From 49df693145bbd94afd0b65a57c5b93d7773ff886 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@kdab.com>
Date: Mon, 1 Jun 2020 11:54:45 +0200
Subject: QPainter: replace manual memory management [5/5]: d_ptrs
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Replace a manually-managed pointer + size with QVarLengthArray,
allowing use of pre-allocated space.

Change-Id: Ife3abea0b3b0f2577bb76c348513d52d46f79641
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
---
 src/gui/painting/qpainter.cpp | 23 +++++------------------
 src/gui/painting/qpainter_p.h |  7 +++++--
 2 files changed, 10 insertions(+), 20 deletions(-)

(limited to 'src/gui/painting')

diff --git a/src/gui/painting/qpainter.cpp b/src/gui/painting/qpainter.cpp
index 82a96960a8..31f8e40381 100644
--- a/src/gui/painting/qpainter.cpp
+++ b/src/gui/painting/qpainter.cpp
@@ -267,20 +267,8 @@ bool QPainterPrivate::attachPainterPrivate(QPainter *q, QPaintDevice *pdev)
     // Save the current state of the shared painter and assign
     // the current d_ptr to the shared painter's d_ptr.
     sp->save();
-    if (!sp->d_ptr->d_ptrs) {
-        // Allocate space for 4 d-pointers (enough for up to 4 sub-sequent
-        // redirections within the same paintEvent(), which should be enough
-        // in 99% of all cases). E.g: A renders B which renders C which renders D.
-        sp->d_ptr->d_ptrs_size = 4;
-        sp->d_ptr->d_ptrs = (QPainterPrivate **)malloc(4 * sizeof(QPainterPrivate *));
-        Q_CHECK_PTR(sp->d_ptr->d_ptrs);
-    } else if (sp->d_ptr->refcount - 1 == sp->d_ptr->d_ptrs_size) {
-        // However, to support corner cases we grow the array dynamically if needed.
-        sp->d_ptr->d_ptrs_size <<= 1;
-        const int newSize = sp->d_ptr->d_ptrs_size * sizeof(QPainterPrivate *);
-        sp->d_ptr->d_ptrs = q_check_ptr((QPainterPrivate **)realloc(sp->d_ptr->d_ptrs, newSize));
-    }
-    sp->d_ptr->d_ptrs[++sp->d_ptr->refcount - 2] = q->d_ptr.data();
+    ++sp->d_ptr->refcount;
+    sp->d_ptr->d_ptrs.push_back(q->d_ptr.data());
     q->d_ptr.take();
     q->d_ptr.reset(sp->d_ptr.data());
 
@@ -325,7 +313,9 @@ void QPainterPrivate::detachPainterPrivate(QPainter *q)
     Q_ASSERT(refcount > 1);
     Q_ASSERT(q);
 
-    QPainterPrivate *original = d_ptrs[--refcount - 1];
+    --refcount;
+    QPainterPrivate *original = d_ptrs.back();
+    d_ptrs.pop_back();
     if (inDestructor) {
         inDestructor = false;
         if (original)
@@ -334,7 +324,6 @@ void QPainterPrivate::detachPainterPrivate(QPainter *q)
         original = new QPainterPrivate(q);
     }
 
-    d_ptrs[refcount - 1] = nullptr;
     q->restore();
     q->d_ptr.take();
     q->d_ptr.reset(original);
@@ -1515,8 +1504,6 @@ QPainter::~QPainter()
         Q_ASSERT(d_ptr->inDestructor);
         d_ptr->inDestructor = false;
         Q_ASSERT(d_ptr->refcount == 1);
-        if (d_ptr->d_ptrs)
-            free(d_ptr->d_ptrs);
     }
 }
 
diff --git a/src/gui/painting/qpainter_p.h b/src/gui/painting/qpainter_p.h
index 09de84f2b2..7f5fe1a6c5 100644
--- a/src/gui/painting/qpainter_p.h
+++ b/src/gui/painting/qpainter_p.h
@@ -198,7 +198,11 @@ public:
     ~QPainterPrivate();
 
     QPainter *q_ptr;
-    QPainterPrivate **d_ptrs = nullptr;
+    // Allocate space for 4 d-pointers (enough for up to 4 sub-sequent
+    // redirections within the same paintEvent(), which should be enough
+    // in 99% of all cases). E.g: A renders B which renders C which renders D.
+    static constexpr qsizetype NDPtrs = 4;
+    QVarLengthArray<QPainterPrivate*, NDPtrs> d_ptrs;
 
     std::unique_ptr<QPainterState> state;
     template <typename T, std::size_t N = 8>
@@ -212,7 +216,6 @@ public:
     QTransform invMatrix;
     uint txinv:1;
     uint inDestructor : 1;
-    uint d_ptrs_size = 0;
     uint refcount = 1;
 
     enum DrawOperation { StrokeDraw        = 0x1,
-- 
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