我应该如何在 3D 引擎中实现视图剪切平面？

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。

失败截图

成功截图

所以我的想法是，也许因为它有时会起作用，所以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，

然后我夹在近平面上

最后我应用投影矩阵并裁剪任何剩余的屏幕外三角形

代码：

这将计算交点。 抱歉，如果它很乱或太长，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，没有为新的裁剪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。