- Qt 5.5
- Qt Quick
- Scene Graph - Two Texture Providers
- xorblender.cpp Example File
- Qt 5.5.1 Reference Documentation

# xorblender.cpp Example File

scenegraph/twotextureproviders/xorblender.cpp

    /****************************************************************************
    **
    ** Copyright (C) 2014 Gunnar Sletta <gunnar@sletta.org>
    ** Contact: http://www.qt.io/licensing/
    **
    ** This file is part of the examples of the Qt Toolkit.
    **
    ** $QT_BEGIN_LICENSE:BSD$
    ** 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.
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    **     notice, this list of conditions and the following disclaimer in
    **     the documentation and/or other materials provided with the
    **     distribution.
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    **     contributors may be used to endorse or promote products derived
    **     from this software without specific prior written permission.
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    **
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    ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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    #include "xorblender.h"

    #include <QtCore/QPointer>

    #include <QtGui/QOpenGLContext>
    #include <QtGui/QOpenGLFunctions>

    #include <QtQuick/QSGSimpleMaterial>
    #include <QtQuick/QSGTexture>
    #include <QtQuick/QSGGeometryNode>
    #include <QtQuick/QSGTextureProvider>

    /* This example could just as well have been implemented all in QML using
     * a ShaderEffect, and for 90% of all usecases, using a ShaderEffect will
     * be sufficient. This example exists to illustrate how to consume
     * texture providers from C++ and how to use multiple texture sources in
     * a custom material.
     */

    struct XorBlendState {
        QSGTexture *texture1;
        QSGTexture *texture2;
    };

    class XorBlendShader : public QSGSimpleMaterialShader<XorBlendState>
    {
        QSG_DECLARE_SIMPLE_SHADER(XorBlendShader, XorBlendState)
    public:

        const char *vertexShader() const {
            return
            "attribute highp vec4 aVertex;              \n"
            "attribute highp vec2 aTexCoord;            \n"
            "uniform highp mat4 qt_Matrix;              \n"
            "varying highp vec2 vTexCoord;              \n"
            "void main() {                              \n"
            "    gl_Position = qt_Matrix * aVertex;     \n"
            "    vTexCoord = aTexCoord;                 \n"
            "}";
        }

        const char *fragmentShader() const {
            return
            "uniform lowp float qt_Opacity;                                             \n"
            "uniform lowp sampler2D uSource1;                                           \n"
            "uniform lowp sampler2D uSource2;                                           \n"
            "varying highp vec2 vTexCoord;                                              \n"
            "void main() {                                                              \n"
            "    lowp vec4 p1 = texture2D(uSource1, vTexCoord);                         \n"
            "    lowp vec4 p2 = texture2D(uSource2, vTexCoord);                         \n"
            "    gl_FragColor = (p1 * (1.0 - p2.a) + p2 * (1.0 - p1.a)) * qt_Opacity;   \n"
            "}";
        }

        QList<QByteArray> attributes() const {
            return QList<QByteArray>() << "aVertex" << "aTexCoord";
        }

        void updateState(const XorBlendState *state, const XorBlendState *) {
            QOpenGLFunctions *f = QOpenGLContext::currentContext()->functions();
            // We bind the textures in inverse order so that we leave the updateState
            // function with GL_TEXTURE0 as the active texture unit. This is maintain
            // the "contract" that updateState should not mess up the GL state beyond
            // what is needed for this material.
            f->glActiveTexture(GL_TEXTURE1);
            state->texture2->bind();
            f->glActiveTexture(GL_TEXTURE0);
            state->texture1->bind();
        }

        void resolveUniforms() {
            // The texture units never change, only the texturess we bind to them so
            // we set these once and for all here.
            program()->setUniformValue("uSource1", 0); // GL_TEXTURE0
            program()->setUniformValue("uSource2", 1); // GL_TEXTURE1
        }
    };

    /* The rendering is split into two nodes. The top-most node is not actually
     * rendering anything, but is responsible for managing the texture providers.
     * The XorNode also has a geometry node internally which it uses to render
     * the texture providers using the XorBlendShader when all providers and
     * textures are all present.
     *
     * The texture providers are updated solely on the render thread (when rendering
     * is happening on a separate thread). This is why we are using preprocess
     * and direct signals between the the texture providers and the node rather
     * than updating state in updatePaintNode.
     */
    class XorNode : public QObject, public QSGNode
    {
        Q_OBJECT
    public:
        XorNode(QSGTextureProvider *p1, QSGTextureProvider *p2)
            : m_provider1(p1)
            , m_provider2(p2)
        {
            setFlag(QSGNode::UsePreprocess, true);

