Archived

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

knight

OpenGL Drawing in OpenGL

Recommended Posts

Hi I am new in OpenGL Programming and I have only gone through some of the NeHe Tutorials(currently 11). What i want to know is that is there any tutorial(s) that teaches how to construct arcs and circles in OpenGL. Does anyone know what is the dimension of the window/display at different zoom level? Thanks Edited by - knight on March 19, 2002 3:54:10 AM

Share this post


Link to post
Share on other sites
Zoom level? What are you asking about? Being the programmer of the app, you are the one who sets the dimensions of the screen, so I would assume you already know... Unless I am reading the question wrong.

Oh well,
Landsknecht

Share this post


Link to post
Share on other sites
knight: about that zoom..?! you should have know that or you did not read tutorials enough deep and also understand them so that you could make same thing now without help.

circles, red book has a piece of code about them, this will more or less be copied from there:
----------------

#define PI 3.14159265
#define circle_points 100

GLint angle;

glBegin(GL_LINE_LOOP);
for (int i=0; i{
angle=2*PI*i/circle_points;
glVertex2f(cos(angle),sin(angle));
}
----------------


[edited by - kren on March 19, 2002 3:05:25 PM]

Share this post


Link to post
Share on other sites
Thanks anyway
Regarding the zoom, what i meant was that if
for example i use glTranslate(0.0f,0.0f,-0.5f), There are more spaces available than using glTranslate(0.0f,0.0f,0.0f) so how is this space calculated?
Are there any online tutorials for ARC and CIRCLES?
Thanks for your help

[edited by - knight on March 19, 2002 8:41:36 PM]

Share this post


Link to post
Share on other sites
Thanks Kren
But what I want is just a simple circle ... I don''t want a circle that is made up of polygons and there an error in the for loop so what should the i variable be limited to?
Is the simple circle possible?

Share this post


Link to post
Share on other sites
no. there are no circles. what do you need if for? HUD? you can draw a circle to a texture and render the texture in ortho projection. if you need to know how to draw a circle, look up bresenham''s circle algorithm.

Share this post


Link to post
Share on other sites

  • Forum Statistics

    • Total Topics
      627763
    • Total Posts
      2978974
  • 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