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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 OpenGL Performance and Optimization

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## Recommended Posts

Hi there,

Like many other poor, unfortunate souls, my OpenGL game engine was based off of the skin and bones of well-known tutorials and articles on the web, which resulted in the engine being heavily based on slow techniques such as glBegin/End loops and other immediate mode junk. I have the feeling now that the performance of my engine can be improved significantly due to its lackluster performance at the moment.

I was wondering what techniques I can use to speed up my engine. Right now, the GL code is scattered in and out of the engine's internal logic and systems, so I'm wondering if GL is getting confused or lagging because it is depending on my engine to handle a bunch of stuff for every frame while it is trying to run in and of itself.

I don't know too much about it, but is there a way to encapsulate all of my OpenGL code in a place where the engine internals and logic aren't slowing it down or messing it up? Someone mentioned that a lot of my OpenGL code is running in software mode, which is not good. I think the general idea should be to get as much of it as possible into hardware mode.

I think I most probably should handle things in this fashion:

1) Perform non-OpenGL, engine and game stuff (or have them in a seperate thread entirely).
2) Update an intermediary "buffer" of data that translates non-OpenGL data (ie. model and sprite positions, animations, deformations etc.) into data that OpenGL can execute when it is time to render (using vertex arrays, vertex buffers, etc.)
3) Render all of the OpenGL stuff without having to manipulate any data (as all of the manipulation has been performed prior to the render call).

The jist that I am getting from people is that I need to stop using glBegin/End loops for literally everything and make as much use from vertex arrays and vertex buffers as possible. I've also been advised that display lists are deprecated, so I think I will try and avoid those.

However, as much as I think I should avoid software (non-OpenGL) processing in the middle of the OpenGL rendering process, there are a few things that I think will be unavoidable, such as setting uniforms in shaders and things like that.

Anyway, basically I'm just looking for pointers on how to optimize my rendering. Am I correct about the things I have stated above? I think that to increase the performance of my engine I need to do the following:

1) Keep the non-OpenGL and OpenGL processing as seperate from one another as possible (and probably in different threads at some point).
2) Translate all necessary data into vertex arrays and vertex buffers before the OpenGL rendering process.
3) Perform all the OpenGL rendering at once.

Feedback very much appreciated. I'd also like to know what aspects of OpenGL are handled in software and what are handled in hardware.

Cheers,
- Sig

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I was wondering what techniques I can use to speed up my engine. Right now, the GL code is scattered in and out of the engine's internal logic and systems, so I'm wondering if GL is getting confused or lagging because it is depending on my engine to handle a bunch of stuff for every frame while it is trying to run in and of itself.
[/quote]

I don't know where you came up with this, but it sounds like BS to me. OpenGL doesn't get 'confused'.

The jist that I am getting from people is that I need to stop using glBegin/End loops for literally everything and make as much use from vertex arrays and vertex buffers as possible. I've also been advised that display lists are deprecated, so I think I will try and avoid those.
[/quote]

This, on the other hand, is a good idea. Immediate mode is terribly slow compared to using vertex buffers. One thing that can slow down opengl is making lots and lots of opengl calls, which is what immediate mode is all about. If you can render a mesh with 5-10 calls that's a big improvement over per-vertex opengl commands.

However, as much as I think I should avoid software (non-OpenGL) processing in the middle of the OpenGL rendering process, there are a few things that I think will be unavoidable, such as setting uniforms in shaders and things like that.
[/quote]
This is wrong. It doesn't matter what you do in between opengl calls. An opengl call just puts a little data in a pushbuffer for the gpu to fetch on its own. This happens totally separate to what's going on in your client side program, and opengl doesn't care if you do other things in between calls. In fact I could imagine this being slightly faster then batching up all of the calls at the end of the frame, as you're giving the GPU more time from when you start handing it work before you're waiting for it to finish to swap the frame. Still you may prefer to put all the opengl code together just for the sake of organization and your sanity

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Your engine probably won't get that much faster if u only modularize everything( divide the rendering from the game logic), but it is highly encouraged, because of all the benefits u get working with it.
Adding new features will become allot more easy and so on.

From a performance perspective you want to talk as less to the GPU as possible, the GPU shouldn't be spending half its time processing commands or data from your engine it should just render things :-)
So storing your geometry data in BufferObjects is of course the first step, because u will only send the data once. The second thing is to somehow order your rendering so as less OpenGL state changes are made as possible(changeing Shader, Textures ...)

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First you should bring all your OpenGL code to one central point, it much easier to have all your rendering code together and you'll need it to be together for some optimizations you can do later.
Start using vertex buffers but dont build them every frame, most of your vertex buffers you will only have to fill on load time (just like textures)

If this isn't a big improvement enough for you you can think about culling, no need to make render calls for objects you wont even see.
Finally you can do sorting / batching, since you got all your rendering in a central place now you can do this relatively easy.
About having a rendering thread i'm not sure but if you insist you can look into command buffers.

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However, as much as I think I should avoid software (non-OpenGL) processing in the middle of the OpenGL rendering process, there are a few things that I think will be unavoidable, such as setting uniforms in shaders and things like that.

This is wrong. It doesn't matter what you do in between opengl calls. An opengl call just puts a little data in a pushbuffer for the gpu to fetch on its own. This happens totally separate to what's going on in your client side program, and opengl doesn't care if you do other things in between calls. In fact I could imagine this being slightly faster then batching up all of the calls at the end of the frame, as you're giving the GPU more time from when you start handing it work before you're waiting for it to finish to swap the frame. Still you may prefer to put all the opengl code together just for the sake of organization and your sanity
[/quote]

This isn't really true, in fact the OP is more on the ball here.
The first thing is that GPU drivers will buffer up a couple of frames worth of calls before they are dispatched. So you might have to issue quite a few draw calls before the card starts processing what you ask it to. (I believe both AMD and NV buffer at least about 2 frames worth of data before getting under way).

In fact the better way to go about it is to buffer up all your GL/D3D calls until you have a list of what you want to process and then blast through it; the reason for this is because each call transistions from your code to the
driver and back, by batching everything up and doing it in one go you get better cache usage on the CPU which can be a win.

An increasingly common method of dealing with this is to figure out what you want to draw and put it into a sorted list (well, some form of contiguous memory buffer anyway), then when you have all this up front you can do the least amount of work possible to render things as you can batch up state block setting and instanced draw calls to make good use of data and instruction caches.

(This setup also lets you assemble the draw list over multiple threads before using a final thread to kick the draw off which can speed things up vs trying to sort and draw everything on a single thread).

All that said the amount you want to worry about all that depends on just how hard you want/need to push the system. Assembling a draw list across multiple threads for example is an extreme end optimisation as it certainly won't be easy to do and do right/quickly.

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Structuring your code better is definitely highly recommended but it's not going to get you anything if you're bottlenecked elsewhere. The first thing you need to do is get away from immediate mode; even just a simple switch to vertex arrays will be of benefit to you here. You also need to examine your code carefully for any potential software fallbacks and cases which could cause your CPU and GPU to need to sync. On modern hardware you can quite easily fall back to software in some places by just using formats that are not natively supported by your hardware. A classic example is glTexSubImage2D; if you're using than anywhere in your code, and if you're using a GL_RGB format, you're probably falling back to software for texture updates. Anything that needs to read back from the GPU will cause a sync so watch out for glReadPixels, occlusion queries, etc.

OpenGL.org has a good Common Mistakes page that you can use a reference for sanity-checking your code; it's explicit purpose is to address bad code that people have picked up from tutorials: "Quite a few websites show the same mistakes and the mistakes presented in their tutorials are copied and pasted by those who want to learn OpenGL" and some of the items discussed on it will probably ring a bell with you.

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occlusion queries have a callback that lets you know when the result is ready
GL_RGB...? can someone verify this? because ive heard the exact opposite

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I have no knowledge about those stuff, but I also heard/read some times about using BGR instead of RGB for some performance reasons

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I have no knowledge about those stuff, but I also heard/read some times about using BGR instead of RGB for some performance reasons

From what I understand, BGR is used for some image formats such as TGA files. Although I am sure there is more to it than just that.