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• By elect
Hi,
ok, so, we are having problems with our current mirror reflection implementation.
At the moment we are doing it very simple, so for the i-th frame, we calculate the reflection vectors given the viewPoint and some predefined points on the mirror surface (position and normal).
Then, using the least squared algorithm, we find the point that has the minimum distance from all these reflections vectors. This is going to be our virtual viewPoint (with the right orientation).
After that, we render offscreen to a texture by setting the OpenGL camera on the virtual viewPoint.
And finally we use the rendered texture on the mirror surface.
So far this has always been fine, but now we are having some more strong constraints on accuracy.
What are our best options given that:
- we have a dynamic scene, the mirror and parts of the scene can change continuously from frame to frame
- we have about 3k points (with normals) per mirror, calculated offline using some cad program (such as Catia)
- all the mirror are always perfectly spherical (with different radius vertically and horizontally) and they are always convex
- a scene can have up to 10 mirror
- it should be fast enough also for vr (Htc Vive) on fastest gpus (only desktops)

Looking around, some papers talk about calculating some caustic surface derivation offline, but I don't know if this suits my case
Also, another paper, used some acceleration structures to detect the intersection between the reflection vectors and the scene, and then adjust the corresponding texture coordinate. This looks the most accurate but also very heavy from a computational point of view.

Other than that, I couldn't find anything updated/exhaustive around, can you help me?

• Hello all,
I am currently working on a game engine for use with my game development that I would like to be as flexible as possible.  As such the exact requirements for how things should work can't be nailed down to a specific implementation and I am looking for, at least now, a default good average case scenario design.
Here is what I have implemented:
Deferred rendering using OpenGL Arbitrary number of lights and shadow mapping Each rendered object, as defined by a set of geometry, textures, animation data, and a model matrix is rendered with its own draw call Skeletal animations implemented on the GPU.   Model matrix transformation implemented on the GPU Frustum and octree culling for optimization Here are my questions and concerns:
Doing the skeletal animation on the GPU, currently, requires doing the skinning for each object multiple times per frame: once for the initial geometry rendering and once for the shadow map rendering for each light for which it is not culled.  This seems very inefficient.  Is there a way to do skeletal animation on the GPU only once across these render calls? Without doing the model matrix transformation on the CPU, I fail to see how I can easily batch objects with the same textures and shaders in a single draw call without passing a ton of matrix data to the GPU (an array of model matrices then an index for each vertex into that array for transformation purposes?) If I do the matrix transformations on the CPU, It seems I can't really do the skinning on the GPU as the pre-transformed vertexes will wreck havoc with the calculations, so this seems not viable unless I am missing something Overall it seems like simplest solution is to just do all of the vertex manipulation on the CPU and pass the pre-transformed data to the GPU, using vertex shaders that do basically nothing.  This doesn't seem the most efficient use of the graphics hardware, but could potentially reduce the number of draw calls needed.

Really, I am looking for some advice on how to proceed with this, how something like this is typically handled.  Are the multiple draw calls and skinning calculations not a huge deal?  I would LIKE to save as much of the CPU's time per frame so it can be tasked with other things, as to keep CPU resources open to the implementation of the engine.  However, that becomes a moot point if the GPU becomes a bottleneck.

