Archived

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

JimmyP

OpenGL Eye vs camera-space coordinates(opengl)

Recommended Posts

I understand that camera-space coordinates are the coords. you get by multiplying vertex coords. by the camera matrix(or more specific C=CM*(V-P) where P is the camera location)whereas eye coords are the ones you get by multiplying with the modelview matrix.Now supposing I only do a glTranslatef() and a couple of glRotatef()s in the beginning of each frame(to place the camera) and then draw a bunch of tris,can I get the ''camera-space'' coords. of these tris by mutiplying with the modelview matrix? What I want to say is that I''m trying to code a terrain engine based on the ROAM algorithm and I need the camera-space coordinates of the triangles to comute priorities.Yet I haven''t implemented a camera model yet(I just use those glRotatef()s and the glTranslatef() calls to place the camera).I''m not sure if the terrain I get is quite correct though so I was wondering if my cam-space coords were correct.Thanx in advance.

Share this post


Link to post
Share on other sites
Normally, when you want to simulate camera movements, you use gluLookAt. This sets up a matrix that (should) be multiplied with the MODELVIEW matrix. You can do the exact same thing with the glRotate/Translate commands. So yes, you can do either way because both were meant to be multiplied to the MODELVIEW matrix. So for instance, moving the camera forward is the same as translating the verts back. (incidentally, the MODELVIEW matrix is named so because the matrix used to transform the MODEL and the VIEW is put into one matrix. at least, that''s what it seems like to me)

Share this post


Link to post
Share on other sites
Yes,but suppose I use either gluLoookAt() or glTranslate()s and glRotate()s to obtain a matrix and multiply it my the MODELVIEW matrix(which is initially an identity) to get the desired view.How do I get camera-space coordinates then?Do I use glGetFloatv() to get the modelview matrix(which is the one I mutilplied since it initially was an identity)and mutiply the world-space coords. by it?Or do I have to do someting to the matrix first(like calculating the inverse or something)?

Share this post


Link to post
Share on other sites
Yes, after you set up the modelview matrix, you can retrieve the matrix with glGetFloatv and multiply it with all the points of the polygons...Just remember the matrix that you get is in COLUMN MAJOR order. Calculating the inverse of the matrix is usually done when you also want to transform the polys'' normals (well, the transform of the inverse of a matrix is used). However, if the matrix is orthogonal (i.e. you only used rotations, translations, and/or uniform scaling), you don''t have to compute the inverse of the matrix to transform the normals.

Share this post


Link to post
Share on other sites

  • Forum Statistics

    • Total Topics
      627762
    • Total Posts
      2978970
  • 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