本文介绍一下OpenGL下绘制三维物体的基本方法。编译环境：OpenTK, c#。
以下是OpenGL的基本绘图函数：
1. 绘制正方体
View Code
//draw a cube: solid
void DrawCube(Color color, Vector3d refMarker, Vector3d size)
{
List points = new List(); //points
//back points (anti-clockwise)
points.Add(refMarker);
points.Add(new Vector3d(points[0].X + size.X, points[0].Y, points[0].Z));
points.Add(new Vector3d(points[0].X + size.X, points[0].Y + size.Y, points[0].Z));
points.Add(new Vector3d(points[0].X, points[0].Y + size.Y, points[0].Z));
//front points (anti-clockwise)
points.Add(new Vector3d(points[0].X, points[0].Y, points[0].Z + size.Z));
points.Add(new Vector3d(points[1].X, points[1].Y, points[1].Z + size.Z));
points.Add(new Vector3d(points[2].X, points[2].Y, points[2].Z + size.Z));
points.Add(new Vector3d(points[3].X, points[3].Y, points[3].Z + size.Z));
//sequency
int[] seqs = {
0, 1, 2, 3, //back side
4, 5, 6, 7, //front side
0, 4, 7, 3, //left side
1, 5, 6, 2, //right side
0, 4, 5, 1, //bottom side
3, 7, 6, 2 //tope side
};
GL.ShadeModel(ShadingModel.Flat);
GL.Color3(color);
GL.Begin(BeginMode.Quads);
foreach (int seq in seqs)
{
GL.Vertex3(points[seq]);
}
GL.End();
}
2. 圆筒
View Code
void DrawCylinder(Color color, Vector3d refMarker, double radius, double length, int segments = 20, int sides = 20)
{
GL.Color3(color);
GL.ShadeModel(ShadingModel.Flat);
double thetaSegments = 2 * Math.PI / segments;
double thetaSides = 2 * Math.PI / sides;
//bottom
GL.Begin(BeginMode.Polygon);
for (double i = 0; i < segments; i++)
{
Vector3d point = new Vector3d();
point.X = refMarker.X + radius * Math.Cos(thetaSegments * i);
point.Y = refMarker.Y + radius * Math.Sin(thetaSegments * i);
point.Z = refMarker.Z;
GL.Vertex3(point);
}
GL.End();
//top
GL.Begin(BeginMode.Polygon);
for (double i = 0; i < segments; i++)
{
Vector3d point = new Vector3d();
point.X = refMarker.X + radius * Math.Cos(thetaSegments * i);
point.Y = refMarker.Y + radius * Math.Sin(thetaSegments * i);
point.Z = refMarker.Z + length;
GL.Vertex3(point);
}
GL.End();
//side
GL.Begin(BeginMode.QuadStrip);
for (double i = 0; i <= sides; i++)
{
Vector3d point1 = new Vector3d();
point1.X = refMarker.X + radius * Math.Cos(thetaSides * i);
point1.Y = refMarker.Y + radius * Math.Sin(thetaSides * i);
point1.Z = refMarker.Z;
GL.Vertex3(point1);
Vector3d point2 = new Vector3d();
point2.X = refMarker.X + radius * Math.Cos(thetaSides * i);
point2.Y = refMarker.Y + radius * Math.Sin(thetaSides * i);
point2.Z = refMarker.Z + length;
GL.Vertex3(point2);
}
GL.End();
}
3. 球型
View Code
//draw a sphere: solid
void DrawSphere(Color color, Vector3d refMarker, double radius)
{
int longitudes = 20;
int latitudes = 20;
GL.Color3(color);
GL.ShadeModel(ShadingModel.Smooth);
for (double i = 0; i < latitudes; i++)
{
double lat0 = -Math.PI / 2 + Math.PI/latitudes * i ;
double z0 = Math.Sin(lat0) * radius;
double r0 = Math.Abs(Math.Cos(lat0) * radius);
double lat1 = -Math.PI / 2 + Math.PI / latitudes * (i + 1);
double z1 = Math.Sin(lat1) * radius;
double r1 = Math.Abs(Math.Cos(lat1) * radius);
GL.Begin(BeginMode.QuadStrip);
for (double j = 0; j < longitudes; j++)
{
double lng = 2 * Math.PI * j / longitudes;
double x = Math.Cos(lng);
double y = Math.Sin(lng);
Vector3d pt0 = new Vector3d(x * r0 + refMarker.X, y * r0 + refMarker.Y, z0 + refMarker.Z);
GL.Normal3(pt0);
GL.Vertex3(pt0);
Vector3d pt1 = new Vector3d(x * r1 + refMarker.X, y * r1 + refMarker.Y, z1 + refMarker.Z);
GL.Normal3(pt1);
GL.Vertex3(pt1);
}
GL.End();
}
}
4. Marker
View Code
//Draw a marker void DrawMarker(Color color, Vector3d origin, double size=1) { DrawMarkerAxis(color, origin, new Vector3d(size, 0, 0)); //x DrawMarkerAxis(color, origin, new Vector3d(0, size, 0)); //y DrawMarkerAxis(color, origin, new Vector3d(0, 0, size)); //z } void DrawMarkerAxis(Color color, Vector3d origin, Vector3d size) { double len1 = 0.1; double len2 = 0.05; Listpoints = new List (); points.Add(origin); points.Add(new Vector3d(origin.X + size.X, origin.Y + size.Y, origin.Z+size.Z)); points.Add(new Vector3d(points[1].X * (1 - len1), points[1].Y * (1 - len1), points[1].Z * (1 - len1))); if (size.X != 0) { points.Add(new Vector3d(points[2].X, points[2].Y - len2, points[2].Z)); points.Add(new Vector3d(points[2].X, points[2].Y + len2, points[2].Z)); points.Add(new Vector3d(points[2].X, points[2].Y, points[2].Z - len2)); points.Add(new Vector3d(points[2].X, points[2].Y, points[2].Z + len2)); } else if (size.Y != 0) { points.Add(new Vector3d(points[2].X - len2, points[2].Y, points[2].Z)); points.Add(new Vector3d(points[2].X + len2, points[2].Y, points[2].Z)); points.Add(new Vector3d(points[2].X, points[2].Y, points[2].Z - len2)); points.Add(new Vector3d(points[2].X, points[2].Y, points[2].Z + len2)); } else { points.Add(new Vector3d(points[2].X - len2, points[2].Y, points[2].Z)); points.Add(new Vector3d(points[2].X + len2, points[2].Y, points[2].Z)); points.Add(new Vector3d(points[2].X, points[2].Y - len2, points[2].Z)); points.Add(new Vector3d(points[2].X, points[2].Y + len2, points[2].Z)); } GL.Color3(color); GL.Begin(BeginMode.Lines); GL.Vertex3(points[0]); GL.Vertex3(points[1]); GL.End(); GL.Begin(BeginMode.LineLoop); GL.Vertex3(points[1]); GL.Vertex3(points[3]); GL.Vertex3(points[4]); GL.End(); GL.Begin(BeginMode.LineLoop); GL.Vertex3(points[1]); GL.Vertex3(points[5]); GL.Vertex3(points[6]); GL.End(); }