Fix possible corrupted text when gl glyph cache becomes full

When the OpenGL glyph cache filled up (the max texture size on the
hardware was exceeded) the characters would be drawn as black blocks
instead. As a work-around for this, the cache will now be cleared and
repopulated whenever this happens, meaning that once in a while (when
a lot of different glyphs have been drawn in a font) there will be a
performance hit. A more complete solution is described in QTBUG-13784,
but this requires so much refactoring that it was deemed too risky for
a patch release. This patch fixes the problem with a small penalty
and low risk.

Task-number: QT-3971
Reviewed-by: Samuel

5 files changed, 38 insertions, 7 deletions

diff --git a/src/gui/painting/qtextureglyphcache.cpp b/src/gui/painting/qtextureglyphcache.cpp
index b609f7b..2cd7780 100644
--- a/src/gui/painting/qtextureglyphcache.cpp
+++ b/src/gui/painting/qtextureglyphcache.cpp
@@ -65,7 +65,7 @@ static inline int qt_next_power_of_two(int v)
     return v;
 }
 
-void QTextureGlyphCache::populate(QFontEngine *fontEngine, int numGlyphs, const glyph_t *glyphs,
+bool QTextureGlyphCache::populate(QFontEngine *fontEngine, int numGlyphs, const glyph_t *glyphs,
                                   const QFixedPoint *)
 {
 #ifdef CACHE_DEBUG
@@ -119,7 +119,7 @@ void QTextureGlyphCache::populate(QFontEngine *fontEngine, int numGlyphs, const
         rowHeight = qMax(rowHeight, glyph_height);
     }
     if (listItemCoordinates.isEmpty())
-        return;
+        return true;
 
     rowHeight += margin * 2 + paddingDoubled;
     if (isNull())
@@ -150,6 +150,13 @@ void QTextureGlyphCache::populate(QFontEngine *fontEngine, int numGlyphs, const
             int new_height = m_h*2;
             while (new_height < m_cy + c.h)
                 new_height *= 2;
+
+	    if (new_height > maxTextureHeight()) {
+	        // We can't make a new texture of the required size, so 
+	        // bail out
+	        return false;
+	    }
+
             // if no room in the current texture - realloc a larger texture
             resizeTextureData(m_w, new_height);
             m_h = new_height;
@@ -165,7 +172,7 @@ void QTextureGlyphCache::populate(QFontEngine *fontEngine, int numGlyphs, const
         ++iter;
     }
 
-
+    return true;
 }
 
 QImage QTextureGlyphCache::textureMapForGlyph(glyph_t g) const
diff --git a/src/gui/painting/qtextureglyphcache_p.h b/src/gui/painting/qtextureglyphcache_p.h
index e6d2b22..f84d1e6 100644
--- a/src/gui/painting/qtextureglyphcache_p.h
+++ b/src/gui/painting/qtextureglyphcache_p.h
@@ -96,7 +96,7 @@ public:
         int baseLineY;
     };
 
-    void populate(QFontEngine *fontEngine, int numGlyphs, const glyph_t *glyphs,
+    bool populate(QFontEngine *fontEngine, int numGlyphs, const glyph_t *glyphs,
                   const QFixedPoint *positions);
 
     virtual void createTextureData(int width, int height) = 0;
diff --git a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
index 37552ac..3ddc15a 100644
--- a/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
+++ b/src/opengl/gl2paintengineex/qpaintengineex_opengl2.cpp
@@ -1499,8 +1499,13 @@ void QGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngineGlyphCache::Type glyp
     // cache so this text is performed before we test if the cache size has changed.
     if (recreateVertexArrays) {
         cache->setPaintEnginePrivate(this);
-        cache->populate(staticTextItem->fontEngine(), staticTextItem->numGlyphs,
-                        staticTextItem->glyphs, staticTextItem->glyphPositions);
+        if (!cache->populate(staticTextItem->fontEngine(), staticTextItem->numGlyphs,
+			     staticTextItem->glyphs, staticTextItem->glyphPositions)) {
+	    // No space in cache. We need to clear the cache and try again
+            cache->clear();
+            cache->populate(staticTextItem->fontEngine(), staticTextItem->numGlyphs,
+			    staticTextItem->glyphs, staticTextItem->glyphPositions);
+	}
     }
 
     if (cache->width() == 0 || cache->height() == 0)
diff --git a/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp b/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
index 28e8c40..705ad09 100644
--- a/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
+++ b/src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp
@@ -78,7 +78,7 @@ void QGLTextureGlyphCache::setContext(QGLContext *context)
             SLOT(contextDestroyed(const QGLContext*)));
 }
 
-QGLTextureGlyphCache::~QGLTextureGlyphCache()
+void QGLTextureGlyphCache::clear() 
 {
     if (ctx) {
         QGLShareContextScope scope(ctx);
@@ -88,7 +88,24 @@ QGLTextureGlyphCache::~QGLTextureGlyphCache()
 
         if (m_width || m_height)
             glDeleteTextures(1, &m_texture);
+
+        m_fbo = 0;
+        m_texture = 0;
+        m_width = 0;
+        m_height = 0;
+        m_w = 0;
+        m_h = 0;
+        m_cx = 0;
+        m_cy = 0;
+        m_currentRowHeight = 0;
+        coords.clear();
     }
+  
+}
+
+QGLTextureGlyphCache::~QGLTextureGlyphCache()
+{
+    clear();
 }
 
 void QGLTextureGlyphCache::createTextureData(int width, int height)
diff --git a/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h b/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h
index fa2b091..aaef350 100644
--- a/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h
+++ b/src/opengl/gl2paintengineex/qtextureglyphcache_gl_p.h
@@ -124,6 +124,8 @@ public Q_SLOTS:
         }
     }
 
+    void clear();
+
 private:
     QGLContext *ctx;