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• ### Similar Content

• 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:
m_pDev->CreatePipelineState(PSODesc, &m_pPSO); Binding Shader Resources
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:

PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new object called Shader Resource Binding (SRB), which is created by the pipeline state:
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 Uniform Buffer Confusion

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Hey everyone, I'm trying to implement my shader system and I was previously hardcoding uniforms but I want to go for a more dynamic approach. I found out about Uniform Buffers. So as I understand, what you want is to potentially have a uniform buffer for the Camera and its properties, a uniform buffer for a potential material, etc. Here is the issue I'm running into.

I have a shader program class and in the shader program class, I want it to store a list of all uniform buffer attributes inside the actual program. So basically, each uniform buffer attribute would tell you the number of indices, the buffer name, the buffer byte size, the offsets, the names of the indices, etc. The problem here is that the buffer index in the program isn't predetermined (if it can be, it still would cause issues since you would have to make sure index 1 is the same for all shader programs). So I wanted to get an output array after linking that would state all the uniform buffer names in the program. From there, I could query all the details I need for each uniform buffer and put that into a Uniform Buffer Attribute class.

When rendering, the Renderable object would have its list of uniform buffers and would check to see if the properties of each uniform buffer in the renderable match that which is in the shader program that it is using to render itself. If true, it would bind it over and if not, I would get an warning.

Unfortunatly, I couldn't find a way online to query the names of all uniform buffers in a shader program. Instead, everyone puts in constant strings since they know before hand what uniform buffers are in the shaders. This doesn't work well since I want my c++ program to easily switch between shader programs/ uniform buffers for each renderable.

An issue that I see with my approach as well is that the same uniform buffer can have different binding indexes for different programs which could remove the benefit of not having to rebind the uniform buffer after switching shader programs.

I'm not sure if there is some general way around this but I couldn't find a answer online. I was looking a lot at this tutorial (http://www.gamedev.net/page/resources/_/technical/opengl/opengl-40-using-uniform-blocks-and-uniform-buffer-objects-r2860) and other links on different sites but they all use glGetUniformBlockIndex with a constant uniform buffer name. Here's how my code looks for my uniform buffer attribute:

class GLUniformBufferAttributes
{
private:
GLuint m_BufferSize;
std::string m_BufferName;

std::vector <GLuint> m_UniformOffsetArray;
std::vector <std::string> m_UniformNameArray;

public:
GLUniformBufferAttributes ();
~GLUniformBufferAttributes ();

bool SetAttributes (GLuint bufferSize, std::string & bufferName, const std::vector<GLuint> & offsetArray,
const std::vector<std::string> & nameArray);
};


My uniform buffer class is sparse and probably has errors since I haven't tried populating it yet but instead getting the querying of attributes to work properly first. As of now, I'm following this link (http://gamedev.stackexchange.com/questions/48926/opengl-fetching-the-names-of-all-uniform-blocks-in-your-program) which does something similar with the index's. The query buffer name should probably be done before the loop but I couldn't find a function to do it. Here's how I'm trying to query the data in my shader program class after linknig:

class GLShaderProgram
{
private:
std::vector <GLUniformBufferAttributes> m_UniformAttributeArray;
};

bool GLShaderProgram::InitializeUniformBlocks ()
{
// Get all uniform buffer specifications
GLint numUniformBlocks; // Get number of uniform buffers

m_UniformAttributeArray = std::vector <GLUniformBufferAttributes> (numUniformBlocks, GLUniformBufferAttributes());

for ( unsigned int index = 0; index < numUniformBlocks; index++ ) // unsafe unsigned vs signed int mistmatch
{
// Query buffer size
GLint blockSize;
glGetActiveUniformBlockiv(m_ShaderProgId, index, GL_UNIFORM_BLOCK_DATA_SIZE, &blockSize);

// Query buffer name
GLchar bufferName;

// Query number of uniforms
GLint numUniforms;
glGetActiveUniformBlockiv(m_ShaderProgId, index, GL_UNIFORM_BLOCK_NAME_LENGTH, &numUniforms);

// Query the names of uniforms
std::vector <GLchar> nameArray;
nameArray.resize(numUniforms);
glGetActiveUniformBlockName(m_ShaderProgId, index, numUniforms, nullptr, &nameArray[0]);

// Query the offsets of uniforms
std::vector <GLint> offsetArray;
glGetActiveUniformBlockiv(m_ShaderProgId, index, GL_UNIFORM_OFFSET, &offsetArray[0]);

//m_UniformAttributeArray[index].SetAttributes(bufferSize, bufferName, offsetArray, nameArray);
}

return true;
}

#version 330

layout (location = 0) in vec3 Position;
layout (location = 1) in vec3 Normal;
layout (location = 2) in vec2 TexCoords;

uniform TestBlock
{
vec4 v1;
float r1;
};

uniform mat4 gWorld;

out vec2 TexCoord;

void main()
{
gl_Position = gWorld * vec4(Position, 1.0);
TexCoord = TexCoords;
}

Another note, I have a uniform defined in my vertex shader which itself executes properly, however I'm assuming the index loop is messed up since when it gets the uniform buffer at index 0, it pulls out a completely different uniform buffer which I'm assuming is the default one in shader programs since it has weird variable names and what not. It has 10 variables in it and they're names are single letters + numbers. Thanks in advance.

