2D Game Programming Tricks - Beginning Android Games - page 417

verticesBuffer[bufferIndex++] = x3;
verticesBuffer[bufferIndex++] = y3;
verticesBuffer[bufferIndex++] = region.u2;
verticesBuffer[bufferIndex++] = region.v1;
verticesBuffer[bufferIndex++] = x4;
verticesBuffer[bufferIndex++] = y4;
verticesBuffer[bufferIndex++] = region.u1;
verticesBuffer[bufferIndex++] = region.v1;
numSprites++;
}
}
We do the same as in the simpler drawing method, except that we construct all four corner
points instead of just the two opposite ones. This is needed for the rotation. The rest is the same
as before.
What about scaling? We do not explicitly need another method, since scaling a sprite only
requires scaling its width and height. We can do that outside the two drawing methods, so
there's no need to have another bunch of methods for the scaled drawing of sprites.
And that's the big secret behind lightning-fast sprite rendering with OpenGL ES.
Using the SpriteBatcher Class
Now we can incorporate the TextureRegion and SpriteBatcher classes in our cannon example.
Copy the TextureAtlas example and rename it SpriteBatcherTest . The classes contained in it
can be called SpriteBatcherTest and SpriteBatcherScreen .
We get rid of the Vertices members in the screen class. We don't need them anymore, since the
SpriteBatcher will do all the dirty work for us. Instead, we add the following members:
TextureRegion cannonRegion;
TextureRegion ballRegion;
TextureRegion bobRegion;
SpriteBatcher batcher;
We now have a TextureRegion for each of the three objects in our atlas, as well as a
SpriteBatcher .
Next, modify the constructor of the screen. Get rid of all the Vertices instantiation and
initialization code, and replace it with a single line of code:
batcher = new SpriteBatcher(glGraphics, 100);
That will set our batcher member to a fresh SpriteBatcher instance that can render 100 sprites
in one batch.