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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 Optimising 3D rendering order

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I've read that the order in which objects are rendered can make a big difference to performance, but there are two different strategies and I'd like to know if one is better than the other or "it depends" etc. They can be used together with major and minor sort orders, but which should be minor and which major? I'm most interested in OpenGL ES 2.0, but I think the same principles would apply to DirectX etc.

The first strategy is to aim to minimise the number of OpenGL state changes because they are allegedly expensive. I wouldn't have thought it would make much difference, but Mario Zechner (who wrote quite a good book about Android game development and libgdx, so I think he knows his stuff) says it can make a huge difference and advocates the use of sprite batchers for 2D rendering (where the alternative of depth sorting is irrelevant). So if you have a number of objects with the same mesh and material/ shader/ textures in different positions, you should only select their VBOs etc once per frame and render them all together before rendering objects of another type. You can go a step further and group all objects with the same shader but different mesh etc.

The other strategy (for 3D only) is depth sorting. Checking the Z-buffer and not overwriting a "nearer" pixel is supposedly much quicker than updating the framebuffer so, somewhat counter-intuitively you should render objects in near-to-far order. But are a few wasted writes to the framebuffer really slower than applying every object's MVP to its centre point and sorting? Can that be done on the GPU? I don't actually know whether GLSL variables can be uses as outputs to be read back by the CPU after running a shader, but I suspect not. And I presume that anything more complicated than sorting on centre points, ignoring whether objects overlap in XY camera space, only considerably increases pain for decreasing gain?

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Unfortunately, "it depends." Different hardware/drivers can have more bottlenecks in managing state changes and others can have more problems with fill rate. It also depends on your scene and how many overlapping complex surfaces you have and how many pieces of state you need to change for each draw.

In general, you should optimize for both. You can minimize buffer state changes by using fewer VBOs (you can stuff multiple objects in each VBO/IBO and then use index ranges to draw a single object out of each). You can minimize texture state changes via atlases and texture arrays. You can minimize shader state changes by using a unified shading model.

It's even quite feasible to just support both sort modes and then use the proper one for the given hardware profile. If you use the method described at http://realtimecollisiondetection.net/blog/?p=86 then you can change up how you generate your sort key based on various compile-time and run-time criteria.

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Personally I'd first go for one and dig deeper if your performance needs it.

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The first strategy is to aim to minimise the number of OpenGL state changes because they are allegedly expensive. I wouldn't have thought it would make much difference, but Mario Zechner (who wrote quite a good book about Android game development and libgdx, so I think he knows his stuff) says it can make a huge difference and advocates the use of sprite batchers for 2D rendering (where the alternative of depth sorting is irrelevant).

I am writing a book on iOS optimizations and he is quite correct in that respect.

The other strategy (for 3D only) is depth sorting.

This does not apply on tile-based deferred renderers such as those used in mobile devices. They already remove hidden surfaces before running the pixel shader, so sorting front-to-back literally does nothing but waste cycles (I have tested it).

But are a few wasted writes to the framebuffer really slower than applying every object's MVP to its center point and sorting?

Since there won’t be any wasted writes thanks to tile-based deferred rendering, you would have technically come to the correct conclusion, except that:
#1: You don’t determine the distance the object is from the camera by multiplying anything by its model-view-projection matrix, you get the distance from the camera via any of several methods involving the camera and the object’s bounding box or bounding sphere (squared distance from camera to bounding volume’s center, dot product between camera forward vector and bounding volume’s center, squared distance from the camera to the edge of the bounding sphere, etc.—take your pick).
#2: You always have to transform the bounding volume by the object’s world matrix anyway, so it’s virtually free, meaning that yes, it often makes up for overdraw, at least on systems that actually have overdraw on standard opaque renders.

And I presume that anything more complicated than sorting on center points, ignoring whether objects overlap in XY camera space, only considerably increases pain for decreasing gain?

You presume incorrectly.
Shader and texture swaps are significantly more expensive than a simple sort, especially if your sort takes advantage of frame-to-frame temporal coherency and swaps indices, not actual items.
Vertex-buffer changes are also typically offenders in performance.

And as mentioned, comparing items for the sort can be as simple as a u64 compare (or a float compare for translucent items).

Of note: You must sort translucent objects back-to-front for proper rendering. State changes be damned.  You will need to handle bounding volumes as I mentioned whether you want to or not.

L. Spiro

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You should combine both- and it costs nothing.

Order your objects by distance from observer (if observer does not move radicaly, it will involve a write free algorithm of the bubbe sort algorithm, that rarely reorders the ordered array), and even, you can stick those render objects pooled, to be neigbors in the very virtual memory for the algorithm so you will be cache lightning friendly sorter/reader/writer in a 0.5 ms.

Then, process this array naive way from beginning a few times over, based on shared gpu states, prior shader, then prior texture, then prior vertex buffer of them, to render "the likes" complete of scene on the shared state. Of course, examine each entity for frustum visibility while at it

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It's even quite feasible to just support both sort modes and then use the proper one for the given hardware profile. If you use the method described at http://realtimecollisiondetection.net/blog/?p=86 then you can change up how you generate your sort key based on various compile-time and run-time criteria.

Thanks. That's a useful technique. You can even put transparent and opaque objects all in the same list provided the transparency flag has the highest priority, negate the depth measurement, and change the priorities so the depth has the highest priority for transparents. But is it more optimal to have two shorter lists/"buckets" or one long one? FWIW I intend to use libgdx (which I don't think has a stock scene graph manager yet), so will most likely be using Java's Collections sort algorithm.

Edited by realh

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realh, on 07 Aug 2014 - 2:47 PM, said:
The other strategy (for 3D only) is depth sorting.
This does not apply on tile-based deferred renderers such as those used in mobile devices. They already remove hidden surfaces before running the pixel shader, so sorting front-to-back literally does nothing but waste cycles (I have tested it).

OK, I think it's easy enough to disable or enable that depending on whether I'm running on mobile or desktop.

#1: You don’t determine the distance the object is from the camera by multiplying anything by its model-view-projection matrix, you get the distance from the camera via any of several methods involving the camera and the object’s bounding box or bounding sphere (squared distance from camera to bounding volume’s center, dot product between camera forward vector and bounding volume’s center, squared distance from the camera to the edge of the bounding sphere, etc.—take your pick).
#2: You always have to transform the bounding volume by the object’s world matrix anyway, so it’s virtually free, meaning that yes, it often makes up for overdraw, at least on systems that actually have overdraw on standard opaque renders.

Good points, I'll take those into account.

realh, on 07 Aug 2014 - 2:47 PM, said:
And I presume that anything more complicated than sorting on center points, ignoring whether objects overlap in XY camera space, only considerably increases pain for decreasing gain?
You presume incorrectly.
Shader and texture swaps are significantly more expensive than a simple sort, especially if your sort takes advantage of frame-to-frame temporal coherency and swaps indices, not actual items.
Vertex-buffer changes are also typically offenders in performance.

I don't think I made myself clear. I wasn't ruling out sorting on state changes as well as depth sorting, but speculating as to whether it's worth using something more complicated than comparing the centres for the depth testing alone. I don't think having multiple lists depending on what objects actually overlap each other in the view would be a good idea, because some objects would be on more than one list and overcomplicate things. OTOH a simple center test may be "good enough" for opaques, but not transparents, because I've realised it's possible even for two simple triangles to overlap in the opposite order from what their centres and nearest vertex to the camera suggest. That raises another question, how do I deal with that? That probably belongs in a separate topic.

Edited by realh