Improve stencil clipping with NVPR

So that it actually performs when clipping the tiger. Add an example.

Change-Id: I7c1c6244710febdb6b02852ebca094665adec417
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

9 files changed, 177 insertions, 30 deletions

diff --git a/examples/quick/pathitem/content/item17.qml b/examples/quick/pathitem/content/item17.qml
index 0197aa5fb6..7f3f06cfb8 100644
--- a/examples/quick/pathitem/content/item17.qml
+++ b/examples/quick/pathitem/content/item17.qml
@@ -70,6 +70,7 @@ Rectangle {
             source: "tiger.qml"
             asynchronous: true
             visible: status == Loader.Ready
+            scale: 0.4
         }
     }
 }
diff --git a/examples/quick/pathitem/content/pathitem.qml b/examples/quick/pathitem/content/pathitem.qml
index e3a28b2bbe..c4a86ff8b1 100644
--- a/examples/quick/pathitem/content/pathitem.qml
+++ b/examples/quick/pathitem/content/pathitem.qml
@@ -58,6 +58,7 @@ Item {
         Component.onCompleted: {
             addExample("PathItem Gallery", "Simple path rendering examples", Qt.resolvedUrl("pathitemgallery.qml"))
             addExample("Interactive paths", "Dynamic path examples", Qt.resolvedUrl("pathiteminteract.qml"))
+            addExample("Clip My Tiger!", "Clip examples, a.k.a. What Not To Do", Qt.resolvedUrl("pathitemtigers.qml"))
         }
     }
 }
diff --git a/examples/quick/pathitem/content/pathitemtigers.qml b/examples/quick/pathitem/content/pathitemtigers.qml
new file mode 100644
index 0000000000..6c8e3a19ce
--- /dev/null
+++ b/examples/quick/pathitem/content/pathitemtigers.qml
@@ -0,0 +1,137 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQuick module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick 2.9 // to get PathItem
+
+Rectangle {
+    id: root
+    width: 1024
+    height: 768
+
+    property color col: "lightsteelblue"
+    gradient: Gradient {
+        GradientStop { position: 0.0; color: Qt.tint(root.col, "#20FFFFFF") }
+        GradientStop { position: 0.1; color: Qt.tint(root.col, "#20AAAAAA") }
+        GradientStop { position: 0.9; color: Qt.tint(root.col, "#20666666") }
+        GradientStop { position: 1.0; color: Qt.tint(root.col, "#20000000") }
+    }
+
+    Rectangle {
+        id: scissorRect
+        width: 200
+        height: 200
+        x: 150
+        property real centerY: parent.height / 2 - height / 2
+        property real dy: 0
+        y: centerY + dy
+        clip: true
+
+        Loader {
+            id: loader1
+            width: parent.width
+            height: parent.height
+            y: 25 - scissorRect.dy
+            source: "tiger.qml"
+            asynchronous: true
+            visible: status === Loader.Ready
+        }
+
+        SequentialAnimation on dy {
+            loops: Animation.Infinite
+            running: loader1.status === Loader.Ready && loader1.item.status === PathItem.Ready
+            NumberAnimation {
+                from: 0
+                to: -scissorRect.centerY
+                duration: 2000
+            }
+            NumberAnimation {
+                from: -scissorRect.centerY
+                to: scissorRect.centerY
+                duration: 4000
+            }
+            NumberAnimation {
+                from: scissorRect.centerY
+                to: 0
+                duration: 2000
+            }
+        }
+    }
+
+    // With a more complex transformation (like rotation), stenciling is used
+    // instead of scissoring, this is more expensive. It may also trigger a
+    // slower code path for PathItems, depending on the path rendering backend
+    // in use, and may affect rendering quality as well.
+    // So in short: do not do this.
+    Rectangle {
+        id: stencilRect
+        width: 300
+        height: 200
+        anchors.right: parent.right
+        anchors.rightMargin: 100
+        anchors.verticalCenter: parent.verticalCenter
+        clip: true // NB! still clips to bounding rect (not shape)
+
+        Loader {
+            id: loader2
+            width: parent.width
+            height: parent.height
+            source: "tiger.qml"
+            asynchronous: true
+            visible: status === Loader.Ready
+        }
+
+        NumberAnimation on rotation {
+            from: 0
+            to: 360
+            duration: 5000
+            loops: Animation.Infinite
+        }
+    }
+}
diff --git a/examples/quick/pathitem/content/tiger.qml b/examples/quick/pathitem/content/tiger.qml
index 7d275ba22f..a9f4abe46a 100644
--- a/examples/quick/pathitem/content/tiger.qml
+++ b/examples/quick/pathitem/content/tiger.qml
@@ -56,7 +56,6 @@ PathItem {
     asynchronous: true
 
