OpenGL ES: A Gentle Introduction - Beginning Android Games - page 311

Enabling Texturing
There's one more thing to complete before we can draw our triangle with the texture. We need
to bind the texture, and we need to tell OpenGL ES that it should actually apply the texture to
all triangles we render. Whether texture mapping is performed or not is another state of OpenGL
ES, which we can enable and disable with the following methods:
GL10.glEnable(GL10.GL_TEXTURE_2D);
GL10.glDisable(GL10.GL_TEXTURE_2D);
These look vaguely familiar. When we enabled/disabled vertex attributes in the previous
sections, we used glEnableClientState() / glDisableClientState() . As we noted earlier,
those are relics from the infancy of OpenGL itself. There's a reason why those are not
merged with glEnable() / glDisable() , but we won't go into that here. Just remember to use
glEnableClientState() / glDisableClientState() to enable and disable vertex attributes, and
use glEnable() / glDisable() for any other states of OpenGL, such as texturing.
Putting It Together
With that out of our way, we can now write a small example that puts all of this together.
Listing 7-7 shows an excerpt of the TexturedTriangleTest.java source file, listing only the
relevant parts of the TexturedTriangleScreen class contained in it.
Listing 7-7. Excerpt from TexturedTriangleTest.java; Texturing a Triangle
class TexturedTriangleScreen extends Screen {
final int VERTEX_SIZE = (2 + 2) * 4;
GLGraphics glGraphics;
FloatBuffer vertices;
int textureId;
public TexturedTriangleScreen(Game game) {
super (game);
glGraphics = ((GLGame) game).getGLGraphics();
ByteBuffer byteBuffer = ByteBuffer. allocateDirect (3 * VERTEX_SIZE);
byteBuffer.order(ByteOrder. nativeOrder ());
vertices = byteBuffer.asFloatBuffer();
vertices.put( new float [] { 0.0f, 0.0f, 0.0f, 1.0f,
319.0f, 0.0f, 1.0f, 1.0f,
160.0f, 479.0f, 0.5f, 0.0f});
vertices.flip();
textureId = loadTexture("bobrgb888.png");
}
public int loadTexture(String fileName) {
try {
Bitmap bitmap = BitmapFactory. decodeStream (game.getFileIO().readAsset(fileName));
GL10 gl = glGraphics.getGL();