Sign in to follow this  

OpenGL Particles: Batching VS instancing

This topic is 1103 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

I was wondering what you guys think the best course of action would be

 

I'm looking to making a particle system. Currently I have a sprite batcher that can handle rotations, scaling, and etc. It works by mapping a VBO with vertex data I need for the sprites I want to draw. Now I'm wondering should I just build my particle system on top of this? Or should I create a whole new system that uses instancing? Would a instance system even be better, would it even help? I ask because I really do not know that much about instancing

 

Does any of this change if want to be able to do effects such as rain, snow, fire, smoke?

What if I want the particles to be textured, eg each particle is a different snowflake image?

 

I'm targeting OpenGL 3.3+ just as fyi too

Edited by noodleBowl

Share this post


Link to post
Share on other sites
Instancing and batching work together in most cases.

With instancing, you'd still need to fill a buffer with any per-instance particle data. Instancing just removes the need for you to compute all the vertices of each particle on the CPU.

You can combine instancing with a geometry shader in order to further cut down on processing. In such a setup, you'd still just generate and send the instance data to the GPU, but then you'd run the vertex shader once per particle on that instance data and use the geometry shader to generate the rest of the vertices for each particle.

Either with or without instancing, you can also use transform feedback or a compute shader to do all of the per-instance updates completely on the GPU.

Share this post


Link to post
Share on other sites

So if I make them separate (my batcher and the particle system), I hope this makes sense, then I'm looking at

 

1 static buffer for my vertex coords [5 floats (x,y,z, uText, vText) * 4 (since it is a quad)] thats filled at init

1 static buffer for my indices [ 6 floats]

1 dynamic buffer for my particle positions [2 floats (x,y) * the max number of particles] that is filled/changes every frame

 

Then I can use the glDrawElementsInstanced call to draw the number of particles to the screen

 

That makes sense right?

Share this post


Link to post
Share on other sites

If you read or re-read the slides I posted, that is the least recommended approach as they benchmark showed it's the slowest version. You should bench on your own to verify their results.

 

Their recommendation was to set:

No vertex buffer.

1 static buffer for your indices [6 * MaxNumOfParticlesPerDraw uint16; filled with zeroes]

1 dynamic UBO or TBO for your particle position [2 floats(x, y) * max number of particles].

Use gl_VertexId in the vertex shader to construct the quad.

 

Use glDrawElements. If you use glDrawArrays, you can avoid the index buffer (but usually comes with the overhead of having to switch between arrays and elements inside the GPU or the driver, since most geometry is indexed).

Edited by Matias Goldberg

Share this post


Link to post
Share on other sites

So my question is should I even bother with a new system?

My current sprite batcher system is already dynamic and uses glDrawElementsBaseVertex to get things done.

 

It made sense to make a new system if I was going to use instancing, but since you and the slides say don't use DrawInstanced.

Making a particle system based on instancing does not make any sense

Share this post


Link to post
Share on other sites

Instancing is likely more performant than batching (sending 1 vertex instead of 4 per particle). It's also a good exercise - that's how I learned instancing with DX9 wink.png.

 

Edit: You can also delegate more to the GPU, in particular: Grant your vertex a scale and rotation and do that in the vertex shader.

Edited by unbird

Share this post


Link to post
Share on other sites
I normally do scale and rotation on the CPU side, which is the case with my batcher. But for particles maybe it makes more sense to be more GPU heavy?
 
Also how does one even construct a quad in the vertex shader? I'm pretty bad when it goes beyond the point of default or simple shaders.
I feel like what I'm currently thinking might be a "bad" way to do it
#version 330 core

in vec2 xyPosition;
out vec2 UV;
uniform mat4 MVP; //orthographic projection matrix passed in

void main()
{
	//For 1x1 sized particle
	vec4 vertexPosition;
	int vertex = gl_VertexId % 4;
	if(vertex == 0)
	{
		vertexPosition.x = 0;
		vertexPosition.y = 0;
	}
	else if(vertex == 1)
	{
		vertexPosition.x = 0;
		vertexPosition.y = 1;
	}
	else if(vertex == 2)
	{
		vertexPosition.x = 1;
		vertexPosition.y = 1;
	}
	else if(vertex == 3)
	{
		vertexPosition.x = 1;
		vertexPosition.y = 0;
	}
	vertexPosition.z = 0;
	vertexPosition.w = 1;
	
	gl_Position = MVP * vertexPosition;
	UV = uvPosition;
}

1 dynamic UBO or TBO for your particle position [2 floats(x, y) * max number of particles].
Use gl_VertexId in the vertex shader to construct the quad.


Also another question, I really don't understand why you say make a UBO for XY positions of the particles. Why not just another VBO?
Is it because of a GPU memeory placement thing? Because I would need VAO for it, where I can get away with not having one if I use a UBO? Something like that?

I'm asking because do not know the true difference between a VBO and UBO, other than a VBO is traditionally for vertex data and UBO is for
sending multiple uniforms to a shader in one go.

Which is something I don't consider, dynamic XY positions that is, to be a uniform item Edited by noodleBowl

Share this post


Link to post
Share on other sites

I really don't understand why you say make a UBO for XY positions of the particles. Why not just another VBO?Is it because of a GPU memeory placement thing? Because I would need VAO for it, where I can get away with not having one if I use a UBO?

Because if you use a vbo, you would need 4 vertices per particles, but the ubo can just hold one entry (the position) per particle.
Your understanding of vbos and ubos is correct. However this is like a hack that works really well. And it works well because GPUs are getting more and more similar to CPUs, and vbos and ubos is just memory getting fetched, that the api put arbitrary restrictions that are no longer necessary.

By setting a null vbo and draw 4 vertices (1 particle), you're basically telling the api "draw 4 vertices of nothing" (aka iterate the vertex shader 4 times with no vertex data) but the vertex shader can fetch data from a different location (the ubo) with the help of gl_vertexid to determine the index in the ubo and the vertex position to generate.

Share this post


Link to post
Share on other sites

By setting a null vbo and draw 4 vertices (1 particle), you're basically telling the api "draw 4 vertices of nothing" (aka iterate the vertex shader 4 times with no vertex data) but the vertex shader can fetch data from a different location (the ubo) with the help of gl_vertexid to determine the index in the ubo and the vertex position to generate.


I hope I can explain this well enough, so please bear with me and let me know if this doesn't makes sense.
Now regardless of VBO or UBO use, does that mean I need to "double up" on my XY positions since the
vertex shader is run 4 times per quad i.g:
 
//Example contents of my buffer for 2 quads

const int FLOATS_PER_QUAD = 8; // 4 vertex * 2 (x, y positions)
int maxParticles = 2;
GLfloat *vertex = new GLfloat[maxParticles * FLOATS_PER_QUAD];

//Quad 1 at position 50x50
vertex[0] = 50.0f; //X pos
vertex[1] = 50.0f; //Y pos
vertex[2] = 50.0f; 
vertex[3] = 50.0f; 
vertex[4] = 50.0f; 
vertex[5] = 50.0f; 
vertex[6] = 50.0f; 
vertex[7] = 50.0f; 

//Quad 2 at position 25x40
vertex[8] = 25.0f; //X pos
vertex[9] = 40.0f; //Y pos
vertex[10] = 25.0f; 
vertex[11] = 40.0f; 
vertex[12] = 25.0f; 
vertex[13] = 40.0f; 
vertex[14] = 25.0f; 
vertex[15] = 40.0f; 


I hope the above is not the case, because that seems silly to have repeat the same data over and over.
When really this should be enough:
 
//The contents of my buffer for 2 quads

const int POSITION_COMP_COUNT = 2; // For XY position
int maxParticles = 2;
GLfloat *vertex = new GLfloat[maxParticles * POSITION_COMP_COUNT];

//Quad 1 at position 50x50
vertex[0] = 50.0f; //X pos
vertex[1] = 50.0f; //Y pos

//Quad 2 at position 25x40
vertex[3] = 25.0f; //X pos
vertex[4] = 40.0f; //Y pos


But I am unsure. How do you tell a shader "do not continue onto the next positions set, until you have ran 4 times"?
Is this solved with the use of a UBO (I ask cause I have never used one)?
I know there is glVertexAttribDivisor for VBOs, which will say only consider the attribute X times for a instance.
But with that being said I beleive this will only work with DrawInstanced calls, which is what we are trying to avoid. Edited by noodleBowl

Share this post


Link to post
Share on other sites
You don't have to increase your data; you only need one XY value per particle.

In the vertex shader you take the vertex ID as an input (can't recall GLSL for this) and then use that to figure out which particle you are (int id = vertex_ID % 4), and use that to index into the UBO to get the data.

[source]
void main(int vertex_id)
{
int particleID = vertex_id % 4;
vec2 pos = particlePostions[particleID];

// do things...

}
[/source]

Share this post


Link to post
Share on other sites

You don't have to increase your data; you only need one XY value per particle.

In the vertex shader you take the vertex ID as an input (can't recall GLSL for this) and then use that to figure out which particle you are (int id = vertex_ID % 4), and use that to index into the UBO to get the data.


