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Rope: Fix possible C4Real overflow

rope
Armin Burgmeier 2012-05-06 14:37:28 +02:00
parent f54b471115
commit a309e52de3
1 changed files with 47 additions and 24 deletions
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71
src/object/C4Rope.cpp
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@ -19,11 +19,6 @@
#include <C4Landscape.h>
#include <C4Rope.h>
// TODO: For all square roots, we must avoid floating point by using an
// integer-based Sqrt algorithm
// TODO: Could also use an approximation which works without Sqrt, especially
// if this becomes a performance bottleneck. http://www.azillionmonkeys.com/qed/sqroot.html
namespace
{
struct Vertex {
@ -39,18 +34,32 @@ namespace
float v;
};
// TODO: For all square roots, we must avoid floating point by using an
// integer-based Sqrt algorithm
// TODO: Could also use an approximation which works without Sqrt, especially
// if this becomes a performance bottleneck. http://www.azillionmonkeys.com/qed/sqroot.html
C4Real Len(C4Real dx, C4Real dy)
{
// Prevent possible overflow
if(Abs(dx) > 120 || Abs(dy) > 120)
return ftofix(sqrt(fixtoi(dx)*fixtoi(dx) + fixtoi(dy)*fixtoi(dy)));
else
return ftofix(sqrt(fixtof(dx*dx + dy*dy)));
}
// For use in initializer list
C4Real ObjectDistance(C4Object* first, C4Object* second)
{
C4Real dx = second->fix_x - first->fix_x;
C4Real dy = second->fix_y - first->fix_y;
return ftofix(sqrt(fixtof(dx*dx + dy*dy))); // TODO: Replace by integer sqrt
return Len(dx, dy);
}
// Helper function for Draw: determines vertex positions for one segment
void VertexPos(Vertex& out1, Vertex& out2, Vertex& out3, Vertex& out4,
const Vertex& v1, const Vertex& v2, float w)
{
// This is for graphics only, so plain sqrt() is OK.
const float l = sqrt( (v1.x - v2.x)*(v1.x - v2.x) + (v1.y - v2.y)*(v1.y - v2.y));
out1.x = v1.x + w/2.0f * (v1.y - v2.y) / l;
@ -129,7 +138,7 @@ namespace
C4Real dy = itofix(Info->py - iY);
Info->px = iX;
Info->py = iY;
Info->d += ftofix(sqrt(fixtof(dx*dx + dy*dy)));
Info->d += Len(dx, dy);
}
}
@ -311,7 +320,7 @@ bool C4RopeElement::SetForceRedirectionByLookAround(const C4Rope* rope, int ox,
C4Real vy1 = -Sin75 * dx + Cos75 * dy;
C4Real vx2 = Cos75 * dx - Sin75 * dy;
C4Real vy2 = Sin75 * dx + Cos75 * dy;
const C4Real v = ftofix(sqrt(fixtof(dx*dx + dy*dy)));
const C4Real v = Len(dx, dy);
// TODO: We should check more than a single pixel. There's some more potential for optimization here.
if(v != Fix0 && !GBackSolid(ox + fixtoi(GetX() + vx1*l/v), oy + fixtoi(GetY() + vy1*l/v)))
@ -326,7 +335,7 @@ bool C4RopeElement::SetForceRedirectionByLookAround(const C4Rope* rope, int ox,
}
C4Rope::C4Rope(C4PropList* Prototype, C4Object* first_obj, C4Object* second_obj, C4Real segment_length, C4DefGraphics* graphics):
C4PropListNumbered(Prototype), Width(5.0f), Graphics(graphics), SegmentCount(itofix(ObjectDistance(first_obj, second_obj))/segment_length),
C4PropListNumbered(Prototype), Width(5.0f), Graphics(graphics), SegmentCount(fixtoi(ObjectDistance(first_obj, second_obj)/segment_length)),
l(segment_length), k(Fix1*3), mu(Fix1*3), eta(Fix1*3), NumIterations(10),
FrontAutoSegmentation(Fix0), BackAutoSegmentation(Fix0), FrontPull(Fix0), BackPull(Fix0)
{
@ -377,10 +386,10 @@ C4Real C4Rope::GetL(const C4RopeElement* prev, const C4RopeElement* next) const
if(FrontAutoSegmentation > Fix0)
if(prev == Front || next == Front)
return Min(itofix(5), ftofix(sqrt(fixtof(dx*dx+dy*dy))));
return Min(itofix(5), Len(dx, dy));
if(BackAutoSegmentation > Fix0)
if(prev == Back || next == Back)
return Min(itofix(5), ftofix(sqrt(fixtof(dx*dx+dy*dy))));
return Min(itofix(5), Len(dx, dy));
return l;
}
@ -483,7 +492,7 @@ void C4Rope::Solve(C4RopeElement* prev, C4RopeElement* next)
const C4Real dx = prev->GetX() - next->GetX();
const C4Real dy = prev->GetY() - next->GetY();
if(dx*dx + dy*dy > Fix0)
if(dx != Fix0 || dy != Fix0) //dx*dx + dy*dy > Fix0)
{
// Get segment length between prev and next
const C4Real l = GetL(prev, next);
@ -507,22 +516,33 @@ void C4Rope::Solve(C4RopeElement* prev, C4RopeElement* next)
// TODO: For objects, run PathFree and PathFinder from vertex which has
// had contact to the landscape previously.
