Add samples property for Item.layer and ShaderEffectSource

[ChangeLog][Qt Quick] Added the properties ShaderEffectSource.samples
and Item.layer.samples to allow requesting MSAA rendering of an item
subtree, without enabling multisampling for the entire scene.

Task-number: QTBUG-58945
Change-Id: I9102cfabba10d4dc1e7ad2aa0b258ada6d9a5a47
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 40 insertions, 0 deletions

diff --git a/src/quick/items/qquickitem.cpp b/src/quick/items/qquickitem.cpp
index f7b9a58329..22ee3f39e4 100644
--- a/src/quick/items/qquickitem.cpp
+++ b/src/quick/items/qquickitem.cpp
@@ -7865,6 +7865,7 @@ QQuickItemLayer::QQuickItemLayer(QQuickItem *item)
     , m_effect(0)
     , m_effectSource(0)
     , m_textureMirroring(QQuickShaderEffectSource::MirrorVertically)
+    , m_samples(0)
 {
 }
 
@@ -7939,6 +7940,7 @@ void QQuickItemLayer::activate()
     m_effectSource->setWrapMode(m_wrapMode);
     m_effectSource->setFormat(m_format);
     m_effectSource->setTextureMirroring(m_textureMirroring);
+    m_effectSource->setSamples(m_samples);
 
     if (m_effectComponent)
         activateEffect();
@@ -8232,6 +8234,44 @@ void QQuickItemLayer::setTextureMirroring(QQuickShaderEffectSource::TextureMirro
 }
 
 /*!
+    \qmlproperty enumeration QtQuick::Item::layer.samples
+    \since 5.10
+
+    This property allows requesting multisampled rendering in the layer.
+
+    By default multisampling is enabled whenever multisampling is
+    enabled for the entire window, assuming the scenegraph renderer in
+    use and the underlying graphics API supports this.
+
+    By setting the value to 2, 4, etc. multisampled rendering can be requested
+    for a part of the scene without enabling multisampling for the entire
+    scene. This way multisampling is applied only to a given subtree, which can
+    lead to significant performance gains since multisampling is not applied to
+    other parts of the scene.
+
+    \note Enabling multisampling can be potentially expensive regardless of the
+    layer's size, as it incurs a hardware and driver dependent performance and
+    memory cost.
+
+    \note This property is only functional when support for multisample
+    renderbuffers and framebuffer blits is available. Otherwise the value is
+    silently ignored.
+ */
+
+void QQuickItemLayer::setSamples(int count)
+{
+    if (m_samples == count)
+        return;
+
+    m_samples = count;
+
+    if (m_effectSource)
+        m_effectSource->setSamples(m_samples);
+
+    emit samplesChanged(count);
+}
+
+/*!
     \qmlproperty string QtQuick::Item::layer.samplerName
 
     Holds the name of the effect's source texture property.