That is the one thing I can't get my head around for some reason. How do I actually only grab one only set of XY positions per particle.
If particlePositions is an array of values, where it has 3 particles worth of data inside, looking like:
particlePositions = {0,0, 50,50, 150,30};

And assuming vertex_id auto increases with each vertex. Then lets say we are on the 3rd pass (vertex_id is 2; since the counter starts at 0)
Then we are going to pull back only value '50'. Even if particlePositions[vertex_id] were to somehow pull back both XY for the particle,
on a subsequent increase of vertex_id the values would be wrong for the quads construction or we would explode since we over ran the array

Share this post


Link to post
Share on other sites

Do your particles affect the world? If they don't then you could just store them in two textures(32bitfloatARGB to store x,y,id,spawntime). Use a shader to "draw" new particles into texture1. A shader that reads texture1 and "draws" updated positions to texture2 after wich you swap the textures around. And a shader that reads the texture1 and draws the particles to the screen. This way you can get 100k+ particles without an impact in performance that only needs the cpu to supply new particles and make a few drawcalls and gpu handles the rest. Granted this takes some work but the results are way more impressive than calculating the particles on the cpu.

 

note that you can supply the update shader vertexdata to use as collisionsurfaces for the particles so the world can affect the particles.

 

The shaders would need a table where they can look up what kind of a particle it is based on its id. Also pass current time to the shaders so you can calculate lifetime from spawn-current.

Share this post


Link to post
Share on other sites

[source]
void main(int vertex_id)
{
int particleID = vertex_id % 4;
vec2 pos = particlePostions[particleID];

// do things...

}
[/source]


Rather:

void main(int vertex_id)
{
    int particleID = vertex_id / 4;
    int quadCornerID = vertex_id % 4;
    vec2 pos = particlePostions[particleID];

    // ...
}

Share this post


Link to post
Share on other sites

int particleID = vertex_id / 4;
Wow, how did I not think of this before!

So how is the UBO supposed to work? I understand the basics of setting them and etc. But say we have X many particles
I dont think a uniform block looking like this is going to work. This block would only be able to account for 1 particle right?

layout (std140) uniform positionBlock{  vec2 particlePositions;};
Should it look something more like:
layout (std140) uniform positionBlock{  vec2 particlePositions[NUMBER_OF_PARTICLES_TO_STIMULATE_THIS_FRAME];};
Edit:
So after some playing around, I'm a little stuck in byte offset hell.

After setting up a UBO and filling it with some test data:



GLfloat *particlePos = new GLfloat[4];//Particle 1 posparticlePos[0] = 50.0f;particlePos[1] = 50.0f;//particle 2 PosparticlePos[2] = 150.0f;particlePos[3] = 150.0f;
I'm able to pass the first particle position and get it to show biggrin.png
But the next particle wouldn't sad.png

I figured out its do to the std140 layout byte offset. If I pad with two 0s for each particle position and try to grab the next particle
everything works. But I really don't want to do that. Is there another layout I can use in my shader to stop this?

Just in case I'm filling my buffer like this [Padding with 0s sad.png ]:
int size = 8;GLfloat *pos = new GLfloat[size];//Particle 1 pospos[0] = 10.0f;pos[1] = 25.0f;pos[2] = 0.0f;pos[3] = 0.0f;//particle 2 Pospos[4] = 50.0f;pos[5] = 50.0f;pos[6] = 0.0f;pos[7] = 0.0f;GLint blockIndex = glGetUniformBlockIndex(shaderProgram.programID, "particleBlock");glUniformBlockBinding(shaderProgram.programID, blockIndex, 0);glBindBuffer(GL_UNIFORM_BUFFER, ubo);glBufferData(GL_UNIFORM_BUFFER, size * sizeof(GLfloat), pos, GL_DYNAMIC_DRAW);glBindBufferBase(GL_UNIFORM_BUFFER, 0, ubo);
One more question, I noticed that (assuming I doing it right) if I set the uniform block to have an 10K vec2 array it completely kills my application. Is this just some shader or UBO limit? I hope this isnt the case, cause how am I supposed to reach 100k or even 1 million particles if that is the case? Maybe I shouldn't be doing that (have a super large vec2 array) maybe its done some otherr way?? Edited by noodleBowl

Share this post


Link to post
Share on other sites

This topic is 1103 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Forum Statistics

    • Total Topics
      628742
    • Total Posts
      2984478
  • Similar Content

    • By alex1997
      I'm looking to render multiple objects (rectangles) with different shaders. So far I've managed to render one rectangle made out of 2 triangles and apply shader to it, but when it comes to render another I get stucked. Searched for documentations or stuffs that could help me, but everything shows how to render only 1 object. Any tips or help is highly appreciated, thanks!
      Here's my code for rendering one object with shader!
       
