Sign in to follow this  

OpenGL VBO slow

This topic is 1761 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

Hi All
 
I've implemented VBO but got a slower render (only 1 fps vs 3 fps without VBO).
After series of experiments I've found the problem is caused by using GL_DOUBLE for at least one chunk (vertices, normals, UVs etc). With GL_FLOAT for everything my results are good: 17 fps with VBO. So my questions are:
 
- is a low speed normal/expected with GL_DOUBLE ?
- how can I make VBO faster yet?
 
My setings are:
 
OpenGL Vendor: ATI Technologies Inc.
OpenGL Renderer: ATI Radeon HD 2600 OpenGL Engine
OpenGL Version: 2.1 ATI-1.6.36
 
Vertices 756,780
Polygons 1,169,235
Objects 150
VBO buffers: 150 * 2 = 300 
(GL_ARRAY_BUFFER_ARB + GL_ELEMENT_ARRAY_BUFFER_ARB) both GL_STATIC_DRAW_ARB
Using glDrawElements
Shading: gourand
Total VBO RAM: 42,513.104
 
Thanks
Tom
Edited by Tommato

Share this post


Link to post
Share on other sites

AFAIK usually you would use floats and not doubles on the GPU

 

Thats a lot of triangles and your GPU doesnt seem that powerful, so i would say your usage of VBO's isnt the problem, simply the amount of work youre trying to do.

 

Assuming your shader isnt full of ifs, what you should do is reduce the amount of triangles you draw. Dont draw objects outside the screen, draw far away stuff with lower detail (LoD)...

Edited by Waterlimon

Share this post


Link to post
Share on other sites

Unless you have the GL_ARB_vertex_attrib_64bit extension available you can safely assume that any GLdouble vertex input is going to be software emulated - in immediate mode by casting your glVertex3d parameters down to float, with VBOs by potentially running your entire per-vertex pipeline in software.  Obviously that would result in VBOs being somewhat slower than immediate mode code, which is exactly what you've observed.

 

Double-precision support in hardware is still relatively new (requiring SM5 hardware IIRC), and the moral of the story is that even if the GL spec allows it for a particular call, don't always assume that it means your hardware supports it (especially if it's from an older part of GL that pre-dates hardware T&L).

 

How can you go faster still?  If you're not already doing it, then consider interleaving your vertex struct.  I.e. instead of:

 

GLfloat positions[ARBITRARY_NUMBER];
GLfloat normals[ARBITRARY_NUMBER];
GLfloat texcoords[ARBITRARY_NUMBER];

 

Use:

 

struct myVertex
{
    GLfloat position[3];
    GLfloat normal[3];
    GLfloat texcoord[2];
};

myVertex vertices[ARBITRARY_NUMBER];

 

This can be a win as it means that your GPU can now read all data for each vertex together, and without having to do any random jumping around in memory.

 

Another thing you can do, since you have an older GPU that only supports GL2.1, is to use GL_UNSIGNED_SHORT instead of GL_UNSIGNED_INT for your GL_ELEMENT_ARRAY_BUFFER, if you can get away with it.  This is also coming back to the "don't always assume that hardware supports what the GL spec allows" point, and a GPU that old may not support 32-bit indices very well (or at all!)

 

Finally, and to cut down on buffer changes, you could consider packing all objects into a single VBO (rather than 150 * 2 separate VBOs) and using the parameters to your glDrawArrays/glDrawElements calls (or the offsets specified by your gl*Pointer calls) to select which object gets drawn.  This may or may not be compatible with using 16-bit indices however, so you'll need to profile both approaches and see which works best for you.

Edited by mhagain

Share this post


Link to post
Share on other sites

you can safely assume that any GLdouble vertex input is going to be software emulated . . . with VBOs by potentially running your entire per-vertex pipeline in software

Perhaps I'm missing something, but it was my understanding that when transferring a static VBO from the client to the GPU, the actual data is copied over--so any doubles ought to have been already converted to floats in this case as well?

In the face of this, I might suspect something else may be afoot; for example, are you sure you're using VBOs, or are you using vertex arrays accidentally instead?

Share this post


Link to post
Share on other sites

Perhaps I'm missing something, but it was my understanding that when transferring a static VBO from the client to the GPU, the actual data is copied over--so any doubles ought to have been already converted to floats in this case as well?