     anchors.fill: parent
-    scale: 0.4
 
     VisualPath {
         fillColor: "#ffffff"
diff --git a/examples/quick/pathitem/pathitem.pro b/examples/quick/pathitem/pathitem.pro
index 8b606a3c50..3c12f35fd2 100644
--- a/examples/quick/pathitem/pathitem.pro
+++ b/examples/quick/pathitem/pathitem.pro
@@ -6,6 +6,7 @@ RESOURCES += pathitem.qrc
 OTHER_FILES += content/pathitem.qml \
                content/pathitemgallery.qml \
                content/pathiteminteract.qml \
+               content/pathitemtigers.qml \
                content/tiger.qml \
                content/item1.qml \
                content/item2.qml \
diff --git a/examples/quick/pathitem/pathitem.qrc b/examples/quick/pathitem/pathitem.qrc
index 5b38d90c0c..d67c918faf 100644
--- a/examples/quick/pathitem/pathitem.qrc
+++ b/examples/quick/pathitem/pathitem.qrc
@@ -7,6 +7,7 @@
         <file alias="pathitem.qml">content/pathitem.qml</file>
         <file alias="pathitemgallery.qml">content/pathitemgallery.qml</file>
         <file alias="pathiteminteract.qml">content/pathiteminteract.qml</file>
+        <file alias="pathitemtigers.qml">content/pathitemtigers.qml</file>
         <file alias="tiger.qml">content/tiger.qml</file>
         <file alias="item1.qml">content/item1.qml</file>
         <file alias="item2.qml">content/item2.qml</file>
diff --git a/src/quick/items/qquickpathitem.cpp b/src/quick/items/qquickpathitem.cpp
index 306e79dc1e..b07a7a6c06 100644
--- a/src/quick/items/qquickpathitem.cpp
+++ b/src/quick/items/qquickpathitem.cpp
@@ -587,7 +587,7 @@ QSGNode *QQuickPathItemPrivate::createNode()
 #ifndef QT_NO_OPENGL
     case QSGRendererInterface::OpenGL:
         if (QQuickPathItemNvprRenderNode::isSupported()) {
-            node = new QQuickPathItemNvprRenderNode(q);
+            node = new QQuickPathItemNvprRenderNode;
             static_cast<QQuickPathItemNvprRenderer *>(renderer)->setNode(
                 static_cast<QQuickPathItemNvprRenderNode *>(node));
         } else {
diff --git a/src/quick/items/qquickpathitemnvprrenderer.cpp b/src/quick/items/qquickpathitemnvprrenderer.cpp
index 9303f698ac..13fab2dc76 100644
--- a/src/quick/items/qquickpathitemnvprrenderer.cpp
+++ b/src/quick/items/qquickpathitemnvprrenderer.cpp
@@ -397,11 +397,6 @@ bool QQuickPathItemNvprRenderNode::nvprInited = false;
 QQuickNvprFunctions QQuickPathItemNvprRenderNode::nvpr;
 QQuickNvprMaterialManager QQuickPathItemNvprRenderNode::mtlmgr;
 
