• Advertisement
Sign in to follow this  

OpenGL Modern OpenGL Transforms, HOW?

This topic is 734 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 have been scouring all the documentation, forums, and general internet searches for this question and I have found a bunch of half answers and I hope someone can help.

 

Now to the question.

 

Lets say I have 1000 objects that use the same mesh, shader, texture, etc. but they all have separate transforms (locations, rotations, scale).

What is the best way to render this without tanking the frame time?

 

I am weary of instancing because there may be many different meshes in the future with different textures/state.

 

The slow way that I know of that is trivial to implement is to sort the geometry by state and make a draw call for each one and passing the transform matrix in through a uniform matrix. This does not work because DrawArrays is extremely slow and completely CPU bound. I have implemented this and know that this seriously destroys my frame time even with a couple of hundred draw calls.

 

I would like to use a single VAO for each object type, but how do you deal with transform data? The solution I have usually seen involves transforming the vertices on the CPU and then updating the VBO before drawing. It seems rather wasteful to do this on the CPU and resubmit the data because the GPU is sooooo much better at doing transforms in the vertex shader. This also may make the program CPU bound yet again.

 

Most explanations I have seen on how to do this always focus on rendering a few object per frame not hundreds let alone thousands. I absolutely know this is possible because i have seen many games pull off hundreds of objects. I know if there is a static environment then it is pretty easy to render because there should only be one transform for the whole environment if done right. That is pre-calculating the model space of a chunk or environment and then just moving the whole chunk or environment. The problem is dynamic objects. I only need a few hundred to about a thousand. I don't imagine that it can be this difficult.

 

I feel like I am missing something important and hope that i can get some information on how most games do it.

 

I have done a large amount of profiling and all roads seem to lead to reducing the number of draw calls, but I am having trouble determining how to do that with so many independent meshes with different transformation matrices.

 

Thanks in advance.

Share this post


Link to post
Share on other sites
Advertisement

Instancing.

 

OK, I know that you said this:

 

 

I am weary of instancing because there may be many different meshes in the future with different textures/state.

 

However, even if you do have different textures and state in the future, that's no reason to make your performance suffer now.  An instancing system can be coded to deal with this; even if you have, say 100 different combinations, that's still 100 draw calls versus 1000.

Share this post


Link to post
Share on other sites

You could load up your model and indices into a VBO/IBO and then setup your VAO + shader with them.  You would then create a uniform buffer object that holds the transform matrices  as an array for all your entities and update that every frame.  Then render all the models at once using either instancing or multidraw rendering.  In your shader use the draw_ID to index into the transform matrix array to get that particular model's transform.

 

If you have multiple models, as long as they use the same shader and have the same vertex format, you could store them all into a single VBO/IBO/VAO and use mulitidraw with different offsets.  You would need to look at putting all the textures in a texture array or using direct state access for the texture data.

 

Instead of a uniform buffer, you could use a shader storage buffer if you have a lot of data to store per instance (transform, material ids, etc), then index into it using the draw_ID.  If you go the SSBO route, you may want to look at triple buffering it and persistently mapping it so that you don't stall out rendering trying to update it.

 

cheers,

 

Bob

Share this post


Link to post
Share on other sites
Thanks for the help. I have tried instancing and it does mostly work for what I'm doing.

Don't UBOs have a relatively low limit for max size?

I'm guess I'm still unsure how AAA games are able to have so many meshes rendered along with things like particle effects

What strategies are employed to reduce the number of draw calls and be able to maintain independent object transformation?

I'm sure instancing is used for particle effects but I'm not sure how this is done in practice because there can be many emitters that (i.e. many explosions) die after some time. Would the buffer that contains the transformations have to be scraped and refreshed every time a particle died?

I'm pretty good at getting an implementation together once I understand the strategies but I'm having trouble finding best practices on this stuff. There are many beginner tutorials our there but I can't seem to get information on how AAA does these things in practice.

Share this post


Link to post
Share on other sites

AAA engines don't necessarily use the most modern strategies out there, but just something that works well enough for the target platform(s) + the game they're running.

 

Typically the most amount of geometry comes from static world geometry, which can be batched together (offline, not runtime) into bigger chunks to reduce draw calls.

 

Something like trees and foliage would just be rendered instanced. When far away, sprite impostors can be used for even lower performance impact.

 

One particle effect with all its particles is usually one draw call, and its vertex buffer is typically completely rewritten each frame when it's visible and updating. Most of the math can be done in vertex shader so that the CPU-side calculations for the update stay light.

 

On modern desktops you can get quite high with the draw call count (a few thousand should be no problem) but on high resolutions and less beefy GPU's the shading would easily become the bottleneck instead.

