Sign in to follow this  
floatingwoods

OpenGL GL_SPOT_EXPONENT and GL_SPOT_CUTOFF not working on Mac OSX

Recommended Posts

Hello,

I have a cross-platform application that was first running on Windows. I ported it to Mac (using the Qt framework) and kept all the OpenGL routines same. Everything works as expected on Mac now, except for the spotlights.

It seems as if the command

glLighti(GL_LIGHT0+activeLightCounter,GL_SPOT_EXPONENT,spotExponentValue);

has no effect at all (i.e. behaves as with a spotExponent of 0 (default)). I tried values between 0 and 128, but nothing changes.

Additionally, following command

glLightf(GL_LIGHT0+activeLightCounter,GL_SPOT_CUTOFF,spotCutoffValue);

behaves strangely on Mac OSX: varying the value between 0 and 90, it seems that the visible cutoff is always around 10-20 degrees or so, and instantly goes to 180 degrees when I specify a value of 90!

This is very odd to me. Would someone have a clue? I need to mention that this happens on all tested Mac machine types (3) and OS versions (leopard, snow leopard and lion).

Is it possible that on Mac there are different default openGl settings? And if yes, which of those might influence the spotlights? (everything else appears same as on Windows).

Thanks for any insight

Share this post


Link to post
Share on other sites
Spot lights behave as point lights so fr their position, make sure that you provide a valid xyzw position. By that, I'm means that w should always be 1.0.
The direction of the spotlight, I don't remember if it was xyz or xyzw. If it takes a w, then w must be set to 0.0.

I'm not a Mac programmer but I know that they have a mailing list, in case you need to let them know about the bug you found.

Share this post


Link to post
Share on other sites
Thanks for the reply V-man.

I could fix my problem, I guess there is a bug in the Mac implementation. Following is what I noticed (Mac only):

- with a spot cutoff of 90, the spot exponent cannot be changed (i.e. appears to be 0)

- glLighti(GL_LIGHT0,GL_SPOT_EXPONENT,spotExponent); doesn't work

- glLightf(GL_LIGHT0,GL_SPOT_EXPONENT,float(spotExponent)); works, but only if the spot cutoff is lower than 90 (see point 1)

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
      627754
    • Total Posts
      2978947
  • 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