D3D12: Fix 'ShaderEffect in a ShaderEffectSource as property value'

Import (and clean up) the dropshadow from the shadereffects example.
This is very useful since it tests a lot more paths and cases than
the wobble.

To overcome the issue of not having some of functionality available before
the item is added to a window, make QQuickGenericShaderEffect smarter and
enhance the documentation.

The handling of vertical mirroring is revised. The GLSL and HLSL version of
the dropshadow shaders produce correct, identical output now.

Change-Id: I94800997bfba781140d80720eb6f340cda480747
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

4 files changed, 96 insertions, 25 deletions

diff --git a/src/quick/items/qquickgenericshadereffect.cpp b/src/quick/items/qquickgenericshadereffect.cpp
index ae34a65a2f..49ed25f799 100644
--- a/src/quick/items/qquickgenericshadereffect.cpp
+++ b/src/quick/items/qquickgenericshadereffect.cpp
@@ -61,6 +61,7 @@ QQuickGenericShaderEffect::QQuickGenericShaderEffect(QQuickShaderEffect *item, Q
     , m_mgr(nullptr)
     , m_dirty(0)
 {
+    connect(m_item, SIGNAL(windowChanged(QQuickWindow*)), this, SLOT(itemWindowChanged(QQuickWindow*)));
 }
 
 QQuickGenericShaderEffect::~QQuickGenericShaderEffect()
@@ -76,7 +77,11 @@ QQuickGenericShaderEffect::~QQuickGenericShaderEffect()
 
 void QQuickGenericShaderEffect::setFragmentShader(const QByteArray &src)
 {
-    if (m_fragShader.constData() == src.constData())
+    // Compare the actual values since they are often just filenames.
+    // Optimizing by comparing constData() is a bad idea since seemingly static
+    // strings in QML may in fact have different addresses when a binding
+    // triggers assigning the "same" value to the property.
+    if (m_fragShader == src)
         return;
 
     m_fragShader = src;
@@ -91,7 +96,7 @@ void QQuickGenericShaderEffect::setFragmentShader(const QByteArray &src)
 
 void QQuickGenericShaderEffect::setVertexShader(const QByteArray &src)
 {
-    if (m_vertShader.constData() == src.constData())
+    if (m_vertShader == src)
         return;
 
     m_vertShader = src;
@@ -192,7 +197,7 @@ QQuickShaderEffect::Status QQuickGenericShaderEffect::status() const
 {
     QSGGuiThreadShaderEffectManager *mgr = shaderEffectManager();
     if (!mgr)
-        return QQuickShaderEffect::Error;
+        return QQuickShaderEffect::Uncompiled;
 
     return QQuickShaderEffect::Status(mgr->status());
 }
@@ -201,7 +206,7 @@ QQuickShaderEffect::ShaderType QQuickGenericShaderEffect::shaderType() const
 {
     QSGGuiThreadShaderEffectManager *mgr = shaderEffectManager();
     if (!mgr)
-        return QQuickShaderEffect::HLSL;
+        return QQuickShaderEffect::ShaderType(0);
 
     return QQuickShaderEffect::ShaderType(mgr->shaderType());
 }
@@ -210,7 +215,7 @@ QQuickShaderEffect::ShaderCompilationType QQuickGenericShaderEffect::shaderCompi
 {
     QSGGuiThreadShaderEffectManager *mgr = shaderEffectManager();
     if (!mgr)
-        return QQuickShaderEffect::OfflineCompilation;
+        return QQuickShaderEffect::ShaderCompilationType(0);
 
     return QQuickShaderEffect::ShaderCompilationType(mgr->shaderCompilationType());
 }
@@ -219,7 +224,7 @@ QQuickShaderEffect::ShaderSourceType QQuickGenericShaderEffect::shaderSourceType
 {
     QSGGuiThreadShaderEffectManager *mgr = shaderEffectManager();
     if (!mgr)
-        return QQuickShaderEffect::ShaderByteCode;
+        return QQuickShaderEffect::ShaderSourceType(0);
 
     return QQuickShaderEffect::ShaderSourceType(mgr->shaderSourceType());
 }
@@ -348,20 +353,41 @@ QSGGuiThreadShaderEffectManager *QQuickGenericShaderEffect::shaderEffectManager(
         if (w && w->isSceneGraphInitialized()) {
             m_mgr = QQuickWindowPrivate::get(w)->context->sceneGraphContext()->createGuiThreadShaderEffectManager();
             if (m_mgr) {
-                QObject::connect(m_mgr, SIGNAL(logAndStatusChanged()), m_item, SIGNAL(logChanged()));
-                QObject::connect(m_mgr, SIGNAL(logAndStatusChanged()), m_item, SIGNAL(statusChanged()));
-                QObject::connect(m_mgr, SIGNAL(textureChanged()), this, SLOT(markGeometryDirtyAndUpdateIfSupportsAtlas()));
+                connect(m_mgr, SIGNAL(logAndStatusChanged()), m_item, SIGNAL(logChanged()));
+                connect(m_mgr, SIGNAL(logAndStatusChanged()), m_item, SIGNAL(statusChanged()));
+                connect(m_mgr, SIGNAL(textureChanged()), this, SLOT(markGeometryDirtyAndUpdateIfSupportsAtlas()));
             }
         } else if (!w) {
-            qWarning("ShaderEffect: Backend specifics cannot be queried until the item has a window");
+            // Wait until itemWindowChanged() gets called. Return null for now.
         } else {
-            qWarning("ShaderEffect: Backend specifics cannot be queried until the scenegraph has initialized");
+            // Have window, but no scenegraph -> ensure the signal is connected. Return null for now.
+            const_cast<QQuickGenericShaderEffect *>(this)->itemWindowChanged(w);
         }
     }
 
     return m_mgr;
 }
 
+void QQuickGenericShaderEffect::itemWindowChanged(QQuickWindow *w)
+{
+    if (w) {
+        if (w->isSceneGraphInitialized())
+            backendChanged();
+        else
+            connect(w, SIGNAL(sceneGraphInitialized()), this, SLOT(backendChanged()), Qt::UniqueConnection);
+    }
+}
+
+void QQuickGenericShaderEffect::backendChanged()
+{
+    disconnect(m_item->window(), SIGNAL(sceneGraphInitialized()), this, SLOT(backendChanged()));
+    emit m_item->logChanged();
+    emit m_item->statusChanged();
+    emit m_item->shaderTypeChanged();
+    emit m_item->shaderCompilationTypeChanged();
+    emit m_item->shaderSourceTypeChanged();
+}
+
 void QQuickGenericShaderEffect::disconnectSignals(Shader shaderType)
 {
     for (auto &sm : m_signalMappers[shaderType]) {
diff --git a/src/quick/items/qquickgenericshadereffect_p.h b/src/quick/items/qquickgenericshadereffect_p.h
index 5f6652ec32..2af7d1156a 100644
--- a/src/quick/items/qquickgenericshadereffect_p.h
+++ b/src/quick/items/qquickgenericshadereffect_p.h
@@ -105,6 +105,8 @@ private slots:
     void sourceDestroyed(QObject *object);
     void markGeometryDirtyAndUpdate();
     void markGeometryDirtyAndUpdateIfSupportsAtlas();
+    void itemWindowChanged(QQuickWindow *w);
+    void backendChanged();
 
 private:
     QSGGuiThreadShaderEffectManager *shaderEffectManager() const;
diff --git a/src/quick/items/qquickshadereffect.cpp b/src/quick/items/qquickshadereffect.cpp
index 36fc7ef3c8..560c49fb7c 100644
--- a/src/quick/items/qquickshadereffect.cpp
+++ b/src/quick/items/qquickshadereffect.cpp
@@ -321,6 +321,12 @@ QT_BEGIN_NAMESPACE
         \endcode
     \endtable
 
+    \note With OpenGL the \c y coordinate runs from bottom to top whereas with
+    Direct 3D it goes top to bottom. For shader effect sources Qt Quick hides
+    the difference by treating QtQuick::ShaderEffectSource::textureMirroring as
+    appropriate, meaning texture coordinates in HLSL version of the shaders
+    will not need any adjustments compared to the equivalent GLSL code.
+
     \section1 ShaderEffect and Item Layers
 
     The ShaderEffect type can be combined with \l {Item Layers} {layered items}.
@@ -644,12 +650,23 @@ QQuickShaderEffect::Status QQuickShaderEffect::status() const
 }
 
 /*!
-    \qmlproperty QtQuick::ShaderEffect::ShaderType QtQuick::ShaderEffect::shaderType
+    \qmlproperty enumeration QtQuick::ShaderEffect::shaderType
 
     This property contains the shading language supported by the current Qt
     Quick backend the application is using.
 
