Please critique my idea for plotting a point in 3D space on a 2D screen

Utwo · 2004-01-13T03:31:00

Ok ok ok. I don''t have a lot of programming experience but I think this might work. I drew visuals too. Really this is all for my own benefit because until I put my ideas down on "paper" but I figured I''d have others take a look as well because frankly I don''t know if I''m even close to being right. I want to be able to define a point in 3D space with x, y, and z coordinates, and then plot it on a 2D screen. I think I have this figured out. Please let me know if I''ve got this wrong. Ok, first, I understand that the cone of vision for the uman eye is 60 degrees. I don''t suppose it really matters what I use for the 3D "camera" though, but I''ll go with 60 degrees just for the hell of it: Alright. First thing I should mention is that the x, y, and z coordinates will be relative to the camera''s point of view. Later if I program any games with this (I have one in mind but I doubt I will finish it, because I never do), I will probably have all the points'' coordinates relative to the game world, and then convert the [i">visible[/i"> points in each from to be relative to the camera to make calculations easier. But for now, I have the field of view devided into 4 quadrantS: Now suppose I plot a point in that field of view: It''s 7 "units" on the z axis away from the camera, 2 units on the x axis to the right, and 2 units high on the y axis. Here''s another visual so you can see what I mean: Now the basic idea here is that I want to know what angles (x and y) exist from the center of the point of view and then determine what percentage of the total 60-degree cone these angles take up. Here''s what I mean: Now here''s a better picture with the useless stuff removed: Knowing that the point is both 7 units away and 2 units high, I can easily figure out that the angle here is 15.9454 degrees. The other angle is also 15.9454 degrees because it has the same measurements, so no need to do the math again this time. This tells me that the 15.9454-degree angle is 26.5756% of the total 60-degree cone. When I apply that percentage to the vertical and horizontal resolution of the display, I find that it equals about 64 and 85 pixels. I have to round because duh you can light a fraction of a pixel. Anyway, so now I know how many pixels away from the center of the screen the point should be, right? And now the finished point: The one thing I did notice that was wrong while typing this is that the cone should probably be 60 degrees wide and 45 degrees tall, since the screen has a 4:3 aspect ratio. This method will probably make everything look a little smooshed. Other than that though it seems it should work. What do you think?

For Beginners

Started by Utwo January 04, 2004 08:31 PM

70 comments, last by Utwo 20 years, 3 months ago

Anonymous

January 05, 2004 11:34 AM

So much detail on the eye for a diagram =P

Bad Maniac

252

January 05, 2004 11:41 AM

quote:Original post by CWizard
Doing error-prone ugly speed hacks

Also posting without having a clue as to what you are talking about is not advicable. Fixed point is as accurate as you make it, and I wouldn''t consider it an ugly speed hack, more like absolutely essential, unless you WANT to write bad code that won''t run on anything below 2 Ghz.
Without Fixed point maths, we would not have had Wolfenstein 3D, Doom, Quake1 or 2, and I''m fairly sure Unreal and Quake 3 has a fair bit of fixed point in them too.
Fair enough fixed point might not be necessary for testing an algorithm, I admit to that, but if it works, why not speed it up tenfold or so but converting to fixed point?

JRA GameDev Website//Bad Maniac

CWizard

127

January 05, 2004 12:17 PM

quote:Original post by Bad Maniac
Also posting without having a clue as to what you are talking about is not advicable.

Very true. However, I do know a fair amount about fixed as well as floating point math.

quote:Fixed point is as accurate as you make it

Yes, and often necessary if you want accuracy.

quote:I wouldn''t consider it an ugly speed hack,

In this context, it is indeed a speed hack. I doubt anyone will claim that fixed point is cleaner or more elegant than native floating point operations. To me, "ugly code" is the opposite to clean and elegant.

quote:more like absolutely essential, unless you WANT to write bad code that won''t run on anything below 2 Ghz.

I did always use fixed point when coding on the Amiga 500, but from my Amiga 1200 with FPU (around 1990), floating point have generally been about as fast.

quote:Fair enough fixed point might not be necessary for testing an algorithm, I admit to that, but if it works, why not speed it up tenfold or so but converting to fixed point?

Exactly my point; it is yet a concept (that sadly probably won''t work out that well). When doing something real of it, I would speed it up twentyfold by letting OpenGL take care of it.

RPGeezus

216

January 05, 2004 03:59 PM

Utwo: Don''t listen to anyone who says that what you did is a waste of time. I think you did an excellet job of explaining your idea. I honestly think it should be part of the articles and resources section here on GameDev.

If I were you I would continue playing about with your own 3D algorithms. OpenGL is all fine and good, but it doesn''t exist everywhere (like on my cellphone), and knowing how to do these things from scratch will allow you to go to any platform.

