Avoid using huge floating point values in the renderer.

We pretransform vertices relative to their batch root and upload these
using single-precision floats. If the offsets are huge then the
floating point numbers start to get unstable and we get rendering
artifacts as a result. This typically happens for lists/tables with
huge models.

Task-number: QTBUG-34312
Change-Id: I2516f2b4fa93f44a1288659d05458fb1af0df943
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>

2 files changed, 32 insertions, 5 deletions

diff --git a/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp b/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
index bb98682b20..3ea4b2ee1e 100644
--- a/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
+++ b/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
@@ -562,6 +562,8 @@ void Element::computeBounds()
         bounds.br.x = FLT_MAX;
     if (!qIsFinite(bounds.br.y))
         bounds.br.y = FLT_MAX;
+
+    boundsOutsideFloatRange = bounds.isOutsideFloatRange();
 }
 
 RenderNodeElement::~RenderNodeElement()
@@ -662,12 +664,26 @@ bool Batch::isTranslateOnlyToRoot() const {
 
 /*
  * Iterates through all the nodes in the batch and returns true if the
- * nodes are all "2D safe" meaning that they can be merged and that
- * the value in the z coordinate is of no consequence.
+ * nodes are all safe to batch. There are two separate criteria:
+ *
+ * - The matrix is such that the z component of the result is of no
+ *   consequence.
+ *
+ * - The bounds are inside the stable floating point range. This applies
+ *   to desktop only where we in this case can trigger a fallback to
+ *   unmerged in which case we pass the geometry straight through and
+ *   just apply the matrix.
+ *
+ *   NOTE: This also means a slight performance impact for geometries which
+ *   are defined to be outside the stable floating point range and still
+ *   use single precision float, but given that this implicitly fixes
+ *   huge lists and tables, it is worth it.
  */
-bool Batch::allMatricesAre2DSafe() const {
+bool Batch::isSafeToBatch() const {
     Element *e = first;
     while (e) {
+        if (e->boundsOutsideFloatRange)
+            return false;
         if (!QMatrix4x4_Accessor::is2DSafe(*e->node->matrix()))
             return false;
         e = e->nextInBatch;
@@ -1637,7 +1653,7 @@ void Renderer::uploadBatch(Batch *b)
                         && (((gn->activeMaterial()->flags() & QSGMaterial::RequiresDeterminant) == 0)
                             || (((gn->activeMaterial()->flags() & QSGMaterial_RequiresFullMatrixBit) == 0) && b->isTranslateOnlyToRoot())
                             )
-                        && b->allMatricesAre2DSafe();
+                        && b->isSafeToBatch();
 
         b->merged = canMerge;
 
diff --git a/src/quick/scenegraph/coreapi/qsgbatchrenderer_p.h b/src/quick/scenegraph/coreapi/qsgbatchrenderer_p.h
index 23985729ef..6d95f83d7a 100644
--- a/src/quick/scenegraph/coreapi/qsgbatchrenderer_p.h
+++ b/src/quick/scenegraph/coreapi/qsgbatchrenderer_p.h
@@ -53,6 +53,8 @@ QT_BEGIN_NAMESPACE
 namespace QSGBatchRenderer
 {
 
+#define QSG_RENDERER_COORD_LIMIT 1000000.0f
+
 struct Vec;
 struct Rect;
 struct Buffer;
@@ -136,6 +138,13 @@ struct Rect {
         bool yOverlap = r.tl.y < br.y && r.br.y > tl.y;
         return xOverlap && yOverlap;
     }
+
+    bool isOutsideFloatRange() const {
+        return tl.x < -QSG_RENDERER_COORD_LIMIT
+                || tl.y < -QSG_RENDERER_COORD_LIMIT
+                || br.x > QSG_RENDERER_COORD_LIMIT
+                || br.y > QSG_RENDERER_COORD_LIMIT;
+    }
 };
 
 inline QDebug operator << (QDebug d, const Rect &r) {
@@ -158,6 +167,7 @@ struct Element {
         , root(0)
         , order(0)
         , boundsComputed(false)
+        , boundsOutsideFloatRange(false)
         , translateOnlyToRoot(false)
         , removed(false)
         , orphaned(false)
@@ -181,6 +191,7 @@ struct Element {
     int order;
 
     uint boundsComputed : 1;
+    uint boundsOutsideFloatRange : 1;
     uint translateOnlyToRoot : 1;
     uint removed : 1;
     uint orphaned : 1;
@@ -242,7 +253,7 @@ struct Batch
     void cleanupRemovedElements();
 
     bool isTranslateOnlyToRoot() const;
-    bool allMatricesAre2DSafe() const;
+    bool isSafeToBatch() const;
 
     // pseudo-constructor...
     void init() {