透视投影 - 我怎么项目，该项目背后“照相机”点？ [英] Perspective projection - how do I project points which are behind 'camera'?

问题描述

我用Java编写自己的软件光栅，我跑了与它的一些麻烦......看看样本图像，请：

I'm writing my own software rasterizer in Java, and I ran into some trouble with it... take a look at a sample image, please:

图片

此示例只是画简单的方形网格在一个平面上。一切工作正常，直到我将相机足够接近一些点来移动它后面。在此之后，他们不再正确投影，你可以看到（垂直线 - 投影到屏幕上方点应该是后面相机）。

This sample just draw simple square grid on a plane. Everything works fine until I move camera close enough for some points to move behind it. After that, they're no longer projected correctly, as you can see (vertical lines - points that should be behind camera are projected on top of the screen).

我的转换矩阵和向量相同的DirectX那些使用（PerspectiveFovLH投影，LookAtLH相机）。

My transformation matrices and vectors are same ones DirectX is using (PerspectiveFovLH for projection, LookAtLH for camera).

我用下面的方法改造项目三维点：

I'm using following transformation method to project 3D point:

1. 3D矢量进行改造创建。
2. 矢量乘以ViewProjection矩阵。

3. 在此之后，点转换使用下面的方法来筛选：

1. 3D vector to be transformed is created.
2. Vector is multiplied by ViewProjection matrix.

3. After that, point is transformed to screen using following method:

// 'vector' is input vector in projection space
// projection to screen
double vX = vector.x / vector.z;        
double vY = vector.y / vector.z;


//translate
//surfaceW is width and surfaceH is height of the rendering window.
vX = (( vX + 1.0f) / 2.0f) * surfaceW;
vY = ((-vY + 1.0f) / 2.0f) * surfaceH;


return new Vector3(vX, vY, vector.z);

正如我刚才所说，它工作正常，直到后面的摄像头点移动。事实是，我可以计算出，当点的背后是相机（通过测试它的Z值后的最终变换），但因为我是画线和其他线路基础的对象，我不能只跳过了这一点。

As I said earlier, it works fine until point moves behind camera. The fact is, I can figure out when the point is behind camera (by testing it's Z value after final transform), but since I'm drawing lines and other line based objects, I can't just skip that point.

然后我试图根据设定我的转换管道的 Direct3D的转换管道的文章在MSDN上。

Then I tried setting my transformation pipeline according to The Direct3D Transformation Pipeline article on MSDN.

不幸的是，我还没有得到任何运气的同时（相同的结果），所以任何帮助将是非常美联社preciated，因为我有点坚持这一点。

Unfortunately, I haven't had any luck with that as well (same results), so any help would be highly appreciated, since I'm a bit stuck on this one.

感谢你。

最好的问候， 亚历克斯

Best Regards, Alex

推荐答案

您需要相交在三维空间中前剪裁平面的线与截断线，所以你只画线段这是明显的：

You need to intersect the line with the front clipping plane in 3d space and truncate the line so you only draw the line segment that's visible:

             |
             |
             |
x------------+-----------o
             |
             |
             |   * - camera
             |
             |
             |
       clipping plane

您已经有了一个行 XO ，其中 X 的裁剪平面的前面， 0 后面。这相交线与裁剪平面生成点 + 。你知道哪些 X 和 0 可见，所以吸取 X中的行到 + 。

You've got a line xo where x in front of the clipping plane and o behind it. Intersect this line with the clipping plane to generate the point +. You know which of x and o is visible so draw the line from x to +.

这样你不投射点，这是背后的摄像头。

This way you're not projecting points which are behind the camera.

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