            // Set up material so it is all set for later..
            m_material = XorBlendShader::createMaterial();
            m_material->state()->texture1 = 0;
            m_material->state()->texture2 = 0;
            m_material->setFlag(QSGMaterial::Blending);
            m_node.setMaterial(m_material);
            m_node.setFlag(QSGNode::OwnsMaterial);

            // Set up geometry, actual vertices will be initialized in updatePaintNode
            m_node.setGeometry(new QSGGeometry(QSGGeometry::defaultAttributes_TexturedPoint2D(), 4));
            m_node.setFlag(QSGNode::OwnsGeometry);

            // If this node is used as in a shader effect source, we need to propegate
            // changes that will occur in this node outwards.
            connect(m_provider1, SIGNAL(textureChanged()), this, SLOT(textureChange()), Qt::DirectConnection);
            connect(m_provider2, SIGNAL(textureChanged()), this, SLOT(textureChange()), Qt::DirectConnection);
        }

        void preprocess() {
            XorBlendState *state = m_material->state();
            // Update the textures from the providers, calling into QSGDynamicTexture if required
            if (m_provider1) {
                state->texture1 = m_provider1->texture();
                if (QSGDynamicTexture *dt1 = qobject_cast<QSGDynamicTexture *>(state->texture1))
                    dt1->updateTexture();
            }
            if (m_provider2) {
                state->texture2 = m_provider2->texture();
                if (QSGDynamicTexture *dt2 = qobject_cast<QSGDynamicTexture *>(state->texture2))
                    dt2->updateTexture();
            }

            // Remove node from the scene graph if it is there and either texture is missing...
            if (m_node.parent() && (!state->texture1 || !state->texture2))
                removeChildNode(&m_node);

            // Add it if it is not already there and both textures are present..
            else if (!m_node.parent() && state->texture1 && state->texture2)
                appendChildNode(&m_node);
        }

        void setRect(const QRectF &rect) {
            // Update geometry if it has changed and mark the change in the scene graph.
            if (m_rect != rect) {
                m_rect = rect;
                QSGGeometry::updateTexturedRectGeometry(m_node.geometry(), m_rect, QRectF(0, 0, 1, 1));
                m_node.markDirty(QSGNode::DirtyGeometry);
            }
        }

    public slots:
        void textureChange() {
            // When our sources change, we will look different, so signal the change to the
            // scene graph.
            markDirty(QSGNode::DirtyMaterial);
        }

    private:
        QRectF m_rect;
        QSGSimpleMaterial<XorBlendState> *m_material;
        QSGGeometryNode m_node;
        QPointer<QSGTextureProvider> m_provider1;
        QPointer<QSGTextureProvider> m_provider2;
    };

    XorBlender::XorBlender(QQuickItem *parent)
        : QQuickItem(parent)
        , m_source1(0)
        , m_source2(0)
        , m_source1Changed(false)
        , m_source2Changed(false)
    {
        setFlag(ItemHasContents, true);
    }

    void XorBlender::setSource1(QQuickItem *i)
    {
        if (i == m_source1)
            return;
        m_source1 = i;
        emit source1Changed(m_source1);
        m_source1Changed = true;
        update();
    }

    void XorBlender::setSource2(QQuickItem *i)
    {
        if (i == m_source2)
            return;
        m_source2 = i;
        emit source2Changed(m_source2);
        m_source2Changed = true;
        update();
    }

    QSGNode *XorBlender::updatePaintNode(QSGNode *old, UpdatePaintNodeData *)
    {
        // Check if our input is valid and abort if not, deleting the old node.
        bool abort = false;
        if (!m_source1 || !m_source1->isTextureProvider()) {
            qDebug() << "source1 is missing or not a texture provider";
            abort = true;
        }
        if (!m_source2 || !m_source2->isTextureProvider()) {
            qDebug() << "source2 is missing or not a texture provider";
            abort = true;
        }
        if (abort) {
            delete old;
            return 0;
        }

        XorNode *node = static_cast<XorNode *>(old);

        // If the sources have changed, recreate the nodes
        if (m_source1Changed || m_source2Changed) {
            delete node;
            node = 0;
            m_source1Changed = false;
            m_source2Changed = false;
        }

        // Create a new XorNode for us to render with.
        if (!node)
            node = new XorNode(m_source1->textureProvider(), m_source2->textureProvider());

        // Update the geometry of the node to match the new bounding rect
        node->setRect(boundingRect());

        return node;
    }

    #include "xorblender.moc"