| game_maker |
Posted - Jun 17 2004 : 7:22:39 PM
Hi
I've seen an example for this in Almar's home page
and I have learned another method for the test from SuperC Here :
http://www.vbgamer.com/msgboard/topic.asp?TOPIC_ID=143
soo here is my test 
Download Attachment:  TriangleCollision.zip
2.86 KB |
| VBBR |
Posted - Jun 20 2004 : 06:35:45 AM
Oh sorry for forgetting that. It's very simple math. A number to the power 2 is always positive because positive*positive=positive and negative*negative=positive also. Since the numbers are the same, they gotta be positive or negative both. Thanks for remembering. |
| game_maker |
Posted - Jun 19 2004 : 6:47:19 PM
VBBR :
My friend we don't need abs() ,,
(a - b) * (a - b)
Is Always positive
assume c = (a - b) then
(a - b) * (a - b)
=
c * c
=
c ^ 2
that's why it's always positive |
| VBBR |
Posted - Jun 19 2004 : 6:29:27 PM
I have just made a small modification, put an "Abs" before the subtract operations in the distance calculations. We must work with absolute values because if you put negative numbers it will go crazy
Download Attachment: Triangle Collision.zip
3.55 KB |
| game_maker |
Posted - Jun 19 2004 : 5:40:05 PM
you can avoid sin & cos functions if you identify your accuracy (you know what I mean ? )
BTW : is there an use for this test (I never programmed 2D Game)  |
| game_maker |
Posted - Jun 19 2004 : 5:36:17 PM
Nice 
this would increase some accuracy at corners
hmmmm, I have add a Circle to Circle Collision to fast our collision
OK now we have :
- Point in Triangle Test
- Point in Circle Test
- Circle-Circle Test
We need all of them to perform a nice Trinagle-Circle test
Download Attachment: Triangle Collision.zip
3.33 KB |
| Serpwidgets |
Posted - Jun 19 2004 : 5:34:55 PM
Hmm... when checking a collision between a line segment and a circle, there are two possible cases where there is an intersection:
1- An endpoint of the segment is within the circle.
2- the line segment collides with a radius of the circle which is perpendicular to the segment.
If neither of these cases are true, there is no collision.
Out of curiosity, are you talking 2-d or 3-d objects (circles or spheres?) and are you working in 2-d or 3-d space?
Here's my method of determining 2-d line segment collisions within 2-d space. I didn't thoroughly check what was in the attachments, but I saw sin and cos and other really slow functions being used, so I thought this might help. :)
----
Public Function CollideSegments(p1 As Vert2d, p2 As Vert2d, p3 As Vert2d, p4 As Vert2d) As Boolean
Dim t As Single, s As Single Dim theta As Single
theta = ((p2.X - p1.X) * (p3.Y - p4.Y)) - ((p2.Y - p1.Y) * (p3.X - p4.X))
s = (((p2.X - p1.X) * (p3.Y - p1.Y)) - ((p2.Y - p1.Y) * (p3.X - p1.X))) / theta
If s < 1 Then If s > 0 Then
t = (((p3.X - p1.X) * (p3.Y - p4.Y)) - ((p3.Y - p1.Y) * (p3.X - p4.X))) / theta
If t < 1 Then
If t > 0 Then
CollideSegments = True
End If End If
End If End If
End Function
|
| VBBR |
Posted - Jun 19 2004 : 4:17:28 PM
See, I just corrected the problem this code had just by adding a point-in-circle test for each vertex 
Also added an FPS counter. Get it here...
EDIT: Also, using this pre-check, an accuracy of 16 should be more than enough. 8 is already good (acceptable) for not very precise checking. (I have tested both)
Download Attachment: TriangleCollision.zip
3.47 KB
Gotta work on the center-point calculation now... |
| VBBR |
Posted - Jun 19 2004 : 4:00:02 PM
Probably it will be needed only once, as long as the triangle shape doesn't change. I will try to do that with this example. |
| Sr. Guapo |
Posted - Jun 19 2004 : 3:52:56 PM
You could just calculate 2 of the side midpoints (very easy since you know the endpoints) and the slope of each of those segments, then you can find the perpendicular lines and their intersection. It may be a little computationally expensive, but as long as you aren't doing it for 100,000 triangles per frame you should be okay... |
| VBBR |
Posted - Jun 19 2004 : 3:23:34 PM
Yeah, I remembered that but I didn't remember exactly if it were the sides of the triangle or the angles or whatever That is what happens if you last about 2 years without seeing a similar thing in school... |
| Sr. Guapo |
Posted - Jun 19 2004 : 1:29:41 PM
There is a way to do it geometrically... It involves bisecting all the sides of the triagle and drawing perpendicular lines through the points. Assuming all goes well, that will give a point that can create a perfect circumscribed circle, the circumscribed midpoint (BTW, If you do a similar thing with the angles, you will get the INSCRIBED midpoint) I'm sure there is a way to do it algebraically, also... Try google |
| VBBR |
Posted - Jun 19 2004 : 08:28:50 AM
Do you know how to find the center point of a triangle? |
| game_maker |
Posted - Jun 18 2004 : 6:52:32 PM
Also True, because we know speed = k / accuracy
You can not (or let say) it's very hard to bind or find a relation between a curve (circle) and poly (triangle) and that's what both test's do
Will if we can find the center of our triangle and make a radius and so a circle then check circler collision if true then check our test
I didn't bring a new Idea for collision the Idea is totally same the procedures is sort of different |
| Sr. Guapo |
Posted - Jun 18 2004 : 5:51:19 PM
But it will be much slower... |
| game_maker |
Posted - Jun 18 2004 : 10:37:38 AM
Yes,True and this is also happening to the code in Almar's home page
that's why I added Accuracy
if you put Accuracy = 256 for example you will have 99.99% (we can say 100%) it will test 256 point (in triangle) |
