Patch|Debug: Check Patch geometry in debug builds

In debug builds test the geometry of Patch format images to determine
whether the declared height in the header matches the "real" height of
the composited posts. If heights are inequal log an INFO message.

doomsday/engine/src/resource/patch.cpp

@@ -19,6 +19,7 @@
  */
 
 #include <QList>
+#include <QRect>
 #include <de/libdeng2.h>
 #include <de/Log>
 
@@ -137,12 +138,65 @@ static Columns readColumns(IByteArray const &data, Patch::Header &hdr)
     return readPosts(readColumnOffsets(hdr.dimensions.width(), from), from);
 }
 
+/**
+ * Process @a columns to calculate the "real" pixel height of the image.
+ */
+#ifdef DENG_DEBUG
+static int calcRealHeight(Columns const &columns)
+{
+    QRect geom(QPoint(0, 0), QSize(1, 0));
+
+    DENG2_FOR_EACH_CONST(Columns, colIt, columns)
+    {
+        int tallTop = -1; // Keep track of pos (clipping).
+
+        DENG2_FOR_EACH_CONST(Posts, postIt, *colIt)
+        {
+            Post const &post = *postIt;
+
+            // Does this post extend the previous one (a so-called "tall-patch").
+            if(post.topOffset <= tallTop)
+                tallTop += post.topOffset;
+            else
+                tallTop = post.topOffset;
+
+            // Skip invalid posts.
+            if(post.length <= 0) continue;
+
+            // Unite the geometry of the post.
+            geom |= QRect(QPoint(0, tallTop), QSize(1, post.length));
+        }
+    }
+
+    return geom.height();
+}
+#endif
+
 static Block load(IByteArray const &data, IByteArray const *xlatTable, bool maskZero)
 {
     // Prepare the column => post map.
     Patch::Header hdr;
     Columns columns = readColumns(data, hdr);
 
+#ifdef DENG_DEBUG
+    // Is the declared height of the image equal to the "real" height of the
+    // composited pixel posts?
+    int const realHeight = calcRealHeight(columns);
+    if(realHeight != hdr.dimensions.height())
+    {
+        int postCount = 0;
+        DENG2_FOR_EACH_CONST(Columns, i, columns)
+        {
+            postCount += i->count();
+        }
+
+        LOG_INFO("Inequal heights, declared: %i != real: %i (%i %s).")
+            << hdr.dimensions.height() << realHeight
+            << postCount << (postCount == 1? "post" : "posts");
+    }
+#endif
+
+    // Determine the dimensions of the output buffer.
     int const       w = hdr.dimensions.width();
     int const       h = hdr.dimensions.height();
     size_t const pels = w * h;