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OpenGL 3D Object file format..

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Hey all, im heaving a hard to time to pick the right object format for OpenGL.. X, 3DS, Obj, Milkshape etc. there are soo many.. but i wanna know wich one is the best and got the most support? i aslo would like an a tutorial of a sample of how to load it.. thanks..

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hey.. unfortunately there is no native opengl support for any model format.. so any format you pick will require you to either use a third party library or you need to right your own loader.
Obj is pretty simple and there are a few loaders online, but it only supports basic features. X is not a great format imo, even MS seem to have abandoned it. I also was looking for a good format so that i could use models created in Maya, but I couldn't find anything that pleased me, and eventually ended up making my own format/importer/exporter..
So out of my lack of success, I wish you luck and hope you find things I didn't.

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yosh! thanks for the info dude..
i guess i gonna use the milkshape file formats cuz i seen it supported most by some tutorials i found online.. ill just have to get an exported to 3dmax for that format..
good luck to me xD

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What about collada? I went through the spec and it seems to cover just about everything. I plan to use it myself. There are also plugins to import/export to/from Maya and 3D Studio.

http://www.khronos.org/collada/

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Hello,
of those who's you mentioned, the strongest is MilkShape file format, I personally use it too.
Why? - It supports skinning mesh animations (with vertex weight), mesh groups, material parameters and so on...
Also Milkshape supports many other file formats, which allows you to model and animate your objects in other software (like 3dsmax or Maya).

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I also agree, obj is ridicolous simple to write own loader for. For static geometry and simple demos it is just fine. It is also trivial to extend it to support own objects such as cameras for example, there is also built-in support for user objects (with 'o' command), but it isn't difficult to add custom commands too, which seems to be quite common thing to do.

It is done to be written by hand, that is reason why it is so easy to work with it. But for same reason, it is not so usefull in production code since there are no forward specs for number of vertices, faces and so on - also there is overhead in parsing it. Adding more advanced features like skinned meshes is probably quite messy, so .obj format is not used so much for animated objects.

Another great and quite used format is lightwave's .lwo format, which is binary chunk-based format, written for fast loading which also has support for many more features than .obj, inclusive skinned meshes and such. It is alwo well docimented and there are lots of code online you can sue.

I found .X to be really great format. It supports skinned meseshes, curves and kitchen sinks. It commes in both binary and text flavour. It is also created with (user) extensibility in mind, so there is well-thaught and documented support for adding custom funcionality.

One of reasons to its un-popularity in past was its implementation. Microsoft shipped a library to read/write .X files only with DirectX, which is ugly written win32 dependent library. So nobody but directx developers really used this format. However it is open format and it is totally possible to write loader/writer for any API, OpenGL included. I think there was some attempt too, google around, there might be some open source library for .X files too.

Another reason to its impopularity is political, due to microsofts popularity of time, .X like everything else microsofts, enjoyed same bottom level popularity in some people minds.

Reason why microsoft seems to abandon the .X is probably due to it's structure - it is not XML. These days everything should be XML, especially if it is going to work with DNA. I am not sure about this, but I guess this is the reason. This is quite bad decision, but MS tried to kill COM and other stuff in flavour of .NET so I am not surprised it they wish to kill .X in favour of something XML.

You can read more about .X: http://local.wasp.uwa.edu.au/~pbourke/dataformats/directx/ or just use google, there are tons of references about it.

If you are starting out I suggest .obj to start with and move on to something better once you start playing with skinned meshes and animation.

If you prefer XML, Collada, W3D or VRML might be something to look at.

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Assimp loads them all.

For simple static meshes, .obj is actually fine. For more complex scenes, Direct3D .x files or Collada .dae files are better. Both support skinning and animation, which you usually need in a game. .3ds is fine for static models, as well - it's not read easily, but there's a lot of programs out there which can output .3ds files.

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I would personally either choose the ms3d, .obj, or .blend formats. Making an obj reader is INCREDIBLY simple, since it's a text based file format. the ms3d format is fairly common, and is created from a great 3d editor. Also, nehe.gamedev.net has some ms3d loading code (lesson 31). As others have said, it's a good format. Finally, i choose the .blend format because it's the native file format for the Blender editor, which is almost as good as milkshape (maybe as good), and it's FREE. So, blender is good if you're on a budget. And why waste so much money for an editor when you can get one almost as good for free (it's only a 30 day trial period that's free)?

So, happy coding! the format that I've used is the .obj format because it's simple to use and very widely known.

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opengl itself has nothing to do with the file format. you can use anyone or something of yourself.

i'd like to use obj files, for the reason that obj is a text file, so i can open the file to check what's inside for quick debugging.

the difficulty of using an obj file is that the file reader is more complicated than a binary file reader.

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I've just written a .obj loader, and I have to say that it's more complicated than it looks, thanks to the .obj's multi-indexed format (separate indexes for verticies, normals and texture co-ordinates).

Regards
elFarto

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      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. Shader variable type must be specified during shader creation by populating an array of ShaderVariableDesc structures and initializing ShaderCreationAttribs::Desc::VariableDesc and ShaderCreationAttribs::Desc::NumVariables members (see example of shader creation above).
      Static variables cannot be changed once a resource is bound to the variable. They are bound directly to the shader object. For instance, a shadow map texture is not expected to change after it is created, so it can be bound directly to the shader:
      PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new Shader Resource Binding object (SRB) that is created by the pipeline state (IPipelineState::CreateShaderResourceBinding()):
      m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
      Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
      m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
      m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
      As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
      This post gives more details about the resource binding model in Diligent Engine.
      Setting the Pipeline State and Committing Shader Resources
      Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
      m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
      The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
      m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
      Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
      m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
      Invoking Draw Command
      The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
      ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // 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); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes 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); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
      Source Code
      Full engine source code is available on GitHub and is free to use. The repository contains two samples, asteroids performance benchmark and example Unity project that uses Diligent Engine in native plugin.
      AntTweakBar sample is Diligent Engine’s “Hello World” example.

       
      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 multiple render targets, using compute shaders and unordered access views, etc.

      Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

      Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

      Future Work
      The engine is under active development. It currently supports Windows desktop, Universal Windows and Android platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and support for more platforms is planned.
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