现代OpenGL：对象选择（C#，OpenTK）。

我正试图使用C#和OpenTK在OpenGL中实现对象拾取。我基于两个来源，为此写了一个类。

OpenGL射线投射（选取）：考虑对象的变换

https:/www.bfilipek.com201206select-mouse-opengl.html

目前我的代码只是用于计算鼠标指针与任意测试坐标(0,0,0)的距离，但一旦工作起来，在场景中的对象中迭代寻找匹配的对象也不需要太多。

方法是在鼠标指针的下方定义一条射线，在近处和远处的剪切平面之间。然后在这条射线上找到离被测试点最近的点，并返回两者之间的距离。当鼠标指针直接在(0,0,0)上方时，这个距离应该为零，随着鼠标指针向任何方向移动，这个距离就会增加。

谁能帮忙解决这个问题？它的执行没有错误，但返回的距离明显不正确。我明白原理，但不明白计算的细微之处。

虽然我在网上找到了各种例子，其中 几乎 做的，它们一般都是在不同的语言或框架中，或者是使用了废弃的方法，或者是不完整的，或者是不能用的。

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;
    }
}

它是这样叫的。

    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递进来的（按照上面的代码）。我相当确定这些矩阵的内容一定是正确的，因为渲染工作正常，我可以成功地旋转zoom。这就是顶点着色器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))";
            "}";

我用Arcball的一个实现来进行旋转. 缩放是用一个平移来完成的，像这样。

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();
    }

Vector4 pos2 = Vector4.Transform(pos, Matrix4.Invert(projection) * Matrix4.Invert(modelView));

Vector4 pos2 = Vector4.Transform(pos, Matrix4.Invert(modelView * projection));

private void GlControl1_MouseMove(object sender, MouseEventArgs e)
{

    float dist = ObjectPicker.DistanceFromPoint(new Point(e.X,e.Y), new Vector3(0,0,0), model * view, projection);
    // do something with the result

}

public class ObjectPicker{

    public static float DistanceFromPoint(Point mouseLocation, Vector3 testPoint, Matrix4 modelView, Matrix4 projection)
    {

        int[] viewport = new int[4];
        OpenTK.Graphics.OpenGL.GL.GetInteger(OpenTK.Graphics.OpenGL.GetPName.Viewport, viewport);
        Vector3 near = UnProject(new Vector3(mouseLocation.X, mouseLocation.Y, 0), modelView, projection); // start of ray (near plane)
        Vector3 far = UnProject(new Vector3(mouseLocation.X, mouseLocation.Y, 1), modelView, projection); // end of ray (far plane)
        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(projection) * Matrix4.Invert(modelView) );
        Vector3 pos_out = new Vector3(pos2.X, pos2.Y, pos2.Z);

        return pos_out / pos2.W;
    }

}

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