-QQuickPathItemNvprRenderNode::QQuickPathItemNvprRenderNode(QQuickPathItem *item)
-    : m_item(item)
-{
-}
-
 QQuickPathItemNvprRenderNode::~QQuickPathItemNvprRenderNode()
 {
     releaseResources();
@@ -528,6 +523,9 @@ void QQuickPathItemNvprRenderNode::updatePath(VisualPathRenderData *d)
         // count == 0 -> no dash
         nvpr.pathDashArray(d->path, d->dashPattern.count(), d->dashPattern.constData());
     }
+
+    if (d->dirty)
+        d->fallbackValid = false;
 }
 
 void QQuickPathItemNvprRenderNode::renderStroke(VisualPathRenderData *d, int strokeStencilValue, int writeMask)
@@ -568,23 +566,28 @@ void QQuickPathItemNvprRenderNode::renderFill(VisualPathRenderData *d)
 
 void QQuickPathItemNvprRenderNode::renderOffscreenFill(VisualPathRenderData *d)
 {
-    QQuickWindow *w = m_item->window();
-    const qreal dpr = w->effectiveDevicePixelRatio();
-    QSize itemSize = QSize(m_item->width(), m_item->height()) * dpr;
-    QSize rtSize = w->renderTargetSize();
-    if (rtSize.isEmpty())
-        rtSize = w->size() * dpr;
+    if (d->fallbackValid && d->fallbackFbo)
+        return;
+
+    GLfloat bb[4];
+    nvpr.getPathParameterfv(d->path, GL_PATH_STROKE_BOUNDING_BOX_NV, bb);
+    QSize sz = QSizeF(bb[2] - bb[0] + 1, bb[3] - bb[1] + 1).toSize();
+    d->fallbackSize = QSize(qMax(32, sz.width()), qMax(32, sz.height()));
+    d->fallbackTopLeft = QPointF(bb[0], bb[1]);
 
-    if (d->fallbackFbo && d->fallbackFbo->size() != itemSize) {
+    if (d->fallbackFbo && d->fallbackFbo->size() != d->fallbackSize) {
         delete d->fallbackFbo;
         d->fallbackFbo = nullptr;
     }
     if (!d->fallbackFbo)
-        d->fallbackFbo = new QOpenGLFramebufferObject(itemSize, QOpenGLFramebufferObject::CombinedDepthStencil);
+        d->fallbackFbo = new QOpenGLFramebufferObject(d->fallbackSize, QOpenGLFramebufferObject::CombinedDepthStencil);
     if (!d->fallbackFbo->bind())
         return;
 
-    f->glViewport(0, 0, itemSize.width(), itemSize.height());
+    GLint prevViewport[4];
+    f->glGetIntegerv(GL_VIEWPORT, prevViewport);
+
+    f->glViewport(0, 0, d->fallbackSize.width(), d->fallbackSize.height());
     f->glDisable(GL_DEPTH_TEST);
     f->glClearColor(0, 0, 0, 0);
     f->glClearStencil(0);
@@ -592,16 +595,20 @@ void QQuickPathItemNvprRenderNode::renderOffscreenFill(VisualPathRenderData *d)
     f->glStencilFunc(GL_NOTEQUAL, 0, 0xFF);
     f->glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
 
-    nvpr.matrixLoadIdentity(GL_PATH_MODELVIEW_NV);
+    QMatrix4x4 mv;
+    mv.translate(-d->fallbackTopLeft.x(), -d->fallbackTopLeft.y());
+    nvpr.matrixLoadf(GL_PATH_MODELVIEW_NV, mv.constData());
     QMatrix4x4 proj;
-    proj.ortho(0, itemSize.width(), itemSize.height(), 0, 1, -1);
+    proj.ortho(0, d->fallbackSize.width(), d->fallbackSize.height(), 0, 1, -1);
     nvpr.matrixLoadf(GL_PATH_PROJECTION_NV, proj.constData());
 
     renderFill(d);
 
     d->fallbackFbo->release();
     f->glEnable(GL_DEPTH_TEST);
-    f->glViewport(0, 0, rtSize.width(), rtSize.height());
+    f->glViewport(prevViewport[0], prevViewport[1], prevViewport[2], prevViewport[3]);
+
+    d->fallbackValid = true;
 }
 
 void QQuickPathItemNvprRenderNode::setupStencilForCover(bool stencilClip, int sv)
@@ -655,8 +662,8 @@ void QQuickPathItemNvprRenderNode::render(const RenderState *state)
     for (VisualPathRenderData &d : m_vp) {
         updatePath(&d);
 
