Prevent continuous painting with viewport QOpenGLWidget

Add the source widget to the texture list (may be null for custom
compositor implementations that add textures not belonging to actual
widgets). This allows us to do proper checks with the
dirtyRenderToTextureWidgets list.

As a result paint events are only sent to a QOpenGLWidget if (1) there
was an update() for it or (2) it was actually marked dirty. (2) was
previously behaving differently: the widget got a paint event when
anything in the window has changed. This is fine for naive animating
OpenGL code but less ideal for QGraphicsView.

Bool properties like stacksOnTop are now stored in a flags value to
prevent future explosion of texture list fields and parameters.

Task-number: QTBUG-43178
Change-Id: I48cbcf93df72ac682c9b5d64982a8b648fe21ef3
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@theqtcompany.com>

2 files changed, 24 insertions, 9 deletions

diff --git a/src/gui/painting/qplatformbackingstore.cpp b/src/gui/painting/qplatformbackingstore.cpp
index e87f796888..76269f6e65 100644
--- a/src/gui/painting/qplatformbackingstore.cpp
+++ b/src/gui/painting/qplatformbackingstore.cpp
@@ -82,9 +82,10 @@ public:
 
 struct QBackingstoreTextureInfo
 {
+    QWidget *widget; // may be null
     GLuint textureId;
     QRect rect;
-    bool stacksOnTop;
+    QPlatformTextureList::Flags flags;
 };
 
 Q_DECLARE_TYPEINFO(QBackingstoreTextureInfo, Q_MOVABLE_TYPE);
@@ -122,10 +123,16 @@ GLuint QPlatformTextureList::textureId(int index) const
     return d->textures.at(index).textureId;
 }
 
-bool QPlatformTextureList::stacksOnTop(int index) const
+QWidget *QPlatformTextureList::widget(int index)
 {
     Q_D(const QPlatformTextureList);
-    return d->textures.at(index).stacksOnTop;
+    return d->textures.at(index).widget;
+}
+
+QPlatformTextureList::Flags QPlatformTextureList::flags(int index) const
+{
+    Q_D(const QPlatformTextureList);
+    return d->textures.at(index).flags;
 }
 
 QRect QPlatformTextureList::geometry(int index) const
@@ -149,13 +156,14 @@ bool QPlatformTextureList::isLocked() const
     return d->locked;
 }
 
-void QPlatformTextureList::appendTexture(GLuint textureId, const QRect &geometry, bool stacksOnTop)
+void QPlatformTextureList::appendTexture(QWidget *widget, GLuint textureId, const QRect &geometry, Flags flags)
 {
     Q_D(QPlatformTextureList);
     QBackingstoreTextureInfo bi;
+    bi.widget = widget;
     bi.textureId = textureId;
     bi.rect = geometry;
-    bi.stacksOnTop = stacksOnTop;
+    bi.flags = flags;
     d->textures.append(bi);
 }
 
@@ -245,7 +253,7 @@ void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &regi
 
     // Textures for renderToTexture widgets.
     for (int i = 0; i < textures->count(); ++i) {
-        if (!textures->stacksOnTop(i)) {
+        if (!textures->flags(i).testFlag(QPlatformTextureList::StacksOnTop)) {
             QRect targetRect = deviceRect(textures->geometry(i), window);
             QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(targetRect, windowRect);
             d_ptr->blitter->blit(textures->textureId(i), target, QOpenGLTextureBlitter::OriginBottomLeft);
@@ -272,7 +280,7 @@ void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &regi
 
     // Textures for renderToTexture widgets that have WA_AlwaysStackOnTop set.
     for (int i = 0; i < textures->count(); ++i) {
-        if (textures->stacksOnTop(i)) {
+        if (textures->flags(i).testFlag(QPlatformTextureList::StacksOnTop)) {
             QRect targetRect = deviceRect(textures->geometry(i), window);
             QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(targetRect, windowRect);
             d_ptr->blitter->blit(textures->textureId(i), target, QOpenGLTextureBlitter::OriginBottomLeft);
diff --git a/src/gui/painting/qplatformbackingstore.h b/src/gui/painting/qplatformbackingstore.h
index 52c263f05d..c69612ca44 100644
--- a/src/gui/painting/qplatformbackingstore.h
+++ b/src/gui/painting/qplatformbackingstore.h
@@ -69,6 +69,11 @@ class Q_GUI_EXPORT QPlatformTextureList : public QObject
     Q_OBJECT
     Q_DECLARE_PRIVATE(QPlatformTextureList)
 public:
+    enum Flag {
+        StacksOnTop = 0x01
+    };
+    Q_DECLARE_FLAGS(Flags, Flag)
+
     explicit QPlatformTextureList(QObject *parent = 0);
     ~QPlatformTextureList();
 
@@ -76,16 +81,18 @@ public:
     bool isEmpty() const { return count() == 0; }
     GLuint textureId(int index) const;
     QRect geometry(int index) const;
-    bool stacksOnTop(int index) const;
+    QWidget *widget(int index);
+    Flags flags(int index) const;
     void lock(bool on);
     bool isLocked() const;
 
-    void appendTexture(GLuint textureId, const QRect &geometry, bool stacksOnTop = false);
+    void appendTexture(QWidget *widget, GLuint textureId, const QRect &geometry, Flags flags = 0);
     void clear();
 
  Q_SIGNALS:
     void locked(bool);
 };
+Q_DECLARE_OPERATORS_FOR_FLAGS(QPlatformTextureList::Flags)
 #endif
 
 class Q_GUI_EXPORT QPlatformBackingStore