[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.cpp

@@ -3,6 +3,7 @@
 #include <QApplication>
 #include <QDomDocument>
 #include <QFile>
+#include <QImageReader>
 #include <QPainter>
 #include <QPalette>
 #include <QSvgRenderer>
@@ -418,6 +419,57 @@ QPixmap DropdownIconPixmapGenerator::generatePixmap(int height, bool expanded)
 
 QMap<QString, QPixmap> DropdownIconPixmapGenerator::pmCache;
 
+namespace
+{
+/// Longest side mana symbols are rendered at before being scaled to their final size.
+constexpr int MASTER_ICON_SIZE = 128;
+
+QString manaSymbolCacheKey(const QString &symbol, const QSize &size)
+{
+    return symbol + QLatin1Char('|') + QString::number(size.width()) + QLatin1Char('x') +
+           QString::number(size.height());
+}
+} // namespace
+
+const QPixmap &ManaSymbolPixmapGenerator::masterIcon(const QString &symbol)
+{
+    auto it = masterCache.constFind(symbol);
+    if (it != masterCache.constEnd()) {
+        return it.value();
+    }
+
+    QImageReader reader("theme:icons/mana/" + symbol);
+    QSize sourceSize = reader.size();
+    if (!sourceSize.isEmpty()) {
+        sourceSize.scale(QSize(MASTER_ICON_SIZE, MASTER_ICON_SIZE), Qt::KeepAspectRatio);
+        reader.setScaledSize(sourceSize);
+    }
+    const QPixmap rendered = QPixmap::fromImageReader(&reader);
+
+    return masterCache.insert(symbol, rendered).value();
+}
+
+QPixmap ManaSymbolPixmapGenerator::generatePixmap(const QString &symbol, const QSize &size)
+{
+    const QString key = manaSymbolCacheKey(symbol, size);
+    auto it = scaledCache.constFind(key);
+    if (it != scaledCache.constEnd()) {
+        return it.value();
+    }
+
+    const QPixmap &icon = masterIcon(symbol);
+    if (icon.isNull()) {
+        return {};
+    }
+
+    QPixmap scaled = icon.scaled(size, Qt::KeepAspectRatio, Qt::SmoothTransformation);
+    scaledCache.insert(key, scaled);
+    return scaled;
+}
+
+QHash<QString, QPixmap> ManaSymbolPixmapGenerator::masterCache;
+QHash<QString, QPixmap> ManaSymbolPixmapGenerator::scaledCache;
+
 QPixmap loadColorAdjustedPixmap(const QString &name)
 {
     if (qApp->palette().windowText().color().lightness() > 200) {