Sign in to follow this  
Matty_alan

OpenGL Speeding Up Obj Loader for OpenGL

Recommended Posts

Iv'e just got my latest project up and running, which is an .Obj loader iv'e been working on for the last few days, However it runs very slowly... like .5 fps if the object is mildly complex This is due because I call glBegin and glEnd for every pollygon, and when there 13,500 pollygons to draw, thats alot of calls to glBegin and glEnd so my main question is this... Is there a way to Draw Multipul Polygons without calling glBegin And glEnd For Every Single One? like some kind of seperator command Also I havn't yet but will put in a binarey tree (as soon as i can get the thing to work) How much speed increase can i expect from putting from a linked list. Any other tips or sugestions are VERY welcome.

Share this post


Link to post
Share on other sites
You don't have to call glBegin/glEnd around every triangle. You can just throw your whole list of vertices and it will make a triangle out of every set of three. However this will still be slow as this is not a good way to draw objects.

You need to learn about Vertex Buffer Objects (called "VBO"). You'll get an enormous speedup over using immediate mode when you implement your model this way.

What you're doing right now is every frame you have to send tens of thousands of calls and megabytes of data to your GPU over the pci bus, which is very slow. When you use VBO you upload all of the model data into the GPU memory once, and then draw it every frame with a single opengl call. You might see a speedup of 10x-100x doing it this way depending on the size of your model.

glBegin is miserably slow and depreciated and you shouldn't use it.

Share this post


Link to post
Share on other sites
What im using now looks something like this:



while(PollyPoint->Next != 0)
{

glBegin(GL_POLYGON);
while(PollyPoint->PollyVPoint->Next != 0)
{

GotoVertex(PollyPoint->PollyVPoint->Polly);

glVertex3f(VertexPoint->x, VertexPoint->y, VertexPoint->z);

PollyPoint->PollyVPoint = PollyPoint->PollyVPoint->Next;
}
glEnd();

PollyPoint = PollyPoint->Next;
PollyPoint->PollyVPoint = PollyPoint->PollyVRoot;



}


I know it's the worst way to go about things but iv'e only been learning openGL for about a week.

Share this post


Link to post
Share on other sites
Load your data from file into memory first. Because, I don't see what a obj loader has to do with rendering speed.
I hope you're not reading data from file as your render it, because that would be terrible.

Share this post


Link to post
Share on other sites
First off, you need to make sure you aren't loading it from the hard drive as you render it. Store it into a data structure first.

Second off, I agree with the above posters that you should not be using glBegin/glEnd. Its deprecated and slow. Use VBO or at least VA.

Third, if you want an IMMEDIATE boost, simply put the glBegin and glEnd calls around that while loop instead of inside it.

Share this post


Link to post
Share on other sites
Quote:
Original post by samster581
I hope you're not reading data from file as your render it, because that would be terrible.


Nuh I have them loaded into a linked list

Share this post


Link to post
Share on other sites
Quote:
Original post by Steve132
Use VBO or at least VA.

If you want an IMMEDIATE boost, simply put the glBegin and glEnd calls around that while loop instead of inside it.


Iv'e herd of VBO but whats VA??

I didn't think i'd be able to but if i change to GL_QUADS I can wrap the glBegin And end calls around, however theres not much change in speed

Share this post


Link to post
Share on other sites
The glBegin/glEnd should be inside the outer while since he is rendering polygons, but as said before, if this model is static you would gain a lot of speed improvement by storing your model in a VBO. That way you won't have to upload it to the graphics card each frame.

Share this post


Link to post
Share on other sites
Quote:

Iv'e herd of VBO but whats VA??

I didn't think i'd be able to but if i change to GL_QUADS I can wrap the glBegin And end calls around, however theres not much change in speed


A vertex array (VA) is syntactically similar to a VBO but it leaves vertex data stored CPU side and transfers it to GPU every frame. It is slower than a VBO and depreciated, so I wouldn't bother trying to implement it.

Also I don't think you're understanding what is being said about glBegin. You don't need to change to GL_QUADS. If you have 1000 triangles then you have 3000 vertices. In this case you can call glBegin, call glVertex 3000 times, then call glEnd. There is no requirement that you "glEnd" after every primitive. Every three vertices is automatically treated as a triangle, so you don't have to tell opengl to start and end each triangle.

Share this post


Link to post
Share on other sites
[quote]Original post by karwosts
Quote:

Also I don't think you're understanding what is being said about glBegin. You don't need to change to GL_QUADS. If you have 1000 triangles then you have 3000 vertices. In this case you can call glBegin, call glVertex 3000 times, then call glEnd. There is no requirement that you "glEnd" after every primitive. Every three vertices is automatically treated as a triangle, so you don't have to tell opengl to start and end each triangle.



If i used GL_POLYGON wraped around the outside of the whiles like this:

glBegin()
while
while
glEnd()

it draws the entire image as one huge polygon and the picture comes out distorted and streched. if it's inside the loops the polygons get broken up; however i can wrap it like that if i use glQuads because it breaks off after every 4 verticies

Share this post


Link to post
Share on other sites
How are your faces stored in your OBJ, are they quads or triangles? If they are quads then go ahead and use GL_QUADS. Sorry I mistakenly assumed you were using GL_TRIANGLES instead of GL_POLYGON.

But still the best advice will be to use VBO if you want speed, you still are sending the data every frame and theres no way to make it that much faster.

Share this post


Link to post
Share on other sites
Quote:
Original post by karwosts
But still the best advice will be to use VBO if you want speed, you still are sending the data every frame and theres no way to make it that much faster.


They were stored as quads, when i saved them (mainly because i didn't know what i was doing at that time) I am going onto reasearching VBO i found a good tutorial on it im going to read tomorrow as it's getting rather late, actually more like rather earily as the sun is beging to rise

Share this post


Link to post
Share on other sites

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
      627736
    • Total Posts
      2978856
  • Similar Content

    • By DelicateTreeFrog
      Hello! As an exercise for delving into modern OpenGL, I'm creating a simple .obj renderer. I want to support things like varying degrees of specularity, geometry opacity, things like that, on a per-material basis. Different materials can also have different textures. Basic .obj necessities. I've done this in old school OpenGL, but modern OpenGL has its own thing going on, and I'd like to conform as closely to the standards as possible so as to keep the program running correctly, and I'm hoping to avoid picking up bad habits this early on.
      Reading around on the OpenGL Wiki, one tip in particular really stands out to me on this page:
      For something like a renderer for .obj files, this sort of thing seems almost ideal, but according to the wiki, it's a bad idea. Interesting to note!
      So, here's what the plan is so far as far as loading goes:
      Set up a type for materials so that materials can be created and destroyed. They will contain things like diffuse color, diffuse texture, geometry opacity, and so on, for each material in the .mtl file. Since .obj files are conveniently split up by material, I can load different groups of vertices/normals/UVs and triangles into different blocks of data for different models. When it comes to the rendering, I get a bit lost. I can either:
      Between drawing triangle groups, call glUseProgram to use a different shader for that particular geometry (so a unique shader just for the material that is shared by this triangle group). or
      Between drawing triangle groups, call glUniform a few times to adjust different parameters within the "master shader", such as specularity, diffuse color, and geometry opacity. In both cases, I still have to call glBindTexture between drawing triangle groups in order to bind the diffuse texture used by the material, so there doesn't seem to be a way around having the CPU do *something* during the rendering process instead of letting the GPU do everything all at once.
      The second option here seems less cluttered, however. There are less shaders to keep up with while one "master shader" handles it all. I don't have to duplicate any code or compile multiple shaders. Arguably, I could always have the shader program for each material be embedded in the material itself, and be auto-generated upon loading the material from the .mtl file. But this still leads to constantly calling glUseProgram, much more than is probably necessary in order to properly render the .obj. There seem to be a number of differing opinions on if it's okay to use hundreds of shaders or if it's best to just use tens of shaders.
      So, ultimately, what is the "right" way to do this? Does using a "master shader" (or a few variants of one) bog down the system compared to using hundreds of shader programs each dedicated to their own corresponding materials? Keeping in mind that the "master shaders" would have to track these additional uniforms and potentially have numerous branches of ifs, it may be possible that the ifs will lead to additional and unnecessary processing. But would that more expensive than constantly calling glUseProgram to switch shaders, or storing the shaders to begin with?
      With all these angles to consider, it's difficult to come to a conclusion. Both possible methods work, and both seem rather convenient for their own reasons, but which is the most performant? Please help this beginner/dummy understand. Thank you!
    • By JJCDeveloper
      I want to make professional java 3d game with server program and database,packet handling for multiplayer and client-server communicating,maps rendering,models,and stuffs Which aspect of java can I learn and where can I learn java Lwjgl OpenGL rendering Like minecraft and world of tanks
    • By AyeRonTarpas
      A friend of mine and I are making a 2D game engine as a learning experience and to hopefully build upon the experience in the long run.

      -What I'm using:
          C++;. Since im learning this language while in college and its one of the popular language to make games with why not.     Visual Studios; Im using a windows so yea.     SDL or GLFW; was thinking about SDL since i do some research on it where it is catching my interest but i hear SDL is a huge package compared to GLFW, so i may do GLFW to start with as learning since i may get overwhelmed with SDL.  
      -Questions
      Knowing what we want in the engine what should our main focus be in terms of learning. File managements, with headers, functions ect. How can i properly manage files with out confusing myself and my friend when sharing code. Alternative to Visual studios: My friend has a mac and cant properly use Vis studios, is there another alternative to it?  
    • By ferreiradaselva
      Both functions are available since 3.0, and I'm currently using `glMapBuffer()`, which works fine.
      But, I was wondering if anyone has experienced advantage in using `glMapBufferRange()`, which allows to specify the range of the mapped buffer. Could this be only a safety measure or does it improve performance?
      Note: I'm not asking about glBufferSubData()/glBufferData. Those two are irrelevant in this case.
    • By xhcao
      Before using void glBindImageTexture(    GLuint unit, GLuint texture, GLint level, GLboolean layered, GLint layer, GLenum access, GLenum format), does need to make sure that texture is completeness. 
  • Popular Now