4-4 下标矩阵

使用下标画矩阵

运行图

result.png

要点

• 修改点的个数,
• 定义索引指向, 0,1,2, 0,2,3
• 绑定 索引buffer 到指定的 target 上面去(GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, indexBufferId);)
• 使用 glDrawElement() 函数来画矩形

做法

1. 修改点的个数, 将点的个数修改为4个.

   static final float squareCoords[] = {
           -0.5f,  0.5f, 0.0f,     1, 0, 0, 0.1f,  // top left
           -0.5f, -0.5f, 0.0f,     0, 1, 0, 0.1f, // bottom left
           0.5f, -0.5f, 0.0f,      0, 0, 1, 0.1f, // bottom right
           0.5f,  0.5f, 0.0f,      1, 1, 0, 0.1f,// top right
   };
   

2. 定义索引指向,并绑定数据到 buffer

   • 定义下标顺序, 3个代表一个三角形.

   static  final short indexs[] = {
           0,1,2,  0,2,3
   };
   

   • 绑定下标属性到的 GL_ELEMENT_ARRAY_BUFFER 上面去

     IntBuffer intBuffer = IntBuffer.allocate(1);
     GLES20.glGenBuffers(1, intBuffer);
     indexBufferId = intBuffer.get(0);

     GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, indexBufferId);
     GLES20.glBufferData(GLES20.GL_ELEMENT_ARRAY_BUFFER, indexs.length * 2, indexBuffer, GLES20.GL_STATIC_DRAW);

     创建 bufferID , 并将bufferID赋值给全局变量, 之后画图的时候调用.

   indexBuffer = BufferUtils.newShortBuffer(indexs.length);
   indexBuffer.put(indexs);
   indexBuffer.position(0);
   
   IntBuffer intBuffer = IntBuffer.allocate(1);
   GLES20.glGenBuffers(1, intBuffer);
   indexBufferId = intBuffer.get(0);
   
   GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, indexBufferId);
   GLES20.glBufferData(GLES20.GL_ELEMENT_ARRAY_BUFFER, indexs.length * 2, indexBuffer, GLES20.GL_STATIC_DRAW);
   

3. 绘制

       //public static native void glDrawElements(        
       //         int mode,
       //        int count,
       //        int type,
       //        int offset
       //);
   
   GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, indexBufferId);
           GLES20.glDrawElements(GLES20.GL_TRIANGLES, indexs.length , GLES20.GL_UNSIGNED_SHORT, 0);
   
   

   ​