Reduce scroll cpu usage from 10% to 1-2% by load image files in another thread but load the texture in the main thread

2 files changed, 19 insertions, 7 deletions

diff --git a/include/Body.hpp b/include/Body.hpp
index 008aa70..9f7c2d8 100644
--- a/include/Body.hpp
+++ b/include/Body.hpp
@@ -10,6 +10,7 @@
 #include "../external/RoundedRectangleShape.hpp"
 #include <json/value.h>
 #include <thread>
+#include <future>
 
 namespace QuickMedia {
     class Program;
@@ -82,6 +83,7 @@ namespace QuickMedia {
     class Body {
     public:
         Body(Program *program, sf::Font *font, sf::Font *bold_font, sf::Font *cjk_font);
+        ~Body();
 
         // Select previous item, ignoring invisible items. Returns true if the item was changed. This can be used to check if the top was hit when wrap_around is set to false
         bool select_previous_item();
@@ -123,7 +125,6 @@ namespace QuickMedia {
         sf::Text progress_text;
         sf::Text replies_text;
         BodyItems items;
-        std::thread thumbnail_load_thread;
         bool draw_thumbnails;
         bool wrap_around;
         // Set to {0, 0} to disable resizing
@@ -134,14 +135,22 @@ namespace QuickMedia {
         void draw_item(sf::RenderWindow &window, BodyItem *item, const sf::Vector2f &pos, const sf::Vector2f &size, const float item_height, const int item_index, const Json::Value &content_progress);
         float get_item_height(BodyItem *item);
     private:
+        enum class LoadingState {
+            NOT_LOADED,
+            LOADING,
+            FINISHED_LOADING,
+            APPLIED_TO_TEXTURE
+        };
+
         struct ThumbnailData {
             bool referenced = false;
-            std::shared_ptr<sf::Texture> texture;
-            bool loaded = false;
+            LoadingState loading_state = LoadingState::NOT_LOADED;
+            sf::Texture texture;
+            std::unique_ptr<sf::Image> image; // Set in another thread, and then reset after loading it into |texture|
         };
         Program *program;
-        std::shared_ptr<sf::Texture> load_thumbnail_from_url(const std::string &url, bool local, sf::Vector2i thumbnail_resize_target_size);
-        std::unordered_map<std::string, ThumbnailData> item_thumbnail_textures;
+        void load_thumbnail_from_url(const std::string &url, bool local, sf::Vector2i thumbnail_resize_target_size, std::shared_ptr<ThumbnailData> thumbnail_data);
+        std::unordered_map<std::string, std::shared_ptr<ThumbnailData>> item_thumbnail_textures;
         bool loading_thumbnail;
         int selected_item;
         int prev_selected_item;
@@ -151,5 +160,6 @@ namespace QuickMedia {
         sf::RectangleShape item_background_shadow;
         sf::RoundedRectangleShape item_background;
         sf::Sprite image;
+        std::future<void> load_thumbnail_future;
     };
 }
\ No newline at end of file
diff --git a/include/ImageViewer.hpp b/include/ImageViewer.hpp
index 93e7d7c..0ca64e9 100644
--- a/include/ImageViewer.hpp
+++ b/include/ImageViewer.hpp
@@ -18,13 +18,15 @@ namespace QuickMedia {
         WAITING,
         LOADING,
         FAILED_TO_LOAD,
-        LOADED
+        LOADED,
+        APPLIED_TO_TEXTURE
     };
 
     struct ImageData {
         sf::Texture texture;
         sf::Sprite sprite;
         ImageStatus image_status;
+        std::unique_ptr<std::string> image_data_str;
         bool visible_on_screen;
     };
 
@@ -47,7 +49,7 @@ namespace QuickMedia {
         int get_focused_page() const;
         int get_num_pages() const { return num_pages; }
     private:
-        void load_image_async(const Path &path, std::shared_ptr<ImageData> image_data, int page);
+        void load_image_async(const Path &path, std::shared_ptr<ImageData> image_data);
         bool render_page(sf::RenderWindow &window, int page, double offset_y);
         sf::Vector2<double> get_page_size(int page);
     private: