Rendering Only Updated Content

Description

This chapter briefly describes how to achieve performance optimization by rendering only updated content.

Introduction

Invalidation Introduction

Basic principles for composing graphical content:

How is it done?

In the render loop of the application all Widgets are updated by calling Candera::WidgetBase::Update(). The basic render loop looks like this:

  // 3D Render Loop

    // handle input events
    // ...

    // update animations by calling AnimationDispatcher::DispatchTime()
    if (m_animationDispatcher3D != 0) {
      m_animationDispatcher3D->SetWorldTimeMs(nowMs);
      m_animationDispatcher3D->DispatchTime();
    }

    // update all widgets
    CgiApp::GetInstance().Update();

    Renderer::RenderAllCameras();

  // end 3D Render Loop

The widgets must now implement a mechanism to tell the application whether associated graphical content needs to be rendered. The following pages explain two ways to achieve this:

Use SetRenderingEnabled() 

Use Candera::Camera::SetRenderingEnabled() / Candera::Camera2D::SetRenderingEnabled()

The example below shows how in CGIApplication all 3D cameras are turned off in first step of render loop.

void CgiApp3dGc::Update() {
    Base::Update();
   
  // Turn off all cameras
    UInt32 cameraCount = Renderer::GetCameraCount();
    for (UInt32 i = 0; i < cameraCount; i++)
    {
        Camera* cam = Renderer::GetCamera(i);
        cam->SetRenderingEnabled(false);
    }

    // Update widgets in all visible scenes
    WidgetBase* widget = 0;
    Vector<SceneContext*>::ConstIterator it = m_sceneContexts.ConstBegin();
    for (; it != m_sceneContexts.ConstEnd(); it++) {
        if ((*it) != 0 && (*it)->GetScene() != 0 && (*it)->GetScene()->IsRenderingEnabled()) {
            widget = (*it)->GetFirstWidget();
            while (widget != 0) {
                widget->Update();
                widget = (*it)->GetNextWidget();
            }
        }
    }
}

The Candera::Widget::Update() method needs to be implemented such that the recently turned off camera is turned on again whenever rendering is required. The Candera::Camera can be either set as a widget property or retrieved inside the scene by masking the widget and the associated camera with the same Candera::ScopeMask value.

void SampleBaseWidget3D::InvalidateCamera(bool value)
{
  m_camera->SetRenderingEnabled(true);
}

void MyWidget::Update()
{
  // update graphical content from cached property value(s)
  //...

  Base::InvalidateCamera(true);
}

Pick Camera to Render

Explicitly Pick Camera to Render

Another method is to maintain a list of cameras by the application.

The render loop has to be changed