Question

我使用地形为这些课程选择了鼠标（但使用了c ++）

https://www.youtube.com/watch?v=DLKN0jExRIM&index=29&listhLoLuZVfUksDP http://antongerdelan.net/opengl/raycasting.html

问题是鼠标的位置与光线与地体相交的地方不对应： problem 在垂直方向上有一个很大的错误，有点水平。不要看阴影，这不是正常的校正地图。有什么不对？我的代码：

  void MousePicker::update() {

  view = cam->getViewMatrix();

  currentRay = calculateMouseRay();
  if (intersectionInRange(0, RAY_RANGE, currentRay)) {
    currentTerrainPoint = binarySearch(0, 0, RAY_RANGE, currentRay);
  }
  else {
    currentTerrainPoint = vec3();
  }
}
vec3 MousePicker::calculateMouseRay() {    
  glfwGetCursorPos(win, &mouseInfo.xPos, &mouseInfo.yPos);
  vec2 normalizedCoords = getNormalizedCoords(mouseInfo.xPos, mouseInfo.yPos);
  vec4 clipCoords = vec4(normalizedCoords.x, normalizedCoords.y, -1.0f, 1.0f);
  vec4 eyeCoords = toEyeCoords(clipCoords);
  vec3 worldRay = toWorldCoords(eyeCoords);

  return worldRay;
}

vec2 MousePicker::getNormalizedCoords(double xPos, double yPos) {
  GLint width, height;
  glfwGetWindowSize(win, &width, &height);
  //GLfloat x = (2.0 * xPos) / width  - 1.0f;   
  GLfloat x = -((width - xPos) / width - 0.5f) * 2.0f;
  //GLfloat y = 1.0f - (2.0f * yPos) / height;
  GLfloat y = ((height - yPos) / height - 0.5f) * 2.0f;
  //float z = 1.0f;
  mouseInfo.normalizedCoords = vec2(x, y);

  return vec2(x,y);
}

vec4 MousePicker::toEyeCoords(vec4 clipCoords) {
  vec4 invertedProjection = inverse(projection) * clipCoords;
  //vec4 eyeCoords = translate(invertedProjection, clipCoords);
  mouseInfo.eyeCoords = vec4(invertedProjection.x, invertedProjection.y, -1.0f, 0.0f);
  return vec4(invertedProjection.x, invertedProjection.y, -1.0f, 0.0f);
}

vec3 MousePicker::toWorldCoords(vec4 eyeCoords) {
  vec3 rayWorld = vec3(inverse(view) * eyeCoords);
  vec3 mouseRay = vec3(rayWorld.x, rayWorld.y, rayWorld.z);
  rayWorld = normalize(rayWorld);
  mouseInfo.worldRay = rayWorld;
  return rayWorld;
}

//*********************************************************************************

vec3 MousePicker::getPointOnRay(vec3 ray, float distance) {
  vec3 camPos = cam->getCameraPos();  
  vec3 start = vec3(camPos.x, camPos.y, camPos.z);
  vec3 scaledRay = vec3(ray.x * distance, ray.y * distance, ray.z * distance);
  return vec3(start + scaledRay);
}

vec3 MousePicker::binarySearch(int count, float start, float finish, vec3 ray) {
  float half = start + ((finish - start) / 2.0f);
  if (count >= RECURSION_COUNT) {
    vec3 endPoint = getPointOnRay(ray, half);
    //Terrain* ter = &getTerrain(endPoint.x, endPoint.z);
    if (terrain != NULL) {
      return endPoint;
    }
    else {
      return vec3();
    }
  }

  if (intersectionInRange(start, half, ray)) {
    return binarySearch(count + 1, start, half, ray);
  }
  else {
    return binarySearch(count + 1, half, finish, ray);
  }  
}

bool MousePicker::intersectionInRange(float start, float finish, vec3 ray) {
  vec3 startPoint = getPointOnRay(ray, start);
  vec3 endPoint = getPointOnRay(ray, finish);
  if (!isUnderGround(startPoint) && isUnderGround(endPoint)) {
    return true;
  }
  else {
    return false;
  }  
}

bool MousePicker::isUnderGround(vec3 testPoint) {
  //Terrain* ter = &getTerrain(testPoint.x, testPoint.z);
  float height = 0;
  if (terrain != NULL) {
    height = terrain->getHeightPoint(testPoint.x, testPoint.z);
    mouseInfo.height = height;
  }
  if (testPoint.y < height) {
    return true;
  }
  else {
    return false;
  }

