Fixed|LogWidget: Rendering glitch related to atlas optimization

As the entry atlas is used in a dynamic fashion, defragmentation is needed
to free up fragmented space. However, if defragmentation occurs during the
rendering of entries, the generated geometry becomes obsolete as the UV
coordinates of all entries will likely change. Therefore, LogWidget needs
to redo the visible range of entries if the atlas is optimized.

doomsday/client/src/ui/widgets/logwidget.cpp

@@ -39,7 +39,9 @@
 
 using namespace de;
 
-DENG2_PIMPL(LogWidget), public Font::RichFormat::IStyle
+DENG2_PIMPL(LogWidget),
+DENG2_OBSERVES(Atlas, Reposition),
+public Font::RichFormat::IStyle
 {
     typedef GLBufferT<Vertex2TexRgba> VertexBuf;
 
@@ -330,6 +332,7 @@ DENG2_PIMPL(LogWidget), public Font::RichFormat::IStyle
     VertexBuf *buf;
     VertexBuf *bgBuf;
     AtlasTexture *entryAtlas;
+    bool entryAtlasLayoutChanged;
     Drawable contents;
     Drawable background;
     GLUniform uMvpMatrix;
@@ -359,6 +362,7 @@ DENG2_PIMPL(LogWidget), public Font::RichFormat::IStyle
           scrollBarWidth(0),
           buf(0),
           entryAtlas(0),
+          entryAtlasLayoutChanged(false),
           uMvpMatrix  ("uMvpMatrix", GLUniform::Mat4),
           uTex        ("uTex",       GLUniform::Sampler2D),
           uShadowColor("uColor",     GLUniform::Vec4),
@@ -503,6 +507,7 @@ DENG2_PIMPL(LogWidget), public Font::RichFormat::IStyle
         entryAtlas = AtlasTexture::newWithRowAllocator(
                 Atlas::BackingStore | Atlas::AllowDefragment,
                 GLTexture::maximumSize().min(Atlas::Size(2048, 1024)));
+        entryAtlas->audienceForReposition += this;
 
         Image solidWhitePixel = Image::solidColor(Image::Color(255, 255, 255, 255),
                                                   Image::Size(1, 1));
@@ -535,6 +540,14 @@ DENG2_PIMPL(LogWidget), public Font::RichFormat::IStyle
         background.clear();
     }
 
+    void atlasContentRepositioned(Atlas &atlas)
+    {
+        if(entryAtlas == &atlas)
+        {
+            entryAtlasLayoutChanged = true;
+        }
+    }
+
     duint contentWidth() const
     {
         return de::max(margin, self.rule().width().valuei() - 2 * margin);
@@ -719,29 +732,46 @@ DENG2_PIMPL(LogWidget), public Font::RichFormat::IStyle
         //prune();
 
         clampVisibleOffset(contentSize.y);
-
-        // Draw in reverse, as much as we need.
-        int yBottom = contentSize.y + visibleOffset;
-
-        maxScroll    = maxVisibleOffset(contentSize.y);
-        visibleRange = Rangei(-1, -1);
+        maxScroll = maxVisibleOffset(contentSize.y);
 
         VertexBuf::Builder verts;
 
-        // Copy all visible entries to the buffer.
-        for(int idx = cache.size() - 1; yBottom > -contentOffset && idx >= 0; --idx)
+        for(int attempt = 0; attempt < 2; ++attempt)
         {
-            CacheEntry *entry = cache[idx];
-            yBottom -= entry->height();
+            // Draw in reverse, as much as we need.
+            int yBottom = contentSize.y + visibleOffset;
+            visibleRange = Rangei(-1, -1);
+            entryAtlasLayoutChanged = false;
 
-            if(yBottom + contentOffset < contentSize.y)
+            // Find the visible range and update all visible entries.
+            for(int idx = cache.size() - 1; yBottom > -contentOffset && idx >= 0; --idx)
             {
-                // This entry is visible.
-                entry->make(verts, yBottom);
+                CacheEntry *entry = cache[idx];
+                yBottom -= entry->height();
 
-                if(visibleRange.end == -1) visibleRange.end = idx;
-                visibleRange.start = idx;
+                if(yBottom + contentOffset < contentSize.y)
+                {
+                    // Rasterize and allocate if needed.
+                    entry->make(verts, yBottom);
+
+                    // Update the visible range.
+                    if(visibleRange.end == -1)
+                    {
+                        visibleRange.end = idx;
+                    }
+                    visibleRange.start = idx;
+                }
             }
+
+            if(entryAtlasLayoutChanged)
+            {
+                // Oops, the atlas was optimized during the loop and some items'
+                // positions are obsolete.
+                verts.clear();
+                continue;
+            }
+
+            break;
         }
 
         // Draw the scroll indicator.

doomsday/libdeng2/include/de/core/range.h

@@ -62,6 +62,12 @@ struct Range
     inline bool operator > (Type const &value) const {
         return start > value && end > value;
     }
+    inline bool operator <= (Type const &value) const {
+        return !(*this > value);
+    }
+    inline bool operator >= (Type const &value) const {
+        return !(*this < value);
+    }
     inline Range<Type> operator + (Type offset) const {
         return Range<Type>(start + offset, end + offset);
     }