Java-Gaming.org Hi !
 Featured games (91) games approved by the League of Dukes Games in Showcase (757) Games in Android Showcase (229) games submitted by our members Games in WIP (844) games currently in development
 News: Read the Java Gaming Resources, or peek at the official Java tutorials
 Home Help Search Login Register
Pages: [1]
 ignore  |  Print
 3D controller, perspective correct interpolation  (Read 4718 times) 0 Members and 1 Guest are viewing this topic.
theagentd
 « Posted 2012-05-19 15:39:29 »

Hello. I want to add a 3D position controller like the red, green and blue arrows in this Maya:

The problem is handling mouse input. The movement has to snap to the axes of the controller. I therefore thought that the best way of doing this is to project the axis to the screen (multiply it by the view and projection matrices) so I simply have a 2D line on the screen. I then find the closest point lying on this line from the mouse. Finally I un-project this point back to world space, and I'll know exactly where the controller has been moved in 3D space.

The problem is that I don't know how to correctly interpolate the depth of the point based on the two end points. I'm pretty sure the solution is perspective correct interpolation which I've glimpsed over for texture mapping, but I only have a line, not a triangle! Given two 3D points on the screen (normalized device coordinates) how do I correctly interpolate the depth value for any point on the line between the two given points? (Linear interpolation does not give the right value due to the 3D perspective.)

Myomyomyo.
Danny02
 « Reply #1 - Posted 2012-05-20 10:33:40 »

let say you figured out how to start dragging your object and now you know the line you want the object to move one (m) and the position of the mouse on screen(Pm).

Now you un-project the mouse position to a line in 3D space(l) (near&far clipping plane).

the next thing is to find the nearest point on (m) to (l), this is the new position of you object.
(to lazy to type hier an example how to do it ask if you have any questions)

Also beware to check if the movement vector has a very smal angle to the mouse vector or even parallel, because will cause problems.
theagentd
 « Reply #2 - Posted 2012-05-20 11:12:56 »

let say you figured out how to start dragging your object and now you know the line you want the object to move one (m) and the position of the mouse on screen(Pm).

Now you un-project the mouse position to a line in 3D space(l) (near&far clipping plane).

the next thing is to find the nearest point on (m) to (l), this is the new position of you object.
(to lazy to type hier an example how to do it ask if you have any questions)

Also beware to check if the movement vector has a very smal angle to the mouse vector or even parallel, because will cause problems.
That's exactly what I want to do, but don't I have to correctly interpolate the depth of the point in a specific way? =S

Myomyomyo.
 Games published by our own members! Check 'em out!
Danny02
 « Reply #3 - Posted 2012-05-20 11:15:35 »

nah I propose to do everything in 3D not in 2D as you explained, also I don't think that you have to snap to the axis

ps:
Quote
Finally I un-project this point back to world space, and I'll know exactly where the controller has been moved in 3D space.
you can not unproject a 2D point to a 3D point, you can only get a line in 3D space out of a 2D point. To get the correct Position in worldspace you have to check where the two lines(unprojected & movment axis) are intersecting.
If you want to do it your way. I think what I did is perhaps cleaner cause you aren'T doing that much conversation between spaces.
Riven

« JGO Overlord »

Medals: 1340
Projects: 4
Exp: 16 years

 « Reply #4 - Posted 2012-05-20 13:02:30 »

how do I correctly interpolate the depth value for any point on the line between the two given points? (Linear interpolation does not give the right value due to the 3D perspective.)
Interpolate linearly in model space, not in screen space.

Hi, appreciate more people! Σ ♥ = ¾
Learn how to award medals... and work your way up the social rankings!
theagentd
 « Reply #5 - Posted 2012-05-20 13:40:04 »

I hate them.

Coding like I'm on fire at the moment, gimme a second to test this crap... >___<

Myomyomyo.
Pages: [1]
 ignore  |  Print

 EgonOlsen (76 views) 2018-06-10 19:43:48 EgonOlsen (56 views) 2018-06-10 19:43:44 EgonOlsen (76 views) 2018-06-10 19:43:20 DesertCoockie (256 views) 2018-05-13 18:23:11 nelsongames (156 views) 2018-04-24 18:15:36 nelsongames (155 views) 2018-04-24 18:14:32 ivj94 (896 views) 2018-03-24 14:47:39 ivj94 (157 views) 2018-03-24 14:46:31 ivj94 (809 views) 2018-03-24 14:43:53 Solater (173 views) 2018-03-17 05:04:08
 Java Gaming Resourcesby philfrei2017-12-05 19:38:37Java Gaming Resourcesby philfrei2017-12-05 19:37:39Java Gaming Resourcesby philfrei2017-12-05 19:36:10Java Gaming Resourcesby philfrei2017-12-05 19:33:10List of Learning Resourcesby elect2017-03-13 14:05:44List of Learning Resourcesby elect2017-03-13 14:04:45SF/X Librariesby philfrei2017-03-02 08:45:19SF/X Librariesby philfrei2017-03-02 08:44:05
 java-gaming.org is not responsible for the content posted by its members, including references to external websites, and other references that may or may not have a relation with our primarily gaming and game production oriented community. inquiries and complaints can be sent via email to the info‑account of the company managing the website of java‑gaming.org