Archived

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

Sqwiddly

OpenGL OpenGL and Lighting

Recommended Posts

Okay sorry if the question I''m about to ask is very easy to answer and requires no thought, but I''m a bit dazed at how the OpenGL lighting system works. I looked in the header and I see GL_LIGHT0 - GL_LIGHT7. Ok I understand that OpenGL can render 8 max lights, but how do you go about rendering many lights? I''ve seen BSP levels that have about 200-400 lights! I''m guessing that the BSP engines just show the lights which are nearest and visible in each room but what if you are in a big open area (such as terrain or any outside environment) and you have to render many street lights and sunlight from above? Do the level editors just cleverly place lights so that OpenGL can pull it off? As you see I''m pretty stumped on the subject so if someone could kindly explain this lighting system. I know that I may sound a bit amateur but I haven''t ever really used OpenGL or Direct3D before, I''ve only used wrappers around those like Genesis3D and CrystalSpace etc. Thank you in advance!

Share this post


Link to post
Share on other sites
I''m not exactly sure about that BSP level stuff, but if you want more than 8 lights on a polygon you can render the polygon with multiple passes changing the light properties each time.

Share this post


Link to post
Share on other sites
Well most BSP engines don''t use real dynamic lighting, or at least not for all of their lights. Mostly they use lightmaps and for some semi-dynamic effects, animated lightmaps. I know this is what Quake and Half-Life do. (Not sure about Q3 or UT or other newer games though)

Dirk "Scarab" Gerrits

''If knowledge is power, than to be unknown is to be unconquerable.''
- Unknown Romulan Centurion

Share this post


Link to post
Share on other sites
Scarab is right. What they do is simply calculate their own lighting values; store them in textures, called lightmaps; and blend these lightmaps over the scene.

Only problem: since everything is precomputed, lights can''t be changed.

Y.

Share this post


Link to post
Share on other sites
Hmm yes that makes a lot more sense. I understand it all a little more now. But what about outdoor based engines? Games like Tribes, Asherons Call etc. Do they just pre calculate lightmaps and display them like a BSP engine would? I''m not thinking about making a Massive online RPG, those were just examples right off of my head.

Share this post


Link to post
Share on other sites
Suppose you have a room with like 20 or so lit candles or light bulbs ot whatever. Or a terrain lit by many objects, moving around. You draw the scene with only 8 lights, then, on a seccond pass, you switch to the next 8 lights and redraw the triangles affected by the lighting, using the appropriate blend functions. If needed, render the polygons again, with the next set of lights and so on, until all lights have been processed.
Should work, maybe a bit slower.
The OpenGL reference manual says that the glLight funcions accept a value for the light number ranging from 0 to GL_MAX_LIGHTS. Weird. I checked my gl.h header and GL_MAX_LIGHTS is 0D31h.



Free your mind.

Share this post


Link to post
Share on other sites
u should never need more than 4 lights lighting one vertice at once ie turning on more lights normally wont make that much of a difference

heres what u do
for each mesh
{
turn on the 4 most important/closest lights
draw mesh
}

of course u wouldnt want to be changing the lights all the time perforamce reasons.
also according to the nvidia perfomance faq using 8 lights is 5x slower than 1 light. ie using a lot of lights doesnt mean a slight perfroamce drop

Share this post


Link to post
Share on other sites
ZedZeek you''re right, except that there''s not only nVidia boards on the market, plus nVidia cards are weak when it comes to lighting.

(I know another card with a L engine more than 8 times faster, but it''s not publicly released *yet* )

Basically you should not care too much about what can be done today since the time it''ll take you to write an engine, at least a year would have passed.

-* So many things to do, so little time to spend. *-

Share this post


Link to post
Share on other sites
OK, So basically I run through the lights which are nearest to the camera and render those in multiple passes using the GL_LIGHT0 through GL_LIGHT7. Makes sense to me, but that wouldn''t cause any flickering? I assume it wouldn''t as long as I keep the light usage down a bit. Well thank you everyone, I understand it all now. Peace

Share this post


Link to post
Share on other sites
>>OK, So basically I run through the lights which are nearest to the camera <<

no for each vertice/mesh choose the closest/most important lights to it + use those, check glut theres a demo that does the exact same thing.

this works on the priciple say youre outside whats the most important light, the sun OK so use that say the person is carry a flaming torch, how much light does it cast on the tree 50m ahead. bugger all so theres no need to have the torch light switched on when u draw the tree

Share this post


Link to post
Share on other sites

  • Forum Statistics

    • Total Topics
      627719
    • Total Posts
      2978796
  • 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