使用下標(biāo)畫矩陣

運(yùn)行圖

result.png

要點(diǎn)

• 修改點(diǎn)的個(gè)數(shù),
• 定義索引指向, 0,1,2, 0,2,3
• 綁定 索引buffer 到指定的 target 上面去(GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, indexBufferId);)
• 使用 glDrawElement() 函數(shù)來(lái)畫矩形

做法

1. 修改點(diǎn)的個(gè)數(shù), 將點(diǎn)的個(gè)數(shù)修改為4個(gè).

   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. 定義索引指向,并綁定數(shù)據(jù)到 buffer

   • 定義下標(biāo)順序, 3個(gè)代表一個(gè)三角形.

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

   • 綁定下標(biāo)屬性到的 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);

     創(chuàng)建 bufferID , 并將bufferID賦值給全局變量, 之后畫圖的時(shí)候調(diào)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. 繪制

       //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);
   
   

   ?