 

One thing to consider is that AAA games on Windows usually use D3D, which can have better optimized drivers. If you have bad luck with OpenGL drivers (Intel?) and an older card the driver may be doing work on CPU which should really be done on GPU. Using VBO's and a good driver, over a thousand draw calls should not be a problem on either D3D or OpenGL.

 

Share this post


Link to post
Share on other sites

Uniform buffers are much smaller than SSBO's.  My graphics card says it supports a max of 65536 bytes in the buffer (64k).  This is enough for 1024 transform matrix's (mat4).  If you need more, or want to triple buffer so you can update without stalling rendering, then you should look at using SSBO's.  SSBO's will be at least be 16MB in size.  

 

Cheers, 

 

Bob

Share this post


Link to post
Share on other sites


I'm guess I'm still unsure how AAA games are able to have so many meshes rendered along with things like particle effects

What strategies are employed to reduce the number of draw calls and be able to maintain independent object transformation?

 

Many mega-particles solutions involve a single draw of a mesh that you can imagine as, f.e., 200 quads floating over each other with small constant gaps between them along an object space axis direction - this means that value of quad on that axis provides a special state to every single quad that you can functionalize in vertex function (create many animated  supper glows, etc.)

 

Many particle-rich effects are a function of time and a single value in vertex, not a per particle transformation individual setters.

 

Now instancing drawings by transformations as well, is not usually a thing that will benefit most of the scenarios, even with army of reproduced meshes- since:

- draw calls that differ only by a uniform changing state in between them are nearly as fast as a single draw (they do run in parallel when issued, doing same amount of vertex function jobs).

- you will loose ability to sort geometry rendering from front to back, frustum culling, fill rate savings, in trivial ways

- you will introduce the second per instance vertex buffer, which you will need to update if still wanting the optimization techniques, and complicate vertex function feed (at each vertex)

- Remember the first point of nearly no benefit as opposed to the separate draw calls issued after each other to gpu.

 

Unless GPU vendors totally revolve GPU architecture, you may consider a whole pile of modern routines in graphic libraries as pure theoretical benefits, doing only harm when introduced today, even when speaking solely of performance only for that matter.

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Tags

  • Advertisement
  • Popular Now

  • Similar Content

    • By reenigne
      For those that don't know me. I am the individual who's two videos are listed here under setup for https://wiki.libsdl.org/Tutorials
      I also run grhmedia.com where I host the projects and code for the tutorials I have online.
      Recently, I received a notice from youtube they will be implementing their new policy in protecting video content as of which I won't be monetized till I meat there required number of viewers and views each month.

      Frankly, I'm pretty sick of youtube. I put up a video and someone else learns from it and puts up another video and because of the way youtube does their placement they end up with more views.
      Even guys that clearly post false information such as one individual who said GLEW 2.0 was broken because he didn't know how to compile it. He in short didn't know how to modify the script he used because he didn't understand make files and how the requirements of the compiler and library changes needed some different flags.

      At the end of the month when they implement this I will take down the content and host on my own server purely and it will be a paid system and or patreon. 

      I get my videos may be a bit dry, I generally figure people are there to learn how to do something and I rather not waste their time. 
      I used to also help people for free even those coming from the other videos. That won't be the case any more. I used to just take anyone emails and work with them my email is posted on the site.

      I don't expect to get the required number of subscribers in that time or increased views. Even if I did well it wouldn't take care of each reoccurring month.
      I figure this is simpler and I don't plan on putting some sort of exorbitant fee for a monthly subscription or the like.
      I was thinking on the lines of a few dollars 1,2, and 3 and the larger subscription gets you assistance with the content in the tutorials if needed that month.
      Maybe another fee if it is related but not directly in the content. 
      The fees would serve to cut down on the number of people who ask for help and maybe encourage some of the people to actually pay attention to what is said rather than do their own thing. That actually turns out to be 90% of the issues. I spent 6 hours helping one individual last week I must have asked him 20 times did you do exactly like I said in the video even pointed directly to the section. When he finally sent me a copy of the what he entered I knew then and there he had not. I circled it and I pointed out that wasn't what I said to do in the video. I didn't tell him what was wrong and how I knew that way he would go back and actually follow what it said to do. He then reported it worked. Yea, no kidding following directions works. But hey isn't alone and well its part of the learning process.

      So the point of this isn't to be a gripe session. I'm just looking for a bit of feed back. Do you think the fees are unreasonable?
      Should I keep the youtube channel and do just the fees with patreon or do you think locking the content to my site and require a subscription is an idea.

