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engine.cpp: lintersect(): fix integer overflow and negative case issue

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git-svn-id: https://svn.eduke32.com/eduke32@7472 1a8010ca-5511-0410-912e-c29ae57300e0
This commit is contained in:
pogokeen 2019-04-05 17:45:19 +00:00 committed by Christoph Oelckers
parent a82eb1d6fe
commit f7f62c4466
1 changed files with 24 additions and 10 deletions
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34
source/build/src/engine.cpp
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@ -7459,7 +7459,7 @@ int32_t lintersect(const int32_t originX, const int32_t originY, const int32_t o
const int32_t rayLengthSquared = ray.x*ray.x + ray.y*ray.y; const int32_t rayLengthSquared = ray.x*ray.x + ray.y*ray.y;
const int32_t rayDotOriginDiff = ray.x*originDiff.x + ray.y*originDiff.y; const int32_t rayDotOriginDiff = ray.x*originDiff.x + ray.y*originDiff.y;
const int32_t rayDotLineEndDiff = rayDotOriginDiff + ray.x*lineVec.x + ray.y*lineVec.y; const int32_t rayDotLineEndDiff = rayDotOriginDiff + ray.x*lineVec.x + ray.y*lineVec.y;
int32_t t = min(rayDotOriginDiff, rayDotLineEndDiff); int64_t t = min(rayDotOriginDiff, rayDotLineEndDiff);
if (rayDotOriginDiff < 0) if (rayDotOriginDiff < 0)
{ {
if (rayDotLineEndDiff < 0) if (rayDotLineEndDiff < 0)
@ -7474,7 +7474,8 @@ int32_t lintersect(const int32_t originX, const int32_t originY, const int32_t o
t = rayDotLineEndDiff; t = rayDotLineEndDiff;
} }
t = divscale24(t, rayLengthSquared); t = tabledivide64(t << 24L, rayLengthSquared);
*intersectionX = originX + mulscale24(ray.x, t); *intersectionX = originX + mulscale24(ray.x, t);
*intersectionY = originY + mulscale24(ray.y, t); *intersectionY = originY + mulscale24(ray.y, t);
*intersectionZ = originZ + mulscale24(destZ-originZ, t); *intersectionZ = originZ + mulscale24(destZ-originZ, t);
@ -7484,20 +7485,33 @@ int32_t lintersect(const int32_t originX, const int32_t originY, const int32_t o
const int32_t originDiffCrossLineVec = originDiff.x*lineVec.y - originDiff.y*lineVec.x; const int32_t originDiffCrossLineVec = originDiff.x*lineVec.y - originDiff.y*lineVec.x;
static const int32_t signBit = 1u<<31u; static const int32_t signBit = 1u<<31u;
// Any point on either line can be expressed as p+t*r and q+u*s
// The two line segments intersect when we can find a t & u such that p+t*r = q+u*s
// If the point is outside of the bounds of the line segment, we know we don't have an intersection.
// t is < 0 if (originDiffCrossLineVec^rayCrossLineVec) & signBit) // t is < 0 if (originDiffCrossLineVec^rayCrossLineVec) & signBit)
// t is > 1 if originDiffCrossLineVec > rayCrossLineVec
// u is < 0 if (originDiffCrossRay^rayCrossLineVec) & signBit // u is < 0 if (originDiffCrossRay^rayCrossLineVec) & signBit
// u is > 1 if originDiffCrossRay > rayCrossLineVec // t is > 1 if abs(originDiffCrossLineVec) > abs(rayCrossLineVec)
// where int32_t u = divscale24(originDiffCrossRay, rayCrossLineVec); // u is > 1 if abs(originDiffCrossRay) > abs(rayCrossLineVec)
if (originDiffCrossLineVec > rayCrossLineVec || // where int32_t u = tabledivide64(((int64_t) originDiffCrossRay) << 24L, rayCrossLineVec);
originDiffCrossRay > rayCrossLineVec || if (((originDiffCrossLineVec^rayCrossLineVec) & signBit) ||
((originDiffCrossLineVec^rayCrossLineVec) & signBit) || ((originDiffCrossRay^rayCrossLineVec) & signBit) ||
((originDiffCrossRay^rayCrossLineVec) & signBit)) abs(originDiffCrossLineVec) > abs(rayCrossLineVec) ||
abs(originDiffCrossRay) > abs(rayCrossLineVec))
{ {
// line segments do not overlap // line segments do not overlap
return 0; return 0;
} }
int32_t t = divscale24(originDiffCrossLineVec, rayCrossLineVec);
int64_t t = tabledivide64(((int64_t) originDiffCrossLineVec) << 24L, rayCrossLineVec);
// For sake of completeness/readability, alternative to the above approach for an early out & avoidance of an extra division:
#if 0
int64_t u = tabledivide64(((int64_t) originDiffCrossRay) << 24L, rayCrossLineVec);
if (u < 0 || u > 1 << 24 || t < 0 || t > 1 << 24)
{
return 0;
}
#endif
*intersectionX = originX + mulscale24(ray.x, t); *intersectionX = originX + mulscale24(ray.x, t);
*intersectionY = originY + mulscale24(ray.y, t); *intersectionY = originY + mulscale24(ray.y, t);
*intersectionZ = originZ + mulscale24(destZ-originZ, t); *intersectionZ = originZ + mulscale24(destZ-originZ, t);