Raycasting to the polygon level
From Ogre Wiki
As developed by gerds in this forum page.
Raycasting to the polygon level (Mogre) is also available.
Contents |
Introducion
An Ogre ray query generally only detect bounding boxes (AABBs), like you see on this image. With this code you can avoid this disadvantage.
Code for initialization
// create the ray scene query object
m_pray_scene_query = m_pscene_manager->createRayQuery(Ogre::Ray(), Ogre::SceneManager::WORLD_GEOMETRY_TYPE_MASK);
if (NULL == m_pray_scene_query)
{
LOG_ERROR << "Failed to create Ogre::RaySceneQuery instance" << ENDLOG;
return (false);
}
m_pray_scene_query->setSortByDistance(true);
Method for raycast
// raycast from a point in to the scene.
// returns success or failure.
// on success the point is returned in the result.
bool OgreVisionEngine::RaycastFromPoint(const Vector3 &point,
const Vector3 &normal,
Vector3 &result)
{
// create the ray to test
Ogre::Ray ray(Ogre::Vector3(point.x, point.y, point.z),
Ogre::Vector3(normal.x, normal.y, normal.z));
// check we are initialised
if (m_pray_scene_query != NULL)
{
// create a query object
m_pray_scene_query->setRay(ray);
// execute the query, returns a vector of hits
if (m_pray_scene_query->execute().size() <= 0)
{
// raycast did not hit an objects bounding box
return (false);
}
}
else
{
LOG_ERROR << "Cannot raycast without RaySceneQuery instance" << ENDLOG;
return (false);
}
// at this point we have raycast to a series of different objects bounding boxes.
// we need to test these different objects to see which is the first polygon hit.
// there are some minor optimizations (distance based) that mean we wont have to
// check all of the objects most of the time, but the worst case scenario is that
// we need to test every triangle of every object.
Ogre::Real closest_distance = -1.0f;
Ogre::Vector3 closest_result;
Ogre::RaySceneQueryResult &query_result = m_pray_scene_query->getLastResults();
for (size_t qr_idx = 0; qr_idx < query_result.size(); qr_idx++)
{
// stop checking if we have found a raycast hit that is closer
// than all remaining entities
if ((closest_distance >= 0.0f) &&
(closest_distance < query_result[qr_idx].distance))
{
break;
}
// only check this result if its a hit against an entity
if ((query_result[qr_idx].movable != NULL) &&
(query_result[qr_idx].movable->getMovableType().compare("Entity") == 0))
{
// get the entity to check
Ogre::Entity *pentity = static_cast<Ogre::Entity*>(query_result[qr_idx].movable);
// mesh data to retrieve
size_t vertex_count;
size_t index_count;
Ogre::Vector3 *vertices;
unsigned long *indices;
// get the mesh information
OgreVE::GetMeshInformation(pentity->getMesh(), vertex_count, vertices, index_count, indices,
pentity->getParentNode()->getWorldPosition(),
pentity->getParentNode()->getWorldOrientation(),
pentity->getParentNode()->_getDerivedScale());
// test for hitting individual triangles on the mesh
bool new_closest_found = false;
for (int i = 0; i < static_cast<int>(index_count); i += 3)
{
// check for a hit against this triangle
std::pair<bool, Ogre::Real> hit = Ogre::Math::intersects(ray, vertices[indices[i]],
vertices[indices[i+1]], vertices[indices[i+2]], true, false);
// if it was a hit check if its the closest
if (hit.first)
{
if ((closest_distance < 0.0f) ||
(hit.second < closest_distance))
{
// this is the closest so far, save it off
closest_distance = hit.second;
new_closest_found = true;
}
}
}
// free the verticies and indicies memory
delete[] vertices;
delete[] indices;
// if we found a new closest raycast for this object, update the
// closest_result before moving on to the next object.
if (new_closest_found)
{
closest_result = ray.getPoint(closest_distance);
}
}
}
// return the result
if (closest_distance >= 0.0f)
{
// raycast success
result = closest_result;
return (true);
}
else
{
// raycast failed
return (false);
}
}
GetMeshInformation
This code is a copy of RetrieveVertexData. (from the first or the optimized version? - from the optimized version)
// Get the mesh information for the given mesh.