// We only run the PathFinder when the distance between the two segments
// is at least twice the nominal distance.
C4Real dx1, dy1, dx2, dy2, d;
PullPathInfo Info = { true, pix, piy, nix, niy, nix, niy, pix, piy, Fix0 };
if(dx*dx+dy*dy > 4*l && !PathFree(pix, piy, nix, niy) && Game.PathFinder.Find(pix, piy, nix, niy, PullPathAccumulator, (intptr_t)&Info))
if((Abs(dx) > 2*l || Abs(dy) > 2*l || dx*dx+dy*dy > 4*l*l) && // The first two checks exist to avoid an overflow in the dx*dx+dy*dy expression
!PathFree(pix, piy, nix, niy) &&
Game.PathFinder.Find(pix, piy, nix, niy, PullPathAccumulator, (intptr_t)&Info))
{
C4Real dpx = itofix(Info.px - pix);
C4Real dpy = itofix(Info.py - piy);
C4Real dp = ftofix(sqrt(fixtof(dpx*dpx + dpy*dpy))); // TODO: Could be computed in accumulator
C4Real dp = Len(dpx, dpy); // TODO: Could be computed in accumulator
C4Real dnx = itofix(Info.nx - nix);
C4Real dny = itofix(Info.ny - niy);
C4Real dn = ftofix(sqrt(fixtof(dnx*dnx + dny*dny))); // TODO: Could be computed in accumulator
C4Real dn = Len(dnx, dny); // TODO: Could be computed in accumulator
if(dp != Fix0)
{ dx1 = dpx / dp; dy1 = dpy / dp; }
else
{ dx1 = Fix0; dy1 = Fix0; }
if(dn != Fix0)
{ dx2 = dnx / dn; dy2 = dny / dn; }
else
{ dx2 = Fix0; dy2 = Fix0; }
dx1 = dpx / dp;
dy1 = dpy / dp;
dx2 = dnx / dn;
dy2 = dny / dn;
d = itofix(Info.d) + dp;
/*printf("Solved %p via PathFinder, from %d/%d to %d/%d\n", this, pix, piy, nix, niy);
@ -531,9 +551,12 @@ void C4Rope::Solve(C4RopeElement* prev, C4RopeElement* next)
}
else
{
d = ftofix(sqrt(fixtof(dx*dx + dy*dy)));
dx1 = -(dx / d);
dy1 = -(dy / d);
d = Len(dx, dy);
if(d != Fix0)
{ dx1 = -(dx / d); dy1 = -(dy / d); }
else
{ dx1 = 0; dx2 = 0; }
dx2 = -dx1;
dy2 = -dy1;
}
@ -586,7 +609,7 @@ void C4Rope::Execute()
{
const C4Real dx = Front->Next->GetX() - Front->GetX();
const C4Real dy = Front->Next->GetY() - Front->GetY();
const C4Real d = ftofix(sqrt(fixtof(dx*dx+dy*dy)));
const C4Real d = Len(dx, dy);
if(d != Fix0)
Front->Next->AddForce(-dx/d * FrontPull, -dy/d * FrontPull);
}
@ -595,7 +618,7 @@ void C4Rope::Execute()
{
const C4Real dx = Back->Prev->GetX() - Back->GetX();
const C4Real dy = Back->Prev->GetY() - Back->GetY();
const C4Real d = ftofix(sqrt(fixtof(dx*dx+dy*dy)));
const C4Real d = Len(dx, dy);
if(d != Fix0)
Back->Prev->AddForce(-dx/d * BackPull, -dy/d * BackPull);
}