Android OpenGL ES 简明开发教程 06

前面的例子尽管使用了OpenGL ES 3D图形库，但绘制的还是二维图形（平面上的正方形）。Mesh（网格，三角面）是构成空间形体的基本元素，前面的正方形也是有两个Mesh构成的。本篇将介绍使用Mesh构成四面体，椎体等基本空间形体。

Design设计

在使用OpenGL 框架时一个好的设计原则是使用“Composite Pattern”，本篇采用如下设计：

Mesh

首先定义一个基类 Mesh,所有空间形体最基本的构成元素为Mesh（三角形网格） ，其基本定义如下：

1 public class Mesh {
2  // Our vertex buffer.
3  private FloatBuffer verticesBuffer = null;
4
5  // Our index buffer.
6  private ShortBuffer indicesBuffer = null;
7
8  // The number of indices.
9  private int numOfIndices = -1;
10
11  // Flat Color
12  private float[] rgba
13  = new float[] { 1.0f, 1.0f, 1.0f, 1.0f };
14
15  // Smooth Colors
16  private FloatBuffer colorBuffer = null;
17
18  // Translate params.
19  public float x = 0;
20
21  public float y = 0;
22
23  public float z = 0;
24
25  // Rotate params.
26  public float rx = 0;
27
28  public float ry = 0;
29
30  public float rz = 0;
31
32  public void draw(GL10 gl) {
33  // Counter-clockwise winding.
34  gl.glFrontFace(GL10.GL_CCW);
35  // Enable face culling.
36  gl.glEnable(GL10.GL_CULL_FACE);
37  // What faces to remove with the face culling.
38  gl.glCullFace(GL10.GL_BACK);
39  // Enabled the vertices buffer for writing and
40  //to be used during
41  // rendering.
42  gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
43  // Specifies the location and data format
44  //of an array of vertex
45  // coordinates to use when rendering.
46  gl.glVertexPointer(3, GL10.GL_FLOAT, 0, verticesBuffer);
47  // Set flat color
48  gl.glColor4f(rgba[0], rgba[1], rgba[2], rgba[3]);
49  // Smooth color
50  if (colorBuffer != null) {
51  // Enable the color array buffer to be
52  //used during rendering.
53  gl.glEnableClientState(GL10.GL_COLOR_ARRAY);
54  gl.glColorPointer(4, GL10.GL_FLOAT, 0, colorBuffer);
55  }
56
57  gl.glTranslatef(x, y, z);
58  gl.glRotatef(rx, 1, 0, 0);
59  gl.glRotatef(ry, 0, 1, 0);
60  gl.glRotatef(rz, 0, 0, 1);
61
62  // Point out the where the color buffer is.
63  gl.glDrawElements(GL10.GL_TRIANGLES, numOfIndices,
64  GL10.GL_UNSIGNED_SHORT, indicesBuffer);
65  // Disable the vertices buffer.
66  gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
67  // Disable face culling.
68  gl.glDisable(GL10.GL_CULL_FACE);
69  }
70
71  protected void setVertices(float[] vertices) {
72  // a float is 4 bytes, therefore
73  //we multiply the number if
74  // vertices with 4.
75  ByteBuffer vbb
76  = ByteBuffer.allocateDirect(vertices.length * 4);
77  vbb.order(ByteOrder.nativeOrder());
78  verticesBuffer = vbb.asFloatBuffer();
79  verticesBuffer.put(vertices);
80  verticesBuffer.position(0);
81  }
82
83  protected void setIndices(short[] indices) {
84  // short is 2 bytes, therefore we multiply
85  //the number if
86  // vertices with 2.
87  ByteBuffer ibb
88  = ByteBuffer.allocateDirect(indices.length * 2);
89  ibb.order(ByteOrder.nativeOrder());
90  indicesBuffer = ibb.asShortBuffer();
91  indicesBuffer.put(indices);
92  indicesBuffer.position(0);
93  numOfIndices = indices.length;
94  }
95
96  protected void setColor(float red, float green,
97  float blue, float alpha) {
98  // Setting the flat color.
99  rgba[0] = red;
100  rgba[1] = green;
101  rgba[2] = blue;
102  rgba[3] = alpha;
103  }
104
105  protected void setColors(float[] colors) {
106  // float has 4 bytes.
107  ByteBuffer cbb
108  = ByteBuffer.allocateDirect(colors.length * 4);
109  cbb.order(ByteOrder.nativeOrder());
110  colorBuffer = cbb.asFloatBuffer();
111  colorBuffer.put(colors);
112  colorBuffer.position(0);
113  }
114 }

