Question

使用Monotouch和OpenTK我试图获得一个3D点的屏幕坐标。我有我的世界视图投影矩阵设置，OpenGL理解它并完美地投影我的3D模型，但是如何使用相同的矩阵从2D到3D投影一个点？

我以为我可以简单地使用：

Vector3.Transform(ref input3Dpos, ref matWorldViewProjection, out projected2Dpos);

然后将投影屏幕坐标设置为projected2DPos。但是生成的Vector4似乎并不代表正确的投影屏幕坐标。而且我不知道如何从那里计算它。

我发现我需要除以Vector4.w，但是我仍然得到错误的值。现在使用这种方法：

private static bool GluProject(OpenTK.Vector3 objPos, OpenTK.Matrix4 matWorldViewProjection, int[] viewport, out OpenTK.Vector3 screenPos)
{
    OpenTK.Vector4 _in;

    _in.X = objPos.X;
    _in.Y = objPos.Y;
    _in.Z = objPos.Z;
    _in.W = 1f;

    Vector4 _out = OpenTK.Vector4.Transform(_in, matWorldViewProjection);

    if (_out.W <= 0.0)
    {
        screenPos = OpenTK.Vector3.Zero;
        return false;
    }

    _out.X /= _out.W;
    _out.Y /= _out.W;
    _out.Z /= _out.W;
    /* Map x, y and z to range 0-1 */
    _out.X = _out.X * 0.5f + 0.5f;
    _out.Y = -_out.Y * 0.5f + 0.5f;
    _out.Z = _out.Z * 0.5f + 0.5f;

    /* Map x,y to viewport */
    _out.X = _out.X * viewport[2] + viewport[0];
    _out.Y = _out.Y * viewport[3] + viewport[1];

    screenPos.X = _out.X;
    screenPos.Y = _out.Y;
    screenPos.Z = _out.Z;

    return true;
}

我看不到任何错误......：S

Answer 1

在第一个问题中，您错过了最后一步：从NDC（规范化设备坐标）映射到视口坐标。这就是行

/* Map x,y to viewport */
_out.X = _out.X * viewport[2] + viewport[0];
_out.Y = _out.Y * viewport[3] + viewport[1];

在你的GluProject做，

Answer 2

您有两种选择。您可以自己计算，或使用glProject功能。我更喜欢第一个。

第1名：

private Vector2 Convert(
  Vector3 pos, 
  Matrix4 viewMatrix, 
  Matrix4 projectionMatrix, 
  int screenWidth, 
  int screenHeight)
{
    pos = Vector3.Transform(pos, viewMatrix);
    pos = Vector3.Transform(pos, projectionMatrix);
    pos.X /= pos.Z;
    pos.Y /= pos.Z;
    pos.X = (pos.X + 1) * screenWidth / 2;
    pos.Y = (pos.Y + 1) * screenHeight / 2;

    return new Vector2(pos.X, pos.Y);
}

2号：

public Vector2 form3Dto2D(Vector3 our3DPoint)
{
    Vector3 our2DPoint;

    float[] modelviewMatrix =  new float[16];
    float[] projectionMatrix = new float[16];
    int[] viewport = new int[4];

    GL.GetFloat(GetPName.ModelviewMatrix, modelviewMatrix);
    GL.GetFloat(GetPName.ProjectionMatrix, projectionMatrix);
    GL.GetInteger(GetPName.Viewport, viewport);

    OpenTK.Graphics.Glu.Project(our3DPoint, convertFloatsToDoubles(modelviewMatrix),
        convertFloatsToDoubles(projectionMatrix), viewport, out our2DPoint);

    return new Vector2(our2DPoint.X, our2DPoint.Y)
}   

public static double[] convertFloatsToDoubles(float[] input)
{
    if (input == null)
    {
        return null; // Or throw an exception - your choice
    }

    double[] output = new double[input.Length];
    for (int i = 0; i < input.Length; i++)
    {
        output[i] = input[i];
    }
    return output;
}

将3D点投影到2D屏幕坐标OpenTK

2 个答案: