Graphics View Optimization: Use a simple style option by default.

QStyleOptionGraphicsItem extends QStyleOption with three values:
1) matrix, 2) levelOfDetail, 3) exposedRect, and they all
involve expensive QTranform operations when calculated. We
pass style option(s) to drawItems() and paint(), but the
extended values are usually not in use. We can therefore gain
quite some nice speedup by making them opt-in with the
QGraphicsItem::ItemUsesExtendedStyleOption flag.

Additionally, QStyleOptionGraphicsItem::levelOfDetail has been
obsoleted, and a new function QStyleOptionGraphicsItem::
levelOfDetailFromTransform(const QTransform &) has been added.

Me and Andreas don't consider this change to be too controversial
even though it changes the behavior.

Auto tests still pass.

Reviewed-by: Andreas

1 files changed, 9 insertions, 8 deletions

diff --git a/demos/chip/chip.cpp b/demos/chip/chip.cpp
index c2b22da..4b6579e 100644
--- a/demos/chip/chip.cpp
+++ b/demos/chip/chip.cpp
@@ -74,8 +74,9 @@ void Chip::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWid
     if (option->state & QStyle::State_MouseOver)
         fillColor = fillColor.light(125);
 
-    if (option->levelOfDetail < 0.2) {
-        if (option->levelOfDetail < 0.125) {
+    const qreal lod = option->levelOfDetailFromTransform(painter->worldTransform());
+    if (lod < 0.2) {
+        if (lod < 0.125) {
             painter->fillRect(QRectF(0, 0, 110, 70), fillColor);
             return;
         }
@@ -100,7 +101,7 @@ void Chip::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWid
     painter->drawRect(QRect(14, 14, 79, 39));
     painter->setBrush(b);
 
-    if (option->levelOfDetail >= 1) {
+    if (lod >= 1) {
         painter->setPen(QPen(Qt::gray, 1));
         painter->drawLine(15, 54, 94, 54);
         painter->drawLine(94, 53, 94, 15);
@@ -108,7 +109,7 @@ void Chip::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWid
     }
 
     // Draw text
-    if (option->levelOfDetail >= 2) {
+    if (lod >= 2) {
         QFont font("Times", 10);
         font.setStyleStrategy(QFont::ForceOutline);
         painter->setFont(font);
@@ -122,17 +123,17 @@ void Chip::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWid
 
     // Draw lines
     QVarLengthArray<QLineF, 36> lines;
-    if (option->levelOfDetail >= 0.5) {
-        for (int i = 0; i <= 10; i += (option->levelOfDetail > 0.5 ? 1 : 2)) {
+    if (lod >= 0.5) {
+        for (int i = 0; i <= 10; i += (lod > 0.5 ? 1 : 2)) {
             lines.append(QLineF(18 + 7 * i, 13, 18 + 7 * i, 5));
             lines.append(QLineF(18 + 7 * i, 54, 18 + 7 * i, 62));
         }
-        for (int i = 0; i <= 6; i += (option->levelOfDetail > 0.5 ? 1 : 2)) {
+        for (int i = 0; i <= 6; i += (lod > 0.5 ? 1 : 2)) {
             lines.append(QLineF(5, 18 + i * 5, 13, 18 + i * 5));
             lines.append(QLineF(94, 18 + i * 5, 102, 18 + i * 5));
         }
     }
-    if (option->levelOfDetail >= 0.4) {
+    if (lod >= 0.4) {
         const QLineF lineData[] = {
             QLineF(25, 35, 35, 35),
             QLineF(35, 30, 35, 40),