• setVertices 允许子类重新定义顶点坐标。
• setIndices 允许子类重新定义顶点的顺序。
• setColor /setColors允许子类重新定义颜色。
• x,y,z 定义了平移变换的参数。
• rx,ry,rz 定义旋转变换的参数。

Plane

有了Mesh定义之后，再来构造Plane，plane可以有宽度，高度和深度，宽度定义为沿X轴方向的长度，深度定义为沿Z轴方向长度，高度为Y轴方向。

Segments为形体宽度，高度，深度可以分成的份数。 Segments在构造一个非均匀分布的Surface特别有用，比如在一个游戏场景中，构造地貌，使的Z轴的值随机分布在-0.1到0.1之间，然后给它渲染好看的材质就可以造成地图凹凸不平的效果。

上面图形中Segments为一正方形，但在OpenGL中我们需要使用三角形，所有需要将Segments分成两个三角形。为Plane 定义两个构造函数：

// Let you decide the size of the plane but still only one segment.
public Plane(float width, float height)

// For alla your settings.
public Plane(float width, float height, int widthSegments, int heightSegments)

比如构造一个1 unit 宽和 1 unit高，并分成4个Segments，使用图形表示如下：

左边的图显示了segments ,右边的图为需要创建的Face（三角形）。

Plane类的定义如下：

1 public class Plane extends Mesh {
2  public Plane() {
3  this(1, 1, 1, 1);
4  }
5
6  public Plane(float width, float height) {
7  this(width, height, 1, 1);
8  }
9
10  public Plane(float width, float height, int widthSegments,
11  int heightSegments) {
12  float[] vertices
13  = new float[(widthSegments + 1)
14  * (heightSegments + 1) * 3];
15  short[] indices
16  = new short[(widthSegments + 1)
17  * (heightSegments + 1)* 6];
18
19  float xOffset = width / -2;
20  float yOffset = height / -2;
21  float xWidth = width / (widthSegments);
22  float yHeight = height / (heightSegments);
23  int currentVertex = 0;
24  int currentIndex = 0;
25  short w = (short) (widthSegments + 1);
26  for (int y = 0; y < heightSegments + 1; y++) {
27  for (int x = 0; x < widthSegments + 1; x++) {
28  vertices[currentVertex] = xOffset + x * xWidth;
29  vertices[currentVertex + 1] = yOffset + y * yHeight;
30  vertices[currentVertex + 2] = 0;
31  currentVertex += 3;
32
33  int n = y * (widthSegments + 1) + x;
34
35  if (y < heightSegments && x < widthSegments) {
36  // Face one
37  indices[currentIndex] = (short) n;
38  indices[currentIndex + 1] = (short) (n + 1);
39  indices[currentIndex + 2] = (short) (n + w);
40  // Face two
41  indices[currentIndex + 3] = (short) (n + 1);
42  indices[currentIndex + 4] = (short) (n + 1 + w);
43  indices[currentIndex + 5] = (short) (n + 1 + w - 1);
44
45  currentIndex += 6;
46  }
47  }
48  }
49
50  setIndices(indices);
51  setVertices(vertices);
52  }
53 }

Cube

下面来定义一个正方体（Cube），为简单起见，这个四面体只可以设置宽度，高度，和深度，没有和Plane一样提供Segments支持。

1 public class Cube extends Mesh {
2  public Cube(float width, float height, float depth) {
3  width  /= 2;
4  height /= 2;
5  depth  /= 2;
6
7  float vertices[] = { -width, -height, -depth, // 0
8  width, -height, -depth, // 1
9  width,  height, -depth, // 2
10  -width,  height, -depth, // 3
11  -width, -height,  depth, // 4
12  width, -height,  depth, // 5