Archived

This topic is now archived and is closed to further replies.

Ranger_One

OpenGL Best OpenGL Optimize method?

Recommended Posts

Ok now that I''m getting into OpenGL bigtime- I have a slew of questions, this one is about optimization. Assuming I have a model that is static, what method is best for optimization of drawing that model for speed? Should I use vertex arrays? DrawElement? or Display lists? I have heard display lists offer no speed increase (another post), so what is their point then? reduce code overhead? Ranger

Share this post


Link to post
Share on other sites
display lists are to reduce code overhead, yes. if you have multiple instances of the same object you can just call the same display list to draw them all.

vertex arrays with glDrawElements are faster than glBegin/glVertex*/glEnd i think mostly b/c of function overhead.

what i''m trying to learn currently is how to cache an objects displaylist/geometry on the vid card. but my sense is that that is an implementation decision left to the card itself. i''m not sure.

-me

Share this post


Link to post
Share on other sites
quote:
Original post by Palidine
what i''m trying to learn currently is how to cache an objects displaylist/geometry on the vid card. but my sense is that that is an implementation decision left to the card itself. i''m not sure.

That''s what NVIDIA''s vertex array range extension does.

Share this post


Link to post
Share on other sites
interesting.

that''s not the same as glDrawRangeElements() is it?

my understanding currently is that the above function is just a restriced version of glDrawElements()?

note to self: STFW

-me

Share this post


Link to post
Share on other sites
Newer cards have vertex arrays, and if it''s a static object, you can use LOCKED vertex arrays.. these are ussually the fastest. I don''t know who told you that Display Lists offer no speed increase, but they do/can. OpenGL (depending on the implementation) does attempt to optomize your display list (minimize state changes, re-order the drawing functions, and it can store your vertices internally as static vertex arrays, etc, etc).

Anyways, to answer your question, I''d have to go with vertex arrays/locked vertex arrays (per card implementation would be best, or support certain cards, and fall back to normal if unkown card)... although, the smaller your vertex arrays are (low poly models), the less of a performance gain you''ll get.

Billy - BillyB@mrsnj.com
(Hey, I''''m no longer anonymous!)

Share this post


Link to post
Share on other sites
when you are talking about card vertex arrays you mean just standard openGL vertex arrays, right?

as in the card just recognizes when you are using them and caches the vertex info?

-me

Share this post


Link to post
Share on other sites
Wow, Billy, you registered.

In regards to locked vertex arrays, generally, you don't see much of an improvement in speed unless you're using some form of multipass rendering. At least, that's been the case in my own code, and I've heard the same from others.

Palidine: the vertex array range extension isn't the same thing as glDrawRangeElements. The former allows you to allocate the memory you use for vertex arrays in video memory; this is the fastest method available on NVIDIA hardware. The latter isn't exactly a restricted version of glDrawElements; rather, it allows you to specify the minimum and maximum indicies used in your vertex array, which allows the video driver to more efficiently cache vertex data.

Share this post


Link to post
Share on other sites
I would stay away from vertex array locking (CVAs). The extension is very ''experimental'', in the sense that it was never finalized. It''s not even a real standard extension, it was more or less a quick''n''dirty function they developed to make Carmack happy. In fact, early nVidia driver versions did only support one single array format in this mode: the one Quake used...

The only thing that CVAs brought me were problems. Their implementation is so extremely driver/manufacturer dependend, you can''t rely on their behaviour in any way.

If you want to be compatible: use standard vertex arrays. They offer good speed, and most modern drivers do a really good job accelerating data transfer through AGP streaming etc. If you want to go for maximum performance, and multi-manufacturer compatibility isn''t really an issue, then go with VAR/VAO. It will allow the highest possible transfer rates that your hardware can handle.

About Draw(Range)Elements: AFAIK, nVidia drivers do not make a difference between both, DrawRangeElements directly calls DrawElements. The speed difference is reportedly 0, and I can confirm that, at least in VAR mode. But there might be a difference with other manufacturers, so it''s probably safer to always use DrawRangeElements.

/ Yann

Share this post


Link to post
Share on other sites
i agree with Yann here, ive never liked cva''s + personally can find no difference speedwise with drawrangeelements vs normal drawelements

http://uk.geocities.com/sloppyturds/gotterdammerung.html

Share this post


Link to post
Share on other sites

  • Announcements

  • Forum Statistics

    • Total Topics
      628342
    • Total Posts
      2982177
  • Similar Content

    • By test opty
      Hi all,
       
      I'm starting OpenGL using a tut on the Web. But at this point I would like to know the primitives needed for creating a window using OpenGL. So on Windows and using MS VS 2017, what is the simplest code required to render a window with the title of "First Rectangle", please?
       
