IIRC, the Mac endians are reversed from PC. Dunno if it has any relevance.

And having programmed on a Mac before, yes, the coordinate system is EXACTLY the same as on a PC.

1 2 3 4..
1
2
3
4
..

I''ve used the same web page when making my own ray tracer. As others have said windows takes the top-left pixel to be the origin. With the positive X axis moving right, and the positive Y axis moving down. However, the coordinate system that the raytracer uses has its origin in the center of the picture, and importantly a positive Y axis moving up as other posters have mentioned. (Left or right handedness isn''t an issue here since both have positive Y as up.) To see this take a look at your ray direction code and have a think about where the ray for the central pixel goes:-

currDirection.mX = x - width/2;
currDirection.mY = y - height/2;

Substitue width/2, height/2 for the central pixel:-

currDirection.mX = width/2 - width/2;
currDirection.mY = height/2 - height/2;

currDirection.mX = 0;
currDirection.mY = 0;

Now take pixel 0,0 top-left of your window, but above and left of the images origin.

currDirection.mX = x - width/2;
currDirection.mY = y - height/2;

Substitue 0, 0:-

currDirection.mX = 0 - width/2;
currDirection.mY = 0 - height/2;

currDirection.mX = -width/2;
currDirection.mY = -height/2;

So we''ve placed this ray in the negative quadrent of the image, below and left of the images origin. Not what we expected. Hence, as you''ve found, the Y axis needs to be reversed between the image coordinates and the screen coordinates:-

currDirection.mX = x - width/2;
currDirection.mY = height/2 - y;

Which explains that you do need to reverse the Y axis, but not why the original website does not. Maybe its a bug with his code, or a difference with mac screen coordinates?

It''s not a bug in his code, since I downloaded his and compiled FINE. 100% complete ABSOLUTELY fine!!


But now, I don''t care anymore. Because I don''t want to track the bug anymore, since it''s obvious that there is none.

I''m using Lab-Rats:
currDirection.mX = x - width/2;
currDirection.mY = y - height/2;


Thanks all! Now it''s time to work on the techniques!!

--
You''re Welcome,
Rick Wong
- sitting in his chair doing the most time-consuming thing..