• Hello!
I would like to introduce Diligent Engine, a project that I've been recently working on. Diligent Engine is a light-weight cross-platform abstraction layer between the application and the platform-specific graphics API. Its main goal is to take advantages of the next-generation APIs such as Direct3D12 and Vulkan, but at the same time provide support for older platforms via Direct3D11, OpenGL and OpenGLES. Diligent Engine exposes common front-end for all supported platforms and provides interoperability with underlying native API. Shader source code converter allows shaders authored in HLSL to be translated to GLSL and used on all platforms. Diligent Engine supports integration with Unity and is designed to be used as a graphics subsystem in a standalone game engine, Unity native plugin or any other 3D application. It is distributed under Apache 2.0 license and is free to use. Full source code is available for download on GitHub.
Features:
True cross-platform Exact same client code for all supported platforms and rendering backends No #if defined(_WIN32) ... #elif defined(LINUX) ... #elif defined(ANDROID) ... No #if defined(D3D11) ... #elif defined(D3D12) ... #elif defined(OPENGL) ... Exact same HLSL shaders run on all platforms and all backends Modular design Components are clearly separated logically and physically and can be used as needed Only take what you need for your project (do not want to keep samples and tutorials in your codebase? Simply remove Samples submodule. Only need core functionality? Use only Core submodule) No 15000 lines-of-code files Clear object-based interface No global states Key graphics features: Automatic shader resource binding designed to leverage the next-generation rendering APIs Multithreaded command buffer generation 50,000 draw calls at 300 fps with D3D12 backend Descriptor, memory and resource state management Modern c++ features to make code fast and reliable The following platforms and low-level APIs are currently supported:
Windows Desktop: Direct3D11, Direct3D12, OpenGL Universal Windows: Direct3D11, Direct3D12 Linux: OpenGL Android: OpenGLES MacOS: OpenGL iOS: OpenGLES API Basics
Initialization
The engine can perform initialization of the API or attach to already existing D3D11/D3D12 device or OpenGL/GLES context. For instance, the following code shows how the engine can be initialized in D3D12 mode:
#include "RenderDeviceFactoryD3D12.h" using namespace Diligent; // ...  GetEngineFactoryD3D12Type GetEngineFactoryD3D12 = nullptr; // Load the dll and import GetEngineFactoryD3D12() function LoadGraphicsEngineD3D12(GetEngineFactoryD3D12); auto *pFactoryD3D11 = GetEngineFactoryD3D12(); EngineD3D12Attribs EngD3D12Attribs; EngD3D12Attribs.CPUDescriptorHeapAllocationSize[0] = 1024; EngD3D12Attribs.CPUDescriptorHeapAllocationSize[1] = 32; EngD3D12Attribs.CPUDescriptorHeapAllocationSize[2] = 16; EngD3D12Attribs.CPUDescriptorHeapAllocationSize[3] = 16; EngD3D12Attribs.NumCommandsToFlushCmdList = 64; RefCntAutoPtr<IRenderDevice> pRenderDevice; RefCntAutoPtr<IDeviceContext> pImmediateContext; SwapChainDesc SwapChainDesc; RefCntAutoPtr<ISwapChain> pSwapChain; pFactoryD3D11->CreateDeviceAndContextsD3D12( EngD3D12Attribs, &pRenderDevice, &pImmediateContext, 0 ); pFactoryD3D11->CreateSwapChainD3D12( pRenderDevice, pImmediateContext, SwapChainDesc, hWnd, &pSwapChain ); Creating Resources
Device resources are created by the render device. The two main resource types are buffers, which represent linear memory, and textures, which use memory layouts optimized for fast filtering. To create a buffer, you need to populate BufferDesc structure and call IRenderDevice::CreateBuffer(). The following code creates a uniform (constant) buffer:
BufferDesc BuffDesc; BufferDesc.Name = "Uniform buffer"; BuffDesc.BindFlags = BIND_UNIFORM_BUFFER; BuffDesc.Usage = USAGE_DYNAMIC; BuffDesc.uiSizeInBytes = sizeof(ShaderConstants); BuffDesc.CPUAccessFlags = CPU_ACCESS_WRITE; m_pDevice->CreateBuffer( BuffDesc, BufferData(), &m_pConstantBuffer ); Similar, to create a texture, populate TextureDesc structure and call IRenderDevice::CreateTexture() as in the following example:
TextureDesc TexDesc; TexDesc.Name = "My texture 2D"; TexDesc.Type = TEXTURE_TYPE_2D; TexDesc.Width = 1024; TexDesc.Height = 1024; TexDesc.Format = TEX_FORMAT_RGBA8_UNORM; TexDesc.Usage = USAGE_DEFAULT; TexDesc.BindFlags = BIND_SHADER_RESOURCE | BIND_RENDER_TARGET | BIND_UNORDERED_ACCESS; TexDesc.Name = "Sample 2D Texture"; m_pRenderDevice->CreateTexture( TexDesc, TextureData(), &m_pTestTex ); Initializing Pipeline State
Diligent Engine follows Direct3D12 style to configure the graphics/compute pipeline. One big Pipelines State Object (PSO) encompasses all required states (all shader stages, input layout description, depth stencil, rasterizer and blend state descriptions etc.)
To create a shader, populate ShaderCreationAttribs structure. An important member is ShaderCreationAttribs::SourceLanguage. The following are valid values for this member:
SHADER_SOURCE_LANGUAGE_DEFAULT  - The shader source format matches the underlying graphics API: HLSL for D3D11 or D3D12 mode, and GLSL for OpenGL and OpenGLES modes. SHADER_SOURCE_LANGUAGE_HLSL  - The shader source is in HLSL. For OpenGL and OpenGLES modes, the source code will be converted to GLSL. See shader converter for details. SHADER_SOURCE_LANGUAGE_GLSL  - The shader source is in GLSL. There is currently no GLSL to HLSL converter. To allow grouping of resources based on the frequency of expected change, Diligent Engine introduces classification of shader variables:
Static variables (SHADER_VARIABLE_TYPE_STATIC) are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. Mutable variables (SHADER_VARIABLE_TYPE_MUTABLE) define resources that are expected to change on a per-material frequency. Examples may include diffuse textures, normal maps etc. Dynamic variables (SHADER_VARIABLE_TYPE_DYNAMIC) are expected to change frequently and randomly. This post describes the resource binding model in Diligent Engine.
The following is an example of shader initialization:
To create a pipeline state object, define instance of PipelineStateDesc structure. The structure defines the pipeline specifics such as if the pipeline is a compute pipeline, number and format of render targets as well as depth-stencil format:
// This is a graphics pipeline PSODesc.IsComputePipeline = false; PSODesc.GraphicsPipeline.NumRenderTargets = 1; PSODesc.GraphicsPipeline.RTVFormats[0] = TEX_FORMAT_RGBA8_UNORM_SRGB; PSODesc.GraphicsPipeline.DSVFormat = TEX_FORMAT_D32_FLOAT; The structure also defines depth-stencil, rasterizer, blend state, input layout and other parameters. For instance, rasterizer state can be defined as in the code snippet below:
// Init rasterizer state RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc; RasterizerDesc.FillMode = FILL_MODE_SOLID; RasterizerDesc.CullMode = CULL_MODE_NONE; RasterizerDesc.FrontCounterClockwise = True; RasterizerDesc.ScissorEnable = True; //RSDesc.MultisampleEnable = false; // do not allow msaa (fonts would be degraded) RasterizerDesc.AntialiasedLineEnable = False; When all fields are populated, call IRenderDevice::CreatePipelineState() to create the PSO:
Shader resource binding in Diligent Engine is based on grouping variables in 3 different groups (static, mutable and dynamic). Static variables are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. They are bound directly to the shader object:

m_pPSO->CreateShaderResourceBinding(&m_pSRB); Dynamic and mutable resources are then bound through SRB object:
m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "tex2DDiffuse")->Set(pDiffuseTexSRV); m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); The difference between mutable and dynamic resources is that mutable ones can only be set once for every instance of a shader resource binding. Dynamic resources can be set multiple times. It is important to properly set the variable type as this may affect performance. Static variables are generally most efficient, followed by mutable. Dynamic variables are most expensive from performance point of view. This post explains shader resource binding in more details.
Setting the Pipeline State and Invoking Draw Command
Before any draw command can be invoked, all required vertex and index buffers as well as the pipeline state should be bound to the device context:
// Clear render target const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); m_pContext->SetPipelineState(m_pPSO); Also, all shader resources must be committed to the device context:
m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); When all required states and resources are bound, IDeviceContext::Draw() can be used to execute draw command or IDeviceContext::DispatchCompute() can be used to execute compute command. Note that for a draw command, graphics pipeline must be bound, and for dispatch command, compute pipeline must be bound. Draw() takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); Tutorials and Samples
The GitHub repository contains a number of tutorials and sample applications that demonstrate the API usage.

AntTweakBar sample demonstrates how to use AntTweakBar library to create simple user interface.

Atmospheric scattering sample is a more advanced example. It demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to textures, using compute shaders and unordered access views, etc.

The repository includes Asteroids performance benchmark based on this demo developed by Intel. It renders 50,000 unique textured asteroids and lets compare performance of D3D11 and D3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

Integration with Unity
Diligent Engine supports integration with Unity through Unity low-level native plugin interface. The engine relies on Native API Interoperability to attach to the graphics API initialized by Unity. After Diligent Engine device and context are created, they can be used us usual to create resources and issue rendering commands. GhostCubePlugin shows an example how Diligent Engine can be used to render a ghost cube only visible as a reflection in a mirror.

• By Yxjmir
I'm trying to load data from a .gltf file into a struct to use to load a .bin file. I don't think there is a problem with how the vertex positions are loaded, but with the indices. This is what I get when drawing with glDrawArrays(GL_LINES, ...):

Also, using glDrawElements gives a similar result. Since it looks like its drawing triangles using the wrong vertices for each face, I'm assuming it needs an index buffer/element buffer. (I'm not sure why there is a line going through part of it, it doesn't look like it belongs to a side, re-exported it without texture coordinates checked, and its not there)
I'm using jsoncpp to load the GLTF file, its format is based on JSON. Here is the gltf struct I'm using, and how I parse the file:
glBindVertexArray(g_pGame->m_VAO);
glDrawElements(GL_LINES, g_pGame->m_indices.size(), GL_UNSIGNED_BYTE, (void*)0); // Only shows with GL_UNSIGNED_BYTE
glDrawArrays(GL_LINES, 0, g_pGame->m_vertexCount);
So, I'm asking what type should I use for the indices? it doesn't seem to be unsigned short, which is what I selected with the Khronos Group Exporter for blender. Also, am I reading part or all of the .bin file wrong?
Test.gltf
Test.bin

• That means how do I use base DirectX or OpenGL api's to make a physics based destruction simulation?
Will it be just smart rendering or something else is required?

# OpenGL Scene Graph/Renderer interface

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## Recommended Posts

Foo. I'm begginning to find that much of the theory about scene graphs that you find on the net is great for drawing pretty graphs and giving presentations that make you sound smart, but very little of it actually applies in a useful manner. No one likes to talk about the nitty gritty (but very important!) details. For example, how does one (cleanly) get a scenegraph to work with a renderer in a nice, modular environment? The details: I've got a fairly nice scene graph set up, which manages our scene objects very nicely. Everything renderable or interact-able is plugged into it. Cameras, lights, static and dynamic meshs, transforms, etc. The basic code is pretty simple:
class CNode
{
public:
CNode( void );
virtual			~CNode( void );

int				Attach( CNode* node );
int				Remove( CNode* node );

void			UpdateNode( void );
void                    RenderNode( void );

private:
virtual void	Update( void );
virtual void	Render( void );

CNode*			next;
CNode*			child;

protected:
uint			type;
};


Everything that can be attached to the scene graph inherits this class. We attach nodes to eachother using the Attach function, and the Remove function removes any instances of the specified node that occur below the node it's passed into. (Most of the time the Root node) UpdateNode and RenderNode are simple recursive function calls that call their own Update/Render function, then that of their child node and finally their next node. (Basically it's a depth first tree) The render function is where our problems come to light, though. Up until recently, I had it so that each type of node was responsible for handling it's own rendering. It worked great except for one problem: This meant putting API calls (OpenGL in this case) directly into the nodes. So, for example, the Camera node would contain a direct call to glLoadMatrixf(). There are several problems with this approach: For one it tied the code directly and inseprably with a single rendering API. Though I have no need for it, I would like to leave the doors open for a DirectX implementation in the future. (Or even a software renderer if I got feeling REALLY ambitious! ^_^) It also meant that it was very difficult to track rendering states across the board, and even harder to insure that one objects render routine wasn't going to interfere with anothers. These problems, along with a few asthetic values and the prompting of some friends helping me with the code pushed me to change the rendering architecture to a more modular and independant design. So, here's our new Render interface (or at least a simplified version):
class CRenderWorld
{
public:
virtual int		Create( HWND hWnd, CViewParams *params ) = NULL;
virtual int		Destroy( void ) = NULL;

virtual void	Begin( void ) = NULL;
virtual void	End( void ) = NULL;

virtual void	Render( CNode *scene ) = NULL;

virtual void	Flip( void ) = NULL;

protected:

CCamera*		camera;
CLight*		        light;
//etc.....
};


The idea, obviously, is that we create one set of basic functions to interface with the rendering, and then create multiple render classes inherited from this to handle individual render pipelines. For example, I would have a CRenderWorldGL class that is an OpenGL implementation of this. To specify the exact renderer you simply say:
CRenderWorld *render = new CRenderWorldGL;