       
    • By DejayHextrix
      Hi, New here. 
      I need some help. My fiance and I like to play this mobile game online that goes by real time. Her and I are always working but when we have free time we like to play this game. We don't always got time throughout the day to Queue Buildings, troops, Upgrades....etc.... 
      I was told to look into DLL Injection and OpenGL/DirectX Hooking. Is this true? Is this what I need to learn? 
      How do I read the Android files, or modify the files, or get the in-game tags/variables for the game I want? 
      Any assistance on this would be most appreciated. I been everywhere and seems no one knows or is to lazy to help me out. It would be nice to have assistance for once. I don't know what I need to learn. 
      So links of topics I need to learn within the comment section would be SOOOOO.....Helpful. Anything to just get me started. 
      Thanks, 
      Dejay Hextrix 
    • By mellinoe
      Hi all,
      First time poster here, although I've been reading posts here for quite a while. This place has been invaluable for learning graphics programming -- thanks for a great resource!
      Right now, I'm working on a graphics abstraction layer for .NET which supports D3D11, Vulkan, and OpenGL at the moment. I have implemented most of my planned features already, and things are working well. Some remaining features that I am planning are Compute Shaders, and some flavor of read-write shader resources. At the moment, my shaders can just get simple read-only access to a uniform (or constant) buffer, a texture, or a sampler. Unfortunately, I'm having a tough time grasping the distinctions between all of the different kinds of read-write resources that are available. In D3D alone, there seem to be 5 or 6 different kinds of resources with similar but different characteristics. On top of that, I get the impression that some of them are more or less "obsoleted" by the newer kinds, and don't have much of a place in modern code. There seem to be a few pivots:
      The data source/destination (buffer or texture) Read-write or read-only Structured or unstructured (?) Ordered vs unordered (?) These are just my observations based on a lot of MSDN and OpenGL doc reading. For my library, I'm not interested in exposing every possibility to the user -- just trying to find a good "middle-ground" that can be represented cleanly across API's which is good enough for common scenarios.
      Can anyone give a sort of "overview" of the different options, and perhaps compare/contrast the concepts between Direct3D, OpenGL, and Vulkan? I'd also be very interested in hearing how other folks have abstracted these concepts in their libraries.
    • By aejt
      I recently started getting into graphics programming (2nd try, first try was many years ago) and I'm working on a 3d rendering engine which I hope to be able to make a 3D game with sooner or later. I have plenty of C++ experience, but not a lot when it comes to graphics, and while it's definitely going much better this time, I'm having trouble figuring out how assets are usually handled by engines.
      I'm not having trouble with handling the GPU resources, but more so with how the resources should be defined and used in the system (materials, models, etc).
      This is my plan now, I've implemented most of it except for the XML parts and factories and those are the ones I'm not sure of at all:
      I have these classes:
      For GPU resources:
      Geometry: holds and manages everything needed to render a geometry: VAO, VBO, EBO. Texture: holds and manages a texture which is loaded into the GPU. Shader: holds and manages a shader which is loaded into the GPU. For assets relying on GPU resources:
      Material: holds a shader resource, multiple texture resources, as well as uniform settings. Mesh: holds a geometry and a material. Model: holds multiple meshes, possibly in a tree structure to more easily support skinning later on? For handling GPU resources:
      ResourceCache<T>: T can be any resource loaded into the GPU. It owns these resources and only hands out handles to them on request (currently string identifiers are used when requesting handles, but all resources are stored in a vector and each handle only contains resource's index in that vector) Resource<T>: The handles given out from ResourceCache. The handles are reference counted and to get the underlying resource you simply deference like with pointers (*handle).  
      And my plan is to define everything into these XML documents to abstract away files:
      Resources.xml for ref-counted GPU resources (geometry, shaders, textures) Resources are assigned names/ids and resource files, and possibly some attributes (what vertex attributes does this geometry have? what vertex attributes does this shader expect? what uniforms does this shader use? and so on) Are reference counted using ResourceCache<T> Assets.xml for assets using the GPU resources (materials, meshes, models) Assets are not reference counted, but they hold handles to ref-counted resources. References the resources defined in Resources.xml by names/ids. The XMLs are loaded into some structure in memory which is then used for loading the resources/assets using factory classes:
      Factory classes for resources:
      For example, a texture factory could contain the texture definitions from the XML containing data about textures in the game, as well as a cache containing all loaded textures. This means it has mappings from each name/id to a file and when asked to load a texture with a name/id, it can look up its path and use a "BinaryLoader" to either load the file and create the resource directly, or asynchronously load the file's data into a queue which then can be read from later to create the resources synchronously in the GL context. These factories only return handles.
      Factory classes for assets:
      Much like for resources, these classes contain the definitions for the assets they can load. For example, with the definition the MaterialFactory will know which shader, textures and possibly uniform a certain material has, and with the help of TextureFactory and ShaderFactory, it can retrieve handles to the resources it needs (Shader + Textures), setup itself from XML data (uniform values), and return a created instance of requested material. These factories return actual instances, not handles (but the instances contain handles).
       
       
      Is this a good or commonly used approach? Is this going to bite me in the ass later on? Are there other more preferable approaches? Is this outside of the scope of a 3d renderer and should be on the engine side? I'd love to receive and kind of advice or suggestions!
      Thanks!
    • By nedondev
      I 'm learning how to create game by using opengl with c/c++ coding, so here is my fist game. In video description also have game contain in Dropbox. May be I will make it better in future.
      Thanks.
  • Popular Now