Edited by D.V.D

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I'm dealing with this issue by suiting the graphics rendering pipeline and the shader scripts together. A specific kind of render pipeline has its specific stages: Forward lighting, material rendering, screen-space lighting, tone mapping, image post-processing, ... whatever. There are several kinds of properties needed: Material properties for physical based shading (or the suitable NPR properties for NPR rendering; let's call this material, too), camera set-up, screen rect, lights, and so on. Different stages have (partially) distinct requirements, but inside a stage the requirements are fixed.

So here is the deal: A camera provides a uniform block with its parameters, the screen provides one with its own parameters, the model provides one with its material, a post-process provides one with its parameters, a pipeline stage provides one, and perhaps other do so. Each block coming from such a source has an equivalent in the respective shader scripts, and there is a standard name used for it: E.g. CameraSetup, ScreenRect, Material, ... So it is convention that every script implementing forward rendering or material rendering has a slot for e.g. a Material block. Hence one can expect to have blocks with a specific name in a script suitable for a specific kind of rendering stage.

The higher level of rendering is implemented inside the stages of the render pipeline. It fetches the suitable blocks from the various sources and generates suitable binding instructions in the state part of the rendering jobs. The lower level of rendering (i.e. the one that calls OpenGL) then has to process those without the need to know the specific meaning of the parameters in a block.

Perhaps it is worth to mention that I use std140 layout. This makes things easier at least if the block is shared over many calls, like e.g. CameraSetup.

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I do it in the following way:

My UniformBuffer has a usage flag, which is "Default" or "Shared". Now we have 2 scenarios on using the UBO:

1) If the UniformBuffer usage is "Shared", then the UBO send an event to the ShaderManager to register this UBO to all the loaded shaders. In my engine it's guaranteed that all the shaders are pre-loaded, so when you create a shared UBO, it's also guaranteed that all the shaders will know about it. When the renderer is binding a shader, it also binds its registered UBOs.

2) If the UniformBuffer usage is "Default", then I manually register the UBO to whichever shader I want.

I use the std140 layout as well.

I am not sure if this approach is 100% correct though. Reading haegarr's approach makes me re-think of my design a bit.

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I'm dealing with this issue by suiting the graphics rendering pipeline and the shader scripts together. A specific kind of render pipeline has its specific stages: Forward lighting, material rendering, screen-space lighting, tone mapping, image post-processing, ... whatever. There are several kinds of properties needed: Material properties for physical based shading (or the suitable NPR properties for NPR rendering; let's call this material, too), camera set-up, screen rect, lights, and so on. Different stages have (partially) distinct requirements, but inside a stage the requirements are fixed.

So here is the deal: A camera provides a uniform block with its parameters, the screen provides one with its own parameters, the model provides one with its material, a post-process provides one with its parameters, a pipeline stage provides one, and perhaps other do so. Each block coming from such a source has an equivalent in the respective shader scripts, and there is a standard name used for it: E.g. CameraSetup, ScreenRect, Material, ... So it is convention that every script implementing forward rendering or material rendering has a slot for e.g. a Material block. Hence one can expect to have blocks with a specific name in a script suitable for a specific kind of rendering stage.

The higher level of rendering is implemented inside the stages of the render pipeline. It fetches the suitable blocks from the various sources and generates suitable binding instructions in the state part of the rendering jobs. The lower level of rendering (i.e. the one that calls OpenGL) then has to process those without the need to know the specific meaning of the parameters in a block.

Perhaps it is worth to mention that I use std140 layout. This makes things easier at least if the block is shared over many calls, like e.g. CameraSetup.

Okay so basically you avoid the whole problem of having to get a uniform buffer's index by making sure all shaders follow a naming convention for their uniform buffers. But what happens when I have a model which in the game, had something happen to it where before it was being rendered by a certain shader program but now were making it rendered by another shader program. This new shader program takes in 4 uniform buffers while the previous one took in 3. Do you just assume that while the renderable was being switched from one shader program to another, that whatever switched it knew it had to provide a new uniform buffer? It still seems weird to me that I can't get the uniform buffer requirments for each shader program by name.

