The source code for the physics interaction (Example 11-54 and Example 11-55) and update (Example 11-56) are presented here for you to study. You can download the complete source code from http://www.threadingbuildingblocks.org/book. Look for errata and notes at this web site as well.
For more in-depth reading on this topic, Intel engineers wrote several articles covering the topic of threading games, which you can download at the web site as well.
Example 11-54. Physics interaction code: InteractTask
class InteractTask : public tbb::task
{
SceneNode* m_node;
size_t m_i;
D3DBlackHole* m_bh;
float m_universeRadius;
size_t m_DummyCount;
public: // Interact all stars in task
InteractTask(SceneNode* node,
size_t i,
D3DBlackHole* bh,
float universeRadius,
size_t DummyCount)
: m_node(node), m_i(i),
m_bh(bh), m_universeRadius(universeRadius),
m_DummyCount(DummyCount)
{}
tbb::task* execute()
{
if (m_node->getChildCount()) {
// High in scene graph, Create parallel domain tasks for the children
size_t i;
tbb::task_list list;
tbb::task& c = *new(allocate_continuation()) tbb::empty_task();
for (i = 0; i < m_node->getChildCount(); ++i) {
list.push_back(*new(c.allocate_child())
InteractTask(m_node->getChild(i),
i, m_bh, m_universeRadius, m_DummyCount));
}
c.set_ref_count((int)i);
c.spawn(list);
}
if (m_node->getUserID() > 0) {
// Low-level object tasks, interact each star serially
D3DStar* pStar = (D3DStar*)m_node;
float elapsedTime = g_elapsedTime - pStar->getTimeStamp();
// TODO: check accuracy of interaction and decide:
// 1. Skip interaction for this short period of time
// 2. Split this long period of time to parts and
// interact for each
pStar->setTimeStamp(g_elapsedTime);
pStar->setElapsedTime(elapsedTime);
if (!pStar->isAlive() && !pStar->isDying()) {
pStar->Reset(m_bh, m_universeRadius);
pStar->NextState();
} else {
// apply attraction to black hole
pStar->Interact(elapsedTime, m_bh,
m_universeRadius, m_DummyCount);
// apply attraction to every other star
SceneNode* node = m_node->getParent();
for (size_t j = (m_i + 1); j < node->getChildCount(); ++j) {
pStar->Interact(elapsedTime,
(D3DStar*)node->getChild(j),
m_DummyCount);
}
}
}
return NULL;
}
};Example 11-55. Physics interaction code: UpdateTask
class UpdateTask : public tbb::task
{
SceneNode* m_node;
public: // Update all star positions based on
// interactions in this frame
UpdateTask(SceneNode* node)
: m_node(node)
{}
tbb::task* execute()
{
if (m_node->getChildCount()) {
// High in scene graph, Create parallel
// domain tasks for the children
size_t i;
tbb::task_list list;
tbb::task& c = *new(allocate_continuation()) tbb::empty_task();
for (i = 0; i < m_node->getChildCount(); ++i) {
list.push_back(*new(c.allocate_child())
UpdateTask(m_node->getChild(i)));
}
c.set_ref_count((int)i);
c.spawn(list);
}
if (m_node->getUserID() > 0) {
// Low-level object tasks, update each star serially
D3DStar* pStar = (D3DStar*)m_node;
// Matrix transformation
pStar->Update(pStar->getElapsedTime());
}
return NULL;
}
};Example 11-56. Update Code
void World::Update(void)
{
static __itt_event ev = __itt_event_create("update", 6);
// Lock out changing k-d tree until interactions
// and updates are done.
Lock();
__itt_event_start(ev);
tbb::tick_count t0 = tbb::tick_count::now();
if (isParallel() && !isChanged()) {
InteractTask& task = *new(tbb::task::allocate_root())
InteractTask(m_bh, 0, m_bh,
m_universeRadius,
m_DummyCount);
tbb::task::spawn_root_and_wait(task);
} else {
// Sequential equivalent to threaded version in InteractTask
for (size_t i = 0; i < m_bh->getChildCount(); ++i) {
GroupNode* grp = (GroupNode*)m_bh->getChild(i);
for (size_t j = 0; j < grp->getChildCount(); ++j) {
D3DStar* pStar = (D3DStar*)grp->getChild(j);
float elapsedTime = g_elapsedTime - pStar->getTimeStamp();
pStar->setTimeStamp(g_elapsedTime);
pStar->setElapsedTime(elapsedTime);
if (!pStar->isAlive() && !pStar->isDying()) {
pStar->Reset(m_bh, m_universeRadius);
pStar->NextState();
continue;
}
// apply attraction to black hole
pStar->Interact(elapsedTime, m_bh,
m_universeRadius, m_DummyCount);
// apply attraction to every other star in group
for (size_t k = (j + 1); k < grp->getChildCount(); ++k) {
pStar->Interact(elapsedTime,
(D3DStar*)grp->getChild(k),
m_DummyCount);
}
}
}
}
tbb::tick_count t1 = tbb::tick_count::now();
m_UpdateTime = (t1-t0).seconds();
__itt_event_end(ev);
t0 = tbb::tick_count::now();
if (isParallel() && !isChanged()) {
UpdateTask& task = *new(tbb::task::allocate_root())
UpdateTask(m_bh);
tbb::task::spawn_root_and_wait(task);
} else {
// Sequential equivalent to threaded version in UpdateTask
for (size_t i = 0; i < m_bh->getChildCount(); ++i) {
GroupNode* grp = (GroupNode*)m_bh->getChild(i);
for (size_t j = 0; j < grp->getChildCount(); ++j) {
D3DStar* pStar = (D3DStar*)grp->getChild(j);
// Matrix transformation
pStar->Update(pStar->getElapsedTime());
}
}
}
float elapsedTime = g_elapsedTime - m_bh->getTimeStamp();
m_bh->setTimeStamp(g_elapsedTime);
m_bh->setElapsedTime(elapsedTime);
// update Black Hole
m_bh->Update(elapsedTime);
t1 = tbb::tick_count::now();
m_TransformTime = (t1-t0).seconds();
// Balance groups here (every 10 frame)
static int balance_counter = 0;
if (!(balance_counter % 10)) {
for (size_t i = 0; i < m_bh->getChildCount(); ++i) {
GroupNode* grp = (GroupNode*)m_bh->getChild(i);
for (size_t j = 0; j < grp->getChildCount(); ++j) {
D3DStar* pStar = (D3DStar*)grp->getChild(j);
if (pStar->isAlive() &&
!grp->isInGroup(pStar->getLocation(0),
pStar->getLocation(1),
pStar->getLocation(2))) {
for (size_t k = 0; k < m_bh->getChildCount(); ++k) {
GroupNode* ngrp = (GroupNode*)m_bh->getChild(k);
if (ngrp != grp &&
ngrp->isInGroup(pStar->getLocation(0),
pStar->getLocation(1),
pStar->getLocation(2))) {
grp->removeChild(pStar);
ngrp->addChild(pStar);
}
}
}
}
}
}
Unlock(); // Ok, now permit changing the k-d tree.
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