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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 Aligning an object to a path

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## Recommended Posts

Hey guys,

Long time since I last posted around here.

I'm trying to make a object follow a certain path using opengl and C++.

The path I created is an 8 figure and as we speak, my object can follow the path through translation but I'm having a very hard time figuring out how to make sure the front of my object faces the direction of the path as it moves forward.

Basically, what I'm trying to figure out is how to rotate my object so that it faces the direction of the tangent of the position at which it is at.

The only thing I have ended up with so far is trying to figure out the angle between the 2 points by making those 2 points the ending points of vectors both having the origin as a starting point and calculating the angle between those and rotating my object. It doesn't well at all and I believe I do not have the proper mathematical knowledge to achieve what I want to do.

What should I look for in order to make my object face the proper direction when moving ?

Thanks!

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Don't compute an angle and rotate by that angle, but use the tangent as forward vector directly. Use the standard method of constructing a orientation matrix from the forward vector and a given up vector (e.g. one that is perpendicular to the figure, or the world up vector, or something else).

How to compute the tangent ... depends on what kind of path you have. If you have a curve that can be differentiated, then you may use the 1st derivative. The mathematical approach can be read in the Frenet Formulas article on wikipedia. Of course, you can ever step a little bit forward and a little bit backward on the curve and use the difference vector after normalization as approximation.

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I expected my method was wrong so that is why I decided to start this thread.

I'm currently using a Lemniscate of Bernoulli for my path. The link also provides both the first and second derivatives but other than that, I have no clue how to obtain the exact information I want or what kind of information.

I find the Frenet-Serret Formulas extremely confusing. The issue also arise from the fact that I have no clue what is my T N and B information from the what I have in my scene or how to obtain it and what to do with it.

I understand the logic behind it from the formula but I can't relate this to the code with my path and objects.

The only thing I understand right now is that my parameter t will provide me with the proper X and Z position on the curve. After that I have no clue numbers I must get from what I have and where to plug them to get the rest of the data I need.

Where should I start?

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The linked article does show derivatives dx/dy and dy/dx, but you're using the parametric form of the curve. Hence you need dx/dt and dy/dt. Setting in t into the both derivatives gives you the x and y components of the unnormalized tangent (which you are using as x and z components, if I understood your latest post correctly). The Frenet Frame article shows this in the section "Other expressions of the frame", where
T(t) = r'(t) / ||r'(t)||
is mentioned (the r' means the derivative dr/dt).

The T is the normalized tangent vector along the curve, the N is the normal (i.e. it is perpendicular to the curve at location t) with a relation to the curvature of the curve at location t, and B is the bi-normal (i.e. also perpendicular to the curve at t). All together, the point at location t, T, N, B define a Cartesian axis, i.e. a local co-ordinate system similar to one used for e.g. model vertices.

Assume that you have a unit-length forward vector f and a unit-length up vector u and both are perpendicular (so f . u = 0). Then you can compute a side vector s using the cross-product
s := f x u
These 3 vectors are pairwise perpendicular and all of unit length. So they build a basis, written as the column vectors (or row vectors, depending on whether you use column or row vector math) of a matrix
[ s f u ]
and you'll have the rotational part of a local space transformation. Append a position p and you have the full transformation matrix:
[ s f u p ]

If the forward vector f and the up vector u' are not perpendicular by itself, you can compute the side vector as usual but with a additional normalization
s' := f x u'
s := s' / ||s'||
and compute the actual up vector from them
u := s x f

So the question is how to get a pair of those vectors.

One way (the simple one) is to compute the forward vector as difference vector between two points on the curve that are both close to the current point p at location t[sub]0[/sub],
p := r( t0 )
so that
d' := r( t[sub]0[/sub] + 0.05 ) - r( t0 - 0.05 )
d := d' / ||d'||
and choosing an up vector u', e.g. [ 0 1 0 ] in your case where the curve is in x-z. Then follow the steps above. Of course, picking a delta (here 0.05) is a bit of voodoo.

Another, more exact way would be to compute dx/dt and dy/dt from your curve to determine the tangent T and use it as forward vector. Choose an up vector like above and complete the matrix as usual.

The 3rd way would be to compute the 2nd derivatives as well to yield in N, and use that as side vector.

Now it's up to you to decide how precise you want the tangent to be, and whether the up vector should be global or curvature dependent or what else. Its easy to mix up the vectors in the above, so check what I wrote if you want to use it.

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The linked article does show derivatives dx/dy and dy/dx, but you're using the parametric form of the curve. Hence you need dx/dt and dy/dt. Setting in t into the both derivatives gives you the x and y components of the unnormalized tangent (which you are using as x and z components, if I understood your latest post correctly). The Frenet Frame article shows this in the section "Other expressions of the frame", where
T(t) = r'(t) / ||r'(t)||
is mentioned (the r' means the derivative dr/dt).

The T is the normalized tangent vector along the curve, the N is the normal (i.e. it is perpendicular to the curve at location t) with a relation to the curvature of the curve at location t, and B is the bi-normal (i.e. also perpendicular to the curve at t). All together, the point at location t, T, N, B define a Cartesian axis, i.e. a local co-ordinate system similar to one used for e.g. model vertices.

Assume that you have a unit-length forward vector f and a unit-length up vector u and both are perpendicular (so f . u = 0). Then you can compute a side vector s using the cross-product
s := f x u
These 3 vectors are pairwise perpendicular and all of unit length. So they build a basis, written as the column vectors (or row vectors, depending on whether you use column or row vector math) of a matrix
[ s f u ]
and you'll have the rotational part of a local space transformation. Append a position p and you have the full transformation matrix:
[ s f u p ]

If the forward vector f and the up vector u' are not perpendicular by itself, you can compute the side vector as usual but with a additional normalization
s' := f x u'
s := s' / ||s'||
and compute the actual up vector from them
u := s x f

So the question is how to get a pair of those vectors.

One way (the simple one) is to compute the forward vector as difference vector between two points on the curve that are both close to the current point p at location t[sub]0[/sub],
p := r( t0 )
so that
d' := r( t[sub]0[/sub] + 0.05 ) - r( t0 - 0.05 )
d := d' / ||d'||
and choosing an up vector u', e.g. [ 0 1 0 ] in your case where the curve is in x-z. Then follow the steps above. Of course, picking a delta (here 0.05) is a bit of voodoo.

Another, more exact way would be to compute dx/dt and dy/dt from your curve to determine the tangent T and use it as forward vector. Choose an up vector like above and complete the matrix as usual.

The 3rd way would be to compute the 2nd derivatives as well to yield in N, and use that as side vector.

Now it's up to you to decide how precise you want the tangent to be, and whether the up vector should be global or curvature dependent or what else. Its easy to mix up the vectors in the above, so check what I wrote if you want to use it.

Thanks for the in depth information. I wanted to have tried something before posting back. I have to admit the math isn't too easy for me but manageable on paper but relating this to OpenGL is confusing as hell.

So far my train is following the curve but it's a bit crappy at points. At 4 spots on my curve, the train suddenly flips over 180degrees and still follows the curve backwards and then will flip back again when it reached another one of those points.

I'll explain what I'm doing. Perhaps you could see what is wrong.

At the moment. I keep the position X and Z as global variables by obtaining the value from T in my parametric equations( Y is always 0). Then, using both points from the position, I pass them in their respective derivative to obtain a set of points that is a vector tangent to the X Z position on my curve.

I then normalize the tangent vector by its length but I'm not sure I'm doing this part right. I know the magnitude of the vector is sqrt(x^2+y^2+z^2) but isn't that only we have a point (X,Y,Z) and the other at (0,0,0) ? At the moment, I have that my length is sqrt(X^2+Z^2) since Y is always 0.

Following from this, I calculate the dot product between my new derived points and the vector (-1,0,0) which is the direction vector in which my train is pointing at initially or pretty much all the time before being translated and rotated.

With the dot product result, I calculate the rotation angle = acos(dotproduct)*(180/pi) and use this angle to rotate my train after I translated it at the proper position. It's not perfect though and no matter how long I try to figure out what is wrong I have no clue what else to do.

Also, For the train flipping issue. I just managed to do a kind of hackjob that detects if the angle change is large and toogle a boolean that I check to rotate the train back 180 degree while it is on. I would like to get rid of this too with proper calculations.

I've also tried to have my camera follow the train from the back but I have no idea how to achieve this. The camera can follow the train from it's origin by changing the eye position but if I try to move the camera as well it becomes erratic and goes crazy.