Archived

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

neonfaktory

OpenGL Object Clipping - Me or OpenGL?

Recommended Posts

Ok, I'm going to have tons of objects/particles, etc. in my game... and ALL of them must be accounted for. Now, as it stands, I am translating to all these objects and drawing them, regardless of whether they are on screen or not. For example, if the camera is at (0,0), and one of my objects is at (10000, 10000) (way off screen), I still tell it to translate to (10000, 10000) and call the display list. Now, is OpenGL going to clip that polygon automagically for me, or will I get a big performance boost if I test if the object is offscreen MYSELF, and then draw the object based on those tests? Thanks for any help you can provide [edited by - neonfaktory on December 25, 2002 9:10:13 PM]

Share this post


Link to post
Share on other sites
You will get a large boost if you test if the object are onscreen yourself. When i did that on the object and traingle level it doubled my frame rate. If you need to know how to do that then goto gametutorials.com and look for their frustum calling tutorial for opengl, and if thats still not a large enough boost, you might want to look into octrees.

Share this post


Link to post
Share on other sites
always let opengl do clipping
BUT i think u meant to say culling (not clipping)
in that case do gross culling yourself, if something is not on screen dont send it to opengl, for large scenes this will result in a large performance boost

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

Share this post


Link to post
Share on other sites
It''s actually a bunch of objects on the same 2D coordinate plane. You can move the camera around on that plane (X,Y) and also zoom in and out on the Z axis. I just wanted some simple test to determine if my objects are withing the viewing range or not... I could probably do it with a simple calc based on the FOV angle... couldn''t I? Or should I just go with the Culling EQs that you can find in most culling tuts? Thanks for the help so far

Share this post


Link to post
Share on other sites
Using a quadtree, you could keep track of all objects that are within a given cell of the quadtree, and if you can calculate that a given cell is not in the view at all, you can ignore all the objects inside the cell, which removes a lot of testing at the object level.

If a cell is in view, then you test all the objects in the cell (if you wish) or just submit them to OpenGL and let the API handle the culling.

Share this post


Link to post
Share on other sites
The API performs its culling just by having the geometry sent to it. You submit polygons, and the API culls it automatically.

Otherwise you are performing your own culling calculations, and if the cull test fails, you just don''t send that polygon to the API.

Share this post


Link to post
Share on other sites
Guest Anonymous Poster
There is a little bit of confusion here...

Clipping clips your polygons against the view frustum, cutting them if they need to be cut, so that the rasterizer works properly (think of the old days, when you would write sw renderers).

Culling is removing polygons from the scene, so that you don''t send them to the graphics card at all.

OpenGL is going to CLIP your polygons anyway, so don''t clip them. If you can easily CULL polygons that have no chance of being seen (in your example, your object at (10000,10000)), then do it.

Other people have mentioned backface culling. This is a culling method supported by graphics APIs and hardware. Enable this.

A good rule of thumb is to let your API do as much as possible. IE, rather than managing all your transforms yourself, use the API''s matrix stacks. Sometimes, you will get hardware acceleration, which is good. Other times, the API will implement it in its software layer, but it will probably do a better job than you can. (They have spent a lot of time on this, they can detect CPU type and use SSE extensions, etc).

Share this post


Link to post
Share on other sites
Yeah, I understand - I made the "clipping" in the topic title before I knew that "culling" was what I was talking about. I''m letting OGL clip everything, but I was looking for a good way to cull my objects (good method to go about it).

I kinda found a good tutorial for it, but it does all this fancy math to find the frustum planes and stuff to compensate for huge 3D worlds, and I think what I''m looking for is alot more simple than that.

I have object x,y coords, and camera x,y coords, along with a camera z coord to simulate a zooming effect. As of right now, my game is 2D, so I just have a bunch of tiles that face the camera with a texture on them. I think with the coordinate & zoom information, coupled with the projection matrix settings I should be able to come up with a simple EQ for testing, ya know?

SO yeah, I think I''m going to find out what PROJECTION matrix angle I''m using and see if I can just use a simple trig EQ to test if my simple polygons are on the screen or not. Unless someone knows a better idea THanks for all the help

Share this post


Link to post
Share on other sites

  • Announcements

  • Forum Statistics

    • Total Topics
      628347
    • Total Posts
      2982204
  • 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