Add support for FrontToBack sorting

A typical renderer with opaque-transparent passes will often want
to use FrontToBack in the opaque pass (even though this is usually
not strictly required).

Change-Id: I071b62424a5446c86d76c6045c126a599534bf80
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/src/render/backend/renderview.cpp b/src/render/backend/renderview.cpp
index dca660ad0..962480f2f 100644
--- a/src/render/backend/renderview.cpp
+++ b/src/render/backend/renderview.cpp
@@ -307,6 +307,15 @@ struct AdjacentSubRangeFinder<QSortPolicy::Material>
     }
 };
 
+template<>
+struct AdjacentSubRangeFinder<QSortPolicy::FrontToBack>
+{
+    static bool adjacentSubRange(RenderCommand *a, RenderCommand *b)
+    {
+        return a->m_depth == b->m_depth;
+    }
+};
+
 template<typename Predicate>
 int advanceUntilNonAdjacent(const QVector<RenderCommand *> &commands,
                             const int beg, const int end, Predicate pred)
@@ -366,6 +375,16 @@ struct SubRangeSorter<QSortPolicy::Material>
     }
 };
 
+template<>
+struct SubRangeSorter<QSortPolicy::FrontToBack>
+{
+    static void sortSubRange(CommandIt begin, const CommandIt end)
+    {
+        std::stable_sort(begin, end, [] (RenderCommand *a, RenderCommand *b) {
+            return a->m_depth < b->m_depth;
+        });
+    }
+};
 
 int findSubRange(const QVector<RenderCommand *> &commands,
                  const int begin, const int end,
@@ -378,6 +397,8 @@ int findSubRange(const QVector<RenderCommand *> &commands,
         return advanceUntilNonAdjacent(commands, begin, end, AdjacentSubRangeFinder<QSortPolicy::BackToFront>::adjacentSubRange);
     case QSortPolicy::Material:
         return advanceUntilNonAdjacent(commands, begin, end, AdjacentSubRangeFinder<QSortPolicy::Material>::adjacentSubRange);
+    case QSortPolicy::FrontToBack:
+        return advanceUntilNonAdjacent(commands, begin, end, AdjacentSubRangeFinder<QSortPolicy::FrontToBack>::adjacentSubRange);
     default:
         Q_UNREACHABLE();
         return end;
@@ -418,6 +439,9 @@ void sortCommandRange(QVector<RenderCommand *> &commands, int begin, const int e
         // Group all same material together (same parameters most likely)
         sortByMaterial(commands, begin, end);
         break;
+    case QSortPolicy::FrontToBack:
+        SubRangeSorter<QSortPolicy::FrontToBack>::sortSubRange(commands.begin() + begin, commands.begin() + end);
+        break;
     default:
         Q_UNREACHABLE();
     }