通过DirectX12工具包进行拾取

Question

我在尝试让3d对象可以用鼠标点击时遇到了问题。对于交叉点检查，我使用光线投射。我找到的代码，为我的解决方案移植：

准确选择

bool RaySphereIntersect(Vector3, Vector3, float);
bool TestIntersection(Matrix projectionMatrix, Matrix viewMatrix, Matrix worldMatrix, Vector3 origin, float radius, int m_screenWidth, int m_screenHeight, int mouseX, int mouseY)
{
float pointX, pointY;
Matrix inverseViewMatrix, translateMatrix, inverseWorldMatrix;
Vector3 direction, rayOrigin, rayDirection;
bool intersect, result;
// Move the mouse cursor coordinates into the -1 to +1 range.
pointX = ((2.0f * (float)mouseX) / (float)m_screenWidth) - 1.0f;
pointY = (((2.0f * (float)mouseY) / (float)m_screenHeight) - 1.0f) * -1.0f;
// Adjust the points using the projection matrix to account for the aspect ratio of the viewport.
pointX = pointX / projectionMatrix._11;
pointY = pointY / projectionMatrix._22;
// Get the inverse of the view matrix.
inverseViewMatrix=XMMatrixInverse(NULL, viewMatrix);
// Calculate the direction of the picking ray in view space.
direction.x = (pointX * inverseViewMatrix._11) + (pointY * inverseViewMatrix._21) + inverseViewMatrix._31;
direction.y = (pointX * inverseViewMatrix._12) + (pointY * inverseViewMatrix._22) + inverseViewMatrix._32;
direction.z = (pointX * inverseViewMatrix._13) + (pointY * inverseViewMatrix._23) + inverseViewMatrix._33;
// Get the origin of the picking ray which is the position of the camera.
// Get the world matrix and translate to the location of the sphere.
// Now get the inverse of the translated world matrix.
inverseWorldMatrix= XMMatrixInverse(NULL, worldMatrix);
// Now transform the ray origin and the ray direction from view space to world space.
rayOrigin=XMVector3TransformCoord(origin, inverseWorldMatrix);
rayDirection=XMVector3TransformNormal(direction, inverseWorldMatrix);
// Normalize the ray direction.
rayDirection=XMVector3Normalize(rayDirection);

// Now perform the ray-sphere intersection test.
intersect = RaySphereIntersect(rayOrigin, rayDirection, radius);
if (intersect == true)
return true;
else
return false;
}

bool RaySphereIntersect(Vector3 rayOrigin, Vector3 rayDirection, float radius)
{
float a, b, c, discriminant;
// Calculate the a, b, and c coefficients.
a = (rayDirection.x * rayDirection.x) + (rayDirection.y * rayDirection.y) + (rayDirection.z * rayDirection.z);
b = ((rayDirection.x * rayOrigin.x) + (rayDirection.y * rayOrigin.y) + (rayDirection.z * rayOrigin.z)) * 2.0f;
c = ((rayOrigin.x * rayOrigin.x) + (rayOrigin.y * rayOrigin.y) + (rayOrigin.z * rayOrigin.z)) - (radius * radius);
// Find the discriminant.
discriminant = (b * b) - (4 * a * c);
// if discriminant is negative the picking ray missed the sphere, otherwise it intersected the sphere.
if (discriminant < 0.0f)
return false;
else
return true;
}

如何创建球体

D3DSphere(float x, float y, float z, float radius, float r, float g, float b, float a)  
{
this->x = x;
this->y = y;
this->z = z;
this->radius = radius;
this->shape = GeometricPrimitive::CreateSphere(radius*2.0f);
this->world = Matrix::Identity;
this->world = XMMatrixMultiply(this->world, Matrix::CreateTranslation(x, y, z));
this->index = vsphere;
d3dsphere[vsphere] = this;
vsphere++;
}

如何将光线投射器称为

void Game::LButtonUp(int x, int y)
{
Vector3 eye(camx, camy, camz);
Vector3 at(Vector3::Zero);
m_view = Matrix::CreateLookAt(eye, at, Vector3::UnitY);
for (int i = 0; i < vsphere; i++)
{
if (TestIntersection(m_projection, m_view, d3dsphere[i]->world, eye, d3dsphere[i]->radius, 800, 600, x, y))
{
MessageBoxW(NULL, L"LOL", L"It works", MB_OK);
break;
}
}
}

单击不会发生任何事情，但如果我垂直于XOY旋转相机，有时单击球体附近，会出现消息框。

---

更新

MessageBox独立地出现在相机角度上，它似乎正确地检测到了交叉点，但相对于窗口中心是镜像的。例如，如果球体位于(0, window.bottom-20)点，那么如果单击(0, 20)点，我将获得MessageBox。

若拾取光线方向的计算是错误的，若它是为左手系统编写的，而我使用右手系统，该怎么办？

Answer 1

可能是因为右手系统，它在DirectX工具包中默认使用，下一节来自caster

pointX = ((2.0f * (float)mouseX) / (float)m_screenWidth) - 1.0f;
pointY = (((2.0f * (float)mouseY) / (float)m_screenHeight) - 1.0f) * -1.0f; 

应更改为

pointX = (((2.0f * (float)mouseX) / (float)m_screenWidth) - 1.0f) * -1.0f;
pointY = (((2.0f * (float)mouseY) / (float)m_screenHeight) - 1.0f); 

重要

由于深度独立性，该代码也会出错，即您可能会选择位于您单击的球体后面的球体。为了解决这个问题，我更改了代码：

float distance3(float x1, float y1, float z1, float x2, float y2, float z2)
{
float dx=x1-x2;
float dy=y1-y2;
float dz=z1-z2;
return sqrt(dx*dx+dy*dy+dz*dz);
}
void Game::LButtonUp(int x, int y)
{
Vector3 eye(camx, camy, camz);
Vector3 at(Vector3::Zero);
m_view = Matrix::CreateLookAt(eye, at, Vector3::UnitY);
int last_index=-1;
float last_distance=99999.0f;//set the obviously highest value, may happen in your scene
for (int i = 0; i < vsphere; i++)
{
if (TestIntersection(m_projection, m_view, d3dsphere[i]->world, eye, d3dsphere[i]->radius, 800, 600, x, y))
{
float distance=distance3(camx,camy,camz, d3dsphere[i]->x, d3dsphere[i]->y, d3dsphere[i]->z);
if(distance<last_distance)
{
last_distance=distance;
last_index=i;
}
}
}
d3dsphere[last_index];//picked sphere 
}