 2> const & p, x_align x, y_align y);
+
+		void draw(ui::painter &) const override {}
+
+	private:
+		box_shape shape_;
+
+		geom::point<float, 2> position_{0.f, 0.f};
+		x_align x_;
+		y_align y_;
+	};
+
+}

libs/ui/source/positioner.cpp

@@ -0,0 +1,64 @@
+#include <psemek/ui/positioner.hpp>
+
+namespace psemek::ui
+{
+
+	shape const & positioner::shape() const
+	{
+		return shape_;
+	}
+
+	void positioner::reshape(geom::box<float, 2> const & box)
+	{
+		shape_.box = box;
+
+		if (!child_)
+			return;
+
+		auto sc = child_->size_constraints();
+
+		geom::vector<float, 2> size;
+		size[0] = sc[0].min;
+		size[1] = sc[1].min;
+
+		geom::box<float, 2> cbox;
+		cbox[0].min = position_[0];
+		cbox[1].min = position_[1];
+		cbox[0].max = cbox[0].min + size[0];
+		cbox[1].max = cbox[1].min + size[1];
+
+		switch (x_)
+		{
+		case x_align::left:
+			break;
+		case x_align::center:
+			cbox[0] -= size[0] / 2.f;
+			break;
+		case x_align::right:
+			cbox[0] -= size[0];
+			break;
+		}
+
+		switch (y_)
+		{
+		case y_align::top:
+			break;
+		case y_align::center:
+			cbox[1] -= size[1] / 2.f;
+			break;
+		case y_align::bottom:
+			cbox[1] -= size[1];
+			break;
+		}
+
+		child_->reshape(cbox);
+	}
+
+	void positioner::set_position(geom::point<float, 2> const & p, x_align x, y_align y)
+	{
+		position_ = p;
+		x_ = x;
+		y_ = y;
+	}
+
+}