software: Fix potential infinite loop with ShaderEffect

With the software backend we entered an infinite loop when having
ShaderEffect items. The previous change introducing the usage of polish
requests to defer shader processing was a bit too keen on trying over and
over again: there is exactly one retry attempt we need, not more. If the
second fails too and everything looks initialized and ready, then we know
the backend has no shader effect support so it is futile to try again.

Change-Id: Ibaaefd45e5b26d0be42dbe7f9c080363b7a939bf
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 10 insertions, 2 deletions

diff --git a/src/quick/items/qquickgenericshadereffect.cpp b/src/quick/items/qquickgenericshadereffect.cpp
index 683453d4ee..9714f39663 100644
--- a/src/quick/items/qquickgenericshadereffect.cpp
+++ b/src/quick/items/qquickgenericshadereffect.cpp
@@ -305,8 +305,16 @@ void QQuickGenericShaderEffect::maybeUpdateShaders()
         m_vertNeedsUpdate = !updateShader(Vertex, m_vertShader);
     if (m_fragNeedsUpdate)
         m_fragNeedsUpdate = !updateShader(Fragment, m_fragShader);
-    if (m_vertNeedsUpdate || m_fragNeedsUpdate)
-        m_item->polish();
+    if (m_vertNeedsUpdate || m_fragNeedsUpdate) {
+        // This function is invoked either from componentComplete or in a
+        // response to a previous invocation's polish() request. If this is
+        // case #1 then updateShader can fail due to not having a window or
+        // scenegraph ready. Schedule the polish to try again later. In case #2
+        // the backend probably does not have shadereffect support so there is
+        // nothing to do for us here.
+        if (!m_item->window() || !m_item->window()->isSceneGraphInitialized())
+            m_item->polish();
+    }
 }
 
 void QQuickGenericShaderEffect::handleItemChange(QQuickItem::ItemChange change, const QQuickItem::ItemChangeData &value)