QPainter: replace manual memory management [2/5]: state/states

Use unique_ptr to indicate ownership. Use std::stack to enforce
stack-ness (QStack doesn't). Requires the addition of a clear()
function, for which we spin a SmallStack wrapper. It also helps to not
have to repeat the value_type...

Because we use unique_ptr, `state` and `states` are now exclusive
(before, `state` was always `states.back()`). Correspondingly, rename
`states` → `savedStates`.

As a drive-by, this fixes an off-by-one error in a qWarning() (checked
`> 1`, but reported one saved state too many).

Change-Id: I8faade59300401be802ddc52c64ce31b8f23dc52
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

1 files changed, 8 insertions, 2 deletions

diff --git a/src/gui/painting/qpainter_p.h b/src/gui/painting/qpainter_p.h
index 71e90c9717..8994bcd3e7 100644
--- a/src/gui/painting/qpainter_p.h
+++ b/src/gui/painting/qpainter_p.h
@@ -66,6 +66,7 @@
 #include <private/qpen_p.h>
 
 #include <memory>
+#include <stack>
 
 QT_BEGIN_NAMESPACE
 
@@ -205,8 +206,12 @@ public:
     QPainter *q_ptr;
     QPainterPrivate **d_ptrs;
 
-    QPainterState *state;
-    QVarLengthArray<QPainterState *, 8> states;
+    std::unique_ptr<QPainterState> state;
+    template <typename T, std::size_t N = 8>
+    struct SmallStack : std::stack<T, QVarLengthArray<T, N>> {
+        void clear() { this->c.clear(); }
+    };
+    SmallStack<std::unique_ptr<QPainterState>> savedStates;
 
     mutable std::unique_ptr<QPainterDummyState> dummyState;
 
@@ -230,6 +235,7 @@ public:
     void updateEmulationSpecifier(QPainterState *s);
     void updateStateImpl(QPainterState *state);
     void updateState(QPainterState *state);
+    void updateState(std::unique_ptr<QPainterState> &state) { updateState(state.get()); }
 
     void draw_helper(const QPainterPath &path, DrawOperation operation = StrokeAndFillDraw);
     void drawStretchedGradient(const QPainterPath &path, DrawOperation operation);