bi: Re-add screen dpi report

This was a casualty of 575286cb86
even though this particular use case is purely diagnostic for
devs reference when handling bug reports.

src/build_info.cpp

@@ -521,6 +521,13 @@ inline std::string geometry_to_string(point p)
 	return std::to_string(p.x) + 'x' + std::to_string(p.y);
 }
 
+template<typename coordinateType>
+inline std::string geometry_to_string(coordinateType horizontal, coordinateType vertical)
+{
+	// Use a stream in order to control significant digits in non-integers
+	return formatter() << std::fixed << std::setprecision(2) << horizontal << 'x' << vertical;
+}
+
 std::string format_sdl_driver_list(std::vector<std::string> drivers, const std::string& current_driver)
 {
 	bool found_current_driver = false;
@@ -562,11 +569,19 @@ list_formatter video_settings_report_internal(const std::string& heading = "")
 	const auto& current_driver = video::current_driver();
 	auto drivers = video::enumerate_drivers();
 
+	const auto& dpi = video::get_dpi();
+	std::string dpi_report;
+
+	dpi_report = dpi.first == 0.0f || dpi.second == 0.0f ?
+				 "<unknown>" :
+				 geometry_to_string(dpi.first, dpi.second);
+
 	fmt.insert("SDL video drivers", format_sdl_driver_list(drivers, current_driver));
 	fmt.insert("Window size", geometry_to_string(video::current_resolution()));
 	fmt.insert("Game canvas size", geometry_to_string(video::game_canvas_size()));
 	fmt.insert("Final render target size", geometry_to_string(video::output_size()));
 	fmt.insert("Screen refresh rate", std::to_string(video::current_refresh_rate()));
+	fmt.insert("Screen dpi", dpi_report);
 
 	const auto& renderer_report = video::renderer_report();
 

src/video.cpp

@@ -828,6 +828,26 @@ void update_buffers(bool autoupdate)
 	}
 }
 
+std::pair<float, float> get_dpi()
+{
+	float hdpi = 0.0f, vdpi = 0.0f;
+	if(window && SDL_GetDisplayDPI(window->get_display_index(), nullptr, &hdpi, &vdpi) == 0) {
+#ifdef TARGET_OS_OSX
+		// SDL 2.0.12 changes SDL_GetDisplayDPI. Function now returns DPI
+		// multiplied by screen's scale factor. This part of code reverts
+		// this multiplication.
+		//
+		// For more info see issue: https://github.com/wesnoth/wesnoth/issues/5019
+		if(sdl::get_version() >= version_info{2, 0, 12}) {
+			float scale_factor = desktop::apple::get_scale_factor(window->get_display_index());
+			hdpi /= scale_factor;
+			vdpi /= scale_factor;
+		}
+#endif
+	}
+	return { hdpi, vdpi };
+}
+
 std::vector<std::pair<std::string, std::string>> renderer_report()
 {
 	std::vector<std::pair<std::string, std::string>> res;

src/video.hpp

@@ -332,6 +332,11 @@ private:
  */
 std::vector<std::pair<std::string, std::string>> renderer_report();
 
+/**
+ * Retrieves the current game screen DPI for the @a build_info API.
+ */
+std::pair<float, float> get_dpi();
+
 
 /**************************/
 /* Implementation details */