      #define GLEW_STATIC #include <stdio.h> #include <GL/glew.h> #include <GLFW/glfw3.h> #include "window.h" #define GLSL(src) "#version 330 core\n" #src // #define ASSERT(expression, msg) if(expression) {fprintf(stderr, "Error on line %d: %s\n", __LINE__, msg);return -1;} int main() { // Init GLFW if (glfwInit() != GL_TRUE) { std::cerr << "Failed to initialize GLFW\n" << std::endl; exit(EXIT_FAILURE); } // Create a rendering window with OpenGL 3.2 context glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); glfwWindowHint(GLFW_RESIZABLE, GL_FALSE); // assing window pointer GLFWwindow *window = glfwCreateWindow(800, 600, "OpenGL", NULL, NULL); glfwMakeContextCurrent(window); // Init GLEW glewExperimental = GL_TRUE; if (glewInit() != GLEW_OK) { std::cerr << "Failed to initialize GLEW\n" << std::endl; exit(EXIT_FAILURE); } // ----------------------------- RESOURCES ----------------------------- // // create gl data const GLfloat positions[8] = { -0.5f, -0.5f, 0.5f, -0.5f, 0.5f, 0.5f, -0.5f, 0.5f, }; const GLuint elements[6] = { 0, 1, 2, 2, 3, 0 }; // Create Vertex Array Object GLuint vao; glGenVertexArrays(1, &vao); glBindVertexArray(vao); // Create a Vertex Buffer Object and copy the vertex data to it GLuint vbo; glGenBuffers(1, &vbo); glBindBuffer(GL_ARRAY_BUFFER, vbo); glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW); // Specify the layout of the vertex data glEnableVertexAttribArray(0); // layout(location = 0) glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, 0); // Create a Elements Buffer Object and copy the elements data to it GLuint ebo; glGenBuffers(1, &ebo); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(elements), elements, GL_STATIC_DRAW); // Create and compile the vertex shader const GLchar *vertexSource = GLSL( layout(location = 0) in vec2 position; void main() { gl_Position = vec4(position, 0.0, 1.0); } ); GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER); glShaderSource(vertexShader, 1, &vertexSource, NULL); glCompileShader(vertexShader); // Create and compile the fragment shader const char* fragmentSource = GLSL( out vec4 gl_FragColor; uniform vec2 u_resolution; void main() { vec2 pos = gl_FragCoord.xy / u_resolution; gl_FragColor = vec4(1.0); } ); GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER); glShaderSource(fragmentShader, 1, &fragmentSource, NULL); glCompileShader(fragmentShader); // Link the vertex and fragment shader into a shader program GLuint shaderProgram = glCreateProgram(); glAttachShader(shaderProgram, vertexShader); glAttachShader(shaderProgram, fragmentShader); glLinkProgram(shaderProgram); glUseProgram(shaderProgram); // get uniform's id by name and set value GLint uRes = glGetUniformLocation(shaderProgram, "u_Resolution"); glUniform2f(uRes, 800.0f, 600.0f); // ---------------------------- RENDERING ------------------------------ // while(!glfwWindowShouldClose(window)) { // Clear the screen to black glClear(GL_COLOR_BUFFER_BIT); glClearColor(0.0f, 0.5f, 1.0f, 1.0f); // Draw a rectangle made of 2 triangles -> 6 vertices glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, NULL); // Swap buffers and poll window events glfwSwapBuffers(window); glfwPollEvents(); } // ---------------------------- CLEARING ------------------------------ // // Delete allocated resources glDeleteProgram(shaderProgram); glDeleteShader(fragmentShader); glDeleteShader(vertexShader); glDeleteBuffers(1, &vbo); glDeleteVertexArrays(1, &vao); return 0; }  
    • By Vortez
      Hi guys, im having a little problem fixing a bug in my program since i multi-threaded it. The app is a little video converter i wrote for fun. To help you understand the problem, ill first explain how the program is made. Im using Delphi to do the GUI/Windows part of the code, then im loading a c++ dll for the video conversion. The problem is not related to the video conversion, but with OpenGL only. The code work like this:

       
      DWORD WINAPI JobThread(void *params) { for each files { ... _ConvertVideo(input_name, output_name); } } void EXP_FUNC _ConvertVideo(char *input_fname, char *output_fname) { // Note that im re-initializing and cleaning up OpenGL each time this function is called... CGLEngine GLEngine; ... // Initialize OpenGL GLEngine.Initialize(render_wnd); GLEngine.CreateTexture(dst_width, dst_height, 4); // decode the video and render the frames... for each frames { ... GLEngine.UpdateTexture(pY, pU, pV); GLEngine.Render(); } cleanup: GLEngine.DeleteTexture(); GLEngine.Shutdown(); // video cleanup code... }  
      With a single thread, everything work fine. The problem arise when im starting the thread for a second time, nothing get rendered, but the encoding work fine. For example, if i start the thread with 3 files to process, all of them render fine, but if i start the thread again (with the same batch of files or not...), OpenGL fail to render anything.
      Im pretty sure it has something to do with the rendering context (or maybe the window DC?). Here a snippet of my OpenGL class:
      bool CGLEngine::Initialize(HWND hWnd) { hDC = GetDC(hWnd); if(!SetupPixelFormatDescriptor(hDC)){ ReleaseDC(hWnd, hDC); return false; } hRC = wglCreateContext(hDC); wglMakeCurrent(hDC, hRC); // more code ... return true; } void CGLEngine::Shutdown() { // some code... if(hRC){wglDeleteContext(hRC);} if(hDC){ReleaseDC(hWnd, hDC);} hDC = hRC = NULL; }  
      The full source code is available here. The most relevant files are:
      -OpenGL class (header / source)
      -Main code (header / source)
       
