Introduce 'nonpreservedtexture'

Provide a texture factory that does not keep a reference to the
QImage. This is intended to lower memory usage in the case of an
embedded system with only a single window that is never hidden or
re-exposed.

See also 8b50a9f00f6f5b693d18c59ff15968e2b902ebf8 in qtdeclarative.

Change-Id: If0a11f6bb37f4fb3b409a577609ebdfce73789b2
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

5 files changed, 91 insertions, 0 deletions

diff --git a/customcontext/context.cpp b/customcontext/context.cpp
index 8ab0a4f..f349213 100644
--- a/customcontext/context.cpp
+++ b/customcontext/context.cpp
@@ -71,6 +71,10 @@
 #include "mactexture.h"
 #endif
 
+#ifdef CUSTOMCONTEXT_NONPRESERVEDTEXTURE
+#include "nonpreservedtexture.h"
+#endif
+
 
 
 namespace CustomContext
@@ -126,6 +130,10 @@ Context::Context(QObject *parent)
     connect(this, SIGNAL(invalidated()), &m_threadUploadManager, SLOT(invalidated()), Qt::DirectConnection);
 #endif
 
+#ifdef CUSTOMCONTEXT_NONPRESERVEDTEXTURE
+    m_nonPreservedTexture = qgetenv("CUSTOMCONTEXT_NO_NONPRESERVEDTEXTURE").isEmpty();
+#endif
+
 
 
 #ifdef CUSTOMCONTEXT_DEBUG
@@ -154,6 +162,9 @@ Context::Context(QObject *parent)
 #ifdef CUSTOMCONTEXT_MACTEXTURE
     qDebug(" - mac textures: %s", m_macTexture ? "yes" : "no");
 #endif
+#ifdef CUSTOMCONTEXT_NONPRESERVEDTEXTURE
+    qDebug(" - non preserved textures: %s", m_nonPreservedTexture ? "yes" : "no");
+#endif
 
 #ifdef CUSTOMCONTEXT_DITHER
     qDebug(" - ordered 2x2 dither: %s", m_dither ? "yes" : "no");
@@ -317,6 +328,11 @@ QQuickTextureFactory *Context::createTextureFactory(const QImage &image)
         return m_threadUploadManager.create(image);
 #endif
 
+#ifdef CUSTOMCONTEXT_NONPRESERVEDTEXTURE
+    if (m_nonPreservedTexture)
+        return new NonPreservedTextureFactory(image);
+#endif
+
     return 0;
 }
 
diff --git a/customcontext/context.h b/customcontext/context.h
index a02d0d6..fff2a56 100644
--- a/customcontext/context.h
+++ b/customcontext/context.h
@@ -121,6 +121,10 @@ private:
     bool m_threadUploadTexture;
 #endif
 
+#ifdef CUSTOMCONTEXT_NONPRESERVEDTEXTURE
+    bool m_nonPreservedTexture;
+#endif
+
 
 
 };
diff --git a/customcontext/customcontext.pro b/customcontext/customcontext.pro
index 62bb5ab..2443360 100644
--- a/customcontext/customcontext.pro
+++ b/customcontext/customcontext.pro
@@ -67,6 +67,16 @@ mactexture:{
     message("mactexture ...............: no")
 }
 
+nonpreservedtexture:{
+    message("nonpreservedtexture ......: yes")
+    DEFINES += CUSTOMCONTEXT_NONPRESERVEDTEXTURE
+    SOURCES += texture/nonpreservedtexture.cpp
+    HEADERS += texture/nonpreservedtexture.h
+    INCLUDEPATH += texture
+} else {
+    message("nonpreservedtexture ......: no")
+}
+
 
 
 ############################################################
diff --git a/customcontext/texture/nonpreservedtexture.cpp b/customcontext/texture/nonpreservedtexture.cpp
new file mode 100644
index 0000000..dbfb4d1
--- /dev/null
+++ b/customcontext/texture/nonpreservedtexture.cpp
@@ -0,0 +1,32 @@
+#include "nonpreservedtexture.h"
+
+#include <private/qsgtexture_p.h>
+
+namespace CustomContext {
+
+/*
+    Typically a texture factory will keep a reference to the
+    QImage so that it can be reused when QQuickWindow::setPersistentSceneGraph(false)
+    is set and the window is hidden and then re-exposed.
+
+    This texture factory does not keep a reference, and is
+    intended to lower memory usage in the case of an embedded
+    system with only a single window that is never hidden or re-exposed.
+*/
+
+NonPreservedTextureFactory::NonPreservedTextureFactory(const QImage &image)
+    : m_image(image)
+{
+    m_size = m_image.size();
+    m_byteCount = m_image.byteCount();
+}
+
+QSGTexture *NonPreservedTextureFactory::createTexture(QQuickWindow *) const
+{
+    QSGPlainTexture *t = new QSGPlainTexture();
+    t->setImage(m_image);
+    m_image = QImage();
+    return t;
+}
+
+} // end of namespace
diff --git a/customcontext/texture/nonpreservedtexture.h b/customcontext/texture/nonpreservedtexture.h
new file mode 100644
index 0000000..65f89a2
--- /dev/null
+++ b/customcontext/texture/nonpreservedtexture.h
@@ -0,0 +1,29 @@
+#ifndef NONPRESERVEDTEXTURE_H
+#define NONPRESERVEDTEXTURE_H
+
+#include <QSize>
+#include <QImage>
+#include <QQuickTextureFactory>
+
+namespace CustomContext {
+
+class NonPreservedTextureFactory : public QQuickTextureFactory
+{
+    Q_OBJECT
+public:
+    NonPreservedTextureFactory(const QImage &image);
+
+    QSGTexture *createTexture(QQuickWindow *window) const;
+    QSize textureSize() const { return m_size; }
+    int textureByteCount() const { return m_byteCount; }
+    QImage image() const { return m_image; }
+
+private:
+    mutable QImage m_image;
+    QSize m_size;
+    int m_byteCount;
+};
+
+}
+
+#endif // NONPRESERVEDTEXTURE_H