      I'm just looking at the fact it is unrealistic to think youtube/google will actually get stuff right or that youtube viewers will actually bother to start looking for more accurate videos. 
    • By Balma Alparisi
      i got error 1282 in my code.
      sf::ContextSettings settings; settings.majorVersion = 4; settings.minorVersion = 5; settings.attributeFlags = settings.Core; sf::Window window; window.create(sf::VideoMode(1600, 900), "Texture Unit Rectangle", sf::Style::Close, settings); window.setActive(true); window.setVerticalSyncEnabled(true); glewInit(); GLuint shaderProgram = createShaderProgram("FX/Rectangle.vss", "FX/Rectangle.fss"); float vertex[] = { -0.5f,0.5f,0.0f, 0.0f,0.0f, -0.5f,-0.5f,0.0f, 0.0f,1.0f, 0.5f,0.5f,0.0f, 1.0f,0.0f, 0.5,-0.5f,0.0f, 1.0f,1.0f, }; GLuint indices[] = { 0,1,2, 1,2,3, }; GLuint vao; glGenVertexArrays(1, &vao); glBindVertexArray(vao); GLuint vbo; glGenBuffers(1, &vbo); glBindBuffer(GL_ARRAY_BUFFER, vbo); glBufferData(GL_ARRAY_BUFFER, sizeof(vertex), vertex, GL_STATIC_DRAW); GLuint ebo; glGenBuffers(1, &ebo); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices,GL_STATIC_DRAW); glVertexAttribPointer(0, 3, GL_FLOAT, false, sizeof(float) * 5, (void*)0); glEnableVertexAttribArray(0); glVertexAttribPointer(1, 2, GL_FLOAT, false, sizeof(float) * 5, (void*)(sizeof(float) * 3)); glEnableVertexAttribArray(1); GLuint texture[2]; glGenTextures(2, texture); glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, texture[0]); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); sf::Image* imageOne = new sf::Image; bool isImageOneLoaded = imageOne->loadFromFile("Texture/container.jpg"); if (isImageOneLoaded) { glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageOne->getSize().x, imageOne->getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageOne->getPixelsPtr()); glGenerateMipmap(GL_TEXTURE_2D); } delete imageOne; glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, texture[1]); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); sf::Image* imageTwo = new sf::Image; bool isImageTwoLoaded = imageTwo->loadFromFile("Texture/awesomeface.png"); if (isImageTwoLoaded) { glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageTwo->getSize().x, imageTwo->getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageTwo->getPixelsPtr()); glGenerateMipmap(GL_TEXTURE_2D); } delete imageTwo; glUniform1i(glGetUniformLocation(shaderProgram, "inTextureOne"), 0); glUniform1i(glGetUniformLocation(shaderProgram, "inTextureTwo"), 1); GLenum error = glGetError(); std::cout << error << std::endl; sf::Event event; bool isRunning = true; while (isRunning) { while (window.pollEvent(event)) { if (event.type == event.Closed) { isRunning = false; } } glClear(GL_COLOR_BUFFER_BIT); if (isImageOneLoaded && isImageTwoLoaded) { glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, texture[0]); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, texture[1]); glUseProgram(shaderProgram); } glBindVertexArray(vao); glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr); glBindVertexArray(0); window.display(); } glDeleteVertexArrays(1, &vao); glDeleteBuffers(1, &vbo); glDeleteBuffers(1, &ebo); glDeleteProgram(shaderProgram); glDeleteTextures(2,texture); return 0; } and this is the vertex shader
      #version 450 core layout(location=0) in vec3 inPos; layout(location=1) in vec2 inTexCoord; out vec2 TexCoord; void main() { gl_Position=vec4(inPos,1.0); TexCoord=inTexCoord; } and the fragment shader
      #version 450 core in vec2 TexCoord; uniform sampler2D inTextureOne; uniform sampler2D inTextureTwo; out vec4 FragmentColor; void main() { FragmentColor=mix(texture(inTextureOne,TexCoord),texture(inTextureTwo,TexCoord),0.2); } I was expecting awesomeface.png on top of container.jpg

    • By khawk
      We've just released all of the source code for the NeHe OpenGL lessons on our Github page at https://github.com/gamedev-net/nehe-opengl. code - 43 total platforms, configurations, and languages are included.
      Now operated by GameDev.net, NeHe is located at http://nehe.gamedev.net where it has been a valuable resource for developers wanting to learn OpenGL and graphics programming.

