[VDS] Cache mana symbol renders and skip redundant resizes (#7167)

* [VDS] Cache mana symbol renders and skip redundant resizes

- Render each mana symbol once at a bounded master size and derive every
  requested size from the cached master, avoiding repeated full-size SVG
  rasterization on the GUI thread
- Share scaled results through a process-wide cache keyed by symbol and
  size, so repeated widget creation and rescales don't redo the work
- Skip redundant resize work in ColorIdentityWidget and ManaSymbolWidget
  when sizes did not change

Took 8 minutes


Took 50 seconds

* Move to pixmap generator

Took 8 minutes

Took 4 seconds

---------

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

cockatrice/src/interface/pixel_map_generator.h

@@ -7,6 +7,7 @@
 #ifndef PIXMAPGENERATOR_H
 #define PIXMAPGENERATOR_H
 
+#include <QHash>
 #include <QIcon>
 #include <QLoggingCategory>
 #include <QMap>
@@ -125,6 +126,34 @@ public:
     }
 };
 
+class ManaSymbolPixmapGenerator
+{
+private:
+    static QHash<QString, QPixmap> masterCache;
+    static QHash<QString, QPixmap> scaledCache;
+
+    /**
+     * @brief Renders \a symbol once at a fixed moderate size, so repeated scalings never
+     * re-rasterize the source file (SVG sources can be very expensive to rasterize).
+     */
+    static const QPixmap &masterIcon(const QString &symbol);
+
+public:
+    /**
+     * @brief Returns a smooth-scaled rendering of the given mana symbol icon.
+     *
+     * Results are shared between all callers via a process-wide cache keyed by symbol
+     * and size, so scaling work is done once per distinct combination instead of once
+     * per widget creation or resize.
+     */
+    static QPixmap generatePixmap(const QString &symbol, const QSize &size);
+    static void clear()
+    {
+        masterCache.clear();
+        scaledCache.clear();
+    }
+};
+
 QPixmap loadColorAdjustedPixmap(const QString &name);
 
 #endif