      Thx in advance if anyone can help me.
    • By DiligentDev
      This article uses material originally posted on Diligent Graphics web site.
      Introduction
      Graphics APIs have come a long way from small set of basic commands allowing limited control of configurable stages of early 3D accelerators to very low-level programming interfaces exposing almost every aspect of the underlying graphics hardware. Next-generation APIs, Direct3D12 by Microsoft and Vulkan by Khronos are relatively new and have only started getting widespread adoption and support from hardware vendors, while Direct3D11 and OpenGL are still considered industry standard. New APIs can provide substantial performance and functional improvements, but may not be supported by older hardware. An application targeting wide range of platforms needs to support Direct3D11 and OpenGL. New APIs will not give any advantage when used with old paradigms. It is totally possible to add Direct3D12 support to an existing renderer by implementing Direct3D11 interface through Direct3D12, but this will give zero benefits. Instead, new approaches and rendering architectures that leverage flexibility provided by the next-generation APIs are expected to be developed.
      There are at least four APIs (Direct3D11, Direct3D12, OpenGL/GLES, Vulkan, plus Apple's Metal for iOS and osX platforms) that a cross-platform 3D application may need to support. Writing separate code paths for all APIs is clearly not an option for any real-world application and the need for a cross-platform graphics abstraction layer is evident. The following is the list of requirements that I believe such layer needs to satisfy:
      Lightweight abstractions: the API should be as close to the underlying native APIs as possible to allow an application leverage all available low-level functionality. In many cases this requirement is difficult to achieve because specific features exposed by different APIs may vary considerably. Low performance overhead: the abstraction layer needs to be efficient from performance point of view. If it introduces considerable amount of overhead, there is no point in using it. Convenience: the API needs to be convenient to use. It needs to assist developers in achieving their goals not limiting their control of the graphics hardware. Multithreading: ability to efficiently parallelize work is in the core of Direct3D12 and Vulkan and one of the main selling points of the new APIs. Support for multithreading in a cross-platform layer is a must. Extensibility: no matter how well the API is designed, it still introduces some level of abstraction. In some cases the most efficient way to implement certain functionality is to directly use native API. The abstraction layer needs to provide seamless interoperability with the underlying native APIs to provide a way for the app to add features that may be missing. Diligent Engine is designed to solve these problems. 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 C++ front-end for all supported platforms and provides interoperability with underlying native APIs. It also supports integration with Unity and is designed to be used as graphics subsystem in a standalone game engine, Unity native plugin or any other 3D application. Full source code is available for download at GitHub and is free to use.
      Overview
      Diligent Engine API takes some features from Direct3D11 and Direct3D12 as well as introduces new concepts to hide certain platform-specific details and make the system easy to use. It contains the following main components:
      Render device (IRenderDevice  interface) is responsible for creating all other objects (textures, buffers, shaders, pipeline states, etc.).
      Device context (IDeviceContext interface) is the main interface for recording rendering commands. Similar to Direct3D11, there are immediate context and deferred contexts (which in Direct3D11 implementation map directly to the corresponding context types). Immediate context combines command queue and command list recording functionality. It records commands and submits the command list for execution when it contains sufficient number of commands. Deferred contexts are designed to only record command lists that can be submitted for execution through the immediate context.
      An alternative way to design the API would be to expose command queue and command lists directly. This approach however does not map well to Direct3D11 and OpenGL. Besides, some functionality (such as dynamic descriptor allocation) can be much more efficiently implemented when it is known that a command list is recorded by a certain deferred context from some thread.
      The approach taken in the engine does not limit scalability as the application is expected to create one deferred context per thread, and internally every deferred context records a command list in lock-free fashion. At the same time this approach maps well to older APIs.
      In current implementation, only one immediate context that uses default graphics command queue is created. To support multiple GPUs or multiple command queue types (compute, copy, etc.), it is natural to have one immediate contexts per queue. Cross-context synchronization utilities will be necessary.
      Swap Chain (ISwapChain interface). Swap chain interface represents a chain of back buffers and is responsible for showing the final rendered image on the screen.
      Render device, device contexts and swap chain are created during the engine initialization.
      Resources (ITexture and IBuffer interfaces). There are two types of resources - textures and buffers. There are many different texture types (2D textures, 3D textures, texture array, cubmepas, etc.) that can all be represented by ITexture interface.
      Resources Views (ITextureView and IBufferView interfaces). While textures and buffers are mere data containers, texture views and buffer views describe how the data should be interpreted. For instance, a 2D texture can be used as a render target for rendering commands or as a shader resource.
      Pipeline State (IPipelineState interface). GPU pipeline contains many configurable stages (depth-stencil, rasterizer and blend states, different shader stage, etc.). Direct3D11 uses coarse-grain objects to set all stage parameters at once (for instance, a rasterizer object encompasses all rasterizer attributes), while OpenGL contains myriad functions to fine-grain control every individual attribute of every stage. Both methods do not map very well to modern graphics hardware that combines all states into one monolithic state under the hood. Direct3D12 directly exposes pipeline state object in the API, and Diligent Engine uses the same approach.
      Shader Resource Binding (IShaderResourceBinding interface). Shaders are programs that run on the GPU. Shaders may access various resources (textures and buffers), and setting correspondence between shader variables and actual resources is called resource binding. Resource binding implementation varies considerably between different API. Diligent Engine introduces a new object called shader resource binding that encompasses all resources needed by all shaders in a certain pipeline state.
