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rather than call setMargin, clench in all the points of a collision-hull toward the center of the hull by the margin amount

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This commit is contained in:
Seth Alves 2015-05-13 13:54:24 -07:00
parent 2ec660bd42
commit 711752bff1
1 changed files with 36 additions and 5 deletions
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41
libraries/physics/src/ShapeInfoUtil.cpp
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@ -14,7 +14,36 @@
#include "ShapeInfoUtil.h"
#include "BulletUtil.h"
const float BULLET_COLLISION_MARGIN = 0.01;
// find the average point on a convex shape
glm::vec3 findCenter(const QVector<glm::vec3>& points) {
glm::vec3 result = glm::vec3(0);
for (int i = 0; i < points.size(); i++) {
result += points[i];
}
return result * (1.0f / points.size());
}
// bullet puts "margins" around all the collision shapes. This can cause shapes will hulls
// to float a bit above what they are sitting on, etc. One option is to call:
//
// compound->setMargin(0.01);
//
// to reduce the size of the margin, but this has some consequences for the
// performance and stability of the simulation. Instead, we clench in all the points of
// the hull by the margin. These clenched points + bullets margin will but the actual
// collision hull fairly close to the visual edge of the object.
QVector<glm::vec3> shrinkByMargin(const QVector<glm::vec3>& points, const glm::vec3 center, float margin) {
QVector<glm::vec3> result(points.size());
for (int i = 0; i < points.size(); i++) {
glm::vec3 pVec = points[ i ] - center;
glm::vec3 pVecNorm = glm::normalize(pVec);
result[ i ] = center + pVec - (pVecNorm * margin);
}
return result;
}
btCollisionShape* ShapeInfoUtil::createShapeFromInfo(const ShapeInfo& info) {
btCollisionShape* shape = NULL;
@ -41,11 +70,12 @@ btCollisionShape* ShapeInfoUtil::createShapeFromInfo(const ShapeInfo& info) {
if (numSubShapes == 1) {
auto hull = new btConvexHullShape();
const QVector<QVector<glm::vec3>>& points = info.getPoints();
foreach (glm::vec3 point, points[0]) {
glm::vec3 center = findCenter(points[0]);
QVector<glm::vec3> shrunken = shrinkByMargin(points[0], center, hull->getMargin());
foreach (glm::vec3 point, shrunken) {
btVector3 btPoint(point[0], point[1], point[2]);
hull->addPoint(btPoint, false);
}
hull->setMargin(BULLET_COLLISION_MARGIN);
hull->recalcLocalAabb();
shape = hull;
} else {
@ -55,14 +85,15 @@ btCollisionShape* ShapeInfoUtil::createShapeFromInfo(const ShapeInfo& info) {
trans.setIdentity();
foreach (QVector<glm::vec3> hullPoints, points) {
auto hull = new btConvexHullShape();
foreach (glm::vec3 point, hullPoints) {
glm::vec3 center = findCenter(points[0]);
QVector<glm::vec3> shrunken = shrinkByMargin(hullPoints, center, hull->getMargin());
foreach (glm::vec3 point, shrunken) {
btVector3 btPoint(point[0], point[1], point[2]);
hull->addPoint(btPoint, false);
}
hull->recalcLocalAabb();
compound->addChildShape (trans, hull);
}
compound->setMargin(BULLET_COLLISION_MARGIN);
shape = compound;
}
}