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• 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?

• I am somewhat new to game development and trying to create a basic 3d engine. I have managed to set up a first person camera and it seems to be working fine for the most part. While I am able to look up, down, left and right just fine the camera is constrained to the mouse movement in the window (i.e when the mouse reaches edges of the window it discontinues camera rotation and mouse is out of window bounds. I tried to use SDL_WarpMouseInWindow(window, center.x,center.y) but when I do this then it messes up the camera and the camera is stuck, even though there is some slight movement of the camera, it keeps going back to the center.
void Camera::UpdateViewByMouse(SDL_Window &window, glm::vec2 mousePosition)
{
float xDistanceFromWindowCenter = mousePosition.x - ((float)1024 / 2) ;
float yDistanceFromWindowCenter = ((float)720 / 2) - mousePosition.y;
yaw = xDistanceFromWindowCenter * cameraRotationSpeed;
pitch = yDistanceFromWindowCenter * cameraRotationSpeed;
SDL_WarpMouseInWindow(&window, 1024 / 2, 768 / 2); }
i’ve been stuck on this for far too long. any help would be much appreciated
i have also tried relative mouse movement,  and .xrel and .yrel to avail. polling mouse state with sdl_event. I do also know that SDL_WarpMouseInWindow makes change to event and have tried also ignore and reenabling to no avail

# OpenGL Concept Clarification - Transformations

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## Recommended Posts

Hello All, I am newto OpenGl and have been refering to The Red Book... for a few days. The book says that you can either view al transformations by taking coordinate axes as fixed or in terms of local coordinate system( tied to a rendered object). Question 1. : the glLoadIdentity maps a window to a [-1,+1] scale ( for each X,Y and Z). Now if I perfrom following glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glPushMatrix(); glRotatef(90.0 , 0.0 ,1.0 , 0.0) ; //Rotation around Y axis , anticlockwise, Will my -X (negative X axis) take on the position of +Z axis and + Z axis replaces +X axis and +X axis replace -Z axis ??? Question 2: My second question reuires the answer of Ques 1 because I am aiming to construct an external control mesh , housing the object. The object I am taking is a cube such that the origin of the axes lie at the centroid of the cube. I am planning to contruct the external control mesh by asking user to mark points near to object , so that the points becomes lines( when I rotate the object). Problem is: At default Y axis is up-down, X is sideways and Z is front-back. When I do anticlockwise rotation across Z and mark point (by calling glVertex3f), the line so drawn is not horizontal but vertical . Any suggestions on my queries? I will post the code also , but need to get a suggestion first. Thanks in advance.

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Quote:
 Original post by CirusQuestion 1. : the glLoadIdentity maps a window to a [-1,+1] scale ( for each X,Y and Z). Now if I perfrom following glMatrixMode(GL_MODELVIEW);glLoadIdentity();glPushMatrix();glRotatef(90.0 , 0.0 ,1.0 , 0.0) ; //Rotation around Y axis , anticlockwise, Will my -X (negative X axis) take on the position of +Z axis and + Z axis replaces +X axis and +X axis replace -Z axis ???

Yes; you should really do the math on some paper to get a better feel for what's actually happening, though.

glRotatef(90, 0, 1, 0) puts this matrix
[ 0  0 1 0 ][ 0  1 0 0 ][ -1 0 0 0 ][ 0  0 0 1 ]

onto the modelview matrix stack (it is postmultiplied by the current contents of the modelview matrix, which happens to be the identity matrix now). Try multiplying (column) vectors with this matrix to get a good feel.

Quote:
 Original post by CirusQuestion 2: My second question reuires the answer of Ques 1 because I am aiming to construct an external control mesh , housing the object. The object I am taking is a cube such that the origin of the axes lie at the centroid of the cube. I am planning to contruct the external control mesh by asking user to mark points near to object , so that the points becomes lines( when I rotate the object). Problem is: At default Y axis is up-down, X is sideways and Z is front-back.When I do anticlockwise rotation across Z and mark point (by calling glVertex3f), the line so drawn is not horizontal but vertical .

I'm not really sure what you mean by this, perhaps you can rephrase your issue?

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Quote:
 Original post by CirusProblem is: At default Y axis is up-down, X is sideways and Z is front-back.When I do anticlockwise rotation across Z and mark point (by calling glVertex3f), the line so drawn is not horizontal but vertical .

Im not sure what your saying here but im going to take a guess..

When you say rotation 'across Z' are you doing:
glRotatef(angle, 0.0, 0.0, 1.0);

If this is the case then your actually rotating around the Z-axis. In this situation if you rotate and plot a point then rotate a little bit more and plot another point (possibly to draw a line?) then it would appear that the points are moving vertically (actually vertically and horizontally), in actual fact if you continued like this you would end up drawing a circle.

To plot points across the Z axis you need to rotate around the Y-axis (as you did in Q1), but bear in mind the points would also be plotted across the X-axis as well as the Z-axis.

Im not sure if that helps at all, if not then re-phrase the question.

Happy Coding

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Regarding Qeus 2:

I am given a task to construct an external contrl mesh around my object.

How do I do this? :
I take the object , and mouse click near to its edges and expect a point there.
This point is not a point but actually a line ( Imagine a line when placed in front can be viewed as a point ) .

To be precise , the line points in +Z direction that is out of computer screen.

Now , after this , I am rotating my object ( coordinate axes) in anti-clock wise Y or X direction .

After performing a rotation the point (the tip of the line ) will be viewed as a line.

Problem:
If a rotate the object around +Z axis and then mouse click I am getting the point at some different position on the screen other than the expected position.

--------------------------------------------------------------------------
void drawPoint()
{
int i =0 ;

glEnable(GL_DEPTH_TEST);
// Set the material color to follow the current color

glMatrixMode(GL_MODELVIEW);

glPushMatrix();
glRotatef(fAngle_Y , 0.0 , 1.0 , 0.0); //Move left
glRotatef(fAngle_X , 1.0 , 0.0 , 0.0); //Move above
glRotatef(fAngle_Z , 0.0 , 0.0 , 1.0); //Move above

glBegin(GL_POINTS);

while( i != iNumOfClicks)
{
glColor3f(1.0 , 0.0 , 1.0);
glVertex3f(pfArray + 0.25, pfArray[i + 1], pfArray[i + 2] );
glVertex3f(pfArray + 0.25, pfArray[i + 1], pfArray[i + 2] - 0.5 );

++i;

}
glEnd();
glPopMatrix();
i = 0; //Reset counter.

if(bFlag_LineDraw)
{
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glRotatef(fAngle_Y , 0.0 , 1.0 , 0.0); //Move left
glRotatef(fAngle_X , 1.0 , 0.0 , 0.0); //Move above
glRotatef(fAngle_Z , 0.0 , 0.0 , 1.0); //Move above
glBegin(GL_LINES);
while( i != iNumOfClicks)
{
glColor3f(1.0 , 0.0 , 1.0);
glVertex3f(pfArray + 0.25, pfArray[i + 1], pfArray[i + 2] );
glVertex3f(pfArray + 0.25, pfArray[i + 1], pfArray[i + 2] - 0.5 );
i++;
}
glEnd();
glPopMatrix();

bFlag_LineDraw = FALSE;
}
-----------------------------------------------------------------------------

This is the function that is converting viewport coordinates to world coordinates {-1,+1] range
----------------------------------------------------------------------------
void MarkPointOnScreen(int iX , int iY, int iWinHt , int iWinWidth, float *pfArray)
{
//Draw the point on screen.
float fx = 0.0f , fy = 0.0f;
if( iX > (iWinWidth/2) )
{
fx = ( (float)iX - (float)iWinWidth/2 ) / (float)(iWinWidth/2);
}
else if( iX == iWinWidth/2)
fx = 0.0f;
else
{

fx = -1 * ( (float)iWinWidth/2 - (float)iX ) / (float)(iWinWidth/2);

}

if(iY > iWinHt/2)
{

fy = -1 * ( (float)iY - (float)(iWinHt/2) ) / (float)(iWinHt/2);
}
else if(iY == iWinHt/2)
fy = 0.0f;
else
{

fy = ( (float)(iWinHt/2) - (float)iY ) / (float)(iWinHt/2);

}

pfArray[iEle++] = fx;
pfArray[iEle++] = fy;
pfArray[iEle++] = 0.0f;

printf("\niX = %d and iY = %d , fx = %f and fy = %f , Clicks = %d \n", iX,iY,fx ,fy, iNumOfClicks);
}