// Code found in Wiki: www.ogre3d.org/wiki/index.php/RetrieveVertexData
void OgreVE::GetMeshInformation(const Ogre::MeshPtr mesh,
size_t &vertex_count,
Ogre::Vector3* &vertices,
size_t &index_count,
unsigned long* &indices,
const Ogre::Vector3 &position,
const Ogre::Quaternion &orient,
const Ogre::Vector3 &scale)
{
bool added_shared = false;
size_t current_offset = 0;
size_t shared_offset = 0;
size_t next_offset = 0;
size_t index_offset = 0;
vertex_count = index_count = 0;
// Calculate how many vertices and indices we're going to need
for (unsigned short i = 0; i < mesh->getNumSubMeshes(); ++i)
{
Ogre::SubMesh* submesh = mesh->getSubMesh( i );
// We only need to add the shared vertices once
if(submesh->useSharedVertices)
{
if( !added_shared )
{
vertex_count += mesh->sharedVertexData->vertexCount;
added_shared = true;
}
}
else
{
vertex_count += submesh->vertexData->vertexCount;
}
// Add the indices
index_count += submesh->indexData->indexCount;
}
// Allocate space for the vertices and indices
vertices = new Ogre::Vector3[vertex_count];
indices = new unsigned long[index_count];
added_shared = false;
// Run through the submeshes again, adding the data into the arrays
for ( unsigned short i = 0; i < mesh->getNumSubMeshes(); ++i)
{
Ogre::SubMesh* submesh = mesh->getSubMesh(i);
Ogre::VertexData* vertex_data = submesh->useSharedVertices ? mesh->sharedVertexData : submesh->vertexData;
if((!submesh->useSharedVertices)||(submesh->useSharedVertices && !added_shared))
{
if(submesh->useSharedVertices)
{
added_shared = true;
shared_offset = current_offset;
}
const Ogre::VertexElement* posElem =
vertex_data->vertexDeclaration->findElementBySemantic(Ogre::VES_POSITION);
Ogre::HardwareVertexBufferSharedPtr vbuf =
vertex_data->vertexBufferBinding->getBuffer(posElem->getSource());
unsigned char* vertex =
static_cast<unsigned char*>(vbuf->lock(Ogre::HardwareBuffer::HBL_READ_ONLY));
// There is _no_ baseVertexPointerToElement() which takes an Ogre::Real or a double
// as second argument. So make it float, to avoid trouble when Ogre::Real will
// be comiled/typedefed as double:
// Ogre::Real* pReal;
float* pReal;
for( size_t j = 0; j < vertex_data->vertexCount; ++j, vertex += vbuf->getVertexSize())
{
posElem->baseVertexPointerToElement(vertex, &pReal);
Ogre::Vector3 pt(pReal[0], pReal[1], pReal[2]);
vertices[current_offset + j] = (orient * (pt * scale)) + position;
}
vbuf->unlock();
next_offset += vertex_data->vertexCount;
}
Ogre::IndexData* index_data = submesh->indexData;
size_t numTris = index_data->indexCount / 3;
Ogre::HardwareIndexBufferSharedPtr ibuf = index_data->indexBuffer;
bool use32bitindexes = (ibuf->getType() == Ogre::HardwareIndexBuffer::IT_32BIT);
unsigned long* pLong = static_cast<unsigned long*>(ibuf->lock(Ogre::HardwareBuffer::HBL_READ_ONLY));
unsigned short* pShort = reinterpret_cast<unsigned short*>(pLong);
size_t offset = (submesh->useSharedVertices)? shared_offset : current_offset;
if ( use32bitindexes )
{
for ( size_t k = 0; k < numTris*3; ++k)
{
indices[index_offset++] = pLong[k] + static_cast<unsigned long>(offset);
}
}
else
{
for ( size_t k = 0; k < numTris*3; ++k)
{
indices[index_offset++] = static_cast<unsigned long>(pShort[k]) +
static_cast<unsigned long>(offset);
}
}
ibuf->unlock();
current_offset = next_offset;
}
}
