Tutorial for 3D Scene Graph and Nodes

• 3D Scenes and Nodes
• 3D Node Transformations
• 3D Node Appearance
• 3D Scene Graph Dynamics
• 3D Render Order
• Searching for Nodes with SearchTreeTraverser
• Vertex Geometry Builder
• Vertex Geometry Modifier
• Candera 3D Listeners

3D Scenes and Nodes

Scenes and Nodes

Candera::Node is an abstract base class for all scene graph nodes.

Each node defines a local coordinate system relative to the coordinate system of the parent node. The functionality to define the local coordinate system is derived from Candera::Transformable and consists of following components:

If the node is transformed from the local coordinate system to the world's coordinate system, then the node's local transformation is multiplied with all its parent's transformations. A node can also store a set of nodes as its children but a node can only have one parent at a time. Cycles are prohibited. The nodes alpha value is multiplied with the alpha value of its descendent nodes.

Candera::Scene is the top level scene node which cannot be part of any other node.

3D Node Transformations

3D Node Manipulation Example

To illustrate basic node transformation operations, the NodeManipulationWidget_3D and the DisplayPositionWidget3D part of the Tutorial Widgets can be used. An usage example for NodeManipulationWidget_3D widget is presented in NodeManipulationSolution_3D solution provided in the content folder of cgi_studio_player.

Please consider:

Translations

Once the NodeManipulationWidget_3D is linked to a node from the static scene tree and enabled, the position coordinates can be set in the Player for this property to change the position.

        // Set node position
        node->SetPosition(m_position);
        // end Set node position

Use TranslateX property to move the node on the x axis with a delta value only. Candera::Transformable::Translate adds the given Vector to the actual position .

       // Translate node on x axis
        node->Translate(Vector3(m_translateX, 0.0F, 0.0F));
        // end Translate node on x axis

Rotations

Similar to translation, rotation can also be applied via Candera::Transformable::SetRotation() or Candera::Transformable::Rotate().

        // Set node rotation
        node->SetRotation(m_rotation);
        // end Set node rotation

Scaling

Again there is also a Candera::Transformable::SetScale and Candera::Transformable::Scale method.

        // set node scale
        node->SetScale(m_scale);
        // end node scale

Pivot Point

It is possible to change your pivot point with the Candera::Transformable::TranslatePivotPoint (or Candera::Transformable::SetPivotPoint) method. The pivot point can be used to define e.g. the rotation point that the node should rotate around. It affects the scaling too.

How to get the screen space coordinates of a node

With the DisplayPositionWidget3D you can retrieve the screen coordinates of an associated node. Please consider that a node and a camera have to be selected in the widget. In the solution the widget is disabled by default. To see the output of the node's display position, enabling the widget and log filter (via CgiAppLog -> Info) in SceneComposer is mandatory. To get the screen space coordinates of an associated node you need the function Candera::Math3D::TransformPointToScreen, which transforms a point in world space into a point in screen space.

3D Node Appearance

Description

Candera::Appearance groups following render attributes:

Render attributes define the distinctive visualization of a geometry like Candera::Mesh, Candera::Billboard, and Candera::PointSprite. Further, render attributes can be shared across multiple objects, which conserve memory and enable sharing of appearance characteristics.

A Candera::Appearance object is mandatory for any object in order to get rendered. Per default no Appearance attributes are attached.

If the Appearance is activated, all render attributes that are set become activated. If no RenderMode is defined (null), then the default RenderMode is used instead.

Appearance: Material

Material Attributes

Candera::Material describes the color attributes of an object's surface and is primarily used for lighting computations. If no material is set, lighting calculations in associated shaders can not be applied.

The color attributes are defined as follows:

Furthermore with Specular Power the sharpness of a specular highlight, if lit by specular light, can be defined.

Create a new Material

    m_material = Material::Create();

Set Colors

This sample code shows how to change the ambient color, the code for changing the diffuse color, the emissive color or the specular color looks similarly.

    // Set ambient color
    if (node->GetAppearance() != 0 && node->GetAppearance()->GetMaterial() != 0){
        node->GetAppearance()->GetMaterial()->SetAmbient(m_color);
    }
    // end Set ambient color

Appearance: Texture 

Description

Candera::Texture encapsulates a Candera::TextureImage and a set of attributes specifying how it is applied to a vertex's texture coordinate. Candera implements a sharing mechanism based on TextureImages. These hold the actual VRAM handle. Multiple textures can share one TextureImage object. The TextureImage manages its upload to the VRAM.

Attention:

Texture Filtering

Following texture filters can be used to improve visual quality of Textures: Magnification to upscale, Minification to downscale.

It specifies how the texture is wrapped:

It specifies the maximum degree of anisotropy to account for in texture filtering for the Texture object. Anisotropic filtering improves the quality of the textures when they are not uniformly scaled because, for example, the textured triangle is not exactly facing the camera. The value of maxAnisotropy must be greater or equal to 1.0f (isotropy) and is limited by the max detail of anisotropy supported by hardware, which can be retrieved with the function Candera::RenderDevice::GetMaxAnisotropySupportedByDevice.

Changing Texture Image And Setting Filters

    m_textureImage = BitmapTextureImage::Create();
    m_textureImage->SetName("LabelTextureImage");
    static_cast<void>(m_textureImage->SetBitmap(m_bitmap));
    if (m_textureImage == 0) {
        FEATSTD_DEBUG_ASSERT(false);
        return; // memory is freed in destructor/UpdateBitmap()
    }


    m_texture = Texture::Create();
    m_texture->SetName("LabelTexture");
    m_texture->SetTextureImage(m_textureImage);
    m_texture->SetWrapModeU(Texture::ClampToEdge);
    m_texture->SetWrapModeV(Texture::ClampToEdge);
    m_texture->SetMinificationFilter(Texture::MinMagLinear);
    m_texture->SetMagnificationFilter(Texture::MinMagLinear);

Appearance: Render Mode 

Description

Candera::RenderMode is an Appearance component that encapsulates polygon-level and per-fragment compositing render attributes. If an object's Appearance has set RenderMode to null, then the default RenderMode is used instead. For details how to set the default render mode, see Candera::Renderer::SetDefaultRenderMode.

