Android OpenGL ES 简明开发教程六真正的3D图形

最新推荐文章于 2021-05-23 08:32:10 发布

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最新推荐文章于 2021-05-23 08:32:10 发布

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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：

public class Mesh { // Our vertex buffer. private FloatBuffer verticesBuffer = null;  // Our index buffer. private ShortBuffer indicesBuffer = null;  // The number of indices. private int numOfIndices = -1;  // Flat Color private float[] rgba = new float[] { 1.0f, 1.0f, 1.0f, 1.0f };  // Smooth Colors private FloatBuffer colorBuffer = null;  // Translate params. public float x = 0;  public float y = 0;  public float z = 0;  // Rotate params. public float rx = 0;  public float ry = 0;  public float rz = 0;  public void draw(GL10 gl) { // Counter-clockwise winding. gl.glFrontFace(GL10.GL_CCW); // Enable face culling. gl.glEnable(GL10.GL_CULL_FACE); // What faces to remove with the face culling. gl.glCullFace(GL10.GL_BACK); // Enabled the vertices buffer for writing and //to be used during // rendering. gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); // Specifies the location and data format //of an array of vertex // coordinates to use when rendering. gl.glVertexPointer(3, GL10.GL_FLOAT, 0, verticesBuffer); // Set flat color gl.glColor4f(rgba[0], rgba[1], rgba[2], rgba[3]); // Smooth color if (colorBuffer != null) { // Enable the color array buffer to be //used during rendering. gl.glEnableClientState(GL10.GL_COLOR_ARRAY); gl.glColorPointer(4, GL10.GL_FLOAT, 0, colorBuffer); }  gl.glTranslatef(x, y, z); gl.glRotatef(rx, 1, 0, 0); gl.glRotatef(ry, 0, 1, 0); gl.glRotatef(rz, 0, 0, 1);  // Point out the where the color buffer is. gl.glDrawElements(GL10.GL_TRIANGLES, numOfIndices, GL10.GL_UNSIGNED_SHORT, indicesBuffer); // Disable the vertices buffer. gl.glDisableClientState(GL10.GL_VERTEX_ARRAY); // Disable face culling. gl.glDisable(GL10.GL_CULL_FACE); }  protected void setVertices(float[] vertices) { // a float is 4 bytes, therefore //we multiply the number if // vertices with 4. ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length * 4); vbb.order(ByteOrder.nativeOrder()); verticesBuffer = vbb.asFloatBuffer(); verticesBuffer.put(vertices); verticesBuffer.position(0); }  protected void setIndices(short[] indices) { // short is 2 bytes, therefore we multiply //the number if // vertices with 2. ByteBuffer ibb = ByteBuffer.allocateDirect(indices.length * 2); ibb.order(ByteOrder.nativeOrder()); indicesBuffer = ibb.asShortBuffer(); indicesBuffer.put(indices); indicesBuffer.position(0); numOfIndices = indices.length; }  protected void setColor(float red, float green, float blue, float alpha) { // Setting the flat color. rgba[0] = red; rgba[1] = green; rgba[2] = blue; rgba[3] = alpha; }  protected void setColors(float[] colors) { // float has 4 bytes. ByteBuffer cbb = ByteBuffer.allocateDirect(colors.length * 4); cbb.order(ByteOrder.nativeOrder()); colorBuffer = cbb.asFloatBuffer(); colorBuffer.put(colors); colorBuffer.position(0); }}

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：

public class Plane extends Mesh { public Plane() { this(1, 1, 1, 1); }  public Plane(float width, float height) { this(width, height, 1, 1); }  public Plane(float width, float height, int widthSegments, int heightSegments) { float[] vertices = new float[(widthSegments + 1) * (heightSegments + 1) * 3]; short[] indices = new short[(widthSegments + 1) * (heightSegments + 1)* 6];  float xOffset = width / -2; float yOffset = height / -2; float xWidth = width / (widthSegments); float yHeight = height / (heightSegments); int currentVertex = 0; int currentIndex = 0; short w = (short) (widthSegments + 1); for (int y = 0; y < heightSegments + 1; y++) { for (int x = 0; x < widthSegments + 1; x++) { vertices[currentVertex] = xOffset + x * xWidth; vertices[currentVertex + 1] = yOffset + y * yHeight; vertices[currentVertex + 2] = 0; currentVertex += 3;  int n = y * (widthSegments + 1) + x;  if (y < heightSegments && x < widthSegments) { // Face one indices[currentIndex] = (short) n; indices[currentIndex + 1] = (short) (n + 1); indices[currentIndex + 2] = (short) (n + w); // Face two indices[currentIndex + 3] = (short) (n + 1); indices[currentIndex + 4] = (short) (n + 1 + w); indices[currentIndex + 5] = (short) (n + 1 + w - 1);  currentIndex += 6; } } }  setIndices(indices); setVertices(vertices); }}

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。

public class Cube extends Mesh { public Cube(float width, float height, float depth) { width  /= 2; height /= 2; depth  /= 2;  float vertices[] = { -width, -height, -depth, // 0 width, -height, -depth, // 1 width,  height, -depth, // 2 -width,  height, -depth, // 3 -width, -height,  depth, // 4 width, -height,  depth, // 5 width,  height,  depth, // 6 -width,  height,  depth, // 7 };  short indices[] = { 0, 4, 5, 0, 5, 1, 1, 5, 6, 1, 6, 2, 2, 6, 7, 2, 7, 3, 3, 7, 4, 3, 4, 0, 4, 7, 6, 4, 6, 5, 3, 0, 1, 3, 1, 2, };  setIndices(indices); setVertices(vertices); }}

Group

Group可以用来管理多个空间几何形体，如果把Mesh比作Android的View ,Group可以看作Android的ViewGroup，Android的View的设计也是采用的“Composite Pattern”。

Group的主要功能是把针对Group的操作（如draw)分发到Group中的每个成员对应的操作（如draw)。

Group定义如下：

public class Group extends Mesh { private Vector<Mesh> children = new Vector<Mesh>();  @Override public void draw(GL10 gl) { int size = children.size(); for( int i = 0; i < size; i++) children.get(i).draw(gl); }  /** * @param location * @param object * @see java.util.Vector#add(int, java.lang.Object) */ public void add(int location, Mesh object) { children.add(location, object); }  /** * @param object * @return * @see java.util.Vector#add(java.lang.Object) */ public boolean add(Mesh object) { return children.add(object); }  /** * * @see java.util.Vector#clear() */ public void clear() { children.clear(); }  /** * @param location * @return * @see java.util.Vector#get(int) */ public Mesh get(int location) { return children.get(location); }  /** * @param location * @return * @see java.util.Vector#remove(int) */ public Mesh remove(int location) { return children.remove(location); }  /** * @param object * @return * @see java.util.Vector#remove(java.lang.Object) */ public boolean remove(Object object) { return children.remove(object); }  /** * @return * @see java.util.Vector#size() */ public int size() { return children.size(); } }