2D Game Programming Tricks - Beginning Android Games - page 414

the Vertices instance used to render the batch. It also stores the indices that we'll define in a
minute. The member numSprites holds the number drawn so far in the current batch.
public SpriteBatcher(GLGraphics glGraphics, int maxSprites) {
this .verticesBuffer = new float [maxSprites*4*4];
this .vertices = new Vertices(glGraphics, maxSprites*4, maxSprites*6, false , true );
this .bufferIndex = 0;
this .numSprites = 0;
short [] indices = new short [maxSprites*6];
int len = indices.length;
short j = 0;
for ( int i = 0; i < len; i += 6, j += 4) {
indices[i + 0] = ( short )(j + 0);
indices[i + 1] = ( short )(j + 1);
indices[i + 2] = ( short )(j + 2);
indices[i + 3] = ( short )(j + 2);
indices[i + 4] = ( short )(j + 3);
indices[i + 5] = ( short )(j + 0);
}
vertices.setIndices(indices, 0, indices.length);
}
Moving to the constructor, we have two arguments: the GLGraphics instance we need for
creating the Vertices instance, and the maximum number of sprites the batcher should be able
to render in one batch. The first thing we do in the constructor is create the float array. We have
four vertices per sprite, and each vertex takes up four floats (two for the x and y coordinates and
another two for the texture coordinates). We can have maxSprites sprites maximally, so that's
4 × 4 × maxSprites floats that we need for the buffer.
Next, we create the Vertices instance. We need it to store maxSprites × 4 vertices and
maxSprites × 6 indices. We tell the Vertices instance that we have not only positional attributes,
but also texture coordinates for each vertex. We then initialize the bufferIndex and numSprites
members to zero. We create the indices for our Vertices instance. We need to do this only once,
as the indices will never change. The first sprite in a batch will always have the indices 0, 1, 2,
2, 3, 0; the next sprite will have 4, 5, 6, 6, 7, 4; and so on. We can precompute these and store
them in the Vertices instance. This way, we only need to set them once, instead of once for
each sprite.
public void beginBatch(Texture texture) {
texture.bind();
numSprites = 0;
bufferIndex = 0;
}
Next up is the beginBatch() method. It binds the texture and resets the numSprites and
bufferIndex members so that the first sprite's vertices will get inserted at the front of the
verticesBuffer float array.
public void endBatch() {
vertices.setVertices(verticesBuffer, 0, bufferIndex);
vertices.bind();