Question

我在网上找到了一个例子，展示了如何在OpenGL中绘制一个锥形，它位于here：它是用C ++编写的，所以我把它翻译成C＃。这是新代码：

        public void RenderCone(Vector3 d, Vector3 a, float h, float rd, int n)
        {
            Vector3 c = new Vector3(a + (-d * h));
            Vector3 e0 = Perp(d);
            Vector3 e1 = Vector3.Cross(e0, d);
            float angInc = (float)(360.0 / n * GrimoireMath.Pi / 180);

            // calculate points around directrix
            List<Vector3> pts = new List<Vector3>();
            for (int i = 0; i < n; ++i)
            {
                float rad = angInc * i;
                Vector3 p = c + (((e0 * (float)Math.Cos((rad)) + (e1 * (float)Math.Sin(rad))) * rd));
                pts.Add(p);
            }

            // draw cone top
            GL.Begin(PrimitiveType.TriangleFan);
            GL.Vertex3(a);
            for (int i = 0; i < n; ++i)
            {
                GL.Vertex3(pts[i]);
            }
            GL.End();

            // draw cone bottom
            GL.Begin(PrimitiveType.TriangleFan);
            GL.Vertex3(c);
            for (int i = n - 1; i >= 0; --i)
            {
                GL.Vertex3(pts[i]);
            }
            GL.End();
        }

        public Vector3 Perp(Vector3 v)
        {
            float min = Math.Abs(v.X);
            Vector3 cardinalAxis = new Vector3(1, 0, 0);
            if (Math.Abs(v.Y) < min)
            {
                min = Math.Abs(v.Y);
                cardinalAxis = new Vector3(0, 1, 0);
            }
            if (Math.Abs(v.Z) < min)
            {
                cardinalAxis = new Vector3(0, 0, 1);
            }
            return Vector3.Cross(v, cardinalAxis);
        }

我认为我正确使用参数（页面在实际功能使用方面并不完全一致）。以下是原创作者提供的图例：

但是当我输入以下参数时：

RenderCone(new Vector3(0.0f, 1.0f, 0.0f), new Vector3(1.0f, 1.0f, 1.0f), 20.0f, 10.0f, 8);

我收到此信息（启用了线框）：

正如你所看到的，无论是在开头还是最后，我都错过了一片。有谁知道这种方法有什么问题？或者我可能做错了会导致锥形不完整？

Answer 1

        // draw cone bottom
        GL.Begin(PrimitiveType.TriangleFan);
        GL.Vertex3(c);
        for (int i = n - 1; i >= 0; --i)
        {
            GL.Vertex3(pts[i]);
        }
        GL.End();

将所有顶点相互连接并居中，但缺少一个连接。从第一个顶点到最后一个顶点没有指定连接。在循环之后添加 GL.Vertex3（pts [n-1]）; 会添加缺少的连接。

Answer 2

解决方案实际上非常简单，我需要将切片数量增加1.如果你问我，那就非常特别。

        public void RenderCone(Vector3 baseToApexLength, Vector3 apexLocation, float height, float radius, int slices)
        {
            Vector3 c = new Vector3(apexLocation + (-baseToApexLength * height));
            Vector3 e0 = Perpendicular(baseToApexLength);
            Vector3 e1 = Vector3.Cross(e0, baseToApexLength);
            float angInc = (float)(360.0 / slices * GrimoireMath.Pi / 180);
            slices++; // this was the fix for my problem.
            /**
             * Compute the Vertices around the Directrix
             */
            Vector3[] vertices = new Vector3[slices];
            for (int i = 0; i < vertices.Length; ++i)
            {
                float rad = angInc * i;
                Vector3 p = c + (((e0 * (float)Math.Cos((rad)) + (e1 * (float)Math.Sin(rad))) * radius));
                vertices[i] = p;
            }

            /**
             * Draw the Top of the Cone.
             */
            GL.Begin(PrimitiveType.TriangleFan);
            GL.Vertex3(apexLocation);
            for (int i = 0; i < slices; ++i)
            {
                GL.Vertex3(vertices[i]);
            }
            GL.End();

            /**
             * Draw the Base of the Cone.
             */
            GL.Begin(PrimitiveType.TriangleFan);
            GL.Vertex3(c);
            for (int i = slices - 1; i >= 0; --i)
            {
                GL.Vertex3(vertices[i]);
            }
            GL.End();
        }

OpenGL Cone功能无法正确绘制

2 个答案: