2D Game Programming Tricks - Beginning Android Games - page 416

And that is all there is to do. We just eliminated a lot of drawing methods simply by buffering
pre-transformed vertices in a float array and rendering them in one go. That will increase our
2D sprite-rendering performance considerably, compared to the method we were using before.
Fewer OpenGL ES state changes and fewer drawing calls make the GPU happy.
There's one more thing we need to implement: a SpriteBatcher.drawSprite() method that can
draw a rotated sprite. All we need to do is construct the four corner vertices without adding
the position, rotate them around the origin, add the position of the sprite so that the vertices
are placed in the world space, and then proceed as in the previous drawing method. We could
use Vector2.rotate() for this, but that would introduce additional function call overhead. We
therefore reproduce the code in Vector2.rotate() , and optimize where possible. The final
method of the SpriteBatcher class looks like Listing 8-18.
Listing 8-18. The Rest of SpriteBatcher.java; a Method to Draw Rotated Sprites
public void drawSprite( float x, float y, float width, float height, float angle,
TextureRegion region) {
float halfWidth = width / 2;
float halfHeight = height / 2;
float rad = angle * Vector2. TO_RADIANS ;
float cos = FloatMath. cos (rad);
float sin = FloatMath. sin (rad);
float x1 = -halfWidth * cos - (-halfHeight) * sin;
float y1 = -halfWidth * sin + (-halfHeight) * cos;
float x2 = halfWidth * cos - (-halfHeight) * sin;
float y2 = halfWidth * sin + (-halfHeight) * cos;
float x3 = halfWidth * cos - halfHeight * sin;
float y3 = halfWidth * sin + halfHeight * cos;
float x4 = -halfWidth * cos - halfHeight * sin;
float y4 = -halfWidth * sin + halfHeight * cos;
x1 += x;
y1 += y;
x2 += x;
y2 += y;
x3 += x;
y3 += y;
x4 += x;
y4 += y;
verticesBuffer[bufferIndex++] = x1;
verticesBuffer[bufferIndex++] = y1;
verticesBuffer[bufferIndex++] = region.u1;
verticesBuffer[bufferIndex++] = region.v2;
verticesBuffer[bufferIndex++] = x2;
verticesBuffer[bufferIndex++] = y2;
verticesBuffer[bufferIndex++] = region.u2;
verticesBuffer[bufferIndex++] = region.v2;