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- /*
- * Copyright (c) 2007 Erin Catto http://www.gphysics.com
- *
- * This software is provided 'as-is', without any express or implied
- * warranty. In no event will the authors be held liable for any damages
- * arising from the use of this software.
- * Permission is granted to anyone to use this software for any purpose,
- * including commercial applications, and to alter it and redistribute it
- * freely, subject to the following restrictions:
- * 1. The origin of this software must not be misrepresented; you must not
- * claim that you wrote the original software. If you use this software
- * in a product, an acknowledgment in the product documentation would be
- * appreciated but is not required.
- * 2. Altered source versions must be plainly marked as such, and must not be
- * misrepresented as being the original software.
- * 3. This notice may not be removed or altered from any source distribution.
- */
- #include "b2Collision.h"
- #include "Shapes/b2Shape.h"
- // This algorithm uses conservative advancement to compute the time of
- // impact (TOI) of two shapes.
- // Refs: Bullet, Young Kim
- float32 b2TimeOfImpact(const b2Shape* shape1, const b2Sweep& sweep1,
- const b2Shape* shape2, const b2Sweep& sweep2)
- {
- float32 r1 = shape1->GetSweepRadius();
- float32 r2 = shape2->GetSweepRadius();
- b2Assert(sweep1.t0 == sweep2.t0);
- b2Assert(1.0f - sweep1.t0 > B2_FLT_EPSILON);
- float32 t0 = sweep1.t0;
- b2Vec2 v1 = sweep1.c - sweep1.c0;
- b2Vec2 v2 = sweep2.c - sweep2.c0;
- float32 omega1 = sweep1.a - sweep1.a0;
- float32 omega2 = sweep2.a - sweep2.a0;
- float32 alpha = 0.0f;
- b2Vec2 p1, p2;
- const int32 k_maxIterations = 20; // TODO_ERIN b2Settings
- int32 iter = 0;
- b2Vec2 normal = b2Vec2_zero;
- float32 distance = 0.0f;
- float32 targetDistance = 0.0f;
- for(;;)
- {
- float32 t = (1.0f - alpha) * t0 + alpha;
- b2XForm xf1, xf2;
- sweep1.GetXForm(&xf1, t);
- sweep2.GetXForm(&xf2, t);
- // Get the distance between shapes.
- distance = b2Distance(&p1, &p2, shape1, xf1, shape2, xf2);
- if (iter == 0)
- {
- // Compute a reasonable target distance to give some breathing room
- // for conservative advancement.
- if (distance > 2.0f * b2_toiSlop)
- {
- targetDistance = 1.5f * b2_toiSlop;
- }
- else
- {
- targetDistance = b2Max(0.05f * b2_toiSlop, distance - 0.5f * b2_toiSlop);
- }
- }
- if (distance - targetDistance < 0.05f * b2_toiSlop || iter == k_maxIterations)
- {
- break;
- }
- normal = p2 - p1;
- normal.Normalize();
- // Compute upper bound on remaining movement.
- float32 approachVelocityBound = b2Dot(normal, v1 - v2) + b2Abs(omega1) * r1 + b2Abs(omega2) * r2;
- if (b2Abs(approachVelocityBound) < B2_FLT_EPSILON)
- {
- alpha = 1.0f;
- break;
- }
- // Get the conservative time increment. Don't advance all the way.
- float32 dAlpha = (distance - targetDistance) / approachVelocityBound;
- //float32 dt = (distance - 0.5f * b2_linearSlop) / approachVelocityBound;
- float32 newAlpha = alpha + dAlpha;
- // The shapes may be moving apart or a safe distance apart.
- if (newAlpha < 0.0f || 1.0f < newAlpha)
- {
- alpha = 1.0f;
- break;
- }
- // Ensure significant advancement.
- if (newAlpha < (1.0f + 100.0f * B2_FLT_EPSILON) * alpha)
- {
- break;
- }
- alpha = newAlpha;
- ++iter;
- }
- return alpha;
- }
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