Keep tiles on disk, add basket curves, undo the image flip

The flip was my mistake. Measured against the service instead of guessed:
fetching a box and its northern half shows the half matching the top of the
whole, so the images arrive with their first row at the north edge and the
default texture coordinates were right all along. Both the base map and the
orthophoto go back to them.

Imagery of a given piece of ground does not change, so a fetched tile is now
kept under editor/cache/orto and the next session starts from it. Until now
the cache lived only in memory, which meant going back to a slow and flaky
service for ground that had already been fetched once.

Gaps can be fitted with a basket curve as well: the library's compound mode,
with clothoids at both ends and a chain of arcs between them. Arcs can be
added and removed; the closing one takes whatever deflection the earlier
ones leave, so its length is not offered for editing.

application/planpanel.cpp

@@ -210,11 +210,10 @@ void plan_panel::render_location_dialog()
 	{
 		// the picture on screen is the one that was fetched, which may lag the current view by a
 		// request; drawing it against its own box keeps it registered while the new one arrives
+		// the image arrives with its first row at the north edge, so the default texture coordinates
+		// already line up: the first row belongs at the top, against the box's northern edge
 		auto const &covered{m_topomap.covered()};
-		// the image arrives with its first row at the north edge, which is the opposite of what the
-		// default texture coordinates assume, so the vertical ones are swapped
-		drawlist->AddImage(reinterpret_cast<ImTextureID>(static_cast<intptr_t>(backdrop)), to_screen(covered.min_x, covered.max_y), to_screen(covered.max_x, covered.min_y), ImVec2(0.0f, 1.0f),
-		                   ImVec2(1.0f, 0.0f));
+		drawlist->AddImage(reinterpret_cast<ImTextureID>(static_cast<intptr_t>(backdrop)), to_screen(covered.min_x, covered.max_y), to_screen(covered.max_x, covered.min_y));
 	}
 
 	auto const picked{to_screen(m_pickx, m_picky)};
@@ -352,9 +351,8 @@ void plan_panel::draw_on_scene()
 			{
 				continue;
 			}
-			// same north-first row order as the picker's base map, so the same swap applies
-			drawlist->AddImageQuad(reinterpret_cast<ImTextureID>(static_cast<intptr_t>(tile.texture)), corners[0], corners[1], corners[2], corners[3], ImVec2(0.0f, 1.0f), ImVec2(1.0f, 1.0f),
-			                       ImVec2(1.0f, 0.0f), ImVec2(0.0f, 0.0f));
+			// first row is the northern edge, which is the corner the default coordinates start from
+			drawlist->AddImageQuad(reinterpret_cast<ImTextureID>(static_cast<intptr_t>(tile.texture)), corners[0], corners[1], corners[2], corners[3]);
 		}
 	}
 
@@ -514,7 +512,7 @@ void plan_panel::render_gaps()
 		return;
 	}
 
-	ImGui::BeginChild("plan_gaps", ImVec2(0.0f, 130.0f), false);
+	ImGui::BeginChild("plan_gaps", ImVec2(0.0f, 220.0f), false);
 	for (std::size_t gap = 0; gap < niweleta->fits.size(); ++gap)
 	{
 		auto &fit{niweleta->fits[gap]};
@@ -522,16 +520,23 @@ void plan_panel::render_gaps()
 
