我应该如何在 3D 引擎中实现视图裁剪平面？

Question

这个项目是在 Java 中完全从头开始编写的。自从 Covid 开始以来我就一直很无聊，所以我想要一些可以占用我时间的东西，并教我一些很酷的东西。不过，我已经在这个问题上停留了大约一个星期了。当我尝试使用我的近平面裁剪方法时，它会将新顶点倾斜到屏幕的另一侧，但有时它工作得很好。

Failure Screenshot

Success Screenshot

所以我的想法可能是因为它有时会起作用，我只是没有在管道中的正确时间进行剪辑？

我从面部剔除和光照开始，

然后我对顶点应用相机视图变换，

然后我在近平面上剪辑

最后我应用了投影矩阵并裁剪了所有剩余的屏幕外三角形

代码：

这将计算交点。抱歉，如果它凌乱或太长，我在编码方面不是很有经验，我的专业是物理，而不是 CS。

public Vertex vectorIntersectPlane(Vector3d planePos, Vector3d planeNorm, Vector3d lineStart, Vector3d lineEnd){

    float planeDot = planeNorm.dotProduct(planePos);
    float startDot = lineStart.dotProduct(planeNorm);
    float endDot = lineEnd.dotProduct(planeNorm);
    float midPoint = (planeDot - startDot) / (endDot - startDot);

    Vector3d lineStartEnd = lineEnd.sub(lineStart);
    Vector3d lineToIntersect = lineStartEnd.scale(midPoint);

    return new Vertex(lineStart.add(lineToIntersect));
}

public float distanceFromPlane(Vector3d planePos, Vector3d planeNorm, Vector3d vert){

    float x = planeNorm.getX() * vert.getX();
    float y = planeNorm.getY() * vert.getY();
    float z = planeNorm.getZ() * vert.getZ();

    return (x + y + z - (planeNorm.dotProduct(planePos)));
}

//When a triangle gets clipped it has 4 possible outcomes
// 1 it doesn't actually need clipping and gets returned
// 2 it gets clipped into 1 new triangle, for testing these are red
// 3 it gets clipped into 2 new triangles, for testing 1 is green, and 1 is blue
// 4 it is outside the view planes and shouldn't be rendered
public void clipTriangles(){

    Vector3d planePos = new Vector3d(0, 0, ProjectionMatrix.fNear, 1f);
    Vector3d planeNorm = Z_AXIS.clone();

    final int length = triangles.size();

    for(int i = 0; i < length; i++) {

        Triangle t = triangles.get(i);

        if(!t.isDraw())
            continue;

        Vector3d[] insidePoint = new Vector3d[3];
        int insidePointCount = 0;

        Vector3d[] outsidePoint = new Vector3d[3];
        int outsidePointCount = 0;

        float d0 = distanceFromPlane(planePos, planeNorm, t.getVerticesVectors()[0]);
        float d1 = distanceFromPlane(planePos, planeNorm, t.getVerticesVectors()[1]);
        float d2 = distanceFromPlane(planePos, planeNorm, t.getVerticesVectors()[2]);

        //Storing distances from plane and counting inside outside points
        {
            if (d0 >= 0){

                insidePoint[insidePointCount] = t.getVerticesVectors()[0];
                insidePointCount++;
            }else{

                outsidePoint[outsidePointCount] = t.getVerticesVectors()[0];
                outsidePointCount++;
            }
            if (d1 >= 0){

                insidePoint[insidePointCount] = t.getVerticesVectors()[1];
                insidePointCount++;
            }else{

                outsidePoint[outsidePointCount] = t.getVerticesVectors()[1];
                outsidePointCount++;
            }
            if (d2 >= 0){

                insidePoint[insidePointCount] = t.getVerticesVectors()[2];
                insidePointCount++;
            }else{

                outsidePoint[outsidePointCount] = t.getVerticesVectors()[2];
            }
        }
     
        //Triangle has 1 point still inside view, remove original triangle add new clipped triangle
        if (insidePointCount == 1) {

            t.dontDraw();

            Vertex newVert1 = vectorIntersectPlane(planePos, planeNorm, insidePoint[0], outsidePoint[0]);
            Vertex newVert2 = vectorIntersectPlane(planePos, planeNorm, insidePoint[0], outsidePoint[1]);
            vertices.add(newVert1);
            vertices.add(newVert2);
            
            //Triangles are stored with vertex references instead of the actual vertex object. 
            Triangle temp = new Triangle(t.getVertKeys()[0], vertices.size() - 2, vertices.size() - 1, vertices);
            temp.setColor(1,0,0, t.getBrightness(), t.getAlpha());
            triangles.add(temp);

            continue;
        }


        //Triangle has two points inside remove original add two new clipped triangles
        if (insidePointCount == 2) {

            t.dontDraw();

            Vertex newVert1 = vectorIntersectPlane(planePos, planeNorm, insidePoint[0], outsidePoint[0]);
            Vertex newVert2 = vectorIntersectPlane(planePos, planeNorm, insidePoint[1], outsidePoint[0]);
            vertices.add(newVert1);
            vertices.add(newVert2);

            Triangle temp = new Triangle(t.getVertKeys()[0], t.getVertKeys()[1], vertices.size() - 1, vertices);
            temp.setColor(0, 1, 0, t.getBrightness(), t.getAlpha());
            triangles.add(temp);

            temp = new Triangle(t.getVertKeys()[0], t.getVertKeys()[1], vertices.size() - 2, vertices);
            temp.setColor(0, 0, 1, t.getBrightness(), t.getAlpha());
            triangles.add(temp);

            continue;
        }
    }
}

Answer 1

我发现了问题，没有为新的剪切三角形提供正确的顶点引用。他们只是被赋予了三角形的第一个顶点，不管它是否在视图内。

我应该如何在 3D 引擎中实现视图裁剪平面？

How should I be implementing a view clipping plane in a 3D Engine?

java

3d

intersection

parametric-equations