-    With OpenGL the value is GLSL.
+    \list
+    \li ShaderEffect.UnknownShadingLanguage - Not yet known due to no window and scenegraph associated
+    \li ShaderEffect.GLSL - GLSL or GLSL ES
+    \li ShaderEffect.HLSL - HLSL
+    \endlist
+
+    \note The value is only up-to-date once the item is associated with a
+    window and the window's scenegraph has initialized. Bindings relying on the
+    value have to keep this in mind since the value may change from
+    ShaderEffect.UnknownShadingLanguage to the actual value after component
+    initialization is complete. This is particularly relevant for ShaderEffect
+    items inside ShaderEffectSource items set as property values.
 
     \since 5.8
     \since QtQuick 2.8
@@ -667,14 +684,26 @@ QQuickShaderEffect::ShaderType QQuickShaderEffect::shaderType() const
 }
 
 /*!
-    \qmlproperty QtQuick::ShaderEffect::ShaderCompilationType QtQuick::ShaderEffect::shaderCompilationType
+    \qmlproperty enumeration QtQuick::ShaderEffect::shaderCompilationType
 
     This property contains a bitmask of the shader compilation approaches
     supported by the current Qt Quick backend the application is using.
 
-    With OpenGL the value is RuntimeCompilation, which corresponds to the
-    traditional way of using ShaderEffect. Non-OpenGL backends are expected to
-    focus more on OfflineCompilation, however.
+    \list
+    \li ShaderEffect.RuntimeCompilation
+    \li ShaderEffect.OfflineCompilation
+    \endlist
+
+    With OpenGL the value is ShaderEffect.RuntimeCompilation, which corresponds
+    to the traditional way of using ShaderEffect. Non-OpenGL backends are
+    expected to focus more on ShaderEffect.OfflineCompilation, however.
+
+    \note The value is only up-to-date once the item is associated with a
+    window and the window's scenegraph has initialized. Bindings relying on the
+    value have to keep this in mind since the value may change from \c 0 to the
+    actual bitmask after component initialization is complete. This is
+    particularly relevant for ShaderEffect items inside ShaderEffectSource
+    items set as property values.
 
     \since 5.8
     \since QtQuick 2.8
@@ -692,16 +721,30 @@ QQuickShaderEffect::ShaderCompilationType QQuickShaderEffect::shaderCompilationT
 }
 
 /*!
-    \qmlproperty QtQuick::ShaderEffect::ShaderSourceType QtQuick::ShaderEffect::shaderSourceType
+    \qmlproperty enumeration QtQuick::ShaderEffect::shaderSourceType
 
     This property contains a bitmask of the supported ways of providing shader
     sources.
 
-    With OpenGL the value is ShaderSourceString, which corresponds to the
-    traditional way of inlining GLSL source code into QML. Other, non-OpenGL Qt
-    Quick backends may however decide not to support inlined shader sources, or
-    even shader sources at all. In this case shaders are expected to be
-    pre-compiled into formats like SPIR-V or D3D shader bytecode.
+    \list
+    \li ShaderEffect.ShaderSourceString
+    \li ShaderEffect.ShaderSourceFile
+    \li ShaderEffect.ShaderByteCode
+    \endlist
+
+    With OpenGL the value is ShaderEffect.ShaderSourceString, which corresponds
+    to the traditional way of inlining GLSL source code into QML. Other,
+    non-OpenGL Qt Quick backends may however decide not to support inlined
+    shader sources, or even shader sources at all. In this case shaders are
+    expected to be pre-compiled into formats like SPIR-V or D3D shader
+    bytecode.
+
+    \note The value is only up-to-date once the item is associated with a
+    window and the window's scenegraph has initialized. Bindings relying on the
+    value have to keep this in mind since the value may change from \c 0 to the
+    actual bitmask after component initialization is complete. This is
+    particularly relevant for ShaderEffect items inside ShaderEffectSource
+    items set as property values.
 
     \since 5.8
     \since QtQuick 2.8
diff --git a/src/quick/items/qquickshadereffect_p.h b/src/quick/items/qquickshadereffect_p.h
index 390703350f..0410514c36 100644
--- a/src/quick/items/qquickshadereffect_p.h
+++ b/src/quick/items/qquickshadereffect_p.h
@@ -90,9 +90,9 @@ public:
     Q_ENUM(Status)
 
     enum ShaderType {
+        UnknownShadingLanguage,
         GLSL,
-        HLSL,
-        Metal
+        HLSL
     };
     Q_ENUM(ShaderType)