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      1 /*
      2  * Copyright (C) 2011 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 package com.example.android.opengl;
     17 
     18 import java.nio.ByteBuffer;
     19 import java.nio.ByteOrder;
     20 import java.nio.FloatBuffer;
     21 
     22 import javax.microedition.khronos.opengles.GL10;
     23 
     24 /**
     25  * A two-dimensional triangle for use as a drawn object in OpenGL ES 1.0/1.1.
     26  */
     27 public class Triangle {
     28 
     29     private final FloatBuffer vertexBuffer;
     30 
     31     // number of coordinates per vertex in this array
     32     static final int COORDS_PER_VERTEX = 3;
     33     static float triangleCoords[] = {
     34             // in counterclockwise order:
     35             0.0f,  0.622008459f, 0.0f,// top
     36            -0.5f, -0.311004243f, 0.0f,// bottom left
     37             0.5f, -0.311004243f, 0.0f // bottom right
     38     };
     39 
     40     float color[] = { 0.63671875f, 0.76953125f, 0.22265625f, 0.0f };
     41 
     42     /**
     43      * Sets up the drawing object data for use in an OpenGL ES context.
     44      */
     45     public Triangle() {
     46         // initialize vertex byte buffer for shape coordinates
     47         ByteBuffer bb = ByteBuffer.allocateDirect(
     48                 // (number of coordinate values * 4 bytes per float)
     49                 triangleCoords.length * 4);
     50         // use the device hardware's native byte order
     51         bb.order(ByteOrder.nativeOrder());
     52 
     53         // create a floating point buffer from the ByteBuffer
     54         vertexBuffer = bb.asFloatBuffer();
     55         // add the coordinates to the FloatBuffer
     56         vertexBuffer.put(triangleCoords);
     57         // set the buffer to read the first coordinate
     58         vertexBuffer.position(0);
     59     }
     60 
     61     /**
     62      * Encapsulates the OpenGL ES instructions for drawing this shape.
     63      *
     64      * @param gl - The OpenGL ES context in which to draw this shape.
     65      */
     66     public void draw(GL10 gl) {
     67         // Since this shape uses vertex arrays, enable them
     68         gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
     69 
     70         // draw the shape
     71         gl.glColor4f(       // set color:
     72                 color[0], color[1],
     73                 color[2], color[3]);
     74         gl.glVertexPointer( // point to vertex data:
     75                 COORDS_PER_VERTEX,
     76                 GL10.GL_FLOAT, 0, vertexBuffer);
     77         gl.glDrawArrays(    // draw shape:
     78                 GL10.GL_TRIANGLES, 0,
     79                 triangleCoords.length / COORDS_PER_VERTEX);
     80 
     81         // Disable vertex array drawing to avoid
     82         // conflicts with shapes that don't use it
     83         gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
     84     }
     85 }
     86