      API Basics
      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. Graphics APIs usually have a native object that represents linear buffer. Diligent Engine uses IBuffer interface as an abstraction for a native buffer. To create a buffer, one needs to populate BufferDesc structure and call IRenderDevice::CreateBuffer() method as in the following example:
      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 ); While there is usually just one buffer object, different APIs use very different approaches to represent textures. For instance, in Direct3D11, there are ID3D11Texture1D, ID3D11Texture2D, and ID3D11Texture3D objects. In OpenGL, there is individual object for every texture dimension (1D, 2D, 3D, Cube), which may be a texture array, which may also be multisampled (i.e. GL_TEXTURE_2D_MULTISAMPLE_ARRAY). As a result there are nine different GL texture types that Diligent Engine may create under the hood. In Direct3D12, there is only one resource interface. Diligent Engine hides all these details in ITexture interface. There is only one  IRenderDevice::CreateTexture() method that is capable of creating all texture types. Dimension, format, array size and all other parameters are specified by the members of the TextureDesc structure:
      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 ); If native API supports multithreaded resource creation, textures and buffers can be created by multiple threads simultaneously.
      Interoperability with native API provides access to the native buffer/texture objects and also allows creating Diligent Engine objects from native handles. It allows applications seamlessly integrate native API-specific code with Diligent Engine.
      Next-generation APIs allow fine level-control over how resources are allocated. Diligent Engine does not currently expose this functionality, but it can be added by implementing IResourceAllocator interface that encapsulates specifics of resource allocation and providing this interface to CreateBuffer() or CreateTexture() methods. If null is provided, default allocator should be used.
      Initializing the Pipeline State
      As it was mentioned earlier, Diligent Engine follows next-gen APIs 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.). This approach maps directly to Direct3D12/Vulkan, but is also beneficial for older APIs as it eliminates pipeline misconfiguration errors. With many individual calls tweaking various GPU pipeline settings it is very easy to forget to set one of the states or assume the stage is already properly configured when in fact it is not. Using pipeline state object helps avoid these problems as all stages are configured at once.
      Creating Shaders
      While in earlier APIs shaders were bound separately, in the next-generation APIs as well as in Diligent Engine shaders are part of the pipeline state object. The biggest challenge when authoring shaders is that Direct3D and OpenGL/Vulkan use different shader languages (while Apple uses yet another language in their Metal API). Maintaining two versions of every shader is not an option for real applications and Diligent Engine implements shader source code converter that allows shaders authored in HLSL to be translated to GLSL. To create a shader, one needs to populate ShaderCreationAttribs structure. SourceLanguage member of this structure tells the system which language the shader is authored in:
      SHADER_SOURCE_LANGUAGE_DEFAULT - The shader source language matches the underlying graphics API: HLSL for Direct3D11/Direct3D12 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. SHADER_SOURCE_LANGUAGE_GLSL - The shader source is in GLSL. There is currently no GLSL to HLSL converter, so this value should only be used for OpenGL and OpenGLES modes. There are two ways to provide the shader source code. The first way is to use Source member. The second way is to provide a file path in FilePath member. Since the engine is entirely decoupled from the platform and the host file system is platform-dependent, the structure exposes pShaderSourceStreamFactory member that is intended to provide the engine access to the file system. If FilePath is provided, shader source factory must also be provided. If the shader source contains any #include directives, the source stream factory will also be used to load these files. The engine provides default implementation for every supported platform that should be sufficient in most cases. Custom implementation can be provided when needed.
      When sampling a texture in a shader, the texture sampler was traditionally specified as separate object that was bound to the pipeline at run time or set as part of the texture object itself. However, in most cases it is known beforehand what kind of sampler will be used in the shader. Next-generation APIs expose new type of sampler called static sampler that can be initialized directly in the pipeline state. Diligent Engine exposes this functionality: when creating a shader, textures can be assigned static samplers. If static sampler is assigned, it will always be used instead of the one initialized in the texture shader resource view. To initialize static samplers, prepare an array of StaticSamplerDesc structures and initialize StaticSamplers and NumStaticSamplers members. Static samplers are more efficient and it is highly recommended to use them whenever possible. On older APIs, static samplers are emulated via generic sampler objects.
      The following is an example of shader initialization:
      ShaderCreationAttribs Attrs; Attrs.Desc.Name = "MyPixelShader"; Attrs.FilePath = "MyShaderFile.fx"; Attrs.SearchDirectories = "shaders;shaders\\inc;"; Attrs.EntryPoint = "MyPixelShader"; Attrs.Desc.ShaderType = SHADER_TYPE_PIXEL; Attrs.SourceLanguage = SHADER_SOURCE_LANGUAGE_HLSL; BasicShaderSourceStreamFactory BasicSSSFactory(Attrs.SearchDirectories); Attrs.pShaderSourceStreamFactory = &BasicSSSFactory; ShaderVariableDesc ShaderVars[] = {     {"g_StaticTexture", SHADER_VARIABLE_TYPE_STATIC},     {"g_MutableTexture", SHADER_VARIABLE_TYPE_MUTABLE},     {"g_DynamicTexture", SHADER_VARIABLE_TYPE_DYNAMIC} }; Attrs.Desc.VariableDesc = ShaderVars; Attrs.Desc.NumVariables = _countof(ShaderVars); Attrs.Desc.DefaultVariableType = SHADER_VARIABLE_TYPE_STATIC; StaticSamplerDesc StaticSampler; StaticSampler.Desc.MinFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MagFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MipFilter = FILTER_TYPE_LINEAR; StaticSampler.TextureName = "g_MutableTexture"; Attrs.Desc.NumStaticSamplers = 1; Attrs.Desc.StaticSamplers = &StaticSampler; ShaderMacroHelper Macros; Macros.AddShaderMacro("USE_SHADOWS", 1); Macros.AddShaderMacro("NUM_SHADOW_SAMPLES", 4); Macros.Finalize(); Attrs.Macros = Macros; RefCntAutoPtr<IShader> pShader; m_pDevice->CreateShader( Attrs, &pShader );
      Creating the Pipeline State Object
