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@@ -865,19 +865,55 @@ public class BoundingBox extends BoundingVolume {
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// plane. Otherwise 'false' is returned in which case the line segment
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// is entirely clipped.
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if (denom > 0.0f) {
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- if (numer > denom * t[1]) {
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+ // This is the old if statement...
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+ // if (numer > denom * t[1]) {
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+ //
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+ // The problem is that what is actually stored is
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+ // numer/denom. In non-floating point, this math should
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+ // work out the same but in floating point there can
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+ // be subtle math errors. The multiply will exaggerate
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+ // errors that may have been introduced when the value
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+ // was originally divided.
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+ //
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+ // This is especially true when the bounding box has zero
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+ // extents in some plane because the error rate is critical.
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+ // comparing a to b * c is not the same as comparing a/b to c
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+ // in this case. In fact, I tried converting this method to
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+ // double and the and the error was in the last decimal place.
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+ //
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+ // So, instead, we now compare the divided version to the divided
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+ // version. We lose some slight performance here as divide
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+ // will be more expensive than the divide. Some microbenchmarks
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+ // show divide to be 3x slower than multiple on Java 1.6.
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+ // BUT... we also saved a multiply in the non-clipped case because
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+ // we can reuse the divided version in both if checks.
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+ // I think it's better to be right in this case.
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+ //
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+ // Bug that I'm fixing: rays going right through quads at certain
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+ // angles and distances because they fail the bounding box test.
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+ // Many Bothans died bring you this fix.
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+ // -pspeed
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+ float newT = numer / denom;
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+ if (newT > t[1]) {
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return false;
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}
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- if (numer > denom * t[0]) {
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- t[0] = numer / denom;
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+ if (newT > t[0]) {
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+ t[0] = newT;
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}
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return true;
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} else if (denom < 0.0f) {
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- if (numer > denom * t[0]) {
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+ // Old if statement... see above
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+ // if (numer > denom * t[0]) {
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+ //
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+ // Note though that denom is always negative in this block.
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+ // When we move it over to the other side we have to flip
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+ // the comparison. Algebra for the win.
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+ float newT = numer / denom;
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+ if (newT < t[0]) {
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return false;
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}
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- if (numer > denom * t[1]) {
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- t[1] = numer / denom;
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+ if (newT < t[1]) {
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+ t[1] = newT;
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}
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return true;
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} else {
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