 

The data type is only specified at the gl*Pointer stage, by which point the VBO has already long been copied over.  glBufferData itself is totally type agnostic; it doesn't care whether you've floats, doubles, plain text or even a JPEG in there - it just transfers a block of memory to the buffer object.  gl*Pointer is what defines how that memory is interpreted.

Share this post


Link to post
Share on other sites

Unless you have the GL_ARB_vertex_attrib_64bit extension available you can safely assume that any GLdouble vertex input is going to be software emulated -

Thanks for your complete answer, clear now

 

Thanks all for your replies. The spedup to 17 fps (from inital 3-4) is a real progress for my app, but how good it is for VBO? Just some articles promises huge speedups like in 100 or more times (although IMO it's out of common sense). In other words should I apply more efforts to achieve better performance or it's already acceptable enough? Note: with GL_DYNAMIC_DRAW_ARB I've 14-15 fps (instead of 17 with static)

 

Thanks

Tom

Share this post


Link to post
Share on other sites

The advantage of a VBO is basically just that the data can be put in there and uploaded once and then used multiple times for drawing(thats what static draw is hinting at). If someone does not follow this pattern and changes the data every frame and then immediately draws from it there is not much to gain for him compared to a vertex array(there you are supposed to give dynamic draw hint though it depends on the driver how/if that makes a difference).

I very much doubt a 100 times speedup even if those people only specified single vertices in immediate mode.

Share this post


Link to post
Share on other sites

I can see how 100x could be achievable.  First of all the program has to be completely vertex-bound, let's say drawing millions of points with each individual point being in it's own glBegin/glEnd pair.  Then, it needs to be doing virtually nothing else on the GPU - so all of those points are offscreen.  Switch that to using a VBO and a single draw call, and you'll see huge performance increases of that magnitude.

 

For more realistic real-world programs that people actually write you're not going to see increases like that at all.

Share this post


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

  • Similar Content

    • 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?
    • By xhcao
      Does sync be needed to read texture content after access texture image in compute shader?
      My simple code is as below,
      glUseProgram(program.get());
      glBindImageTexture(0, texture[0], 0, GL_FALSE, 3, GL_READ_ONLY, GL_R32UI);
      glBindImageTexture(1, texture[1], 0, GL_FALSE, 4, GL_WRITE_ONLY, GL_R32UI);
      glDispatchCompute(1, 1, 1);
      // Does sync be needed here?
      glUseProgram(0);
      glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
      glFramebufferTexture2D(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                                     GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, texture[1], 0);
      glReadPixels(0, 0, kWidth, kHeight, GL_RED_INTEGER, GL_UNSIGNED_INT, outputValues);
       
      Compute shader is very simple, imageLoad content from texture[0], and imageStore content to texture[1]. Does need to sync after dispatchCompute?
    • By Jonathan2006
      My question: is it possible to transform multiple angular velocities so that they can be reinserted as one? My research is below:
      // This works quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); quat quaternion2 = GEMultiplyQuaternions(quaternion1, GEQuaternionFromAngleRadians(angleRadiansVector2)); quat quaternion3 = GEMultiplyQuaternions(quaternion2, GEQuaternionFromAngleRadians(angleRadiansVector3)); glMultMatrixf(GEMat4FromQuaternion(quaternion3).array); // The first two work fine but not the third. Why? quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); vec3 vector1 = GETransformQuaternionAndVector(quaternion1, angularVelocity1); quat quaternion2 = GEQuaternionFromAngleRadians(angleRadiansVector2); vec3 vector2 = GETransformQuaternionAndVector(quaternion2, angularVelocity2); // This doesn't work //quat quaternion3 = GEQuaternionFromAngleRadians(angleRadiansVector3); //vec3 vector3 = GETransformQuaternionAndVector(quaternion3, angularVelocity3); vec3 angleVelocity = GEAddVectors(vector1, vector2); // Does not work: vec3 angleVelocity = GEAddVectors(vector1, GEAddVectors(vector2, vector3)); static vec3 angleRadiansVector; vec3 angularAcceleration = GESetVector(0.0, 0.0, 0.0); // Sending it through one angular velocity later in my motion engine angleVelocity = GEAddVectors(angleVelocity, GEMultiplyVectorAndScalar(angularAcceleration, timeStep)); angleRadiansVector = GEAddVectors(angleRadiansVector, GEMultiplyVectorAndScalar(angleVelocity, timeStep)); glMultMatrixf(GEMat4FromEulerAngle(angleRadiansVector).array); Also how do I combine multiple angularAcceleration variables? Is there an easier way to transform the angular values?
  • Popular Now