I''m writing a pinball game, and i''ll describe objects in polygons (array with coords).
I can detect if a point lies in a polygon, but when the ball has a high speed, it can jump through walls.
So i must not check if a point lies in a polygon, but if a line (oldpostitionvector ball, newpositionvector ball) crosses a polygonline.
I need:
- the exact point of intersection
- the two points (which forms a polygon line) the intersectionpoint lies between, so then i can calculate with the dot product the angle. (function has been made already).
Can anyone explain it to me as simple as possible??
Thanks in advance,
Kind regards, Spikey
polygon line intersection test
Author
Maybe the question has been asked a dozen time, sorry for that
I''m writing a pinball game, and i''ll describe objects in polygons (array with coords).
I can detect if a point lies in a polygon, but when the ball has a high speed, it can jump through walls.
So i must not check if a point lies in a polygon, but if a line (oldpostitionvector ball, newpositionvector ball) crosses a polygonline.
I need:
- the exact point of intersection
- the two points (which forms a polygon line) the intersectionpoint lies between, so then i can calculate with the dot product the angle. (function has been made already).
Can anyone explain it to me as simple as possible??
Thanks in advance,
Kind regards, Spikey
I''m writing a pinball game, and i''ll describe objects in polygons (array with coords).
I can detect if a point lies in a polygon, but when the ball has a high speed, it can jump through walls.
So i must not check if a point lies in a polygon, but if a line (oldpostitionvector ball, newpositionvector ball) crosses a polygonline.
I need:
- the exact point of intersection
- the two points (which forms a polygon line) the intersectionpoint lies between, so then i can calculate with the dot product the angle. (function has been made already).
Can anyone explain it to me as simple as possible??
Thanks in advance,
Kind regards, Spikey
There is literally _loads_ of info on "line-triangle-interstion-tests". Try either GameDev''s search or go to Google.
Author
Did i said "explain as simple plz??"
Oh yes, I did
I don''t get all the "experienced" tutorials. So i''d like to have a good explaination otherwise i didn''t had to post here
Oh yes, I did
I don''t get all the "experienced" tutorials. So i''d like to have a good explaination otherwise i didn''t had to post here
You have to try the intersection between the line segment of the ball, and every line segment of the polygon, one by one.
It''s quite easy, really.
y = ax + b ->First line
y = cx + d ->Second line
ax + b = cx + d
x = (d - b) / (a - c)
Now you check if x is between x0 and x1 for the first line segment, then the second line segment.
HTH,
Cédric
It''s quite easy, really.
y = ax + b ->First line
y = cx + d ->Second line
ax + b = cx + d
x = (d - b) / (a - c)
Now you check if x is between x0 and x1 for the first line segment, then the second line segment.
HTH,
Cédric
If you use bounding spheres for the objects in your game, you can use a ray to sphere test which I have. It also returns a point of intersection.
//// Ray to sphere collision test// http://www.cs.unc.edu/~rademach/xroads-RT/RTarticle.html//const bool Util::RaySphereTest( D3DXVECTOR3* vPofI, const D3DXVECTOR3* vSpherePos, const float fRadius, const D3DXVECTOR3* vRayStartPos, const D3DXVECTOR3* vRayEndPos ){ // Ray''s direction D3DXVECTOR3 vRayNormal = *vRayEndPos - *vRayStartPos; Normalize( &vRayNormal, &vRayNormal ); // Get distance of a vector from ray origin to sphere''s center pos projected on the ray D3DXVECTOR3 vRaySphere = *vSpherePos - *vRayStartPos; float dist = DotProd( &vRaySphere, &vRayNormal ); // Find distance from point of intersection to vector perpendicular to ray and goes through sphere''s // center (that''s the idea anyway) float disc = (fRadius * fRadius) - (DotProd( &vRaySphere, &vRaySphere ) - (dist * dist) ); if( disc < 0.0f ) return false; // No intersection // They intersect if( vPofI ) { // Find point of intersection float d = (float)sqrt( disc ); *vPofI = *vRayStartPos + ((dist - d) * vRayNormal); } return true;}
how did u test whether a point is inside a polygon or not ? Did u use the method of angle calculation which checks whether the sum of the angles is 360 or not ? Well... this method applies pretty well for convave polygons but fails in non-cocave ones. Not to mention, angle-calculation method is also very slow.
I''m looking for somone who has tried the line-intersection method and got it to work successfully, specially with the corners of the polygon. Anyone ?
I''m looking for somone who has tried the line-intersection method and got it to work successfully, specially with the corners of the polygon. Anyone ?
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