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      */
Triangle()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      */
draw(GL10 gl)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