Qt 5.11 | Qt Quick | Scene Graph - Two Texture Providers | xorblender.cpp Example File

Qt 5.11.3 Reference Documentation

# xorblender.cpp Example File

scenegraph/twotextureproviders/xorblender.cpp

      /****************************************************************************
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      ** Copyright (C) 2014 Gunnar Sletta <gunnar@sletta.org>
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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 override {
              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 override {
              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 override {
              return QList<QByteArray>() << "aVertex" << "aTexCoord";
          }

          void updateState(const XorBlendState *state, const XorBlendState *) override {
              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() override {
              // 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 = nullptr;
              m_material->state()->texture2 = nullptr;
              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.data(), &QSGTextureProvider::textureChanged, this, &XorNode::textureChange, Qt::DirectConnection);
              connect(m_provider2.data(), &QSGTextureProvider::textureChanged, this, &XorNode::textureChange, Qt::DirectConnection);
          }

          void preprocess() override {
              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(nullptr)
          , m_source2(nullptr)
          , 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 nullptr;
          }

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

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