Pretty basic OOP stuff, yes? Okay, here comes the fun bits. First off: Obviously at this point we're stuck with providing a lot of new methods for each node to pass out the nessicary information to the renderer, which means that when programming new nodes you have to anticipate which information the renderer will need, which may be different from renderer to renderer. To an extent this is unavoidable with the OOP style of programming, but it's made more aggravating here by the needs of the system. Secondly: For every new node that is added, we now are faced with going into the core rendering code and adding new render routines to accomidate the new node type. In my opinion this kills a lot of the usefulness of the scene graph, since a big plus (in my mind) was the ability to add new items in a very simple and modular manner. In the end, I feel like I traded one set of problems for an entirely new set of them. I feel that there must be a better way of handling this, and am wondering how others with more complete rendering systems have handled this. Is there a more elegant way, or am I simply facing the cold hard reality of how it's done and just don't know it yet? (If you'd like any more details on how my code is structured just ask, I simply feel like this post is long enough as it it and don't want to scare anyone away ^_^)

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This is a massive subject with many pro/con arguments to different implementations.

Probably the best reference I found while constructing my scene graph was here and is what my graph is now based on. It uses a Renderer interface so all low level calls are hidden from the main engine, and then the concept of Global states and local Effects to apply variation to model data.

The Book includes a full source and is very well written it helped me out a lot.

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Thanks for the suggestion. I've been eyeing that book for a while now, maybe I'll have to finally just go for it!

I realize this is a pretty big topic, and I don't honestly expect a quick concise reply that's going to solve all of my problems. Actually, the post above was more of a thereputic thing for me than anything else. I find that if I take the time to write out my problems in detail it helps me visualise it, and may bring out solutions I hadn't thought about till I put it all down in writing.

My little thinking process goes something like this: I'll usually stew about a problem for a few days, writing up little chunks of code to help me see how it all connects together. If I haven't found a solution by then, I begin writing a Gamedev post asking for help on the subject, trying to be as detailed as possible. Many times once the post has been written I've had this great new idea that I can go and fiddle with, in which case the post is scrapped and I go back to work. If I still am stumped, however, I click post and hope for the best.

A good 90% of the questions I write out never actually make it to the forum ^_^

Anyway, thanks again for the suggestion, and I'm still more than willing to hear any others that people have to offer! In the meantime, I've caught a notion or two that I'm going to play with...

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Its very true that formulating a question sometimes becomes the answer itself!

After raving about that book, I should mention that it does have a number of things missing for a complete game such as integration of sound networking etc, have a look at the table of contents on Amazon. If you just want to look at the source go to http://www.geometrictools.com/ and pick through it, though its much easier with the book.

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(Nice book by the way, may have to read it myself)

Anyway, the solution to your problem is indeed to create a render class that can be inherited from for multiple platform/API render systems. Now you may think that there is a plethora of information that you have to store in your objects, but if you code it right, you only have to store the mesh and the textures, plus pointers to material. The example I will use here is my engine. Scene graph nodes in my engine store a mesh, their textures, and a pointer to the material which defines the way in which the mesh wants to look. The render device traverses my scene graph (in my implementation using both quad tree culling(for landscapes) and portal rendering(for indoor scenes)) and requests from each object a pointer to its geometry descriptors (a geom Desc is a collection of a mesh,texture set, and material, of course objects can return that they dont have any geometry information). It then stores the info in geom pots by shader. And at the end all the triangles are dropped to the shaders and everything is rendered. Now the only other thing, and the solution to your problem is this. The material defines a material type and a few parameters, which are then passed to the render device on initialization. The render device returns an ID of the shader that will fullfill the needs of the material. And this is stored in the material for later use by the render device. Thus all calls to libraries are now in a render system using pluggable shaders. This implementation is now extremely flexible as to what is done with data in the shaders, as well as cross platform/API by simply writing a new render class and shader set.

I hope this helps. I'm not sure if it's the best method to implement this functionality, but it seems to do an effective job for me.

- Matlock

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Thanks Nihilistic!