 		ImGui::Text("gap %d", static_cast<int>(gap));
 		ImGui::SameLine(70.0f);
-		ImGui::SetNextItemWidth(150.0f);
-		if (ImGui::Combo("##mode", &fit.mode, "none\0arc\0arc + clothoids\0"))
+		ImGui::SetNextItemWidth(170.0f);
+		// the library numbers these; 3 is the unified compound, any number of arcs eased by clothoids
+		if (ImGui::Combo("##mode", &fit.mode, "none\0arc\0arc + clothoids\0compound\0"))
 		{
 			if (fit.mode != 0 && fit.radius <= 0.0)
 			{
 				fit.radius = 300.0; // something drawable to start from, rather than a rejected fit
 			}
+			if (fit.mode == 3 && fit.arcs.empty())
+			{
+				// a basket needs at least two arcs to be one; the last absorbs the leftover deflection
+				fit.arcs.push_back({600.0, 60.0, 0.0});
+				fit.arcs.push_back({300.0, 0.0, 0.0});
+			}
 			solve();
 		}
-		if (fit.mode != 0)
+		if (fit.mode == 1 || fit.mode == 2)
 		{
 			ImGui::SameLine();
 			ImGui::SetNextItemWidth(120.0f);
@@ -549,6 +554,10 @@ void plan_panel::render_gaps()
 				solve();
 			}
 		}
+		if (fit.mode == 3)
+		{
+			render_compound(fit);
+		}
 		// a fit the library could not produce is simply absent from its answer; say so rather than
 		// leaving the parameters looking as though they took effect
 		if (fit.mode != 0 && false == fit_applied(gap))
@@ -562,6 +571,83 @@ void plan_panel::render_gaps()
 	ImGui::EndChild();
 }
 
+void plan_panel::render_compound(maj0sted::web::GapFit &Fit)
+{
+	ImGui::Indent();
+
+	ImGui::SetNextItemWidth(110.0f);
+	if (ImGui::InputDouble("entry", &Fit.entry_t, 5.0, 20.0, "%.1f"))
+	{
+		solve();
+	}
+	ImGui::SameLine();
+	ImGui::SetNextItemWidth(110.0f);
+	if (ImGui::InputDouble("exit", &Fit.exit_t, 5.0, 20.0, "%.1f"))
+	{
+		solve();
+	}
+	ImGui::SameLine();
+	ImGui::TextDisabled("end clothoids");
+
+	for (std::size_t i = 0; i < Fit.arcs.size(); ++i)
+	{
+		auto &arc{Fit.arcs[i]};
+		auto const last{i + 1 == Fit.arcs.size()};
+		ImGui::PushID(static_cast<int>(i));
+
+		ImGui::Text("%d.", static_cast<int>(i + 1));
+		ImGui::SameLine();
+		ImGui::SetNextItemWidth(110.0f);
+		if (ImGui::InputDouble("R", &arc.radius, 10.0, 100.0, "%.1f"))
+		{
+			solve();
+		}
+		// the closing arc takes up whatever deflection the earlier ones leave, so its length is not
+		// ours to set, and there is no arc after it to ease into
+		if (false == last)
+		{
+			ImGui::SameLine();
+			ImGui::SetNextItemWidth(110.0f);
+			if (ImGui::InputDouble("len", &arc.length, 10.0, 50.0, "%.1f"))
+			{
+				solve();
+			}
+			ImGui::SameLine();
+			ImGui::SetNextItemWidth(110.0f);
+			if (ImGui::InputDouble("ease", &arc.transition_to_next, 5.0, 20.0, "%.1f"))
+			{
+				solve();
+			}
+		}
+		else
+		{
+			ImGui::SameLine();
+			ImGui::TextDisabled("closes the curve");
+		}
+
+		ImGui::PopID();
+	}
+
+	if (ImGui::SmallButton("Add arc"))
+	{
+		// inserted before the closing arc, so that one stays the one that closes the curve
+		auto const radius{Fit.arcs.empty() ? 300.0 : Fit.arcs.back().radius};
+		Fit.arcs.insert(Fit.arcs.end() - (Fit.arcs.empty() ? 0 : 1), {radius, 60.0, 0.0});
+		solve();
+	}
+	if (Fit.arcs.size() > 2)
+	{
+		ImGui::SameLine();
+		if (ImGui::SmallButton("Remove arc"))
+		{
+			Fit.arcs.erase(Fit.arcs.end() - 2);
+			solve();
+		}
+	}
+
+	ImGui::Unindent();
+}
+
 void plan_panel::render_storage()
 {
 	ImGui::Separator();

application/planpanel.h

@@ -32,6 +32,8 @@ class plan_panel : public ui_panel
 	// methods
 	void render_toolbar();
 	void render_gaps();
+	// parameters of a basket curve: the end clothoids and the chain of arcs between them
+	void render_compound(maj0sted::web::GapFit &Fit);
 	void render_storage();
 	// asks what kind of scenery is being started, and where on the map it sits
 	void render_newmap_dialog();

editor/orthophoto.cpp

@@ -230,6 +230,12 @@ std::vector<orthophoto_source::ready_tile> orthophoto_source::collect(maj0sted::
 	std::vector<ready_tile> tiles;
 	for (auto const &key : maj0sted::web::TileGrid::tiles_for_view(View, maj0sted::web::TileGrid::kLevel, Maxtiles))
 	{
+		// a tile kept from an earlier session seeds the cache, so no request goes out for it at all
+		if (false == m_service.has(key))
+		{
+			load_from_disk(key);
+		}
+
 		auto const status = m_service.request(key);
 		if (status == maj0sted::web::TileStatus::Failed)
 		{
@@ -244,6 +250,8 @@ std::vector<orthophoto_source::ready_tile> orthophoto_source::collect(maj0sted::
 		auto found = m_textures.find(key);
 		if (found == m_textures.end())
 		{
+			// the first time a tile is drawn is also the moment its bytes are known to be good
+			save_to_disk(key);
 			found = m_textures.emplace(key, upload(key)).first;
 		}
 		if (found->second != 0)
@@ -288,6 +296,53 @@ unsigned int orthophoto_source::upload(maj0sted::web::TileKey const &Key)
 	return texture;
 }
 
+std::string orthophoto_source::tile_path(maj0sted::web::TileKey const &Key)
+{
+	return "editor/cache/orto/" + std::to_string(Key.zoom) + "_" + std::to_string(Key.x) + "_" + std::to_string(Key.y) + ".img";
+}
+
+bool orthophoto_source::load_from_disk(maj0sted::web::TileKey const &Key)
+{
+	std::ifstream file(tile_path(Key), std::ios::binary);
+	if (false == file.is_open())
+	{
+		return false;
+	}
+
+	std::vector<std::uint8_t> bytes{std::istreambuf_iterator<char>(file), std::istreambuf_iterator<char>()};
+	if (bytes.empty())
+	{
+		return false;
+	}
+
+	m_service.store(Key, std::move(bytes));
+
+	return true;
+}
+
+void orthophoto_source::save_to_disk(maj0sted::web::TileKey const &Key)
+{
+	auto const *image = m_service.peek(Key);
+	if (image == nullptr || image->bytes.empty())
+	{
+		return;
+	}
+
+	auto const path = tile_path(Key);
+	std::error_code error;
+	std::filesystem::create_directories(std::filesystem::path(path).parent_path(), error);
+	if (std::filesystem::exists(path, error))
+	{
+		return; // came from the disk in the first place
+	}
+
+	std::ofstream file(path, std::ios::binary);
+	if (file.is_open())
+	{
+		file.write(reinterpret_cast<char const *>(image->bytes.data()), static_cast<std::streamsize>(image->bytes.size()));
+	}
+}
+
 std::size_t orthophoto_source::pending() const
 {
 	return m_inflight.load();

editor/orthophoto.h

@@ -68,6 +68,11 @@ class orthophoto_source
 	void worker();
 	// decodes the cached bytes of a tile and uploads them; returns 0 when the image is unusable
 	unsigned int upload(maj0sted::web::TileKey const &Key);
+	// imagery of a given piece of ground never changes, so a fetched tile is kept on disk and the
+	// next session starts with it instead of going back to a service that is slow and flaky
+	static std::string tile_path(maj0sted::web::TileKey const &Key);
+	bool load_from_disk(maj0sted::web::TileKey const &Key);
+	void save_to_disk(maj0sted::web::TileKey const &Key);
 	// members
 	maj0sted::web::TileService m_service;
 	std::unordered_map<maj0sted::web::TileKey, unsigned int, maj0sted::web::TileKeyHash> m_textures;