Make huge images work under OpenGL (at least memory-ineficient)

src/map/image.cpp

@@ -1,9 +1,12 @@
 #include <QPainter>
+#include <QPixmapCache>
 #include "config.h"
 #include "image.h"
 
 
-Image::Image(const QString &fileName) : _img(fileName)
+#define TILE_SIZE 256
+
+Image::Image(const QString &fileName) : _img(fileName), _fileName(fileName)
 {
 }
 
@@ -17,8 +20,25 @@ void Image::draw(QPainter *painter, const QRectF &rect, Map::Flags flags)
 	QRectF sr(rect.topLeft() * ratio, rect.size() * ratio);
 
 	if (flags & Map::OpenGL) {
-		QImage img(_img.copy(sr.toRect()));
-		painter->drawImage(rect.topLeft(), img);
+		for (int i = sr.left()/TILE_SIZE; i <= sr.right()/TILE_SIZE; i++) {
+			for (int j = sr.top()/TILE_SIZE; j <= sr.bottom()/TILE_SIZE; j++) {
+				QString key = _fileName + "-" + QString::number(i) + "_"
+				  + QString::number(j);
+				QPoint tl(i * TILE_SIZE, j * TILE_SIZE);
+				QPixmap pm;
+
+				if (!QPixmapCache::find(key, &pm)) {
+					QRect tile(tl, QSize(TILE_SIZE, TILE_SIZE));
+					pm = QPixmap::fromImage(_img.copy(tile));
+					if (!pm.isNull())
+						QPixmapCache::insert(key, pm);
+				}
+#ifdef ENABLE_HIDPI
+				pm.setDevicePixelRatio(ratio);
+#endif // ENABLE_HIDPI
+				painter->drawPixmap(tl/ratio, pm);
+			}
+		}
 	} else
 		painter->drawImage(rect.topLeft(), _img, sr);
 }

src/map/image.h

@@ -16,6 +16,7 @@ public:
 
 private:
 	QImage _img;
+	QString _fileName;
 };
 
 #endif // IMAGE_H