      View full story
    • By TheChubu
      The Khronos™ Group, an open consortium of leading hardware and software companies, announces from the SIGGRAPH 2017 Conference the immediate public availability of the OpenGL® 4.6 specification. OpenGL 4.6 integrates the functionality of numerous ARB and EXT extensions created by Khronos members AMD, Intel, and NVIDIA into core, including the capability to ingest SPIR-V™ shaders.
      SPIR-V is a Khronos-defined standard intermediate language for parallel compute and graphics, which enables content creators to simplify their shader authoring and management pipelines while providing significant source shading language flexibility. OpenGL 4.6 adds support for ingesting SPIR-V shaders to the core specification, guaranteeing that SPIR-V shaders will be widely supported by OpenGL implementations.
      OpenGL 4.6 adds the functionality of these ARB extensions to OpenGL’s core specification:
      GL_ARB_gl_spirv and GL_ARB_spirv_extensions to standardize SPIR-V support for OpenGL GL_ARB_indirect_parameters and GL_ARB_shader_draw_parameters for reducing the CPU overhead associated with rendering batches of geometry GL_ARB_pipeline_statistics_query and GL_ARB_transform_feedback_overflow_querystandardize OpenGL support for features available in Direct3D GL_ARB_texture_filter_anisotropic (based on GL_EXT_texture_filter_anisotropic) brings previously IP encumbered functionality into OpenGL to improve the visual quality of textured scenes GL_ARB_polygon_offset_clamp (based on GL_EXT_polygon_offset_clamp) suppresses a common visual artifact known as a “light leak” associated with rendering shadows GL_ARB_shader_atomic_counter_ops and GL_ARB_shader_group_vote add shader intrinsics supported by all desktop vendors to improve functionality and performance GL_KHR_no_error reduces driver overhead by allowing the application to indicate that it expects error-free operation so errors need not be generated In addition to the above features being added to OpenGL 4.6, the following are being released as extensions:
      GL_KHR_parallel_shader_compile allows applications to launch multiple shader compile threads to improve shader compile throughput WGL_ARB_create_context_no_error and GXL_ARB_create_context_no_error allow no error contexts to be created with WGL or GLX that support the GL_KHR_no_error extension “I’m proud to announce OpenGL 4.6 as the most feature-rich version of OpenGL yet. We've brought together the most popular, widely-supported extensions into a new core specification to give OpenGL developers and end users an improved baseline feature set. This includes resolving previous intellectual property roadblocks to bringing anisotropic texture filtering and polygon offset clamping into the core specification to enable widespread implementation and usage,” said Piers Daniell, chair of the OpenGL Working Group at Khronos. “The OpenGL working group will continue to respond to market needs and work with GPU vendors to ensure OpenGL remains a viable and evolving graphics API for all its customers and users across many vital industries.“
      The OpenGL 4.6 specification can be found at https://khronos.org/registry/OpenGL/index_gl.php. The GLSL to SPIR-V compiler glslang has been updated with GLSL 4.60 support, and can be found at https://github.com/KhronosGroup/glslang.
      Sophisticated graphics applications will also benefit from a set of newly released extensions for both OpenGL and OpenGL ES to enable interoperability with Vulkan and Direct3D. These extensions are named:
      GL_EXT_memory_object GL_EXT_memory_object_fd GL_EXT_memory_object_win32 GL_EXT_semaphore GL_EXT_semaphore_fd GL_EXT_semaphore_win32 GL_EXT_win32_keyed_mutex They can be found at: https://khronos.org/registry/OpenGL/index_gl.php
      Industry Support for OpenGL 4.6
      “With OpenGL 4.6 our customers have an improved set of core features available on our full range of OpenGL 4.x capable GPUs. These features provide improved rendering quality, performance and functionality. As the graphics industry’s most popular API, we fully support OpenGL and will continue to work closely with the Khronos Group on the development of new OpenGL specifications and extensions for our customers. NVIDIA has released beta OpenGL 4.6 drivers today at https://developer.nvidia.com/opengl-driver so developers can use these new features right away,” said Bob Pette, vice president, Professional Graphics at NVIDIA.
      "OpenGL 4.6 will be the first OpenGL release where conformant open source implementations based on the Mesa project will be deliverable in a reasonable timeframe after release. The open sourcing of the OpenGL conformance test suite and ongoing work between Khronos and X.org will also allow for non-vendor led open source implementations to achieve conformance in the near future," said David Airlie, senior principal engineer at Red Hat, and developer on Mesa/X.org projects.

      View full story
    • By _OskaR
      Hi,
      I have an OpenGL application but without possibility to wite own shaders.
      I need to perform small VS modification - is possible to do it in an alternative way? Do we have apps or driver modifictions which will catch the shader sent to GPU and override it?
  • Advertisement