-        const bool hasFill = !qFuzzyIsNull(d.fillColor.w()) || d.fillGradientActive;
-        const bool hasStroke = d.strokeWidth >= 0.0f && !qFuzzyIsNull(d.strokeColor.w());
+        const bool hasFill = d.hasFill();
+        const bool hasStroke = d.hasStroke();
 
         if (hasFill && stencilClip) {
             // Fall back to a texture when complex clipping is in use and we have
@@ -686,8 +693,10 @@ void QQuickPathItemNvprRenderNode::render(const RenderState *state)
                     m_fallbackBlitter.create();
                 f->glStencilFunc(GL_EQUAL, sv, 0xFF);
                 f->glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
+                QMatrix4x4 mv = *matrix();
+                mv.translate(d.fallbackTopLeft.x(), d.fallbackTopLeft.y());
                 m_fallbackBlitter.texturedQuad(d.fallbackFbo->texture(), d.fallbackFbo->size(),
-                                               *state->projectionMatrix(), *matrix(),
+                                               *state->projectionMatrix(), mv,
                                                inheritedOpacity());
             }
         }
@@ -729,11 +738,6 @@ QSGRenderNode::RenderingFlags QQuickPathItemNvprRenderNode::flags() const
     return DepthAwareRendering; // avoid hitting the less optimal no-opaque-batch path in the renderer
 }
 
-QRectF QQuickPathItemNvprRenderNode::rect() const
-{
-    return QRect(0, 0, m_item->width(), m_item->height());
-}
-
 bool QQuickPathItemNvprRenderNode::isSupported()
 {
     static const bool nvprDisabled = qEnvironmentVariableIntValue("QT_NO_NVPR") != 0;
diff --git a/src/quick/items/qquickpathitemnvprrenderer_p.h b/src/quick/items/qquickpathitemnvprrenderer_p.h
index 1617de17e6..61f8b5ebb9 100644
--- a/src/quick/items/qquickpathitemnvprrenderer_p.h
+++ b/src/quick/items/qquickpathitemnvprrenderer_p.h
@@ -176,14 +176,12 @@ private:
 class QQuickPathItemNvprRenderNode : public QSGRenderNode
 {
 public:
-    QQuickPathItemNvprRenderNode(QQuickPathItem *item);
     ~QQuickPathItemNvprRenderNode();
 
     void render(const RenderState *state) override;
     void releaseResources() override;
     StateFlags changedStates() const override;
     RenderingFlags flags() const override;
-    QRectF rect() const override;
 
     static bool isSupported();
 
@@ -204,6 +202,12 @@ private:
         bool fillGradientActive;
         QQuickPathItemGradientCache::GradientDesc fillGradient;
         QOpenGLFramebufferObject *fallbackFbo = nullptr;
+        bool fallbackValid = false;
+        QSize fallbackSize;
+        QPointF fallbackTopLeft;
+
+        bool hasFill() const { return !qFuzzyIsNull(fillColor.w()) || fillGradientActive; }
+        bool hasStroke() const { return strokeWidth >= 0.0f && !qFuzzyIsNull(strokeColor.w()); }
     };
 
     void updatePath(VisualPathRenderData *d);
@@ -216,7 +220,6 @@ private:
     static QQuickNvprFunctions nvpr;
     static QQuickNvprMaterialManager mtlmgr;
 
-    QQuickPathItem *m_item;
     QQuickNvprBlitter m_fallbackBlitter;
     QOpenGLExtraFunctions *f = nullptr;