Dark Bit Factory & Gravity

PROGRAMMING => General coding questions => Topic started by: Pixel_Outlaw on September 12, 2007

Title: Light in OpenGL that ignores distance.
Post by: Pixel_Outlaw on September 12, 2007

Hello,
Is there a type of light in OpenGL that just takes direction into account and ignores distance? I would like to do this so I just need one universal light. A "sun" if you would.

I'm looking to have everything lighted with the exact same intensity. Perhaps I'm thinking about this in the wrong way.

Still fairly new to OpenGL. :)

Title: Re: Light in OpenGL that ignores distance.
Post by: Jim on September 12, 2007

That's how OpenGL lights are set by default.  If the default isn't what you want, then you need to look at

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glLight(GL_LIGHTi, GL_CONSTANT_ATTENUATION, ...)
glLight(GL_LIGHTi, GL_LINEAR_ATTENUATION, ...)
glLight(GL_LIGHTi, GL_QUADRATIC_ATTENUATION, ...)

Jim

Title: Re: Light in OpenGL that ignores distance.
Post by: Pixel_Outlaw on September 13, 2007

Thanks, looks like a rotation was throwing off the position. ;)


Next question is how to set up the perspective view so that it has a 640x480 chunk of screen in the view with the "vanishing point" at x=320,y=240.

Title: Re: Light in OpenGL that ignores distance.
Post by: Jim on September 13, 2007

Here's how I set up my view for 3d

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glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective((CAMERA_ANGLE*SCREEN_HEIGHT)/SCREEN_WIDTH,SCREEN_WIDTH/(float)SCREEN_HEIGHT,0.125,32768.0);

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
I have CAMERA_ANGLE=90.
That puts 0,0 in the middle of the screen, with +Y going up, +X going right, and -Z going into the screen - a very typical OpenGL view setup.  It also sets nearz to 0.125 and farz to 32768.

Jim

Title: Re: Light in OpenGL that ignores distance.
Post by: Pixel_Outlaw on September 16, 2007

Ok, I've tinkered around a bit and I'm still a bit confused.

This project has already been made and I'm switching from the standard 2d computer system to openGL for 3d graphics. I decided to do a special 3D version of the 2d game. I can't really recode all the objects movements for the coordinate system as you have shown. I did try out your code and understand it fairly well. The game is coded to move in the following view:


(0,0)___________________(640,0)
|
|
|
|
|
|
|
|
|
(0,480)---------------------(640,480)


I guess I'm just looking to emulate that view with 3D models, 320,240 being the focal point or origin of the view. Is it as simple as setting the camera postion?

Title: Re: Light in OpenGL that ignores distance.
Post by: Jim on September 16, 2007

OK, I see what you want.  Replace the  gluPerspective with

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glOrtho(0.0, (GLdouble)SCREEN_WIDTH, (GLdouble)SCREEN_HEIGHT, 0.0, 0.0, 1.0);
That way there's no perspective calculation, the x and y are just mapped direct to screen coordinates.  You might need to tinker with the near/far z values though, depending on what you're setting the z values to.

Jim