360 Degree Bounce

[geothefaust]

Hi all,


I'm creating a custom movement engine, and am having a hard time trying to code the bounce section of it. I've searched the forums already but have found limited resources (Probably due to the forum change-over. As I recall there were a lot of examples before said change-over.). Could any one point me to some examples of custom bouncing? Thanks!

[happygreenfrog]

How about you search the old forums?

[geothefaust]

Hi thanks! Good to know those are still around. I poke around a bit, but, I found more information in one of your posts. This here:

"Player" is overlapping "Obstacle"
Repeat while "W" is pressed
Subtract Sin(Angle("Player")+90)*3 from Alterable Value X
Subtract Sin(Angle("Player")+90)*3 from Alterable Value Y

From Post:
http://community.clickteam.com/showthread.php?t=71308&p=530106&viewfull=1#post530 106

That was very helpful and what I recall using in the past. So thanks! But now the question is, say the player object is rotated in one direction and moving in another. How would you calculate the difference here so that the player would still bounce properly?

I'm sure it's right under my nose, and am probably making it more complicated then it needs to be. Heh.

[Jacob]

You would only ever use the movement angle, which should be equal to atan2(-Yspeed,Xspeed)

[happygreenfrog]

I don't know, actually. The other thing was actually just a copied version of the code the person asking the question used to move forwards, only I used subtraction instead of addition.

[geothefaust]

You would only ever use the movement angle, which should be equal to atan2(-Yspeed,Xspeed)

Thanks Jacob! That returns a usable value. I'm only having to find out where to use it at now. Thoughts on that?

I don't know, actually. The other thing was actually just a copied version of the code the person asking the question used to move forwards, only I used subtraction instead of addition.

No worries, thanks anyway.

[Jacob]

You'd use that as your object's movement angle in an equation that gets you the reflecting angle, which was said by Looki in a post a few days ago:

The general formula to reflect an angle is (2*Plane - Angle). Angle is the angle you're going at, Plane is obviously the plane's angle. That should do it. The Y axis has an angle of 0, the X axis an angle of 90.

EDIT: Although if you're setting a value or something other than the actual angle of the object, you'll have to account for angle wrapping, so this formula should take care of it: ((2*Plane+360-Angle) mod 360)

[Pixelthief]

In order to have a proper reflection you need to know the normal angle of the surface that is being struck- very easy in a vertex-point 3d engine, but in a sprite-based 2d engine, there is no such thing.
If you're using flat surfaces that are just up and down and left and right, all at 90 degree angles, there are simpler tricks- just come up with a way to find if you're hitting a vertical or horizontal plane, and reflect accordingly. But if you're using smooth surfaces and curves and other angles, you'll need something like the algorithm I talk about in this article;
http://community.clickteam.com/showthread.php?t=60695

[geothefaust]

Hi guys, thanks for the responses! I really appreciate it.

You'd use that as your object's movement angle in an equation that gets you the reflecting angle, which was said by Looki in a post a few days ago:

EDIT: Although if you're setting a value or something other than the actual angle of the object, you'll have to account for angle wrapping, so this formula should take care of it: ((2*Plane+360-Angle) mod 360)

Thanks Jacob! This really helped out, the only problem I'm seeing now is that sometimes the player controlled object will continue moving to then fully penetrate the surface area it should be bouncing off of. I've put together a test scene to work in, any chance you could look at it? Here is the URL:

https://www.dropbox.com/s/7792qiqo3w...tion%200.2.mfa

In order to have a proper reflection you need to know the normal angle of the surface that is being struck- very easy in a vertex-point 3d engine, but in a sprite-based 2d engine, there is no such thing.
If you're using flat surfaces that are just up and down and left and right, all at 90 degree angles, there are simpler tricks- just come up with a way to find if you're hitting a vertical or horizontal plane, and reflect accordingly. But if you're using smooth surfaces and curves and other angles, you'll need something like the algorithm I talk about in this article;
http://community.clickteam.com/showthread.php?t=60695

Wow this looks really interesting! I'm more of an artist then a programmer, so I might have some trouble implementing it. How would one go about using this in a MMF way with out using the LAU script? On a similar note, you mention it is easier in 3D... And you are so right. If this were a 3D engine I could simply get the vertex indices and get a normal, of just grab a poly and use the normal from there. Anyway, it's interesting to see how it is done in this regard. I would love to further understand it. Is there by chance an example file that one could explore? Thanks!

[Jacob]

I haven't studied his algorithm, but basically you can make two actives at 1px with the hotspot set to the radius of the object you're bouncing, then you can use a fastloop to spin them around in opposite directions until they hit an obstacle. The angle between them will be the angle of the plane, and the normal angle will be plane+90.

EDIT: Are you planning on having angled and curved surfaces to bounce off of? If you only have 45 and 90 degree turns, you can find out which sides of the objects are touching the wall (and therefore know what the angle of the wall is) and simply reverse the X or Y position. If the top or bottom collide, reverse Y. If the left or right collide, reverse X.