I wrote a lot of different 3D effects from scratch (voxels, raycasters, polygons, lighting models, reflections, textures, springs, etc..) and I''m really glad that I did. The knowledge you will gain is priceless. Besides, if you know how to do it from scratch, how hard can an API be after that?

Good job!
Will

------------------http://www.nentari.com

Bad Maniac

252

January 05, 2004 04:03 PM

You would also miss out the fun of doing it yourself, wich it seems most people thses days have no idea what it means. And saying that floating point has been faster than fixed point since the amiga 1200 of 1990 is a lie, fixed point is still faster and more accurate on P4 and modern Athlons usually. The only reason it''s not used as widely is because 3D api''s use floats internally, so people never need to concern themselves with it.
Us poor bastards who actually want to come up with something on or own and get it working only keep hearing -Do it in 3D HW and stop "reinventing the wheel".- Well some of us might just want to figure out something for ourselves rather than letting an Api do it for us.

Why make a movie, or write a book, it has already been done?
Why infact write a game using a 3D API, it has already been done. using ogl, talk about reinventing the wheel... (ok, not quite, but I wanted to be sarcastic)

JRA GameDev Website//Bad Maniac

Anonymous

January 05, 2004 05:26 PM

Hey everyone.. ive got a great idea, not sure how correct it is though. Im thinking of inventing a programming language, it will be like C but with classes, maybe i could call it C++!
Heres a picture to demonstrate what i mean.

<img src="www.topfunpages.com/imgs/page_imgs/ib0402/idiot.gif"></img>

and then i could add operator overloading.. something like this..
<img src="homepage.interaccess.com/~whizbang/idiot.gif"></img>

OMGOMGOGMOGOMGMOGMOG!!!

Newfound Ajarn

122

January 05, 2004 05:46 PM

quote:Original post by Anonymous Poster
Hey everyone.. ive got a great idea, not sure how correct it is though. Im thinking of inventing a programming language, it will be like C but with classes, maybe i could call it C++!
Heres a picture to demonstrate what i mean.

<img src="www.topfunpages.com/imgs/page_imgs/ib0402/idiot.gif"></img>

and then i could add operator overloading.. something like this..
<img src="homepage.interaccess.com/~whizbang/idiot.gif"></img>

OMGOMGOGMOGOMGMOGMOG!!!

Idiot

VLAjarn: Cause it (linux) NEVER crashesMrPr0Grmer: lol ur wrongMrPr0Grmer: RedHat crashesVLAjarn: I'm saying good builds of linux

maxd gaming

100

January 05, 2004 06:26 PM

quote:Original post by Utwo
i h8 u guys

Just kidding I don''t. But damn I looked at the thread listings and thought I had 2 replies.

Sorry, It just looked to long for me to read

so I replyed "..."

It''s Maxd Gaming, put in an underscore and I will beat you with a rubber ducky!
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Utwo

100

Author

January 05, 2004 06:37 PM

Haha I know I was j/k.

Hey guys I have this great idea for image tags. It's called putting an "http://" in the "src=" part so that the image actually shows up.

Hey check out this visual and you will see what I mean:

WOW!

[edited by - utwo on January 5, 2004 7:40:10 PM]

---signature---" Actually, at the time, I didn't give a damn about the FoxNews issue... just that you would come swooping in with your Super Mith cape flapping behind you and debunk it just because it didn't happen in your living room." - InnocuousFox

CWizard

127

January 05, 2004 10:57 PM

quote:Original post by Bad Maniac
And saying that floating point has been faster than fixed point since the amiga 1200 of 1990 is a lie

I did not say it was faster, but "generally about as fast". I did not say this to be true on other hardware either. Also, I admit that I didn''t consider other operations than multiplication and divition; add/sub/bit shifts are of course still faster as fixed point (I think) on modern hardware.

quote:Us poor bastards who actually want to come up with something on or own and get it working only keep hearing -Do it in 3D HW and stop "reinventing the wheel".- Well some of us might just want to figure out something for ourselves rather than letting an Api do it for us.

Good attitude; I very much encourage people to try to figure out as much as possible by themselves.

@ Utwo: I recognize what you are doing, I recognize your formulae. I did spend an awful lot of time in my youthood trying to do projection by calculating angles etc. Can you imagine my surprise (and anger) when I realized that it was as simple as (x / z * d)? Think about that you are not going to plot the pixels on your very eye, but on a flat plane that your eye will look at as any other object.

Please critique my idea for plotting a point in 3D space on a 2D screen

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Please critique my idea for plotting a point in 3D space on a 2D screen

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