Function update

tests/cpp-tests/Source/ChipmunkTestBed/demo/Convex.cpp:31–69

static cpShape* shape;

static void update(cpSpace* space, double dt)
{
    cpFloat tolerance = 2.0;

    if (ChipmunkDemoRightClick && cpShapePointQuery(shape, ChipmunkDemoMouse, NULL) > tolerance)
    {
        cpBody* body = cpShapeGetBody(shape);
        int count    = cpPolyShapeGetCount(shape);

        // Allocate the space for the new vertexes on the stack.
        cpVect* verts = (cpVect*)alloca((count + 1) * sizeof(cpVect));

        for (int i = 0; i < count; i++)
        {
            verts[i] = cpPolyShapeGetVert(shape, i);
        }

        verts[count] = cpBodyWorldToLocal(body, ChipmunkDemoMouse);

        // This function builds a convex hull for the vertexes.
        // Because the result array is the same as verts, it will reduce it in place.
        int hullCount = cpConvexHull(count + 1, verts, verts, NULL, tolerance);

        // Figure out how much to shift the body by.
        cpVect centroid = cpCentroidForPoly(hullCount, verts);

        // Recalculate the body properties to match the updated shape.
        cpFloat mass = cpAreaForPoly(hullCount, verts, 0.0f) * DENSITY;
        cpBodySetMass(body, mass);
        cpBodySetMoment(body, cpMomentForPoly(mass, hullCount, verts, cpvneg(centroid), 0.0f));
        cpBodySetPosition(body, cpBodyLocalToWorld(body, centroid));

        // Use the setter function from chipmunk_unsafe.h.
        // You could also remove and recreate the shape if you wanted.
        cpPolyShapeSetVerts(shape, hullCount, verts, cpTransformTranslate(cpvneg(centroid)));
    }

    cpSpaceStep(space, dt);
}

static cpSpace* init(void)
{