Sign in to follow this  
Specchum

OpenGL Doing without gluLookAt?

Recommended Posts

We are using OpenGL ES for a mobile project. The problem is that there is no gluLookAt function since GLUT is not available in our case. Now, I'm trying to develop a FPS camera and is the routine have calculated a forward, right and up vector to maintain my camera orientation. So far, so good. However, how do I build my camera matrix with these three vectors without gluLookAt? I read something about using the inverse camera transforms or something like that, but frankly, it all went right over my head! Anyone care to tell me how to go about this?

Share this post


Link to post
Share on other sites
Don't know about OpenGL ES, but I'll try to help.

One idea would be to calculate your own modelview matrix and place it on stack instead of calling any view routine. Apply necessary transformation to your matrix.

But as you already have vectors calculated, you can use glTranslate and glRotate instead of gluLookAt.

Tell me what exactly vectors you have (what each of them represent) and I'll try to help you with the transformations.

Share this post


Link to post
Share on other sites
gluLookAt is not a part of GLUT, but GLU. Don't know if you have GLU though, but missing GLUT does not mean missing gluLookAt.

Anyway, if you still want to implement your own, you can download the source for Mesa, which includes, if I'm not mistaken, two complete implementations of the GLU library. Have a look there how they do it.

Share this post


Link to post
Share on other sites
Quote:
Original post by Specchum
... The problem is that there is no gluLookAt function since GLUT is not available in our case. ...


gluLookAt belongs to GLU not GLUT.

You must understand geometry transformations and matrix manipulation before doing you LookAt version.

Share this post


Link to post
Share on other sites
See this thread at the Khronos group's website: http://www.khronos.org/message_boards/viewtopic.php?t=541.

You could also download the mesa3d source code and see their gluLookAt() implementation, which is different from the implementation in the above thread and uses glRotate() and glTranslate(). Link is http://www.mesa3d.org.

Share this post


Link to post
Share on other sites
if you want glulookat without glu look into opengl sample implementation from SGI, but if you want here is my pascal equivalent of their code, sorry about weird syntax highlightning but gamedev forums have no pascal highlighter it seems:

[source=pascal]
// this is glulookat equivalent translated from ogl-sample.
// matrix should be single but i use single precision

procedure normalize(var v: array of single);
var
r: single;
begin
r:= sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);

if (r = 0) then exit;

v[0]:= v[0] / r;
v[1]:= v[1] / r;
v[2]:= v[2] / r;
end;

procedure crossp(var v1, v2, result: array of single);
begin
result[0]:= v1[1]*v2[2] - v1[2]*v2[1];
result[1]:= v1[2]*v2[0] - v1[0]*v2[2];
result[2]:= v1[0]*v2[1] - v1[1]*v2[0];
end;

procedure LookAt(eyex, eyey, eyez, centerx, centery, centerz, upx, upy, upz: single);
var
i: integer;
forw, side, up: array[0..2] of single;
m: TMatrix4f;
begin
forw[0]:= centerx - eyex;
forw[1]:= centery - eyey;
forw[2]:= centerz - eyez;

up[0]:= upx;
up[1]:= upy;
up[2]:= upz;

normalize(forw);

(* Side:= forw x up *)
crossp(forw, up, side);
normalize(side);

(* Recompute up as: up:= side x forw *)
crossp(side, forw, up);

m:= IdentityHmgMatrix;
m[0][0]:= side[0];
m[0][1]:= side[1];
m[0][2]:= side[2];

m[1][0]:= up[0];
m[1][1]:= up[1];
m[1][2]:= up[2];

m[2][0]:= -forw[0];
m[2][1]:= -forw[1];
m[2][2]:= -forw[2];

glMultMatrixf(@m);
glTranslated(-eyex, -eyey, -eyez);
end;

Share this post


Link to post
Share on other sites
Quote:
Original post by Specchum
Now, I'm trying to develop a FPS camera and is the routine have calculated a forward, right and up vector to maintain my camera orientation.


If you already got that you wouldn't want to have gluLookAt throw away half your results and rebuild the matrix, anyway.

Your camera matrix is already there: right/up/forward/position.

Now you want to transform everything the other way, ie. you want to load the inverse of this matrix as modelview before rendering your scene. That part was basically posted, but to make it easier and more OpenGL matrix like you need to know that your typical transformation matrix (assuming normalized right/up/fwd vectors) is very user friendly. Transpose the 3x3 rotational part and transform the old position by the new rotation.

So, with Transform being your camera matrix in the usual ogl way (0-4:right, 5-8:up, etc. actually, I like having extra pointers called right,up,fwd into the array for clarities sake).


float viewmatrix[16]={
Transform[0], Transform[4], -Transform[8], 0,
Transform[1], Transform[5], -Transform[9], 0,
Transform[2], Transform[6], -Transform[10], 0,
-(Transform[0]*Transform[12] + Transform[1]*Transform[13] + Transform[2]*Transform[14]),
-(Transform[4]*Transform[12] + Transform[5]*Transform[13] + Transform[6]*Transform[14]),
Transform[8]*Transform[12] + Transform[9]*Transform[13] + Transform[10]*Transform[14], 1};

or:

float viewmatrix[16]={
right.x, up.x, -fwd.x, 0,
right.y, up.y, -fwd.y, 0,
right.z, up.z, -fwd.z, 0,
-(right.x*pos.x + right.y*pos.y + right.z*pos.z),
-(up.x*pos.x + up.y*pos.y + up.z*pos.z,
fwd.x*pos.x + fwd.y*pos.y + fwd.z*pos.z, 1};


Note that z/fwd is inverted and the new position coords are simply -(pos dot old_axis).

Share this post


Link to post
Share on other sites
Guest Anonymous Poster
Apologies for the delay in getting back but things at work needed my attention. :)

Right. Thanks for all the lovely information. It looks like that's exactly what I was after and hopefully I should get it to work at this end. Provided I can sort out my fixed point mathematics first! No end of trouble with it. Bah!

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
      627740
    • Total Posts
      2978883
  • 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