}

Terrain MousePicker::getTerrain(float worldX, float worldZ) {
  return *terrain;
}

Answer 1

在透视投影中，从眼睛位置到屏幕上的点的光线可以由2个点定义。第一点是 eye （相机）位置，在视图空间中是（0,0,0）。第二点必须通过屏幕上的位置计算必须将屏幕位置转换为范围从（-1，-1）到（1,1）的标准化设备坐标。

w = with of the viewport
h = height of the viewport
x = X position of the mouse
y = Y position ot the mouse

GLfloat ndc_x = 2.0 * x/w - 1.0;
GLfloat ndc_y = 1.0 - 2.0 * y/h; // invert Y axis

要计算光线上的一个点，该点穿过相机位置并通过屏幕上的点，必须知道视野和透视投影的纵横比：

fov_y  = vertical field of view angle in radians
aspect = w / h

GLfloat   tanFov = tan( fov_y * 0.5 );
glm::vec3 ray_P  = vec3( ndc_x * aspect * tanFov, ndc_y * tanFov, -1.0 ) );

从相机位置到屏幕上某点的光线可以通过以下位置（P0）和标准化方向（dir）在世界空间中定义：

view = view matrix

glm::mat4 invView = glm::inverse( view );

glm::vec3 P0  = invView * glm::vec3(0.0f, 0.0f, 0.0f); 
           // = glm::vec3( view[3][0], view[3][1], view[3][2] ); 

glm::vec3 dir = glm::normalize( invView * ray_P - P0 );

在这种情况下，以下问题的答案也会很有趣：

应用于您的代码会导致以下更改：

透视投影矩阵如下所示：

r = right, l = left, b = bottom, t = top, n = near, f = far

2*n/(r-l)      0              0               0
0              2*n/(t-b)      0               0
(r+l)/(r-l)    (t+b)/(t-b)    -(f+n)/(f-n)   -1    
0              0              -2*f*n/(f-n)    0

它如下：

aspect = w / h
tanFov = tan( fov_y * 0.5 );

p[0][0] = 2*n/(r-l) = 1.0 / (tanFov * aspect)
p[1][1] = 2*n/(t-b) = 1.0 / tanFov

从屏幕（鼠标）坐标转换为标准化设备坐标：

vec2 MousePicker::getNormalizedCoords(double x, double y) {

    GLint w, h;
    glfwGetWindowSize(win, &width, &height);

    GLfloat ndc_x = 2.0 * x/w - 1.0;
    GLfloat ndc_y = 1.0 - 2.0 * y/h; // invert Y axis
    mouseInfo.normalizedCoords = vec2(ndc_x, ndc_x);
    return vec2(ndc_x, ndc_x);
}

通过世界空间中屏幕上的一个点（鼠标位置）计算摄像机位置的光线：

vec3 MousePicker::calculateMouseRay( void ) {    
    glfwGetCursorPos(win, &mouseInfo.xPos, &mouseInfo.yPos);
    vec2 normalizedCoords = getNormalizedCoords(mouseInfo.xPos, mouseInfo.yPos);

    ray_Px = normalizedCoords.x / projection[0][0]; // projection[0][0] == 1.0 / (tanFov * aspect)
    ray_Py = normalizedCoords.y / projection[1][1]; // projection[1][1] == 1.0 / tanFov
    glm::vec3 ray_P = vec3( ray_Px, ray_Py, -1.0f ) );

    vec3      camPos  = cam->getCameraPos();  // == glm::vec3( view[3][0], view[3][1], view[3][2] );     
    glm::mat4 invView = glm::inverse( view ); 

    glm::vec3 P0  = camPos; 
    glm::vec3 dir = glm::normalize( invView * ray_P - P0 );
    return dir;
}

老鼠采摘小姐

1 个答案: