Why does it take 40-50 ms to draw text, and especially set bold/italic...

.vscode/settings.json

@@ -67,6 +67,7 @@
         "bit": "cpp",
         "qsizepolicy": "cpp",
         "qgraphicsscene": "cpp",
-        "qstring": "cpp"
+        "qstring": "cpp",
+        "qtglobal": "cpp"
     }
 }

src/mainwindow.cc

@@ -3,6 +3,10 @@
 #include "md-parser.h"
 #include "md-render.h"
 
+#include <chrono>
+#include <iostream>
+
+
 #ifdef LEGACY_CXX
 #include <experimental/filesystem>
 namespace n_fs = ::std::experimental::filesystem;
@@ -64,17 +68,31 @@ void MainWindow::setupParser()
     std::string filePath = exePath.append("/../../test.md");
     printf("Path: %s\n", filePath.c_str());
 
+
+    typedef std::chrono::high_resolution_clock Time;
+    typedef std::chrono::milliseconds ms;
+    typedef std::chrono::duration<float> fsec;
+
     cmark_node *root_node = parser->parseFile(filePath);
     if (root_node != NULL) {
         htmlOutput = parser->renderHTML(root_node);
 
+        auto t0 = Time::now();
+        
         // Render AST to scene
         renderer->renderDocument(root_node);
 
+        auto t1 = Time::now();
+        fsec fs = t1 - t0;
+        ms d = std::chrono::duration_cast<ms>(fs);
+        printf("Duration\n");
+        std::cout << "ms: " << d.count() << std::endl;
+
         cmark_node_free(root_node);
     }
 
     setOutputToTextEdit(QString::fromStdString(htmlOutput));
+
 }
 
 /**

src/md-render.cc

@@ -11,6 +11,7 @@
 
 Renderer::Renderer(Scene* scene) : 
     scene(scene),
+    defaultFontSize(12),
     sceneMarginX(3.0),
     sceneMarginY(3.0),
     bold(false),
@@ -26,6 +27,9 @@ Renderer::Renderer(Scene* scene) :
     headingHeightOffset(10.0),
     listXOffset(15.0),
     bulletWithTemp(0.0) {
+    font = new QFont();
+    font->setPixelSize(defaultFontSize);
+    font->setFamily(fontFamilty);
 }
 
 /**
@@ -207,49 +211,47 @@ QRectF const Renderer::drawText(const QString& text)
     // We can still extend the QGraphicsSimpleTextItem class (or QAbstractGraphicsShapeItem) and override paint method.
     // Or just use QPainter with a paint device (like QWidgets), to have maximal control.
     QGraphicsSimpleTextItem *textItem = new QGraphicsSimpleTextItem(text);
-    QFont font;
-    if (bold)
-        font.setBold(true);
-    if (italic)
-        font.setItalic(true);
-    
+    font->setBold(bold);
+    font->setItalic(italic);
+
     if (headingLevel > 0) {
-        font.setBold(true);
+        font->setBold(true);
         switch(headingLevel) {
         case 1:
-            font.setPixelSize(24);
+            font->setPixelSize(24);
             break;
         case 2:
-            font.setPixelSize(20);
+            font->setPixelSize(20);
             break;
         case 3:
-            font.setPixelSize(16);
+            font->setPixelSize(16);
             break;
         case 4:
-            font.setPixelSize(14);
+            font->setPixelSize(14);
             break;
         case 5:
-            font.setPixelSize(12);
+            font->setPixelSize(12);
             break;
         default:
             break;
         }
     }
 
-    font.setFamily(fontFamilty);
-    textItem->setFont(font);
+    textItem->setFont(*font);
     textItem->setPos(currentX, currentY);
     scene->addItem(textItem);
 
+    if (headingLevel > 0) {
+        font->setPixelSize(defaultFontSize);
+    }
+
     return textItem->boundingRect();
 }
 
 QRectF const Renderer::drawBullet()
 {
     QGraphicsSimpleTextItem *bullet = new QGraphicsSimpleTextItem("\u2022");
-    QFont font;
-    font.setFamily(fontFamilty);
-    bullet->setFont(font);
+    bullet->setFont(*font);
     bullet->setPos(currentX, currentY);
     scene->addItem(bullet);
     return bullet->boundingRect();

src/md-render.h

@@ -8,6 +8,7 @@
 
 class Scene;
 class QRectF;
+class QFont;
 
 /**
  * The Renderer will use Qt to render AST directly to a QGraphicsScene
@@ -20,6 +21,8 @@ public:
 
 private:
     Scene *scene;
+    QFont *font;
+    int defaultFontSize;
     qreal sceneMarginX;
     qreal sceneMarginY;
     bool bold;