From 884a7c745bfae2d461dc507df8742d4e6b626b94 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Fri, 11 Mar 2022 14:51:49 +0300
Subject: [PATCH] Optimize ui painter to not draw elements not in the current
 bbox

---
 libs/ui/include/psemek/ui/painter_impl.hpp |  2 ++
 libs/ui/source/controller.cpp              |  9 +++++++--
 libs/ui/source/painter_impl.cpp            | 20 ++++++++++++++++++--
 3 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/libs/ui/include/psemek/ui/painter_impl.hpp b/libs/ui/include/psemek/ui/painter_impl.hpp
index 6b66f55e..2664f9b8 100644
--- a/libs/ui/include/psemek/ui/painter_impl.hpp
+++ b/libs/ui/include/psemek/ui/painter_impl.hpp
@@ -26,7 +26,9 @@ namespace psemek::ui
 		void commit_stencil() override;
 		void end_stencil() override;
 
+		void start_frame(geom::box<float, 2> const & bbox);
 		void render(geom::matrix<float, 4, 4> const & transform);
+		geom::box<float, 2> current_bbox() const;
 
 	private:
 		psemek_declare_pimpl
diff --git a/libs/ui/source/controller.cpp b/libs/ui/source/controller.cpp
index 57abd2bc..fa274538 100644
--- a/libs/ui/source/controller.cpp
+++ b/libs/ui/source/controller.cpp
@@ -173,12 +173,17 @@ namespace psemek::ui
 
 	void controller::render(gfx::render_target const & rt)
 	{
+		impl().painter.start_frame(geom::cast<float>(rt.viewport));
+
 		auto visitor = util::recursive([&](auto && self, element * elem) -> void {
 			if (elem->hidden()) return;
-			elem->draw(impl().painter);
+			bool const visible = !(impl().painter.current_bbox() & elem->shape().bbox()).empty();
+			if (visible)
+				elem->draw(impl().painter);
 			for (auto c : elem->children())
 				if (c) self(c);
-			elem->post_draw(impl().painter);
+			if (visible)
+				elem->post_draw(impl().painter);
 		});
 
 		visitor(impl().root.get());
diff --git a/libs/ui/source/painter_impl.cpp b/libs/ui/source/painter_impl.cpp
index 17896fba..17b91771 100644
--- a/libs/ui/source/painter_impl.cpp
+++ b/libs/ui/source/painter_impl.cpp
@@ -219,6 +219,7 @@ void main()
 
 		int stencil_level = 0;
 		static constexpr int max_stencil_level = 8;
+		std::vector<geom::box<float, 2>> stencil_bbox;
 
 		geom::box<float, 2> draw_bbox;
 
@@ -405,6 +406,7 @@ void main()
 		batch.dpass = gl::REPLACE;
 
 		++impl().stencil_level;
+		impl().draw_bbox = {};
 	}
 
 	void painter_impl::commit_stencil()
@@ -420,6 +422,8 @@ void main()
 		batch.sfail = gl::KEEP;
 		batch.dfail = gl::KEEP;
 		batch.dpass = gl::KEEP;
+
+		impl().stencil_bbox.push_back(impl().draw_bbox);
 	}
 
 	void painter_impl::end_stencil()
@@ -438,7 +442,7 @@ void main()
 			clear_batch.dpass = gl::REPLACE;
 		}
 
-		draw_rect(impl().draw_bbox, {0, 0, 0, 255});
+		draw_rect(impl().stencil_bbox.back(), {0, 0, 0, 255});
 
 		{
 			auto & batch = impl().batch<stencil_batch>({});
@@ -457,6 +461,13 @@ void main()
 		}
 
 		--impl().stencil_level;
+
+		impl().stencil_bbox.pop_back();
+	}
+
+	void painter_impl::start_frame(geom::box<float, 2> const & bbox)
+	{
+		impl().stencil_bbox.push_back(bbox);
 	}
 
 	void painter_impl::render(geom::matrix<float, 4, 4> const & transform)
@@ -524,13 +535,18 @@ void main()
 		for (auto const & b : impl().batches)
 			std::visit(batch_visitor, b);
 
-
 		impl().max_batch_count = std::max(impl().max_batch_count, impl().batches.size());
 
 		impl().depth = 0;
 		impl().batches.clear();
 		impl().stencil_level = 0;
+		impl().stencil_bbox.clear();
 		impl().draw_bbox = {};
 	}
 
+	geom::box<float, 2> painter_impl::current_bbox() const
+	{
+		return impl().stencil_bbox.back();
+	}
+
 }