• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
PureSnowX

Handling Angles and Sin/Cos

7 posts in this topic

I'm currently trying to build an 2D ray casting engine, however I'm on the fly learning the trigonometry as well.
I'm currently working my head around angles in degrees and radians.

I'm trying to use 0-360 degrees system that when the double reaches a value of 0 or 360 it wraps around so lets say the angle is increased/decreased by 90.

[quote]Going from 360 + 90 = 90
Going from 0 - 90 = 270[/quote]


This works when trying to move with cos and sin for the angular movement. But I realized that 0* and 360* is not the same value for sin ( cos 0 and 360 is equal to 0 ).

[quote]sin(0*) = 0
sin(360*) = -1 * 10^-13[/quote]


While I realize that this number is incredible small and wouldn't make a noticeable difference, it's still a factor that can change the output of movement.

When checking a real time example of it ( Example Movement ):
[quote]y = 5
sin(0*(Pi/180) )*(-6) = 6*10^-13
sin(360*(Pi/1780) )*(-6) = 0[/quote]


[quote]It's obvious that these are not the same, though the calculator and computer outputs the same number if it was supposed to add to y, say: 5 + 0 = 5 and 5 + 6*10^-13 = 5 ( Computer output and Ti-84+ Calculator ).[/quote]


But when trying to compare these as equal each other in an if statement it did not validate as true, so there is a very small difference.

My current wrap-around code looks like this:
[CODE]
if( sf::Keyboard::isKeyPressed( sf::Keyboard::A ) )
{
player.rot -= 5;
if( player.rot < 0 )
{
player.rot = ( 360 + player.rot );
}
}
if( sf::Keyboard::isKeyPressed( sf::Keyboard::D ) )
{
player.rot += 5;
if( player.rot > 360 )
{
player.rot = ( player.rot - 360 );
}
}
[/CODE]

So, is this going to be a problem in the future or is it so small that it's negligible? After all it's only a problem on the 0 and 360 degrees.

* Converted to radians under the hood when inserted into cos or sin functions. Edited by Moonkis
0

Share this post


Link to post
Share on other sites
This is just something you have to learn to live with when you're using floating point numbers and you shouldn't worry about it (also, this issue is pretty much independent of trig).

You almost never should check for equality of floating point numbers, because any non-trivial calculation is going to introduce some error.
2

Share this post


Link to post
Share on other sites
OpenGL, if I'm not mistaken, converts angles to radians, just saying. Trigonometric ratios (sine, cosine, tangent) are not difficult to learn. One little mnemonic device American teachers use (or at least used) is the gibberish phrase "soh-cah-toa." If you remember that, you remember sine, cosine, and tangent. soh is sine which is opposite side divided by hypotenuse (soh), cosine is the adjacent side divided by hypotenuse (cah), and tangent is the opposite side divided by the adjacent side (toa).
0

Share this post


Link to post
Share on other sites
Ironically I just finished a couple detailed gamedev math tutorials, one on [url="http://www.gamefromscratch.com/post/2012/11/18/GameDev-math-recipes-Rotating-to-face-a-point.aspx"]rotating to face a point[/url] and one on [url="http://www.gamefromscratch.com/post/2012/11/22/GameDev-math-recipes-Velocity.aspx"]Angular (and non-angular) velocity[/url], which combined cover exactly the topic you are talking about.

That said, your issue is as others have already stated, more about floating point rounding off. I simply mention it here if anyone else working with handling angles comes into the thread looking for help. :)
2

Share this post


Link to post
Share on other sites
I'll take the opportunity to mention that you probably don't need angles. I should really write a journal entry or something of that sort to describe what I mean by that. But essentially, if instead of an angle you use a unit-length vector (effectively (cos(angle),sin(angle)), you often end up with code that is cleaner, faster and easier to get right.
1

Share this post


Link to post
Share on other sites
[quote name='Álvaro' timestamp='1354145202' post='5005120']
I should really write a journal entry or something of that sort to describe what I mean by that.
[/quote]
Please do, I love reading people's articles/journals as they are very interesting.
0

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  
Followers 0