Allow more control over memory/speed tradeoff in the atlas.

QSG_ATLAS_TRANSIENT_IMAGE_THRESHOLD can be used to define a threshold
for retaining the QImage associated with an atlas texture. This gives
more control to the developer on platforms where removing a texture
from the atlas (e.g. for use in a ShaderEffect) can be prohibitively
expensive.

Change-Id: I13fd01ebbe94dd960fdcb3ee20b4ff40dcc5694f
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>
Reviewed-by: Brett Stottlemyer <bstottle@ford.com>
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

1 files changed, 10 insertions, 1 deletions

diff --git a/src/quick/scenegraph/util/qsgatlastexture.cpp b/src/quick/scenegraph/util/qsgatlastexture.cpp
index 8e8e870505..832510148c 100644
--- a/src/quick/scenegraph/util/qsgatlastexture.cpp
+++ b/src/quick/scenegraph/util/qsgatlastexture.cpp
@@ -121,6 +121,7 @@ Atlas::Atlas(const QSize &size)
     : m_allocator(size)
     , m_texture_id(0)
     , m_size(size)
+    , m_atlas_transient_image_threshold(0)
     , m_allocated(false)
 {
 
@@ -170,6 +171,11 @@ Atlas::Atlas(const QSize &size)
 
     m_use_bgra_fallback = qEnvironmentVariableIsSet("QSG_ATLAS_USE_BGRA_FALLBACK");
     m_debug_overlay = qEnvironmentVariableIsSet("QSG_ATLAS_OVERLAY");
+
+    // images smaller than this will retain their QImage.
+    // by default no images are retained (favoring memory)
+    // set to a very large value to retain all images (allowing quick removal from the atlas)
+    m_atlas_transient_image_threshold = qt_sg_envInt("QSG_ATLAS_TRANSIENT_IMAGE_THRESHOLD", 0);
 }
 
 Atlas::~Atlas()
@@ -392,7 +398,10 @@ void Atlas::bind(QSGTexture::Filtering filtering)
         } else {
             upload(t);
         }
-        t->releaseImage();
+        const QSize textureSize = t->textureSize();
+        if (textureSize.width() > m_atlas_transient_image_threshold ||
+                textureSize.height() > m_atlas_transient_image_threshold)
+            t->releaseImage();
 
         qCDebug(QSG_LOG_TIME_TEXTURE).nospace() << "atlastexture uploaded in: " << qsg_renderer_timer.elapsed()
                                            << "ms (" << t->textureSize().width() << "x"