If a Camera has a RenderMode attached [camera->GetApperance()->SetRenderMode(...)], then the Camera's RenderMode overrules the DefaultRenderMode during its render pass. Thus, all Nodes rendered by the Camera that do not have their own RenderMode set, use the RenderMode applied to the Camera.

If a RenderMode has set an inheritance bit for a certain render attribute, then the property of the base render mode is used, this is either the Camera's RenderMode if set or the DefaultRenderMode otherwise.

        bool m_isColorWriteRedEnabled;       // Default value: true
        bool m_isColorWriteGreenEnabled;     // Default value: true
        bool m_isColorWriteBlueEnabled;      // Default value: true
        bool m_isColorWriteAlphaEnabled;     // Default value: true
        bool m_isDepthWriteEnabled;          // Default value: true
        bool m_isDepthTestEnabled;           // Default value: true
        bool m_isStencilTestEnabled;         // Default value: false
        bool m_isBlendingEnabled;            // Default value: false

Set a rendermode:

    SharedPointer<RenderMode> rm = RenderMode::Create();
    rm->SetBlendingEnabled(true);
    rm->SetBlendMode(RenderMode::SourceAlpha, RenderMode::InverseSourceAlpha, RenderMode::Add);
    rm->SetDepthTestEnabled(false);
    rm->SetDepthWriteEnabled(false);
    appearance->SetRenderMode(rm);

Render Mode Attributes

The next chapter Color Blending describes possible blending operations in detail.

Culling determines which side of a polygon is removed before rasterisation.

Winding defines the front face of a polygon. A polygon side is the front-face if its screen-space vertices are in the same order as the winding specifies.

Candera::RenderMode::ComparisonFunction can be used with depth-, stencil-, or sampler state operations. It specifies how the source (new) data is compared against the destination (existing) data before passing the comparison operations (storing the data).

Depth bias that can be applied to co-planar primitives to reduce z-fighting, according to following function: Depth bias = (max * scaleFactor) + (r * units); where max is the maximum depth slope of the triangle being rendered and r is an implementation-defined constant that is guaranteed to produce the smallest resolvable offset.

Via Candera::RenderMode::SetDepthBias the depth bias can be set and Candera::RenderMode::SetDepthTestEnabled and Candera::RenderMode::SetDepthWriteEnabled enables it.

StencilPlane specifies the face associated with the provided stencil function, which are FrontFace, BackFace and FrontAndBackFace. Front face stencil affects non-polygons and front-facing polygons whereas back face stencil affects back-facing polygons only.
StencilOperation defines the stencil-buffer operation.

Appearance: Render Mode - Color Blending 

Description

When Blending is enabled, the output from the fragment shader is blended with the current contents of the frame buffer, rather than merely overwriting it. Blending is mostly used to make objects appear transparent, but can also produce various other effects. (eg. anti-aliasing, DOF, or multi-pass rendering.) There are multiple ways of using blending, but generally, the procedure is as follows:

Blend Operations

        enum BlendOperation
        {
            Add = 0,               
            Subtract = 1,          
            ReverseSubtract = 2,   
            Min = 3,               
            Max = 4                
        };

Blend Factor

        enum BlendFactor
        {
            Zero = 0,                   
            One  = 1,                   
            SourceColor = 2,            
            InverseSourceColor = 3,     
            SourceAlpha = 4,            
            InverseSourceAlpha = 5,     
            DestColor = 6,              
            InverseDestColor = 7,       
            DestAlpha = 8,              
            InverseDestAlpha = 9,       
            ConstantColor = 10,         
            InverseConstantColor = 11,  
            ConstantAlpha = 12,         
            InverseConstantAlpha = 13,  
            SourceAlphaSaturate = 14    
        };

BlendMode combines the source and destination blend factors with the operation used in blending equation.

For the Blending Options ConstantColor, InverseConstantColor, ConstantAlpha, or InverseConstantAlpha a blending color can be set.

Set blending:

    SharedPointer<RenderMode> rm = RenderMode::Create();
    rm->SetBlendingEnabled(true);
    rm->SetBlendMode(RenderMode::SourceAlpha, RenderMode::InverseSourceAlpha, RenderMode::Add);
    rm->SetDepthTestEnabled(false);
    rm->SetDepthWriteEnabled(false);
    appearance->SetRenderMode(rm);

Appearance: Shader 

Description

Candera::Shader is an Appearance component representing a graphical processing unit (GPU) program, thus a vertex and fragment shader pair.

Candera and SceneComposer offer reference shaders of both vertex and fragment shaders.
For details refer to section Shader Usage.

In SceneComposer via the appearance of a node its ShaderProgram can be chanced easily. Further it is possible to change shaders, the default shader configuration, to create new shaders and combine two of them to a new ShaderProgram.

The Default Shader Configuration in SceneComposer

Appearance: Shader Parameter Setters 

Description

The Candera::ShaderParamSetter class is used to pass uniform parameters to a Shader program. The most relevant methods for this class are Candera::ShaderParamSetter::SetUniform which creates a new uniform (see example below):

    shaderParamSetter->SetUniform(m_uniformName, Shader::Float, &m_uniformValue);

and the Candera::ShaderParamSetter::Activate which activates all the uniforms previously set by the SetUniform method in the Shader.

Generic Shader Param Setters

Candera::GenericShaderParamSetter is a class derived from Candera::ShaderParamSetter which bundles uniform shader parameters that are calculated by Candera. The class interface offers, for each of these parameters, a specialized method which enables / disables the parameter.

    shaderParamSetter->SetModelMatrix4Enabled(true);
    shaderParamSetter->SetModelMatrix3Enabled(true);
    shaderParamSetter->SetNormalModelMatrix3Enabled(true);
    shaderParamSetter->SetModelViewMatrix4Enabled(true);
    shaderParamSetter->SetModelViewMatrix3Enabled(true);
    shaderParamSetter->SetNormalModelViewMatrix3Enabled(true);
    shaderParamSetter->SetModelViewProjectionMatrix4Enabled(true);
    shaderParamSetter->SetCameraLookAtVectorEnabled(true);
    shaderParamSetter->SetCameraPositionEnabled(true);
    shaderParamSetter->SetLightActivationEnabled(true);
    shaderParamSetter->SetMaterialActivationEnabled(true);
    shaderParamSetter->SetTextureActivationEnabled(true);
    shaderParamSetter->SetLightsCoordinateSpace(Light::World);

If a parameter is enabled then it will be calculated and passed to the shader, if disabled the parameter is neither calculated nor passed.

Default Parameters

Some often needed shader parameters are enabled by default:

If needed, for performance reasons, those parameters might be disabled.

Generic Param Setters in SceneComposer

In SceneComposer the generic parameter setters are accessible through the graphic interface in two ways:

SceneComposer provides the following predefined uniform setters:

The table below shows some examples of shaders that can be set by each of the predefined shader parameter setters:

Shader parameter setters can be applied to a 3D node by selecting it in the panel and then drag-and-drop it in the Appearance list of the node.

Customized Shader Parameter Setter 

Customized Shader Parameter Setter - Example

If for any reason the standard shader parameter setters are not sufficient, it is possible to create a customized shader parameter setter. However, a custom shader parameter setter cannot be configured in SceneComposer, it must be associated to the desired node by coding.

The following example explains how to create and use a customized shader parameter setter in a widget. Refer to the

The widget ShaderParamSetterWidget allows to set the u_Material.emissive and the u_MVPMatrix uniform parameters for any node using an appropriate shader program (for example, the nodes in the ShaderParamSetterSolution are using the RefTransLight1_RefColor shader program).

Simple Shader Parameter Setter for u_Material.emissive & u_MVPMatrix Uniforms

In order to pass the u_Material.emissive and u_MVPMatrix uniforms to a shader program, the widget uses an instance of the class SimpleShaderParameterSetter:

    // Create uniform setter instance
    // m_shaderParamSetter is of type SharedPointer<SimpleShaderParamSetter> ;
    m_shaderParamSetter = SimpleShaderParamSetter::Create();
    // end Create uniform setter instance

The only method that needs to be overridden in the SimpleShaderParameterSetter is Candera::ShaderParamSetter::Activate.

The example ShaderParamSetterWidget uses this SimpleShaderParameterSetter by attaching the created instance to the node, which is associated to the widget:

    // Attach uniform setter
    if ( (GetNode() != 0) && (GetNode()->GetAppearance() != 0) ) {
        GetNode()->GetAppearance()->SetShaderParamSetter(m_shaderParamSetter);
    }
    // end Attach uniform setter

Whenever the widget property "Uniform Color" is modified, the widget sets the given color value (m_color) as u_Material.emissive uniform to the SimpleShaderParameterSetter:

    // Set u_Material.emissive uniform
    FEATSTD_UNUSED(m_shaderParamSetter->SetUniform(ShaderParamNames::GetUniformName(ShaderParamNames::MaterialEmissive), Shader::FloatVec4, reinterpret_cast<Float*>(&m_shaderColor[0]), 1));
    // end Set u_Material.emissive uniform

The node vertices are mapped from the model space to the screen space using the Model-View-Projection Matrix (u_MVPMatrix). SimpleShaderParameterSetter calculates the u_MVPMatrix using the node and camera attributes and then passes it to the shader:

    // Set u_MVPMatrix uniform
    const Matrix4 mvpMatrix = node.GetWorldTransform() * RenderDevice::GetActiveCamera()->GetViewProjectionMatrix();
    return shader.SetUniform( mvpMatrix.GetData(), ShaderParamNames::GetUniformName(ShaderParamNames::ModelViewProjectionMatrix4), Shader::FloatMat4 );
    // end Set u_MVPMatrix uniform

Modifications made using the SetUniform method become effective each time the camera renders the scene because the method Activate is invoked internally by the node.

Multipass Appearance 

Description

A Candera::MultiPassAppearance is a dedicated Appearance which enables a node to be rendered multiple times with different appearance settings which are blended in order to achieve a certain visual result like e.g. fur or blurred rendering.

The sequence of render passes is created by chaining instances of MultiPassAppearance using the SetNextPass method:

    multiPassAppearance1->SetNextPass(multiPassAppearance2);
    multiPassAppearance2->SetNextPass(multiPassAppearance3);

3D Scene Graph Dynamics

Description

Usually all required nodes are already specified and preconfigured via SceneComposer, so in most cases it won't be necessary to make any adaptations within the scene graph loaded from an asset at runtime.

However, some use cases might require such adaptations. This tutorial covers the most common means to manipulate the scene graph structure dynamically.

Example Solution

Adding and Removing 3D Nodes 

3D Scene Graph Dynamics Example

For creating and adding a new node, the following can be used:

As an example use case, a Candera::Billboard can be created, added and removed. Use the SceneGraphDynamicsWidget_3D properties described below:

        // Definition of WidgetProperty "AddBillboard"
        CdaProperty(AddBillboard, bool, GetAddBillboard, SetAddBillboard)
            CdaDescription("If AddBillboard is enabled a new Billboard is created and added to the widget Candera::Node. If disabled, the Billboard will be removed.")
        CdaPropertyEnd()
        // End Definition of WidgetProperty "AddBillboard"

Creating a new Billboard

The following code snippet generates a basic Candera::Billboard (size 30 x 30) with a Candera::Material and a matching Candera::Shader. The Shader has to be provided in the asset and is delivered through the AssetProvider by its name. Further, some translation is applied to the new Billboard.

        // Create and init a new Billboard

        SharedPointer<Appearance> myAppearance = Appearance::Create();
        SharedPointer<Material> myMaterial = Material::Create();
        myMaterial->SetEmissive(Color(0.5F, 0.0F, 0.0F, 1.0F));
        myAppearance->SetMaterial(myMaterial);
        myAppearance->SetShader(Base::GetAssetProvider()->GetShader(CgiAssetNames::RefTransLight1_RefColor));
        myAppearance->SetName("Generated Appearance");

        m_billboard = Billboard::Create(30.0F, 30.0F);
        m_billboard->SetAppearance(myAppearance);
        m_billboard->Translate(Vector3(30.0F, 0.0F, 0.0F));

        // end Create and init a new Billboard

Adding the new Billboard to the scene graph

Next the Billboard is uploaded to VRAM and appended to the node associated with the widget.

        // Add Billboard

        static_cast<void>(m_billboard->Upload());
        static_cast<void>(node->AddChild(m_billboard));

        // end Add Billboard

Removing and destructing the Billboard

To remove the Billboard simply from the scene graph, use Candera::Node::RemoveChild. If the Billboard will be used for further operations e.g. attaching it to an other node removing would be enough. Since in this example the Billboard isn't used further it should not only be removed but also be destructed completely (freeing the resources).

The following code snippet removes the previously generated billboard from its parents, unloads the Billboard from VRAM and frees with Candera::Node::Dispose the resources.

        // Remove previously generated billboard and destruct it

        Node* parent = m_billboard->GetParent();
        if (parent != 0){
            static_cast<void>(parent->RemoveChild(m_billboard));
            FEATSTD_LOG_ERROR("- Node %s removed from parent %s ...\n", m_billboard->GetName(), parent->GetName());
        }
        // Destruct node

        static_cast<void>(m_billboard->Unload());
        m_billboard->Dispose();
        m_billboard = 0;

        // end Destruct node

        // end Remove previously generated billboard and destruct it

As Candera::Node::Dispose internally calls the Candera::Node::RemoveChild on parent node following code would be enough for removing and destructing a node.

        // Destruct node

        static_cast<void>(m_billboard->Unload());
        m_billboard->Dispose();
        m_billboard = 0;

        // end Destruct node

In SceneComposer the newly added Node does not appear in the Scene Tree view because it is only added dynamically by the widget.
- The used Shader for the generated Billboard in the widget has to be included when generating an asset from the solution - ensure that "Always include in asset" flag is marked at the Shaders properties.
- The widget must control memory and VRAM management of its internal dynamic subtree autonomously.

Widget Interaction in the Player

First, the asset must be exported and loaded in the Player. Then, one of the two existing SceneGraphDynamicsWidget_3D widgets must be selected for the 3D scene. After, ChangeAppearance, CloneOperation and AddBillboard properties can be enabled/disabled (1/0) to obtain different results.

Changing Appearance and other 3D Node Attachments 

For changing the appearance of a node, the following property of the SceneGraphDynamicsWidget_3D can be used:

        // Definition of WidgetProperty "ChangeAppearance"
        CdaProperty(ChangeAppearance, bool, GetChangeAppearance, SetChangeAppearance)
            CdaDescription("If ChangeAppearance is enabled, the appearance will be exchanged to a new generated appearance. If disabled, the previus appearance will be restored.")
        CdaPropertyEnd()
        // End Definition of WidgetProperty "ChangeAppearance"

Try the ChangeAppearance property at the SceneGraphDynamics_3D_Billboard widget in the example solution to change the Billboards appearance from a texture appearance to a material appearance.

Creating and changing an Appearance

The following code snippet generates a basic Candera::Appearance. A Candera::Material is created and its emissive color is set to a light green. The material and a proper shader is set to the Appearance. The shader has to be provided in the asset and is delivered through the AssetProvider by its name.

    // Create and set a new Appearance

    SharedPointer<Appearance> myAppearance = Appearance::Create();
    myAppearance->SetMaterial(Material::Create());
    myAppearance->GetMaterial()->SetEmissive(Color(0.0F, 0.5F, 0.0F, 1.0F));
    myAppearance->SetShader(Base::GetAssetProvider()->GetShader(CgiAssetNames::RefTransLight1_RefColor));
    myAppearance->SetName("Generated Appearance");

    // end Create and set new Appearance

In the next step the node's previous Appearance is saved (for restoring purpose) and the new generated appearance is set to the node associated with the widget.

    // Change Appearance

    m_previousAppearance = node->GetAppearance();
    node->SetAppearance(myAppearance);
    static_cast<void>(myAppearance->Upload());

    // end Change Appearance

Restoring / releasing an Appearance

Restore the previous Appearance and destruct the dynamically generated appearance.

        // Restoring appearance and destructing

        SharedPointer<Appearance> currentAppearance = node->GetAppearance();
        static_cast<void>(currentAppearance->Unload());
        currentAppearance.Release();
        node->SetAppearance(m_previousAppearance);

        // end Restoring appearance and destructing

In SceneComposer the changed Appearance does not appear in the Appearance panel because it is only changed dynamically by the widget.
- The used shader for the generated Billboard in the widget has to be included when generating an asset from the solution - ensure that "Always include in asset" flag is marked at the Shaders properties.
- The widget must control memory and VRAM management of dynamically created node attachments autonomously.

Cloning 3D Nodes 

For cloning a node, the following property of the SceneGraphDynamicsWidget_3D can be used:

        // Definition of WidgetProperty "NodeToClone"
        CdaProperty(NodeToClone, Candera::Node*, GetNodeToClone, SetNodeToClone)
            CdaDescription("Select a Candera::Node which shall be cloned and added to the widget Candera::Node. The Candera::Node must be a child of this widget's scene.")
        CdaPropertyEnd()
        // End Definition of WidgetProperty "NodeToClone"

        // Definition of WidgetProperty "CloneOperation"
        CdaProperty(CloneOperation, bool, GetCloneOperation, SetCloneOperation)
            CdaDescription("If CloneOperation is enabled, the Candera::Node to clone will be cloned and added to the widget Candera::Node. If disabled, the clone will be removed.")
        CdaPropertyEnd()
        // End Definition of WidgetProperty "CloneOperation"

For the cloning operation, refer to Candera::Node::Clone. The following code snippets illustrate, what the SceneGraphDynamicsWidget_3D is actually doing for cloning a node and destructing it again.

Validating Node to Clone

This example should allow to clone nodes, which are part of the scene graph the widget is linked to. The scene graph can be traversed from a given node up to its actual top level scene node to check whether it is part of the scene graph.

    // Search the parent scene of a given node

    Node* currentNode = node;

    while (currentNode != 0) {
        if (currentNode->IsTypeOf(Scene::GetTypeId())) {
            return static_cast<Scene*>(currentNode);
        }
        currentNode = currentNode->GetParent();
    }
    return 0;

    // end Search the parent scene of a given node

Creating and Adding Clone

If the widget node and the node to clone have same top level scene, the node can be cloned and added to the widget node according to the following code snippet.

        // Clone the node and add it to the widgets associated node

        m_clonedNode = TreeCloner().CreateClone(*m_nodeToClone);
        static_cast<void>(node->AddChild(m_clonedNode));
        static_cast<void>(m_clonedNode->UploadAll());
        m_clonedNode->SetName("Clone");

        // end Clone the node and add it to the widgets associated node

TreeCloner and Cloning Strategies

For more complex cloning see Candera::TreeCloner and Candera::TreeCloneStrategy. Candera::TreeClonerBase is provided for cloning trees.

Removing and Destructing Clone

Analogous to Removing and destructing the Billboard (removing/destructing a 3D node) the cloned node is destructed.

        // Remove a previously cloned node

        static_cast<void>(m_clonedNode->UnloadAll());
        m_clonedNode->Dispose();
        m_clonedNode = 0;

        // end Remove a previously cloned node

In SceneComposer the newly added node clone does not appear in the Scene Tree view because it is only added dynamically by the widget.
- It is not allowed to modify the scene graph maintained by SceneComposer outside of the subtree owned by the widget!
- The widget must control memory and VRAM management of its internal dynamic subtree autonomously.

3D Render Order

Description

There are various reasons why sorting of objects to render is required:

Render Order: Involved Classes 

Involved Render Order Classes

Default Render Order: Sorting by Distance to Camera 

Default Render Order

By default, all objects part of a scene are automatically sorted by Candera according to their render attributes into two predefined render order bins:

Both default bins are protected, which means that they are under control of Candera and cannot be deleted.

Predefined Render Order in SceneComposer

In SceneComposer, each 3D scene gets the predefined render order bins assigned by default:

Predefined Render Order in Candera

To apply the default behaviour with auto-assignment of transparent and opaque objects via Candera API, refer to following example:

// Create default render order with 2 default bins and max. number of 10 nodes each (opaque and transparent bin).
// Default rank for opaque bin is 10 and transparent bin is 20
static RenderOrder* renderOrder = RenderOrder::Create(10, 10);
// Assign render order to scene.
m_scene->SetRenderOrder(&renderOrder);

Fixed Render Order 

To customize the default render order with a fixed render order, scene nodes must be assigned to custom render order bins sorted by explicit rank values.

Code Example: Fixed Render Order

As an example, create a render order with 3 bins and max. number of 10 nodes for O&T bin:

static RenderOrder renderOrder(3, 10, 10);
m_scene->SetRenderOrder(&renderOrder);

Create new render order bin with name "UserBin", rank "30", max. Number of 10 nodes:

renderOrder.CreateBin("UserBin", 30, 10);

Create dedicated order criterion which sorts nodes by its render order rank:

static RankOrderCriterion userCriterion;

Assign order criterion to UserBin:

renderOrder.SetBinOrderCriterion("UserBin", &userCriterion);

Assign nodes to dedicated bins:

m_mesh1->SetRenderOrderBinAssignment("UserBin");
m_mesh2->SetRenderOrderBinAssignment("UserBin");

Set dedicated render order rank for nodes:

m_mesh1->SetRenderOrderRank(2);
m_mesh2->SetRenderOrderRank(1);

Performance Optimized Render Order 

Candera::RenderStateOrderCriterion implements a proof of concept OrderCriterion used for batching nodes to minimize render state changes. It takes into consideration the nodes shader, texture and render mode, whose changes are considered the most expensive.

The batching continues until the least expensive state change (CullingMode).

- Usage of Candera::RenderStateOrderCriterion does not guarantee best batching algorithm, which should be implemented after benchmarking the target render device's state change costs.
- RenderStateOrderCriterion groups the nodes only by their first appearance and texture. Nodes with multi-pass rendering (MultiPassAppearance), or with multiple texture units, most probably will break the batches and cancel some performance gains.
- CANDERA_RENDER_STATE_CACHING_ENABLED should be defined to use Candera's render state caching mechanism.

Searching for Nodes with SearchTreeTraverser

Searching for Nodes

With Candera::SearchTreeTraverser it is possible to find nodes within a given scene tree by certain criteria. The search scene graph traverser is a Candera::TreeTraverserBase implementation that evaluates each node with a given Candera::SearchCriterion.

Following code snippets illustrate how to use the traverser.

Creating a plugin that registers a configuration and uses the default configuration editor.

First create a Candera::SearchTreeTraverser and then set its Candera::SearchCriterion. The search criterion validates nodes based on the implemented criterion.

In the example below the criterion is a Candera::ScopeMaskSearchCriterion.

    // Create criterion
    ScopeMaskSearchCriterion<Node> scopeMaskCriterion;
    scopeMaskCriterion.SetScopeMask(scopeA);
    
    // Create SearchTreeTraverser
    SearchTreeTraverser<Node> scopeSearchTraverser;
    scopeSearchTraverser.SetSearchCriterion(&scopeMaskCriterion);

Tree Traversing

To start a search within a node tree, call Candera::SearchTreeTraverser::Traverse(). With the Candera::SearchTreeTraverser::SetOnFoundAction you can define if the search should stop after the first node that fulfills the search criterion is found, or if it should continue to gather all valid nodes.

Possible TraverserActions are:

The nodes fulfilling the search criterion are retained and are available to be later retrieved. Get the nodes one by one with Candera::SearchTreeTraverser::GetSearchResult. The order of the nodes is not defined and each node can be retrieved only once. When no more nodes are available, the method returns 0.

Following are examples for the different TraverserActions.

ProceedTraversing

This action is used if the traversing should continue with the next child (if the current node has any) or with the next sibling.

First define the action and then call the Traverse() method. All nodes that fulfill the search criterion are found and stored internally in a list.

    // Set on found action and traverse
    scopeSearchTraverser.SetOnFoundAction(Candera::TreeTraverserBase<Node>::ProceedTraversing);
    scopeSearchTraverser.Traverse(*groupRoot);
    
    // Get results
    UInt32 nodeCount = 0;
    for (Node* node = scopeSearchTraverser.GetSearchResult(); node != 0; node = scopeSearchTraverser.GetSearchResult()) {
        nodeCount++;
    }

StopTraversingForDescendants

Used if the traversing should stop for all child nodes and continue with the next sibling.

    // Set on found action and traverse
    scopeSearchTraverser.SetOnFoundAction(Candera::TreeTraverserBase<Node>::StopTraversingForDescendants);
    scopeSearchTraverser.Traverse(*groupRoot);

StopTraversing

If you search for only one node which fulfills your criteria, you can use StopTraversing. The traversing will stop immediately after the first node is found.

    // Set on found action and traverse
    scopeSearchTraverser.SetOnFoundAction(Candera::TreeTraverserBase<Node>::StopTraversing);
    scopeSearchTraverser.Traverse(*groupRoot);
    Node* resultNode = scopeSearchTraverser.GetSearchResult();

Vertex Geometry Builder

Description

The Candera::VertexGeometryBuilder class helps effectively build Candera::VertexGeometry objects.

Procedural Geometry 

Example: Wireframe Cube with LineList

First example shows how to generate a wireframe cube using a Candera::LineList object.

The vertex geometry will be generated procedurally using a Candera::VertexGeometryBuilder object (e.g. m_builder).

Vertex Element Format: Position and Color

At the beginning we have to specify what kind of information will be set in the vertices. Of course we need information about the position and, optionally, for an improved visual effect, we could also add color information.

    // Set the data type to be used: position & color
    m_builder.SetVertexElementFormat(VertexGeometry::Position, 0, VertexGeometry::Float32_3);
    m_builder.SetVertexElementFormat(VertexGeometry::Color, 0, VertexGeometry::Float32_4);

Vertex Data: Position

The position information for the vertices is obtained from the array c_cubeData which, in fact, stores the coordinates of the points A and G. The coordinates for the rest of the vertices are obtained relatively to this points (e.g. F(X_A, Y_G, Z_G) or D(X_G, Y_A, Z_A)

// Coordinates for the points A & G
static const Float c_cubeData[2][3] = {
    {-1.0F, -1.0F, -1.0F },
    {1.0F, 1.0F, 1.0F }
};

VertexGeometryBuilder: Set Vertex Elements

Because the LineType property of the LineList object will be set to LineType::Lines, the vertex buffer will have to contain a pair of vertices for each line of the cube: 2 vertices/line * 12 lines = 24 vertices.

    // Set the position & color information for each vertex
    // Line segment AD
    m_builder.SetVertexElement(VertexGeometry::Position, 0, c_cubeData[0][0], c_cubeData[0][1], c_cubeData[0][2]); // A
    m_builder.SetVertexElement(VertexGeometry::Color, 0, 1.F, 0.F, 1.F, 1.F); // magenta
    // Increment the vertex cursor
    m_builder.IncrementVertexCursor();
    m_builder.SetVertexElement(VertexGeometry::Position, 0, c_cubeData[1][0], c_cubeData[0][1], c_cubeData[0][2]); // D
    m_builder.SetVertexElement(VertexGeometry::Color, 0, 1.F, 1.F, 1.F, 1.F); // white
    m_builder.IncrementVertexCursor();
    // Line segment AB
    m_builder.SetVertexElement(VertexGeometry::Position, 0, c_cubeData[0][0], c_cubeData[0][1], c_cubeData[0][2]); // A
    m_builder.SetVertexElement(VertexGeometry::Color, 0, 1.F, 0.F, 1.F, 1.F); // magenta
    m_builder.IncrementVertexCursor();
    m_builder.SetVertexElement(VertexGeometry::Position, 0, c_cubeData[0][0], c_cubeData[0][1], c_cubeData[1][2]); // B
    m_builder.SetVertexElement(VertexGeometry::Color, 0, 1.F, 1.F, 0.F, 1.F); // yellow
    // ...

