//helper function for ray terrain intersection
static bool cellIntersect(float h1, float h2, float h3, float h4, float X, float Y,
const WFMath::Vector<3> &nDir, float dirLen,
const WFMath::Point<3> &sPt, WFMath::Point<3> &intersection,
WFMath::Vector<3> &normal, float &par)
{
//ray plane intersection roughly using the following:
//parametric ray eqn: p=po + par V
//plane eqn: p dot N + d = 0
//
//intersection:
// -par = (po dot N + d ) / (V dot N)
//
//
// effectively we calculate the ray parametric variable for the
// intersection of the plane corresponding to each triangle
// then clip them by endpints of the ray, and by the sides of the square
// and by the diagonal
//
// if they both still intersect, then we choose the earlier intersection
//intersection points for top and bottom triangles
WFMath::Point<3> topInt, botInt;
//point to use in plane equation for both triangles
WFMath::Vector<3> p0 = WFMath::Vector<3>(X, Y, h1);
// square is broken into two triangles
// top triangle |/
bool topIntersected = false;
WFMath::Vector<3> topNormal(h2-h3, h1-h2, 1.0);
topNormal.normalize();
float t = Dot(nDir, topNormal);
float topP=0.0;
if ((t > 1e-7) || (t < -1e-7)) {
topP = - (Dot((sPt-WFMath::Point<3>(0.,0.,0.)), topNormal)
- Dot(topNormal, p0)) / t;
topInt = sPt + nDir*topP;
//check the intersection is inside the triangle, and within the ray extents
if ((topP <= dirLen) && (topP > 0.0) &&
(topInt[0] >= X ) && (topInt[1] <= Y + 1 ) &&
((topInt[0] - topInt[1]) <= (X - Y)) ) {
topIntersected=true;
}
}
// bottom triangle /|
bool botIntersected = false;
WFMath::Vector<3> botNormal(h1-h4, h4-h3, 1.0);
botNormal.normalize();
float b = Dot(nDir, botNormal);
float botP=0.0;
if ((b > 1e-7) || (b < -1e-7)) {
botP = - (Dot((sPt-WFMath::Point<3>(0.,0.,0.)), botNormal)
- Dot(botNormal, p0)) / b;
botInt = sPt + nDir*botP;
//check the intersection is inside the triangle, and within the ray extents
if ((botP <= dirLen) && (botP > 0.0) &&
(botInt[0] <= X + 1 ) && (botInt[1] >= Y ) &&
((botInt[0] - botInt[1]) >= (X - Y)) ) {
botIntersected = true;
}
}
if (topIntersected && botIntersected) { //intersection with both
if (botP <= topP) {
intersection = botInt;
normal = botNormal;
par=botP/dirLen;
if (botP == topP) {
normal += topNormal;
normal.normalize();
}
return true;
}
else {
intersection = topInt;
normal = topNormal;
par=topP/dirLen;
return true;
}
}
else if (topIntersected) { //intersection with top
intersection = topInt;
normal = topNormal;
par=topP/dirLen;
return true;
}
else if (botIntersected) { //intersection with bot
intersection = botInt;
normal = botNormal;
par=botP/dirLen;
return true;
}
return false;
}
//helper function for ray terrain intersection
static bool cellIntersect(float h1, float h2, float h3, float h4,
float X, float Y,
const std::tuple<float, float, float> &nDir, float dirLen,
const WFMath::Point<3> &sPt,
WFMath::Point<3> &intersection,
std::tuple<float, float, float> &normal, float &par)
{
//ray plane intersection roughly using the following:
//parametric ray eqn: p=po + par V
//plane eqn: p dot N + d = 0
//
//intersection:
// -par = (po dot N + d ) / (V dot N)
//
//
// effectively we calculate the ray parametric variable for the
// intersection of the plane corresponding to each triangle
// then clip them by endpints of the ray, and by the sides of the square
// and by the diagonal
//
// if they both still intersect, then we choose the earlier intersection
//intersection points for top and bottom triangles
WFMath::Point<3> topInt, botInt;
//point to use in plane equation for both triangles
std::tuple<float, float, float> p0 = std::tuple<float, float, float>(X, Y, h1);
// square is broken into two triangles
// top triangle |/
bool topIntersected = false;
std::tuple<float, float, float> topNormal(h2 - h3, h1 - h2, 1.0);
normalise_i(topNormal);
float t = dot(nDir, topNormal);
decltype(t) topP = 0.0;
if ((t > 1e-7) || (t < -1e-7))
{
topP = -(dot(std::tuple<float, float, float>(sPt[0], sPt[1], sPt[2]), topNormal)
- dot(topNormal, p0)) / t;
topInt = translate(sPt, scale(nDir, topP));
//check the intersection is inside the triangle, and within the ray extents
if ((topP <= dirLen) && (topP > 0.0) &&
(topInt[0] >= X ) && (topInt[1] <= Y + 1 ) &&
((topInt[0] - topInt[1]) <= (X - Y)) )
{
topIntersected = true;
}
}
// bottom triangle /|
bool botIntersected = false;
std::tuple<float, float, float> botNormal(h1 - h4, h4 - h3, 1.0);
normalise_i(botNormal);
auto b = dot(nDir, botNormal);
decltype(b) botP = 0.0;
if ((b > 1e-7) || (b < -1e-7))
{
botP = -(dot(std::tuple<float, float, float>(sPt[0], sPt[1], sPt[2]), botNormal)
- dot(botNormal, p0)) / b;
botInt = translate(sPt, scale(nDir, botP));
//check the intersection is inside the triangle, and within the ray extents
if ((botP <= dirLen) && (botP > 0.0) &&
(botInt[0] <= X + 1 ) && (botInt[1] >= Y ) &&
((botInt[0] - botInt[1]) >= (X - Y)) )
{
botIntersected = true;
}
}
if (topIntersected && botIntersected) //intersection with both
{
if (botP <= topP)
{
intersection = botInt;
normal = botNormal;
par = botP / dirLen;
if (botP == topP)
{
add_i(normal, topNormal);
normalise_i(normal);
}
return true;
}
else
{
intersection = topInt;
normal = topNormal;
par = topP / dirLen;
return true;
}
}
else if (topIntersected) //intersection with top
{
intersection = topInt;
normal = topNormal;
par = topP / dirLen;
return true;
}
else if (botIntersected) //intersection with bot
{
intersection = botInt;
normal = botNormal;
par = botP / dirLen;
return true;
}
return false;
}
