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Fix a bug in the initialization (and debug-output) of BSP trees

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On a horizontal split the current rectangle is split along the y-axis,
creating two children with the dimensions [x, y, width, height / 2]
and [x, y + height / 2, width, height / 2] respectively. When the
BSP tree is initialized, the type of the root node is set to
"Horizontal". However, the offset of the root node is wrongly
initialized with a split along the x-axis instead of the y-axis.
This leads to wrong behavior on QGraphicsScenes with a non square
aspect ratio. E.g on a QGraphicsScene with an apsect ratio favoring
the y-axis, every item between yItem = sceneWidth/2 and
yItem = sceneHeight/2 will be added to the wrong leaf.

[ChangeLog][QWidgets][QGraphicsScene] Fixed a bug in the initialization
of BSP trees to increase the performance of QGraphicsScenes with non
quadratic scene rectangles.

Fixes: QTBUG-87174
Pick-to: 5.15
Change-Id: I360033e94e22eb961f820278993754d10bfc1e45
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
This commit is contained in:
Andreas Klots 2020-10-05 16:19:11 +02:00 committed by Lars Knoll
parent 62fed23fef
commit 40874625f9
1 changed files with 2 additions and 2 deletions
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4
src/widgets/graphicsview/qgraphicsscene_bsp.cpp
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@ -190,7 +190,7 @@ void QGraphicsSceneBspTree::initialize(const QRectF &rect, int depth, int index)
Node *node = &nodes[index]; Node *node = &nodes[index];
if (index == 0) { if (index == 0) {
node->type = Node::Horizontal; node->type = Node::Horizontal;
node->offset = rect.center().x(); node->offset = rect.center().y();
} }
if (depth) { if (depth) {
@ -272,7 +272,7 @@ QRectF QGraphicsSceneBspTree::rectForIndex(int index) const
QRectF rect = rectForIndex(parentIdx); QRectF rect = rectForIndex(parentIdx);
const Node *parent = &nodes.at(parentIdx); const Node *parent = &nodes.at(parentIdx);
if (parent->type == Node::Horizontal) { if (parent->type == Node::Vertical) {
if (index & 1) if (index & 1)
rect.setRight(parent->offset); rect.setRight(parent->offset);
else else