Optimise rendering of pages with flashing characters

Previously every character on the page was drawn up to six times. Now the
page is drawn once, quickly copied up to five times and then only the
flashing characters are redrawn on the copies.

render.h

@@ -21,7 +21,6 @@
 #define RENDER_H
 
 #include <QBitmap>
-#include <QSet>
 #include <QPixmap>
 
 #include "decode.h"
@@ -67,14 +66,14 @@ protected:
 	QPixmap* m_pagePixmap[6];
 	unsigned char m_controlCodeCache[25][40];
 	bool m_reveal, m_mix, m_showControlCodes;
-	QSet<QPair<int, int>> m_flash1HzCells;
-	QSet<QPair<int, int>> m_flash2HzCells;
 	int m_flashBuffersHz;
+	int m_flashingRow[25];
 
 private:
 	inline void drawFromFontBitmap(QPainter &, int, int, unsigned char, int, TeletextPageDecode::CharacterFragment);
 	inline void drawCharacter(QPainter &, int, int, unsigned char, int, int, TeletextPageDecode::CharacterFragment);
-	void updateFlashBuffers();
+	void renderRow(int, int, bool force=false);
+	void setRowFlashStatus(int, int);
 
 	TeletextPageDecode *m_decoder;
 };