【发布时间】：2020-05-30 20:12:04
【问题描述】：
我正在尝试使用 C# 和 OpenTK 在 OpenGL 中实现对象拾取。我基于两个来源为此目的编写了一个类：
OpenGL ray casting (picking): account for object's transform
https://www.bfilipek.com/2012/06/select-mouse-opengl.html
目前我的代码仅用于计算鼠标指针与 (0,0,0) 的任意测试坐标的距离，但一旦工作，迭代场景中的对象以找到匹配项并不需要太多。
该方法是在鼠标指针下方在近剪裁平面和远剪裁平面之间定义一条射线。然后找到该射线上最接近被测点的点，并返回两者之间的距离。当鼠标指针直接位于 (0,0,0) 上方时，该值应为零，并随着它向任何方向移开而增加。
谁能帮忙解决这个问题？它执行没有错误，但返回的距离显然不正确。我了解原理，但不了解计算的细节。
虽然我在网上找到了各种几乎的例子，但它们通常使用不同的语言或框架和/或使用过时的方法和/或不完整或不起作用。
public class ObjectPicker{
public static float DistanceFromPoint(Point mouseLocation, Vector3 testPoint, Matrix4 modelView, Matrix4 projection)
{
Vector3 near = UnProject(new Vector3(mouseLocation.X, mouseLocation.Y, 0), modelView, projection); // start of ray
Vector3 far = UnProject(new Vector3(mouseLocation.X, mouseLocation.Y, 1), modelView, projection); // end of ray
Vector3 pt = ClosestPoint(near, far, testPoint); // find point on ray which is closest to test point
return Vector3.Distance(pt, testPoint); // return the distance
}
private static Vector3 ClosestPoint(Vector3 A, Vector3 B, Vector3 P)
{
Vector3 AB = B - A;
float ab_square = Vector3.Dot(AB, AB);
Vector3 AP = P - A;
float ap_dot_ab = Vector3.Dot(AP, AB);
// t is a projection param when we project vector AP onto AB
float t = ap_dot_ab / ab_square;
// calculate the closest point
Vector3 Q = A + Vector3.Multiply(AB, t);
return Q;
}
private static Vector3 UnProject(Vector3 screen, Matrix4 modelView, Matrix4 projection)
{
int[] viewport = new int[4];
OpenTK.Graphics.OpenGL.GL.GetInteger(OpenTK.Graphics.OpenGL.GetPName.Viewport, viewport);
Vector4 pos = new Vector4();
// Map x and y from window coordinates, map to range -1 to 1
pos.X = (screen.X - (float)viewport[0]) / (float)viewport[2] * 2.0f - 1.0f;
pos.Y = 1 - (screen.Y - (float)viewport[1]) / (float)viewport[3] * 2.0f;
pos.Z = screen.Z * 2.0f - 1.0f;
pos.W = 1.0f;
Vector4 pos2 = Vector4.Transform( pos, Matrix4.Invert(modelView) * projection );
Vector3 pos_out = new Vector3(pos2.X, pos2.Y, pos2.Z);
return pos_out / pos2.W;
}
}
它是这样称呼的：
private void GlControl1_MouseMove(object sender, MouseEventArgs e)
{
float dist = ObjectPicker.DistanceFromPoint(new Point(e.X,e.Y), new Vector3(0,0,0), model, projection);
this.Text = dist.ToString(); // display in window caption for debugging
}
我知道矩阵是如何被传入的（根据上面的代码）。我很确定这些矩阵的内容一定是正确的，因为渲染效果很好，而且我可以成功地旋转/缩放。这是顶点着色器 FWIW：
string vertexShaderSource =
"# version 330 core\n" +
"layout(location = 0) in vec3 aPos;" +
"layout(location = 1) in vec3 aNormal;" +
"uniform mat4 model; " +
"uniform mat4 view;" +
"uniform mat4 projection;" +
"out vec3 FragPos;" +
"out vec3 Normal;" +
"void main()" +
"{" +
"gl_Position = projection * view * model * vec4(aPos, 1.0);" +
"FragPos = vec3(model * vec4(aPos, 1.0));" +
"Normal = vec3(model * vec4(aNormal, 1.0))";
"}";
我使用 Arcball 的实现进行旋转。缩放是使用翻译完成的，如下所示：
private void glControl1_MouseWheel(object sender, System.Windows.Forms.MouseEventArgs e)
{
zoom += (float)e.Delta / 240;
view = Matrix4.CreateTranslation(0.0f, 0.0f, zoom);
SetMatrix4(Handle, "view", view);
glControl1.Invalidate();
}
【问题讨论】：
标签： c# opengl glsl opentk perspectivecamera