Android OpenGL：爲什麼我缺少2個三角形？

Question

我學習OpenGL（在Android上），在我的代碼中，我指定了4個三角形，形成了一個四面體，但由於某種原因，其中2個邊似乎缺失，我不明白爲什麼。我幾乎以任何我能想到的方式調整了它，但仍然沒有運氣。

這是我的代碼，請告訴我，如果我做錯了什麼。

import java.nio.ByteBuffer; 
import java.nio.ByteOrder; 
import java.nio.FloatBuffer; 
import java.nio.IntBuffer; 

import javax.microedition.khronos.opengles.GL10; 

public class Tetrahedron { 

    private IntBuffer ver; 
    private IntBuffer nor; 
    private ByteBuffer ind; 
    private float[] mat_ambient; 
    private float[] mat_diffuse; 
    private float[] mat_specular; 
    private float[] mat_emission; 

    public Tetrahedron() { 

     int one = toInt(1.0f); 
     int vertices[] = { 
       //face 1 
       -one, -one, one, //point 1 
        0 , one, 0 , //point 2 
       one, -one, one, //point 3 

       //face 2 
        0 , one, 0 , //point 2 
       one, -one, one, //point 3 
        0 , 0 , -one, //point 4 

       //face 3 
       one, -one, one, //point 3 
        0 , 0 , -one, //point 4 
       -one, -one, one, //point 1 

       //face 4 
        0 , 0 , -one, //point 4 
       -one, -one, one, //point 1 
        0 , one, 0 //point 2 

     }; 
     int normals[] = { 
       -one, -one, one, 
        0 , one, one, 
       one, -one, one, 

       one, one, -one, 
       one, 0 , 0 , 
       one, one, -one, 

       one, -one, one, 
        0 , -one, -one, 
       -one, -one, one, 

       -one, one, -one, 
       -one, 0 , 0 , 
       -one, one, -one 
     }; 

     byte indices[] = { 
       0, 1, 2, 
       3, 4, 5, 
       6, 7, 8, 
       9,10,11 

     }; 

     ver=getIntBuffer(vertices); 
     nor=getIntBuffer(normals); 
     ind=getByteBuffer(indices); 

     mat_ambient = new float[4]; 
     mat_ambient[0] = 0.3f; 
     mat_ambient[1] = 0.3f; 
     mat_ambient[2] = 0.3f; 
     mat_ambient[3] = 1.0f; 

     mat_diffuse = new float[4]; 
     mat_diffuse[0] = 0.9f; 
     mat_diffuse[1] = 0.9f; 
     mat_diffuse[2] = 0.9f; 
     mat_diffuse[3] = 1.0f; 

     mat_specular = new float[4]; 
     mat_specular[0] = 0.1f; 
     mat_specular[1] = 0.1f; 
     mat_specular[2] = 0.1f; 
     mat_specular[3] = 1.0f; 

     mat_emission = new float[4]; 
     mat_emission[0] = 0.0f; 
     mat_emission[1] = 1.0f; 
     mat_emission[2] = 0.0f; 
     mat_emission[3] = 1.0f; 

    } 
    private IntBuffer getIntBuffer(int[] data){ 
     ByteBuffer byteBuf = ByteBuffer.allocateDirect(data.length * 4); 
     byteBuf.order(ByteOrder.nativeOrder()); 
     IntBuffer buf = byteBuf.asIntBuffer(); 
     buf.put(data); 
     buf.position(0); 
     return buf; 
    } 
    private ByteBuffer getByteBuffer(byte[] data){ 
     ByteBuffer buf = ByteBuffer.allocateDirect(data.length); 
     buf.put(data); 
     buf.position(0); 
     return buf; 
    } 
    private int toInt(float num){ 
     return (int)(num*65536); 
    } 

    public void draw(GL10 gl){ 
     gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); 
     gl.glEnableClientState(GL10.GL_NORMAL_ARRAY); 


     gl.glMaterialfv(GL10.GL_FRONT_AND_BACK, GL10.GL_AMBIENT, mat_ambient, 0); 
     gl.glMaterialfv(GL10.GL_FRONT_AND_BACK, GL10.GL_DIFFUSE, mat_diffuse, 0); 
     gl.glMaterialfv(GL10.GL_FRONT_AND_BACK, GL10.GL_SPECULAR, mat_specular, 0); 
     gl.glMaterialfv(GL10.GL_FRONT_AND_BACK, GL10.GL_EMISSION, mat_emission, 0); 
     gl.glMaterialf(GL10.GL_FRONT, GL10.GL_SHININESS, 56); 

     gl.glFrontFace(GL10.GL_CW); 
     gl.glVertexPointer(3, GL10.GL_FIXED, 0, ver); 
     gl.glNormalPointer(GL10.GL_FIXED, 0, nor); 
     gl.glDrawElements(GL10.GL_TRIANGLES, ind.capacity(), GL10.GL_UNSIGNED_BYTE, ind); 

     gl.glDisableClientState(GL10.GL_NORMAL_ARRAY); 
     gl.glDisableClientState(GL10.GL_VERTEX_ARRAY); 
    } 
} 

Answer 1

你可以嘗試禁用臉撲殺，只是爲了確保你沒有這些面孔倒退：

gl.glDisable(GL10.GL_CULL_FACE); 
//You should also comment out this: gl.glFrontFace(GL10.GL_CW); 

如果這能解決問題，扭轉問題的三角形的繞組（開關點1和3），然後恢復臉部剔除。