Path: chuka.playstation.co.uk!news
From: "Miles Buzzing" <miles@guildfrd.demon.co.uk>
Newsgroups: scee.yaroze.programming.2d_graphics
Subject: Re: Collision detection with rotating sprites
Date: 3 Dec 1998 07:45:43 GMT
Organization: PlayStation Net Yaroze (SCEE)
Lines: 48
Message-ID: <01be1e90$e7e94160$0a3ddec2@guildfoc>
References: <01be1d86$03a1a160$0a3ddec2@guildfoc> <742u50$9lv3@chuka.playstation.co.uk>
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George Bain <george_bain@playstation.sony.com> wrote in article
<742u50$9lv3@chuka.playstation.co.uk>...
> Hi there,
> 
> Try a bounding sphere.
> 
> George

Thanks for the quick response George, but as far as I can see, spheres or
boxes the issue is the same. Below is a sample of the code i've since
written.

 'pS2' is a pointer to an extended sprite structure that can hold details
of up to four bounding boxes per sprite. As you can see in the code, if the
offset of the collision box (ox/oy) from the centre of the sprite is not
equal to zero, then I rotate the bounding box(s) around the sprite's
centre.

//is bounding box offset from sprite centre
if(CollisionRect[iCount1].ox | CollisionRect[iCount1].oy)
{
	//convert the bounding box offset to fixed-point
	fpCx = TO_FIXED(pS2->CollisionRect[iCount2].ox);
	fpCy = TO_FIXED(pS2->CollisionRect[iCount2].oy);
			
	//rotate it around the sprite z axis
	iCx = FP_MULTIPLY(fpCx,fp_cos(pS2->gsSprite.rotate)) -
FP_MULTIPLY(fpCy,fp_sin(pS2->gsSprite.rotate));
	iCy = FP_MULTIPLY(fpCy,fp_cos(pS2->gsSprite.rotate)) +
FP_MULTIPLY(fpCx,fp_sin(pS2->gsSprite.rotate));
			
	//back to normal
	iCx = FROM_FIXED(iCx);
	iCy = FROM_FIXED(iCy);
	
	.............
}

The reason I have to do this is that the sprite in question is a rectangle
at least twice as long as it is wide - so I use two bounding boxes/spheres.


- Miles