I do it in the following way:

My UniformBuffer has a usage flag, which is "Default" or "Shared". Now we have 2 scenarios on using the UBO:

1) If the UniformBuffer usage is "Shared", then the UBO send an event to the ShaderManager to register this UBO to all the loaded shaders. In my engine it's guaranteed that all the shaders are pre-loaded, so when you create a shared UBO, it's also guaranteed that all the shaders will know about it. When the renderer is binding a shader, it also binds its registered UBOs.

2) If the UniformBuffer usage is "Default", then I manually register the UBO to whichever shader I want.

I use the std140 layout as well.

I am not sure if this approach is 100% correct though. Reading haegarr's approach makes me re-think of my design a bit.

I see, it still doesn't make sense how you would know if the uniform buffers provided fulfill the shader program requirments.

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Okay so basically you avoid the whole problem of having to get a uniform buffer's index by making sure all shaders follow a naming convention for their uniform buffers. But what happens when I have a model which in the game, had something happen to it where before it was being rendered by a certain shader program but now were making it rendered by another shader program. This new shader program takes in 4 uniform buffers while the previous one took in 3. Do you just assume that while the renderable was being switched from one shader program to another, that whatever switched it knew it had to provide a new uniform buffer?

A shader script is part of a rendering pipeline. As such a specific script has to do what the pipeline needs at the stage where the script is used, and the script can use whatever the stage (directly and indirectly) provides but nothing more. Moreover, there is a correspondence of the scripts functionality and the parameters provided by the uniform buffers. For example, if a game entity should be rendered by using the Gooch NPR technique, the entity must provide the suitable parameters in its "material" block. Switching over to the Toon shader requires the material block to be switched, too.

In fact I don't try to avoid requesting indexes of uniform blocks (which can simply be requested once and stored for later use). Instead I define how scripts have to work in specific situations. So I know which names to use for the uniform blocks of scripts of a specific type. If a particular script can be replaced by another one where the latter uses an additional parameter block, then it means that the former script simply does without it because it doesn't need it although it could use it. In other words, I don't allow for arbitrary scripts because they would not fit into the bigger architecture.

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I see, it still doesn't make sense how you would know if the uniform buffers provided fulfill the shader program requirments.

Personally, if the shader does not contain the specific uniform buffer name (using glGetUniformBlockIndex), I ignore it/send a warning to the console.

Moreover, my renderer is a deferred renderer so I more or less know exactly what kind of shaders I have at any given time.

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Okay so basically you avoid the whole problem of having to get a uniform buffer's index by making sure all shaders follow a naming convention for their uniform buffers. But what happens when I have a model which in the game, had something happen to it where before it was being rendered by a certain shader program but now were making it rendered by another shader program. This new shader program takes in 4 uniform buffers while the previous one took in 3. Do you just assume that while the renderable was being switched from one shader program to another, that whatever switched it knew it had to provide a new uniform buffer?

A shader script is part of a rendering pipeline. As such a specific script has to do what the pipeline needs at the stage where the script is used, and the script can use whatever the stage (directly and indirectly) provides but nothing more. Moreover, there is a correspondence of the scripts functionality and the parameters provided by the uniform buffers. For example, if a game entity should be rendered by using the Gooch NPR technique, the entity must provide the suitable parameters in its "material" block. Switching over to the Toon shader requires the material block to be switched, too.

In fact I don't try to avoid requesting indexes of uniform blocks (which can simply be requested once and stored for later use). Instead I define how scripts have to work in specific situations. So I know which names to use for the uniform blocks of scripts of a specific type. If a particular script can be replaced by another one where the latter uses an additional parameter block, then it means that the former script simply does without it because it doesn't need it although it could use it. In other words, I don't allow for arbitrary scripts because they would not fit into the bigger architecture.

Okay I'm slightly understand this. I haven't seen a shader script before but from what I understand, you get the parameters for each uniform buffer from the shader script which also describes how the uniform buffers must be set when you switch from one shader script to another. But then you need to specify how a shader script must populate its uniform buffers from all possible switches between shader scripts. So switching between toon/phong/physically based shading requires each shader script for toon/phong/... to have info on how to set its uniform buffers when switching between any of the other types of shaders. Doesn't that kind of reliance on other shader scripts cause a lot of potential for errors or am I completely misunderstanding this?

I see, it still doesn't make sense how you would know if the uniform buffers provided fulfill the shader program requirments.

Personally, if the shader does not contain the specific uniform buffer name (using glGetUniformBlockIndex), I ignore it/send a warning to the console.

Moreover, my renderer is a deferred renderer so I more or less know exactly what kind of shaders I have at any given time.

Sorry I should have rephrased it, what happens if you don't give a required uniform buffer for a shader because the object being rendered doesn't have it? In that case, you can't figure out if one of the uniform buffers needed for the shader hasn't been given since you can't query the names of all uniform buffers in a shader. Its weird that I can't query that since I can do that for uniforms, is there maybe a variant of glGetProgramiv that lets me get all the uniform buffer names in a shader program?

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Okay I'm slightly understand this. I haven't seen a shader script before but from what I understand, you get the parameters for each uniform buffer from the shader script which also describes how the uniform buffers must be set when you switch from one shader script to another. But then you need to specify how a shader script must populate its uniform buffers from all possible switches between shader scripts. So switching between toon/phong/physically based shading requires each shader script for toon/phong/... to have info on how to set its uniform buffers when switching between any of the other types of shaders. Doesn't that kind of reliance on other shader scripts cause a lot of potential for errors or am I completely misunderstanding this?

Let us assume that the toon shading script, Phong shading script and the physically based shading script are all implemented as forward lighting scripts. The set of parameter used by a toon shader differ from the set of parameters used by a Phong shader and differ from the set of parameters used by a physically based shader. However, all those shaders have a block which can be understood as a material which encapsulates such set of parameters although the sets themselves differ in their structure and content.

The graphic rendering pipeline implements forward lighting. Hence each of the said shader scripts fit into one of the stages of the pipeline. This stage of the pipeline is aware that scripts plugged into it may be interested in something that is a material uniform block (besides others like a CameraSetup, Ligths, etc; but let us stay with the material, because it is the only one that may change due to what kind of shading the script implements).

When it comes to rendering, the particular pipeline stage is fed with the list of models (which have passed the visibility culling and are already sorted for minimal state switching costs; but that is another topic). The stage "asks" the next model which shading to be used and it requests the material block to be used. Notice that this step defines the script and the uniform block. The pipeline stage does not investigate the material block. Instead it looks at it as a black box. It simply binds it to the shader script as the block named "material". In other words, it relies on the kind of script, the script itself, and the provided material block fit together.

Obviously, if the kind of shading is switched, the actual material parameter block has to be switched, too. Details of the process are implementation dependent, of course. For example, you may have a constant field in the C/C++/Java/... implementation of the material that directly or indirectly refers to the kind of shading. Then switching to another kind of material automatically refers to another kind of shading and hence scripts.

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Hey, sorry for such a late reply. Midterms came along and ate way more time than I thought they would.

So using the shader script, you assume that the given parameters, block names, and what not match up with the required uniform buffers for a shader program. It also seems like your shader program stores a list of buffers that it requests from the Renderable, and then binds them to the proper indices (which I’m probably going to do too, seems to work really well). Okay so I did some wrapping and implementation and got my GLShaderProgram class to support my GLUniformBuffer class. As shown before, my Uniform buffer class stores a class called UniformBufferAttributes which holds the name of the Uniform Buffer, the size of the uniform buffer, and the array of offsets. Originally, I also wanted GLShaderProgram to store a list of UniformBufferAttributes which it would then use to compare each uniform buffer thats being binded. That way, I could verify before binding whether or not I'm passing the properly encoded uniform buffer to the shader instead of passing and then waiting for an error.

I still think this process has some benefits since the drivers might let the Uniform Buffer shader run even if it’s missing some of the parameters. As an example, if I give 3 vertex locations in my shader but only have 2 in the actual data + only 2 enabled using glEnableVertexAttribute, the program still renders the cube correctly on my hardware. I'm assuming other driver implementations might throw an error so I'm debating keeping Uniform Buffer attributes just for proper error checking.

On the opposite side of the argument, storing the offsets to do comparisons each frame for each UBO is probably a lot of extra overhead just for error checking, so instead of having uniform buffer attributes, I might be better off with only keeping the UBO name and letting OpenGL throw the error itself. I'm not sure if it will consistently come up on glGetError if not enough parameters are given to the UBO or if it will just give 0 values and run.

As for the shader scripting part to give parameters to UBO's, I think I might go with having some kind of special Uniform Buffers. My idea now is that via shader script (which I'm assuming is just some XML file stored with a model we are loading), I can give init values for all my required parameters, however certain UBO's will change every frame. An example is a UBO for orientation, it needs to have the orientation updated every frame so we need a way of distinguishing it from other UBO's.

Lastly, about the example of switching lighting from Phong to Physically Based to Toon, I think in my implementation, it would make sense if the shader script had a uniform buffer specified for each case. So then when the shader requests a uniform buffer, it just pulls the Toon shader one vs the others since the names could be different. Then as a backup, there could be a default uniform buffer created by the GLShaderProgram if no toon shader buffer is provided.

I think I'm starting to get how the whole thing should work :D