如何解决拾取问题自定义unProject函数
我目前正在使用STL文件查看器。这个使用了Arcball相机:
要在此查看器上提供更多功能(可以处理多个对象),我想实现单击选择。为此,我使用了picking(Pseudo code I have used)
这时,我的代码可以检查2点之间的任何对象3D。但是,将鼠标位置转换为正确的向量集是行不通的:
glm::vec3 range = transform.GetPosition() + ( transform.GetFront() * 1000.0f);
// x and y are cursor position on the screen
glm::vec3 start = UnProject(x,y,transform.GetPosition().z);
glm::vec3 end = UnProject(x,range.z);
/*
The code which iterate over all objects in the scene and checks for collision
between my start / end and the object hitbox
*/
如您所见,我已经尝试过(也许是愚蠢的)将我的起点和终点之间的z距离设置为100 *相机的Front矢量。但这不起作用,因为我得到的向量是不连贯的。
例如,将摄像机放在0 0 0且正面为0 0 -1的位置上,就给了我这组矢量:
开始:0.0000〜,0.0000〜,0.0000〜
末尾:0.0000〜,0.0000〜,0.0000〜
(根据我的逻辑)这是不连贯的,我本来应该更像(Start:0,0,0)(End:0,0,-1000)
我认为我的UnProject函数有问题:
glm::vec3 UnProject(float winX,float winY,float winZ)
{
// Compute (projection x modelView) ^ -1:
glm::mat4 modelView = GetViewMatrix() * glm::mat4(1.0f);
glm::mat4 projection = GetProjectionMatrix(ScreenSize);
const glm::mat4 m = glm::inverse(projection * modelView);
// Need to invert Y since screen Y-origin point down,// while 3D Y-origin points up (this is an OpenGL only requirement):
winY = ScreenSize.cy - winY;
// Transformation of normalized coordinates between -1 and 1:
glm::vec4 in;
in.x = winX / ScreenSize.cx * 2.0 - 1.0;
in.y = winY / ScreenSize.cy * 2.0 - 1.0;
in.z = 2.0 * winZ - 1.0;
in.w = 1.0;
// To world coordinates:
glm::vec4 out(m * in);
if (out.w == 0.0) // Avoid a division by zero
{
return glm::vec3(0.0f);
}
out.w = 1.0 / out.w;
return glm::vec3(out.x * out.w,out.y * out.w,out.z * out.w);
}
由于此函数是伪代码(from here)的基本重写,而且我对数学的了解还很差我真的不知道会出什么问题...
PS:我的视图矩阵(由GetViewMatrix()提供)是正确的(因为我使用它来显示场景)
我的投影矩阵也是正确的
ScreenSize对象带有我的视口大小
解决方法
我发现了问题所在,返回vec3应该通过将每个分量除以透视图而不是乘以透视图来完成。这是新的UnProject函数:
glm::vec3 UnProject2(float winX,float winY,float winZ){
glm::mat4 View = GetViewMatrix() * glm::mat4(1.0f);
glm::mat4 projection = GetProjectionMatrix(ScreenSize);
glm::mat4 viewProjInv = glm::inverse(projection * View);
winY = ScreenSize.cy - winY;
glm::vec4 clickedPointOnSreen;
clickedPointOnSreen.x = ((winX - 0.0f) / (ScreenSize.cx)) *2.0f -1.0f;
clickedPointOnSreen.y = ((winY - 0.0f) / (ScreenSize.cy)) * 2.0f -1.0f;
clickedPointOnSreen.z = 2.0f*winZ-1.0f;
clickedPointOnSreen.w = 1.0f;
glm::vec4 clickedPointOrigin = viewProjInv * clickedPointOnSreen;
return glm::vec3(clickedPointOrigin.x / clickedPointOrigin.w,clickedPointOrigin.y / clickedPointOrigin.w,clickedPointOrigin.z / clickedPointOrigin.w);
}
我还更改了开始和结束的计算方式:
glm::vec3 start = UnProject2(x,y,0.0f);
glm::vec3 end = UnProject2(x,1.0f);
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