Fixed antialiased rasterization bug in raster engine.

When rasterization in the gray raster fails due to out of memory there
might already have been a number of spans flushed. To avoid flushing
these spans multiple times and thus getting overdraw artifacts we need
to keep track of how many spans to skip when we redo the rasterization.

This fixes the rendering error in arthur test paths_aa.qps

Reviewed-by: Yoann Lopes

3 files changed, 41 insertions, 7 deletions

diff --git a/src/gui/painting/qgrayraster.c b/src/gui/painting/qgrayraster.c
index f348f7fa8a..d0e25a9193 100644
--- a/src/gui/painting/qgrayraster.c
+++ b/src/gui/painting/qgrayraster.c
@@ -317,6 +317,7 @@
     PCell*     ycells;
     int        ycount;
 
+    int        skip_spans;
   } TWorker, *PWorker;
 
 
@@ -330,7 +331,12 @@
 
   } TRaster, *PRaster;
 
-
+  int q_gray_rendered_spans(TRaster *raster)
+  {
+    if ( raster && raster->worker )
+      return raster->worker->skip_spans > 0 ? 0 : -raster->worker->skip_spans;
+    return 0;
+  }
 
   /*************************************************************************/
   /*                                                                       */
@@ -1178,6 +1184,7 @@
   {
     QT_FT_Span*  span;
     int       coverage;
+    int       skip;
 
 
     /* compute the coverage line's coverage, depending on the    */
@@ -1228,9 +1235,16 @@
 
       if ( ras.num_gray_spans >= QT_FT_MAX_GRAY_SPANS )
       {
-        if ( ras.render_span )
-          ras.render_span( ras.num_gray_spans, ras.gray_spans,
+        if ( ras.render_span && ras.num_gray_spans > ras.skip_spans )
+        {
+          skip = ras.skip_spans > 0 ? ras.skip_spans : 0;
+          ras.render_span( ras.num_gray_spans - skip,
+                           ras.gray_spans + skip,
                            ras.render_span_data );
+        }
+
+        ras.skip_spans -= ras.num_gray_spans;
+
         /* ras.render_span( span->y, ras.gray_spans, count ); */
 
 #ifdef DEBUG_GRAYS
@@ -1600,7 +1614,8 @@
     TBand* volatile  band;
     int volatile     n, num_bands;
     TPos volatile    min, max, max_y;
-    QT_FT_BBox*         clip;
+    QT_FT_BBox*      clip;
+    int              skip;
 
     ras.num_gray_spans = 0;
 
@@ -1741,9 +1756,15 @@
       }
     }
 
-    if ( ras.render_span && ras.num_gray_spans > 0 )
-        ras.render_span( ras.num_gray_spans,
-                         ras.gray_spans, ras.render_span_data );
+    if ( ras.render_span && ras.num_gray_spans > ras.skip_spans )
+    {
+        skip = ras.skip_spans > 0 ? ras.skip_spans : 0;
+        ras.render_span( ras.num_gray_spans - skip,
+                         ras.gray_spans + skip,
+                         ras.render_span_data );
+    }
+
+    ras.skip_spans -= ras.num_gray_spans;
 
     if ( ras.band_shoot > 8 && ras.band_size > 16 )
       ras.band_size = ras.band_size / 2;
@@ -1764,6 +1785,9 @@
     if ( !raster || !raster->buffer || !raster->buffer_size )
       return ErrRaster_Invalid_Argument;
 
+    if ( raster->worker )
+      raster->worker->skip_spans = params->skip_spans;
+
     // If raster object and raster buffer are allocated, but
     // raster size isn't of the minimum size, indicate out of
     // memory.
diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index 09a87aa252..36e1082fd0 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -4148,6 +4148,10 @@ void QRasterPaintEnginePrivate::rasterize(QT_FT_Outline *outline,
     rasterize(outline, callback, (void *)spanData, rasterBuffer);
 }
 
+extern "C" {
+    int q_gray_rendered_spans(QT_FT_Raster raster);
+}
+
 void QRasterPaintEnginePrivate::rasterize(QT_FT_Outline *outline,
                                           ProcessSpans callback,
                                           void *userData, QRasterBuffer *)
@@ -4212,10 +4216,13 @@ void QRasterPaintEnginePrivate::rasterize(QT_FT_Outline *outline,
     bool done = false;
     int error;
 
+    int rendered_spans = 0;
+
     while (!done) {
 
         rasterParams.flags |= (QT_FT_RASTER_FLAG_AA | QT_FT_RASTER_FLAG_DIRECT);
         rasterParams.gray_spans = callback;
+        rasterParams.skip_spans = rendered_spans;
         error = qt_ft_grays_raster.raster_render(*grayRaster.data(), &rasterParams);
 
         // Out of memory, reallocate some more and try again...
@@ -4244,6 +4251,8 @@ void QRasterPaintEnginePrivate::rasterize(QT_FT_Outline *outline,
 #endif
             Q_CHECK_PTR(rasterPoolBase); // note: we just freed the old rasterPoolBase. I hope it's not fatal.
 
+            rendered_spans += q_gray_rendered_spans(*grayRaster.data());
+
             qt_ft_grays_raster.raster_done(*grayRaster.data());
             qt_ft_grays_raster.raster_new(grayRaster.data());
             qt_ft_grays_raster.raster_reset(*grayRaster.data(), rasterPoolBase, rasterPoolSize);
diff --git a/src/gui/painting/qrasterdefs_p.h b/src/gui/painting/qrasterdefs_p.h
index 19a0b16974..4131e4b77d 100644
--- a/src/gui/painting/qrasterdefs_p.h
+++ b/src/gui/painting/qrasterdefs_p.h
@@ -1088,6 +1088,7 @@ QT_FT_BEGIN_HEADER
     QT_FT_Raster_BitSet_Func   bit_set;      /* doesn't work! */
     void*                   user;
     QT_FT_BBox                 clip_box;
+    int                     skip_spans;
 
   } QT_FT_Raster_Params;