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

1 files changed, 24 insertions, 16 deletions

diff --git a/src/ImageViewer.cpp b/src/ImageViewer.cpp
index 86e7138..97ef7c9 100644
--- a/src/ImageViewer.cpp
+++ b/src/ImageViewer.cpp
@@ -34,22 +34,18 @@ namespace QuickMedia {
         has_size_vertical_cursor = size_vertical_cursor.loadFromSystem(sf::Cursor::SizeVertical);
     }
 
-    void ImageViewer::load_image_async(const Path &path, std::shared_ptr<ImageData> image_data, int page) {
+    void ImageViewer::load_image_async(const Path &path, std::shared_ptr<ImageData> image_data) {
         image_data->image_status = ImageStatus::LOADING;
         image_data->texture.setSmooth(true);
         assert(!loading_image);
         loading_image = true;
-        image_loader_thread = std::thread([this, image_data, path, page]() {
-            std::string image_data_str;
-            if(file_get_content(path, image_data_str) == 0) {
-                if(image_data->texture.loadFromMemory(image_data_str.data(), image_data_str.size())) {
-                    image_data->sprite.setTexture(image_data->texture, true);
-                    page_size[page].size = get_page_size(page);
-                    page_size[page].loaded = true;
-                    image_data->image_status = ImageStatus::LOADED;
-                } else {
-                    image_data->image_status = ImageStatus::FAILED_TO_LOAD;
-                }
+        image_loader_thread = std::thread([this, image_data, path]() {
+            auto image_data_str = std::make_unique<std::string>();
+            if(file_get_content(path, *image_data_str) == 0) {
+                image_data->image_data_str = std::move(image_data_str);
+                image_data->image_status = ImageStatus::LOADED;
+            } else {
+                image_data->image_status = ImageStatus::FAILED_TO_LOAD;
             }
             loading_image = false;
         });
@@ -60,8 +56,20 @@ namespace QuickMedia {
         if(page < 0 || page >= (int)image_data.size())
             return false;
 
-        const sf::Vector2<double> image_size = get_page_size(page);
         std::shared_ptr<ImageData> &page_image_data = image_data[page];
+        if(page_image_data && page_image_data->image_status == ImageStatus::LOADED) {
+            if(page_image_data->texture.loadFromMemory(page_image_data->image_data_str->data(), page_image_data->image_data_str->size())) {
+                page_image_data->sprite.setTexture(page_image_data->texture, true);
+                page_size[page].size = get_page_size(page);
+                page_size[page].loaded = true;
+                page_image_data->image_status = ImageStatus::APPLIED_TO_TEXTURE;
+            } else {
+                page_image_data->image_status = ImageStatus::FAILED_TO_LOAD;
+                page_image_data->image_data_str.reset();
+            }
+        }
+
+        const sf::Vector2<double> image_size = get_page_size(page);
         sf::Vector2<double> render_pos(std::floor(window_size.x * 0.5 - image_size.x * 0.5), - image_size.y * 0.5 + scroll + offset_y);
         if(render_pos.y + image_size.y <= 0.0 || render_pos.y >= window_size.y) {
             if(page_image_data)
@@ -80,7 +88,7 @@ namespace QuickMedia {
         }
 
         if(page_image_data) {
-            if(page_image_data->image_status == ImageStatus::LOADED) {
+            if(page_image_data->image_status == ImageStatus::APPLIED_TO_TEXTURE) {
                 page_image_data->sprite.setPosition(render_pos.x, render_pos.y);
                 window.draw(page_image_data->sprite);
             } else {
@@ -90,7 +98,7 @@ namespace QuickMedia {
                     if(!loading_image) {
                         Path image_path = chapter_cache_dir;
                         image_path.join(page_str);
-                        load_image_async(image_path, page_image_data, page);
+                        load_image_async(image_path, page_image_data);
                     }
                     msg = "Loading image for page " + page_str;
                 } else if(page_image_data->image_status == ImageStatus::LOADING) {
@@ -320,7 +328,7 @@ namespace QuickMedia {
         for(auto &page_data : image_data) {
             if(page_data && !page_data->visible_on_screen) {
                 fprintf(stderr, "ImageViewer: Unloaded page %d\n", 1 + i);
-                page_data = nullptr;
+                page_data.reset();
             }
             ++i;
         }