      After all required shaders are created, the rest of the fields of the PipelineStateDesc structure provide depth-stencil, rasterizer, and blend state descriptions, the number and format of render targets, input layout format, etc. For instance, rasterizer state can be described as follows:
      PipelineStateDesc PSODesc; RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc; RasterizerDesc.FillMode = FILL_MODE_SOLID; RasterizerDesc.CullMode = CULL_MODE_NONE; RasterizerDesc.FrontCounterClockwise = True; RasterizerDesc.ScissorEnable = True; RasterizerDesc.AntialiasedLineEnable = False; Depth-stencil and blend states are defined in a similar fashion.
      Another important thing that pipeline state object encompasses is the input layout description that defines how inputs to the vertex shader, which is the very first shader stage, should be read from the memory. Input layout may define several vertex streams that contain values of different formats and sizes:
      // Define input layout InputLayoutDesc &Layout = PSODesc.GraphicsPipeline.InputLayout; LayoutElement TextLayoutElems[] = {     LayoutElement( 0, 0, 3, VT_FLOAT32, False ),     LayoutElement( 1, 0, 4, VT_UINT8, True ),     LayoutElement( 2, 0, 2, VT_FLOAT32, False ), }; Layout.LayoutElements = TextLayoutElems; Layout.NumElements = _countof( TextLayoutElems ); Finally, pipeline state defines primitive topology type. When all required members are initialized, a pipeline state object can be created by IRenderDevice::CreatePipelineState() method:
      // Define shader and primitive topology PSODesc.GraphicsPipeline.PrimitiveTopologyType = PRIMITIVE_TOPOLOGY_TYPE_TRIANGLE; PSODesc.GraphicsPipeline.pVS = pVertexShader; PSODesc.GraphicsPipeline.pPS = pPixelShader; PSODesc.Name = "My pipeline state"; m_pDev->CreatePipelineState(PSODesc, &m_pPSO); When PSO object is bound to the pipeline, the engine invokes all API-specific commands to set all states specified by the object. In case of Direct3D12 this maps directly to setting the D3D12 PSO object. In case of Direct3D11, this involves setting individual state objects (such as rasterizer and blend states), shaders, input layout etc. In case of OpenGL, this requires a number of fine-grain state tweaking calls. Diligent Engine keeps track of currently bound states and only calls functions to update these states that have actually changed.
      Binding Shader Resources
      Direct3D11 and OpenGL utilize fine-grain resource binding models, where an application binds individual buffers and textures to certain shader or program resource binding slots. Direct3D12 uses a very different approach, where resource descriptors are grouped into tables, and an application can bind all resources in the table at once by setting the table in the command list. Resource binding model in Diligent Engine is designed to leverage this new method. It introduces a new object called shader resource binding that encapsulates all resource bindings required for all shaders in a certain pipeline state. It also introduces the classification of shader variables based on the frequency of expected change that helps the engine group them into tables under the hood:
      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. Shader variable type must be specified during shader creation by populating an array of ShaderVariableDesc structures and initializing ShaderCreationAttribs::Desc::VariableDesc and ShaderCreationAttribs::Desc::NumVariables members (see example of shader creation above).
      Static variables cannot be changed once a resource is bound to the variable. They are bound directly to the shader object. For instance, a shadow map texture is not expected to change after it is created, so it can be bound directly to the shader:
      PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new Shader Resource Binding object (SRB) that is created by the pipeline state (IPipelineState::CreateShaderResourceBinding()):
      m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
      Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
      m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
      m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
      As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
      This post gives more details about the resource binding model in Diligent Engine.
      Setting the Pipeline State and Committing Shader Resources
      Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
      m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
      The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
      m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
      Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
      m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
      Invoking Draw Command
      The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
      ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // 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); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes 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); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
      Source Code
      Full engine source code is available on GitHub and is free to use. The repository contains two samples, asteroids performance benchmark and example Unity project that uses Diligent Engine in native plugin.
      AntTweakBar sample is Diligent Engine’s “Hello World” example.

       
      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 multiple render targets, using compute shaders and unordered access views, etc.

      Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

      Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

      Future Work
      The engine is under active development. It currently supports Windows desktop, Universal Windows and Android platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and support for more platforms is planned.
    • By michaeldodis
      I've started building a small library, that can render pie menu GUI in legacy opengl, planning to add some traditional elements of course.
      It's interface is similar to something you'd see in IMGUI. It's written in C.
      Early version of the library
      I'd really love to hear anyone's thoughts on this, any suggestions on what features you'd want to see in a library like this? 
      Thanks in advance!
    • By Michael Aganier
      I have this 2D game which currently eats up to 200k draw calls per frame. The performance is acceptable, but I want a lot more than that. I need to batch my sprite drawing, but I'm not sure what's the best way in OpenGL 3.3 (to keep compatibility with older machines).
      Each individual sprite move independently almost every frame and their is a variety of textures and animations. What's the fastest way to render a lot of dynamic sprites? Should I map all my data to the GPU and update it all the time? Should I setup my data in the RAM and send it to the GPU all at once? Should I use one draw call per sprite and let the matrices apply the transformations or should I compute the transformations in a world vbo on the CPU so that they can be rendered by a single draw call?
  • Popular Now