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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 Why do most tutorials on making an API-agnostic renderer suggest that it's done at buffer/texture level?

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Ive always wondered about this.I wanna port my renderer to OpenGL(currently only using DirectX), however it would seem that having, for instance, a class Mesh that has directx or opengl buffers in it would be way simpler than making a buffer class that either encapsulates an opengl or a d3d buffer, since stuff would get really messy when encapsulating things that differ too much between APIs.For instance in D3D all shaders inherit the same interface and are created and used the same way, while as far as I know in OpenGL shaders required for geometry or tessellation are used a little differently, so making a Shader class that encapsulates all d3d shader functionality might be easy, but making one that can be used for both D3D and GL would be way harder and messier than just making a higher-level RenderEffect class, where you write in it whatever you want for either the d3d or gl code as long as the end result is the same.I'm even considering making an entirely different renderer for OpenGL, it just seems so much easier to do the abstraction on a higher level than the lower one.

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A few reasons I can think of:

1) it requires (at least superficially) the least amount of thinking / planning to just wrap the low-level API objects

2) by keeping the abstraction at low level you should, theoretically, be able to construct complex API-agnostic higher level rendering code, and not have to duplicate eg. the functionality of Mesh for different APIs

3) A tutorial stays more generally applicable if it doesn't impose its own higher-level constructs

It has potential to get messy, though. For an example here's a list, from my engine, of D3D / OpenGL differences that "leak" from the low level abstraction to the higher. It's not unmanageable, but not pretty either. https://code.google.com/p/urho3d/wiki/APIDifferences

Edited by AgentC

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The answer is pretty simple, actually. Most people that write tutorials on the Internet, while certainly well-meaning, have fairly little idea what it is they're doing/talking about. Doubly so for how to explain it. I'll get back to this in a moment.

You're on the right track, though, good to see you've managed to pick the proper level of abstraction.

EDIT: From personal experience, having mesh/particle, light and camera primitives (while exposing some things like shader parameters) seems a good jumping-off point. This is generally flexible enough that you can create most any rendering effect with minimal overhead. I also suggest designing your system to be both very content-oriented and minimally retained; this puts the power in the hands of the artist(s) and also makes debugging/multithreading easier, as all information is usually on-hand.

I don't mean to pick on you, AgentC, but a rebuttal:

A few reasons I can think of:

1) it requires (at least superficially) the least amount of thinking / planning to just wrap the low-level API objects

2) by keeping the abstraction at low level you should, theoretically, be able to construct complex API-agnostic higher level rendering code, and not have to duplicate eg. the functionality of Mesh for different APIs

3) A tutorial stays more generally applicable if it doesn't impose its own higher-level constructs

It has potential to get messy, though. For an example here's a list, from my engine, of D3D / OpenGL differences that "leak" from the low level abstraction to the higher. It's not unmanageable, but not pretty either. https://code.google.com/p/urho3d/wiki/APIDifferences

1) So, in essence, you're making code harder to follow by splitting it up at a very fine level, adding runtime overhead by adding superfluous virtual function calls, etc. just so that you can be typing code into an IDE *right this instant*? That seems a *very* poor tradeoff. This seems to be the thought process behind a lot of tutorials, actually.

EDIT 3: This kind of thinking is also what gave us JavaScript, FWIW.

2) Maybe in theory. By your own admission, though, there are often fundamental differences in how the API works that render this 'abstraction' meaningless anyway-- you still need to add more of them at different levels, which will in turn make code harder to follow.

3) Isn't the point of a tutorial to demonstrate how to take the low-level API and map it to higher-level constructs *anyway*?

Edited by InvalidPointer

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[..] it just seems so much easier to do the abstraction on a higher level than the lower one.

Whether it's a generic interface to renderer(s) or something else, abstractions tend to work better at a higher level. Otherwise you may as well stick to the low level code minus the abstraction in the first place.

Designing this well is another issue...

 You seem to have come to these conclusions on your own. Perhaps you are just seeking validation.

Edited by achild

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1) So, in essence, you're making code harder to follow by splitting it up at a very fine level, adding runtime overhead by adding superfluous virtual function calls, etc. just so that you can be typing code into an IDE *right this instant*? That seems a *very* poor tradeoff. This seems to be the thought process behind a lot of tutorials, actually.

EDIT 3: This kind of thinking is also what gave us JavaScript, FWIW.

2) Maybe in theory. By your own admission, though, there are often fundamental differences in how the API works that render this 'abstraction' meaningless anyway-- you still need to add more of them at different levels, which will in turn make code harder to follow.

3) Isn't the point of a tutorial to demonstrate how to take the low-level API and map it to higher-level constructs *anyway*?

Note that I was not trying to advocate a low-level abstraction, but to explain why such approach might be chosen. Like you said, tutorials are many times written without sufficient insight. A *good* low-level abstraction (if one can exist) certainly takes careful planning, and it shouldn't involve virtual functions :)

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It has potential to get messy, though. For an example here's a list, from my engine, of D3D / OpenGL differences that "leak" from the low level abstraction to the higher. It's not unmanageable, but not pretty either. https://code.google.com/p/urho3d/wiki/APIDifferences

Thanks. This is a good list of potential problems to look out for.

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IMO the portable graphics layer should be:
• Not just a thin wrapper of the underlying API; some abstraction should be done.
• At the very least, the "state machine" behavior of the underlying API must be abstracted away (so that higher level rendering code does not have to worry about 'which states were previously set').
• The majority of API differences should be hidden, and helpers provided for any that do leak (thing like D3D9's idiotic pixel coords, or GL's idiotic NDC are hard to fully hide).
• Keeping the above in mind, it should be as low level as possible so that new rendering code can easily be written across platforms using these abstractions.
• Pet peeve: please don't use abstract base classes (virtual) to separate the interface and implementation(s) of your API. It's unnecessary, it's a huge cause of poor cache behavior and it's a violation of OO design to boot.

I've worked as a graphics-programmer on a game team and on an engine team, so I've been a user of these abstractions and an implementer of them.
When working on the game side, our abstract render layer was hiding about 5 different graphics APIs underneath. I had a lot of unique effects that I had to make for the game, which required low-level graphics programming -- I would much rather do this work once on an abstract API as described above rather than doing it 5 times!

In my API, I expose textures, vertex buffers, index buffers, constant buffers, input layouts (buffer->shader binding), render states and a high-level shader object (vertex/pixel/etc all set in one go) because then you can write nearly any graphical effect on top of this API, instead of repeating work.
As long as you abstract away the state machine and submission of commands, it's fairly easy to hide most underlying API differences.

It kinda depends on who the target users of your abstract API are. If you don't want/need the users to be able to implement new lighting pipelines, shadowing techniques or special effects, then you can make your API very high level without any worries. You then implement this high level API once for each 'back-end' API, with a large amount of very different code. A graphics programmer maintains the back-end.
If however, you're making an engine that should be able to be used by graphics programmer to implement new features, then your API needs to be a bit lower level, as described above. You have graphics-programmers maintaining the fairly thin/simple back-ends (not any real graphical techniques here, just mapping one abstraction to another) and you also have graphics-programmers implementing graphical techniques on top of your API.

I actually recommend a 3-tier system, where I've described the lowest tier above (the abstraction of D3D/GL/etc into a single stateless API), then there's a middle tier that implements lighting/shadows/effects/etc on top of this API and exposes high level objects like lights and models, which are used by the top tier to build a game without specialist graphics knowledge.