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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 Compiling and running on different OpenGL versions

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## Recommended Posts

Hello,

I'm trying to understand a basic principle on how OpenGL works when the compilation/linking is done with one version of OpenGL, but the program actually runs on a different version.

I understand that if the runtime version of OpenGL is greater than the one it was built in this is not a problem: OpenGL is backward compatible so the program will run on a machine where a newer version of OpenGL is installed.

My problem is the other way around. My program is heavily dependent on advanced shader technology. So I have function calls such as glUniform... throughout the code.

So let's assume I built my program on a machine with the latest version of OpenGL. Now I'm going to take it to a machine running an older version. Quite possibly, a function such as glUniform... is not even present there. Given that nobody distributes software with OpenGL - either DLLs on Windows or shared libraries on Linux - will my program simply crash if I run it on a machine with an older version of OpenGL?

I'm used to building applications that rely on other libraries - but their shared libraries are usually shipped along with the application. But I don't think OpenGL follows this practice: people usually have OpenGL on their machines and use their own version.

Can somebody explain to me how this works in the general case? For example, can I just query OpenGL at runtime for the version number and simply skip calls that rely on newer versions? Will the application even load properly?

Thanks.

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Most of the openGL functions you use, are fetched from at runtime in the form of a function pointer (see openGL wiki on function loading).

Usually youd use a helper library like GLEW to automatically do the loading (it declares all the functions as function pointers and attempts to load them I assume).

So, presumably, if a function is not supported, the function pointer returned when trying to load a GL function at runtime will be nullptr or some other value (not sure what platforms wouldnt return nullptr) that will cause your program to crash if you try to call it...

This also means, you can always do checks at runtime to ensure you have the correct opengl version available, and even individual functions. If youre using a lower opengl version, you can try loading some functions not available in your gl version as an extension as well (like if theres something specific you need from the higher version, but you cant ask for full support of that version for some reason)

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Hi Waterlimon,

Thanks! Very clear.

So, if I understand this correctly, I can build my application on, say, OpenGL 4.2. Then, at runtime, use glGetString (GL_VERSION), parse the string to determine the version, and avoid calling functions that probably won't be available.

For example,

#ifdef GL_VERSION_4_2
/* use 4.2 functionality here */
if(parsedversion(glGetString(GL_VERSION)) >= 42) {
/* use the functionality here */
}
#endif


where "parsedversion" is some simple function that just parses the string with the version and generates an equivalent integer I can use for comparison purposes.

Of course, I could have a  "} else {" statement for a fall back approach to the functionality in case 42 is not available on the running machine. But, at this point, all I want is to make sure it won't crash.

If everything is about call a function with a null pointer, then the above code should prevent the crash. Correct?

Thanks!

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One more thing - although I'm not sure this is the place for the question:

I'm using GLEW on Windows, and include the GLEW DLL with the distribution.

Suppose I build with the latest version of GLEW then I try to run on a machine that is so old that the graphics card is unable to support the version I include in my distribution. Would glewInit() fail? Or - because the DLL is from the latest version of GLEW - could I see that glGetString returns a version I believe would work (because it is my GLEW DLL they are using), but the call could still fail?

In other words, I'm trying to protect myself from a crash. I have no problem reporting that a feature is not supported, but I cannot have the application crash. If glewInit() fails that's no problem because I will report this as an error.

Thanks again.

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Something else to be aware of... you've said "advanced shader technology" and then you mention glUniform calls.  glUniform is not advanced.  In fact hardware that supports shaders has been around for longer than hardware that doesn't.  It's perfectly reasonable to require this level of hardware as a bare minimum in 2015/2016, and not even worry about fallbacks.

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Hi mhagain,

Thanks.

Unfortunately, what we distribute is a library that gets embedded into an end-user application that may go to thousands of end users. And I have no control over what end users are still using (you'd be surprised!).

So I have to assume the worst - even if that means people may still be at GL 1 (ok... maybe not that far back). But my source is full of #ifdef GL_VERSION_X_Y so that the end-user application can be compiled regardless of the version of GL they choose to use, and their end users can run it also regardless of what they have on their machine.

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OpenGL versions can be kind of messy.

The easy way is to just check for a minimum OpenGL version at the start of your application and then just use everything that is available in that version.
The older the hardware is you want to support, the more work and/or limits you have.

There are Onboard and integrated GPUs that have lower OpenGL support. Lot of people are using Intel iGPUs on PC.
Then there are mobile devices and micro computers (Like the Raspberry Pi) that only support OpenGL ES.
Also mesa (oss Linux drivers) and Mac OS drivers only support higher OpenGL versions as Core version. (Core = no backwards compatibility)

You won't target most of that anyway, but I hope that gives a raw overview.

Extensions:

There are "Core Extensions" like ARB_direct_state_access (not to be confused with EXT_direct_state_access) that are always present starting with a specific version of OpenGL. In the case of ARB_direct_state_access it is Core since OpenGL 4.5 .

Core Extensions may also be supported when you have a lower OpenGL version. You just ask the driver if ARB_direct_state_access is supported and if yes, you can use the associated functions exactly the same.
Note that OpenGL may not list Core Extensions if you use a Version where the extension is garantied to be present.
E.g. if you use OpenGL 4.5 you may not find ARB_direct_state_access in the list of supported extensions.

If you go way back in time you find that many older ARB extensions (Before GL3.0 I think) still use ARB suffix in function and other names. Therefore they are never the same naming then the equal core version.

And then you have a lot of EXT or NV/ATI/AMD ect... extensions that are never guarantied to be present.
But some of them are basicly always avaiable. For example GL_EXT_texture_compression_s3tc.

Also the NV/ATI/AMD ... is only the name of the creator of the extension. You find nv extensions in AMD drivers and AMD extensiosn in nvidia drivers, etc...

The messy part is that you don't have to enable extensions.
So you may use functions of a extension withotu testing if the extension is supported.
As long as you run your application on hardware/drivers that support this extension, you will not notice this!

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Osbios,

Messy all right...

Following the link that Waterlimon posted I learned that glGetString(GL_VERSION) is deprecated and has been removed in 3.1. So in order to find out the version I'm using at runtime I need to first know the version (!) so I know which function to call. I can certainly use #ifdef GL_VERSION_3_1 to decide which function to call depending on the compiler being used. But then I need to retrieve the runtime version to decide what to do.

For the moment we use no extensions, only the #ifdef GL_VERSION_X_Y at compile time, and glGetString(GL_VERSION) at runtime. I'm sure in the near future this will need to change...

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Considering I created my own OpenGL header files from scratch after using the mess of GLEW I can understand why you have trouble with it.

Does GLEW still have the glGetString bug? If I remember correctly that should have been fixed a long time ago.

So if you use glew, you just check the OpenGL version at runtime

//some init code to make the gl context

GLenum err = glewInit();

if (GLEW_OK != err) {

//Problem: glewInit failed, blablabla...

//And then we kill the application :'(

}

if (!GLEW_VERSION_3_3) {

//terrible sad error here where we tell the customer he needs better hardware or drivers

//And then we kill the application :'(

}

//if we reach this we are in happy OpenGL 3.3 land and can use everything OpenGL 3.3ish

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not sure what platforms wouldnt return nullptr