That actually sound a lot like what I was thinking of doing with the exception that I was thinking about having the renderer (or at least a resource manager within it) store the actual data rather than the nodes themselves, which instead would store a handle to the appropriate dataset. Still haven't actually tried IMPLEMENTING it, but it sounds nice in theory! ^_^ (Doesn't it always?)

Still wide open for suggestions, though!

[Edited by - Toji on July 19, 2005 11:21:14 PM]

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My approach is slightly different. I use the scenegraph purely to describe the scene data. The nodes do not even contain a Render function. Once the user has finished updating the graph and requests it to be rendered, the traversal function will sort the graph into a list of renderables (i.e. typically the geometries and lights in the scene). This sorting can be important as it allows you to group objects by texture or shader.

In the next step, this sorted list of objects is passed on to a pipeline of processor modules. (Processor is my own terminology; accepting suggestions for a better name). Each processor performs operations on the list of objects. The first processor is typically a culler that marks all objects out of the frustum as culled. The next processor could be an OpenGL (or Direct3D or software) renderer that uses a specific API to render the contents of the list.

In my library there are many more processors. For example: a processor for retrieving some statistics on the list (such as the number of triangles in it) that is useful for debugging, and a range of processors used for creating a distributed scenegraph over a set of PCs (I do parallel rendering).

This way you'll have a really flexible system that allows for very easy configuration (just choose the processors in the pipeline) that can be changed while running.

I'm not stating here that my solution is the best and without flaws; it's simply another option...

Tom

EDIT: One example of a drawback of this approach is that your second problem:
Quote:
 For every new node that is added, we now are faced with going into the core rendering code and adding new render routines to accomidate the new node type. In my opinion this kills a lot of the usefulness of the scene graph, since a big plus (in my mind) was the ability to add new items in a very simple and modular manner.

is also true for my approach. However, I believe that if your node requires you to add/modify code in the rendering core, you would have had to implement it's rendering routines anyway, because it apparently has unique rendering behviour (if not, it could have been derived from an existing scene node class). Only the place where this rendering code is inserted is more ackward (far away from the object in the rendering core).

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Hm... I like that idea very much! The whole "processor" idea ("Render Stage" maybe?) is intruiging. I'm thinking that if you could make the stages pretty generalized in their interfaces you could plug them into the render pipeline on the fly, allowing users to define new stages to go along with new geometry types. That probably isn't nearly as easy in code form as I made it sound (it never is), but it's worth looking into.

Oh, and just for kicks: One of the better scenegraph papers I've found thus far is This One. He sticks very close to the practical details, so anyone who's interested may want to take a look!

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Quote:
 Original post by TojiHm... I like that idea very much! The whole "processor" idea ("Render Stage" maybe?) is intruiging. I'm thinking that if you could make the stages pretty generalized in their interfaces you could plug them into the render pipeline on the fly, allowing users to define new stages to go along with new geometry types. That probably isn't nearly as easy in code form as I made it sound (it never is), but it's worth looking into.

Thats how my engine works. I have 'Graph-operators' which all inherit from a base SG_Operator. These can be thown together in any way e.g. UpdateOp->CullOp->RenderOp.

Any given operator conforms to 1 of 4 different classifications of graph-operators. An operator is first classified by the type of dispatch: Static or Dynamic. Static dispatch is achieved through the visitor pattern and fixed at compile time, dynamic dispatch is done through functors and can be changed at run-time. Next an operator is classified by what it dispatched for: Per-nodeType or static(all-nodeTypes). Per-nodeType operators perform a different operation for each type of node (geometry, transform, etc), Static operators perform the same operation for every node (such as culling).

Creating new scene-operators is easy so new operations can be added without changing the node base-class or adding new virtual functions. Adding new nodes is possible but for static dispatch scene-operators new functions must be added (as is the major con of the visitor pattern) but the dynamic dispatch operators have no such problem provided new nodes register their own functors for each operation (unless they're anti-social :)

scene-operators can be removed from the pipeline and even replaced during run-time. The engine maintains one single pipeline of scene-operators but there's no reason why the user can't maintain a pipe-line themselves (for some neat tricks.

The RenderOp doesn't render geometry directly it batches it up, sorts it by material etc (all of which can be customized through functors and virtual functions) and then renders it. Static geometry is pre-processed so after some culling its all ready to go.

Hope that helps :)

[Edited by - dmatter on October 12, 2005 11:42:46 AM]