Create Vertex Buffer

Create a Candera::VertexBuffer object and attach to it the vertex geometry obtained from the Candera::VertexGeometryBuilder:

    VertexGeometry* vertexGeom = m_builder.GetVertexGeometry();
    SharedPointer<VertexBuffer> vertexBuffer = VertexBuffer::Create();
    static_cast<void>(vertexBuffer->SetVertexGeometry(vertexGeom, VertexBuffer::VertexGeometryDisposer::Dispose));
    vertexBuffer->SetPrimitiveType(VertexBuffer::Lines);

Create LineList using the Vertex Buffer

Attach the vertex buffer to LineList object:

    // Create and configure the line list object
    m_lineList = LineList::Create();
    m_lineList->SetAppearance(Appearance::Create());
    m_lineList->GetAppearance()->SetMaterial(Material::Create());
    m_lineList->GetAppearance()->GetMaterial()->SetEmissive(Color(1.0F, 1.0F, 0.0F));
    m_lineList->GetAppearance()->SetShader(m_shaderLightMaterial);
    m_lineList->SetLineType(LineList::Lines);
    m_lineList->SetWidth(1.0);
    m_lineList->SetIntersectionTestEnabled(false);
    m_lineList->SetVertexBuffer(vertexBuffer);
    m_lineList->SetScopeMask(ScopeMask(false));
    static_cast<void>(m_lineList->SetScopeEnabled(1, true));
    m_lineList->SetRenderingEnabled(true);
    m_lineList->SetName("Wireframe");
    static_cast<void>(m_lineList->Upload());

Wireframe Cube Result

The image below shows the resulting wireframe cube:

Indexed Geometry 

Example: Solid Cube from one Triangle Strip

The next example will show how to create a solid cube from one triangle strip using a Candera::Mesh object. In this case the cube is determined by only 14 vertices which have to be ordered in a special way.

The figure below presents a cube unfolded and a possible solution of ordering the vertices:

Indexed Vertex Sequence

The vertex sequence is stored in the c_index_order array, encoding the order:

Each array element represents an offset it the vertex buffer.

// The vertex sequence - triangle strip
static const UInt16 c_index_order[] = { 12, 11, 7, 3, 0, 11, 1, 17, 0, 5, 7, 17, 12, 11 };

The vertex geometry builder object used in the previous example has already 24 vertices set with position and color information. Because only 14 vertices out of 24 are needed in this case and, also, because their sequence has to be different, an index buffer is added:

    // Change the order of the vertices using indexes
    for (Int index = 0; index < 14; index++) {
        // Define the value of the index
        m_builder.SetIndexElement(c_index_order[index]);
        // Increment the index cursor
        m_builder.IncrementIndexCursor();
    }

Create TriangleStrip Vertex Buffer

Create the vertex buffer using the geometry from the builder:

    VertexGeometry* vertexGeom = m_builder.GetVertexGeometry();
    SharedPointer<VertexBuffer> vertexBuffer = VertexBuffer::Create();
    static_cast<void>(vertexBuffer->SetVertexGeometry(vertexGeom, VertexBuffer::VertexGeometryDisposer::Dispose));
    vertexBuffer->SetPrimitiveType(VertexBuffer::TriangleStrip);

Create Mesh using the Vertex Buffer

Configure mesh and attach the vertex buffer:

    m_mesh = Mesh::Create();
    m_mesh->SetVertexBuffer(vertexBuffer);
    m_mesh->SetAppearance(appearance);
    m_mesh->SetRenderingEnabled(false);
    m_mesh->SetName("SolidNonTextured");
    static_cast<void>(m_mesh->Upload());

Solid Cube Result

The image below shows the resulting solid cube:

Remove & Add Vertex Elements 

Example: Textured Cube

In this example the vertex geometry builder object will be used to generate the vertex geometry for a textured cube.

Adding texture to a mesh requires that its vertices should contain specific information like normal and texture coordinate. Also, the color information is no longer needed so it can be removed:

    // Vertex Elements Manipulation
    // Remove color data associated to the vertices
    m_builder.RemoveVertexElement(VertexGeometry::Color,0);
    // Add data type to be used: texture coordinate & normal
    m_builder.SetVertexElementFormat(VertexGeometry::TextureCoordinate, 0, VertexGeometry::Float32_2);
    m_builder.SetVertexElementFormat(VertexGeometry::Normal, 0, VertexGeometry::Float32_3);

Vertex Data: Normals and Texture Coordinates

After adding the new data types for the vertices it is time to add the corresponding information. First, add normals for vertices:

    // Move the cursor to the first vertex
    m_builder.SetVertexCursor();
    for (UInt32 i = 0; i < m_builder.GetVertexCount(); i++ )
    {
        m_builder.SetVertexElement(VertexGeometry::Normal, 0, 0.0F, 0.0F, 1.0F);
        m_builder.IncrementVertexCursor();
    }

In order to map the UV texture coordinate values correctly, the cube faces should be drawn using 4 vertices per face, so, in this case, all 24 vertices will be used. Of course, the vertex order has to be adjusted.

The new vertex order is stored in the c_indexDataTexturedCube array.

// Vertex order - textured cube
static const UInt16 c_indexDataTexturedCube[24] = {
    1,17,0,5,
    2,6,3,7,
    9,8,11,12,
    13,14,19,21,
    15,23,16,22,
    4,10,20,18
};

Now, reorder the vertices:

    // Overwrite the index buffer
    // Move the cursor to the first index
    m_builder.SetIndexCursor();
    for (UInt32 i = 0; i < m_builder.GetVertexCount(); i++ )
    {
        // Define the value of the index
        m_builder.SetIndexElement(c_indexDataTexturedCube[i]);
        m_builder.IncrementIndexCursor();
    }

The vertices of each face of the cube should be set with texture coordinate information as shown below:

Set the texture coordinates for vertices:

    Int idx = 0;
    for (Int nb_of_faces = 0; nb_of_faces<6; nb_of_faces++) {
        for (Int u=0; u<=1; u++) {
            for (Int v=0; v<=1; v++) {
                //Set the position of the vertex cursor
                m_builder.SetVertexCursor(c_indexDataTexturedCube[idx]);
                m_builder.SetVertexElement(VertexGeometry::TextureCoordinate, 0, static_cast<Float>(u), static_cast<Float>(v));
                idx++;
            }
        }
    }

The vertex buffer is created and configured in the same way as in the previous example.

The mesh setup is also similar but, unlike the solid cube, the textured cube appearance has to be set with a texture and a texture shader.

Textured Cube Result

Here is the final result:

Range Data Usage 

Example: Solid Cube using Range Data

This example will show how to create a solid cube as in the second example but using range data.

First, all existing data from the vertex geometry builder is removed.

    // Clear all data stored by the builder
    m_builder.Clear();

The vertex data is taken from the two buffers c_positionData and c_colorData.

static const Float c_positionData[8][3] = {
    { -1.0F, 1.0F, 1.0F},
    { 1.0F, 1.0F, 1.0F},
    { -1.0F, -1.0F, 1.0F},
    { 1.0F, -1.0F, 1.0F},
    { -1.0F, 1.0F, -1.0F},
    { 1.0F, 1.0F, -1.0F},
    { -1.0F, -1.0F, -1.0F},
    { 1.0F, -1.0F, -1.0F}
};

static const Float c_colorData[8][4] = {
    { 0.0F, 0.0F, 1.0F, 1.0F},
    { 0.0F, 1.0F, 0.0F, 1.0F},
    { 0.0F, 1.0F, 1.0F, 1.0F},
    { 1.0F, 0.0F, 0.0F, 1.0F},
    { 1.0F, 0.0F, 1.0F, 1.0F},
    { 1.0F, 1.0F, 0.0F, 1.0F},
    { 1.0F, 1.0F, 1.0F, 1.0F},
    { 1.0F, 0.5F, 1.0F, 1.0F}
};

The vertex sequence is taken from the array c_indexData.

// Range data index
static const UInt16 c_indexData[] = {3, 2, 1, 0, 4, 2, 6, 3, 7, 1, 5, 4, 7, 6 };

Use the methods Candera::VertexGeometryBuilder::SetVertexElementRange and Candera::VertexGeometryBuilder::SetIndexElementRange to add the required information.

    // Add position, color and an index from range data
    // Splice values to the position buffer starting with the first vertex
    static_cast<void>(m_builder.SetVertexElementRange(VertexGeometry::Position, 0, 0, VertexGeometry::Float32_3,
        8, 3*sizeof(Float), c_positionData ));
    // Splice values to the color buffer starting with the first vertex
    static_cast<void>(m_builder.SetVertexElementRange(VertexGeometry::Color, 0, 0, VertexGeometry::Float32_4,
        8, 4*sizeof(Float), c_colorData ));

    // Splice values to the index buffer starting with the first index
    static_cast<void>(m_builder.SetIndexElementRange(0, sizeof(c_indexData)/sizeof(UInt16),c_indexData));

The vertex buffer configuration and the mesh setup are identical with the ones from the second example.

Here is the final result:

Concatenate Geometries 

VertexGeometryBuilder::SpliceGeometry

In some cases it might be useful to concatenate two vertex geometries. This can be done by using the Candera::VertexGeometryBuilder::SpliceGeometry method as shown below:

    m_builder.SpliceGeometry(0, 0, vertexGeometry1);
    m_builder.SpliceGeometry(vertexGeometry1->GetVertexCount(), vertexGeometry1->GetIndexCount(), vertexGeometry2);
    vertexGeometry1cat2 = builder.GetGeometry();

Vertex Geometry Modifier

Overview

The VertexGeometryModifier, in conjunction with a VertexAccessor, helps to modify VertexGeometry objects by the means of the setters offered by the class interface. The interface offers also getters which are helpful to retrieve the values of the vertex elements from a given vertex buffer.

Example

The example below shows how to change the position values for the vertices from a vertex buffer of a given mesh.

            VertexGeometry* vertexGeom;
            bool isMutable = m_mesh3->GetVertexBuffer()->GetVertexGeometry()->GetVertexArrayResourceHandle().m_isMutable;
            // Get the vertex geometry of the mesh
            if (isMutable) {
                vertexGeom = m_mesh3->GetVertexBuffer()->GetVertexGeometry();
            }
            else {
                DiagnosticPlatform::ConsoleOut("VertexGeometryData not mutable");
                break;
            }
             // The vertex accessor will be used by the vertex geometry modifier to access the vertices
            VertexAccessor accessor(*vertexGeom);

            // Create a vertex geometry modifier specifying as usage the type of vertex attribute
            // which will be changed
            VertexGeometryModifier modifier(*vertexGeom, VertexGeometry::Position, 0);
            Float vertexData[3];
            for(Int i = 0; i<8; i++) {
                if(s_inflate) {
                // Retrieve the position data of the vertex "i" in the vertexData array
                modifier.GetVertexElement(accessor.GetVertex(i), vertexData, 3);

                // Alter the data and set it back
                modifier.SetVertexElement(accessor.GetMutableVertex(i), vertexData[0]*1.3F, vertexData[1]*1.3F, vertexData[2]*1.3F);
                } 
                else {
                    // Set the position of the vertex with data get from an array (Float c_positionData[8][3])
                    modifier.SetVertexElement(accessor.GetMutableVertex(i), c_positionData[i], 3);
                }
            }

            // Update the vertex buffer on the mesh
            m_mesh3->GetVertexBuffer()->Update(0, m_mesh3->GetVertexBuffer()->GetVertexGeometry()->GetVertexCount());

Candera 3D Listeners

Applications can receive notifications on scene graph events. Therefore implement and use a listener, which defines hooks to receive those notifications.

Following listener interfaces are provided in Candera 3D:

In order to register a listener simply derive from the listener class and override pure virtual functions with custom code.

Example Listener Implementation

Refer to Using Animation Callback Functions for an example how to implement and use an Animation listener.