Olimi

Preface#

The content of this column is from the online course "Fundamentals of 3D Game Engine Architecture Design" by XuetangX. I have converted it into a text and image version (I personally prefer text tutorials as they are much faster to read), for easy reference.
Original course link: Fundamentals of 3D Game Engine Architecture Design.

Scene Rendering#

Rendering Overview and Culling Methods#

Rendering is the process of transforming a scene described in three-dimensional vectors into a scene described in two-dimensional pixels. It is the most important part of the entire game engine.

Related concepts include:

To improve rendering efficiency, invisible object culling can be used, including:

• Culling objects outside the view frustum based on the camera position (can be done using bounding volumes).

• Determining occlusion relationships among objects within the view frustum and culling occluded objects (can be done using bounding volumes).

• Culling back faces of visible objects.

In realistic rendering, the following calculations and blending are used to obtain the rendering result.

• Lighting: Rendering the scene based on the lighting model defined by the scene's lights, materials, etc. The lighting model includes local lighting models, global lighting models, lighting rendering algorithms, etc. Lighting calculations are performed based on the light source, the vertex normal of the triangle face, and material properties. Light sources are not rendered but are used as attributes for calculating realistic scenes.

• Textures: Texture mapping is a method to enhance the realism of scene mesh models. Textures are represented by pixels and are associated with mesh models in the form of texture mapping. Texture mapping files include .jpg, .tga, .bmp, .png, .tif, etc., and can be combined with lighting, shadows, special effects, etc. Texture mapping methods include multi-texturing, bump mapping, gloss mapping, projection mapping, environment mapping, etc.

• Shadows: Shadows can create depth and three-dimensional effects in a scene. The shadow region is an area that is visible from the viewpoint but invisible from the light source. The diagram below illustrates this:

In the case of soft shadows, if an object is illuminated by a planar light source, the shadow region appears as a soft shadow, which consists of a fully shadowed region and a partially shadowed region, as shown below:

• Visual Effects: Visual effects can create dynamic lighting and shadow effects and are generally implemented using billboards or particle systems.

Important parts of rendering implementation: GPU and shader programming:

Requirements for game engines:

• LOD (Level of Detail)

LOD (Level of Detail) refers to using fewer details to represent smaller, farther, or less important objects in a scene during rendering. Implementation methods include discrete LOD (static LOD), continuous LOD (dynamic LOD), and view-dependent LOD.

Scene Rendering Examples#

OGRE Scene Rendering#

OGRE main rendering loop:

OGRE main rendering sequence:

Rendering operations of the OGRE SceneManager class:

1. SceneManager::_renderScene(Camera *camera, Viewport *vp, bool includeOverlays)
   

2. SceneManager::_renderVisibleObjects(void)
   

3. SceneManager::renderVisibleObjectsDefaultSequence(void)
   

4. SceneManager::_renderQueueGroupObjects(RenderQueueGroup *pGroup, QueuedRenderableCollection::OrganisationMode om)
   

5. SceneManager::renderBasicQueueGroupObjects(RenderQueueGroup *pGroup, QueuedRenderableCollection::OrganisationMode om)
   Bold style

6. SceneManager::renderObjects(...);
   QueuedRenderableCollection::acceptVisitorGrouped(...)
   QueuedRenderableCollection::acceptVisitor(...);

7. SceneManager::SceneMgrRenderableVistor::VISIT(Pass *p, Renderable *r);
   

8. SceneManager::renderSignleObject(...)

9. SceneManager::_issueRenderOp(...)

   GLRenderSystem::_render(RenderOperation &op)//Using OpenGL for rendering
   

Summary of the above steps:

Panda3D Scene Rendering#

Panda3D rendering process:

Panda3D rendering core classes and class relationships:

Here are detailed descriptions of several core classes for Panda3D scene rendering:

Panda3D rendering management:

1. Application starts rendering.

2. For the view frustum, cull invisible objects, build rendering queues and states, and sort them.

3. Perform rendering and obtain a frame of rendering result.

4. Application updates the scene, starts the next frame rendering loop, go to step 2.

Panda3D main rendering process:

Here are several sub-processes:

1. Asynchronous task-driven rendering process:
   

2. Multi-threaded rendering:
   

3. Culling operation:
   

4. Rendering operation: