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OpenGL OpenGL doesn't do fog??!?

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I''m pretty new to this 3D stuff, and recently, someone I know (whom I kinda respect) mentioned that OpenGL doesn''t do fog. I kindly corrected him, telling him the there is a function called glFog() (and others like glFogi, etc). Then he went on to some sort of BS about OpenGL doesn''t natively supporting fog(?), unlike Direct3D8. The point is, being a 3D newbie, I''m pretty confused and I need clarification.

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Simple Demonstration

GLfloat colours[4] = {(GLfloat) 0.75, (GLfloat) 0.75, (GLfloat) 1, (GLfloat) 0.25};

//*** TEST FOG
glFogi(GL_FOG_MODE, GL_LINEAR);
glFogfv(GL_FOG_COLOR, colours); // same as clear colour
glFogf(GL_FOG_START, 8.0);
glFogf(GL_FOG_END, 30.0);
glFogf(GL_FOG_DENSITY, 0.2);
glEnable(GL_FOG);

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then maybe you should READ the OpenGL and Direct3D specifications to clarify.

To the vast majority of mankind, nothing is more agreeable than to escape the need for mental exertion... To most people, nothing is more troublesome than the effort of thinking.

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That''s bullsh*t. OpenGL definately does fog, and can also do everything Direct3D can (arguably more through the extension mechanism); such features will either be part of OpenGL itself or extensions.

Also, we must not forget that since nobody but Microsoft makes an OpenGL binding on Windows, Windows platforms are stuck at API version 1.1, while 1.3 hardware compliance already exists...

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merlin9x9: that''s why people should stop answering these kinds of POST''s. if the original poster knows that there are functions such as "glFog" incorporated into the OpenGL API, then why would they ask if OpenGL has support for fogging. yeah, i thought "glFog" was for vertex arrays or something the first time i saw that function, and "glVertex" is for texture coordinates. furthermore, if the original poster, read any of the OpenGL programmer''s guide, reference guide, or any OpenGL documentation at all then they would have been able to conclude the answer to that question on their own. unfortunately, the world seems to think that becoming a professional programmer does NOT require years of training, practicing and most of all, THINKING. that''s it, everyone, keep jumpin'' on the programming bandwagon.

To the vast majority of mankind, nothing is more agreeable than to escape the need for mental exertion... To most people, nothing is more troublesome than the effort of thinking.

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Jenova ... I agree with you

Nuffsaid ... I don''t mean this unkindly, but try searching Google or similar for glFog ... you''ll get all the answers you need

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In fact - just to add to the above ...

The graphics cards themselves support many advanced rendering techniques - NOT the API. The API only exposes the functionality of the cards. Which is why (in many respects - no flame wars please) OpenGL is better - this advanced functionality is exposed very quickly via OpenGL extensions - whereas Microsoft DriectX fans have to wait for a new version of DirectX!

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The thing I need clarification isn''t whether OpenGL does fog (which I know as I posted about glFog, etc), I just need some explanation about the BS bit like OpenGL doesn''t do fog natively(?).

This friend of mine said something like OpenGL uses the Alpha channel to do fog which is like a cheap hack, and is different from the way D3D does, and he went on to a long lecture about some stuff that I''ve never even heard off.

Sorry if I pissed anyone off, the title should have been something like "OpenGL doesn''t support fog natively?". I''ve searched Google, opengl.org and the MSDN about this, and I''ve come up zip, or with stuff that''s way over my head.

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To answer your question, yes OpenGL supports fog natively and it does not use the alpha chanel (as far as I know). It uses the z-buffer value in a formula that calculates the amount of fog then multiplys that to the fog color and finally adds that to the pixel color to get the final result. (the exact same way D3D does it).
In fact if the hardware supports fog then both OpenGL and D3D will be useing the same hardware calls to do the fog.
Nothing personal and not to start flames but your friend sounds like a microsoft zombie. any BS that ms puts out he believes. He''s one of those OpenGL is an obsolete API that can''t do anything people because that''s what MS say''s. I''d like to see them sit down and learn OpenGL once to see that it can do everything d3D can and usually is easyer to program.
I like meating people like that and busting there bubbles Maybe you should send him over to my house so I can set him straight?

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Yes, it has native support for fog. That is, fog is supported in all versions of OpenGL ( 1.1, 1.2, 1.3 ) without having to use an extension. What''s true however is that if your hardware doesn''t support fogging, it will get emulated by OpenGL, probably with that alpha-blending trick you mentionned. I think that''s what happens with old Vaudoos. But well, if there is no hardware support, D3D is no way different then.

Y.

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here is a link to the entire OpenGL reference manual and programmers guide. full OpenGL 1.1 function call specifications, as well as detailed information of the algorithms used to calculate fogging, projection, etc. and examples and source code. it''s a good place to start if you are SERIOUS about becoming a OpenGL developer.

http://ask.ii.uib.no/ebt-bin/nph-dweb/dynaweb/SGI_Developer/OpenGL_RM

http://ask.ii.uib.no/ebt-bin/nph-dweb/dynaweb/SGI_Developer/OpenGL_RG

peace.

To the vast majority of mankind, nothing is more agreeable than to escape the need for mental exertion... To most people, nothing is more troublesome than the effort of thinking.

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Guest Anonymous Poster
quote:

What''s true however is that if your hardware doesn''t support fogging, it will get emulated by OpenGL, probably with that alpha-blending trick you mentionned. I think that''s what happens with old Vaudoos.



No, even the oldset Voodoo-1 did per-pixel fog in hardware.
The only place where it emulates it by vertex alpha blending is in software mode, or if you specifically ask for it.

- AH

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Guest Anonymous Poster
quote:
Original post by merlin9x9
Also, we must not forget that since nobody but Microsoft makes an OpenGL binding on Windows, Windows platforms are stuck at API version 1.1, while 1.3 hardware compliance already exists...


Use the Silicon Graphics Incorporated libraries instead. Firstly they are at higher versions, secondly they rendered textures, smooth and rendered polygons faster (lines are slower) and thirdly the source is available.

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So we can get v1.3 from sgi for windows?

Another thign I dont understand. If people realy want OpenGL for Windows, why hasn't a 3rd party or even SGI taken control back of the Windows implementation. MS is not supporting it anymore, so what is stopping someone from writing there own version of the libs? I would figure then that all card manufacturers do that. But why not just have 1 3rd party write the standar 1.3 libs with all the latest features of the ARB and have the card manufactures include there extra features through extensions. To my understanding to get the 1.3 features of OGL working with windows 1.1, the card manufactures have to implement them as extensions.

Edited by - ANSI2000 on November 14, 2001 12:44:24 PM

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i can''t believe this POST received 14, i mean 15 replies.

To the vast majority of mankind, nothing is more agreeable than to escape the need for mental exertion... To most people, nothing is more troublesome than the effort of thinking.

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quote:
Original post by ANSI2000
So we can get v1.3 from sgi for windows?

Another thign I dont understand. If people realy want OpenGL for Windows, why hasn''t a 3rd party or even SGI taken control back of the Windows implementation. MS is not supporting it anymore, so what is stopping someone from writing there own version of the libs?


ms wont let anyone else make a vesion of opengl32.dll. my bet is when opengl2.0 comes out all these problems will be solved (ie a clean break).

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quote:
Original post by zedzeek
ms wont let anyone else make a vesion of opengl32.dll. my bet is when opengl2.0 comes out all these problems will be solved (ie a clean break).



What makes you say that? AFAIK, there''s nothing stopping MS from preventing anyone else from making a new version of opengl32.dll.

But what I don''t get is, why no just change the name of the DLL to SGI''s DLL, which is just opengl.dll & glu.dll? Wouldn''t that circumvent MS''s restriction?

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quote:
Original post by NuffSaid
What makes you say that? AFAIK, there''s nothing stopping MS from preventing anyone else from making a new version of opengl32.dll.

But what I don''t get is, why no just change the name of the DLL to SGI''s DLL, which is just opengl.dll & glu.dll? Wouldn''t that circumvent MS''s restriction?


There are potential legal issues with updating the OpenGL MCD shipped with Windows, but nothing is certain until it happens. The OpenGL ARB is getting pretty ticked off at Microsoft (read the ARB notes), since they (SGI) have had up-to-date MCD''s for Windows ready to go for years (Microsoft has had the longest ''testing'' period in history specially made just for the MCD''s). You are able to replace them yourself, but how many people will do that?

[Resist Windows XP''s Invasive Production Activation Technology!]

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      // Define input layout InputLayoutDesc &Layout = PSODesc.GraphicsPipeline.InputLayout; LayoutElement TextLayoutElems[] = {     LayoutElement( 0, 0, 3, VT_FLOAT32, False ),     LayoutElement( 1, 0, 4, VT_UINT8, True ),     LayoutElement( 2, 0, 2, VT_FLOAT32, False ), }; Layout.LayoutElements = TextLayoutElems; Layout.NumElements = _countof( TextLayoutElems ); Finally, pipeline state defines primitive topology type. When all required members are initialized, a pipeline state object can be created by IRenderDevice::CreatePipelineState() method:
      // Define shader and primitive topology PSODesc.GraphicsPipeline.PrimitiveTopologyType = PRIMITIVE_TOPOLOGY_TYPE_TRIANGLE; PSODesc.GraphicsPipeline.pVS = pVertexShader; PSODesc.GraphicsPipeline.pPS = pPixelShader; PSODesc.Name = "My pipeline state"; m_pDev->CreatePipelineState(PSODesc, &m_pPSO); When PSO object is bound to the pipeline, the engine invokes all API-specific commands to set all states specified by the object. In case of Direct3D12 this maps directly to setting the D3D12 PSO object. In case of Direct3D11, this involves setting individual state objects (such as rasterizer and blend states), shaders, input layout etc. In case of OpenGL, this requires a number of fine-grain state tweaking calls. Diligent Engine keeps track of currently bound states and only calls functions to update these states that have actually changed.
      Binding Shader Resources
      Direct3D11 and OpenGL utilize fine-grain resource binding models, where an application binds individual buffers and textures to certain shader or program resource binding slots. Direct3D12 uses a very different approach, where resource descriptors are grouped into tables, and an application can bind all resources in the table at once by setting the table in the command list. Resource binding model in Diligent Engine is designed to leverage this new method. It introduces a new object called shader resource binding that encapsulates all resource bindings required for all shaders in a certain pipeline state. It also introduces the classification of shader variables based on the frequency of expected change that helps the engine group them into tables under the hood:
      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 tutorials, sample applications, asteroids performance benchmark and an example Unity project that uses Diligent Engine in native plugin.
      Atmospheric scattering sample 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, Linux, Android, MacOS, and iOS platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and Metal backend is in the plan.
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