Game Development Reference
In-Depth Information
Removing Unnecessary State Changes
Let's look at the
present()
method of
BobTest
and see what we can change. Here's the snippet,
in which we add the
FPSCounter
and also use
glRotatef()
and
glScalef()
):
@Override
public void
present(
float
deltaTime) {
GL10 gl = glGraphics.getGL();
gl.glViewport(0, 0, glGraphics.getWidth(), glGraphics.getHeight());
gl.glClearColor(1,0,0,1);
gl.glClear(GL10.
GL_COLOR_BUFFER_BIT
);
gl.glMatrixMode(GL10.
GL_PROJECTION
);
gl.glLoadIdentity();
gl.glOrthof(0, 320, 0, 480, 1, -1);
gl.glEnable(GL10.
GL_TEXTURE_2D
);
bobTexture.bind();
gl.glMatrixMode(GL10.
GL_MODELVIEW
);
for
(
int
i = 0; i <
NUM_BOBS
; i++) {
gl.glLoadIdentity();
gl.glTranslatef(bobs[i].x, bobs[i].y, 0);
gl.glRotatef(45, 0, 0, 1);
gl.glScalef(2, 0.5f, 1);
bobModel.draw(GL10.
GL_TRIANGLES
, 0, 6);
}
fpsCounter.logFrame();
}
The first thing we could do is move the calls to
glViewport()
and
glClearColor()
, as well as
the method calls that set the projection matrix to the
BobScreen.resume()
method. The clear
color will never change; the viewport and the projection matrix won't change either. Why not
put the code to set up all persistent OpenGL states like the viewport or projection matrix
in the constructor of
BobScreen
? Well, we need to battle context loss. All OpenGL ES state
modifications we perform will get lost, and when our screen's
resume()
method is called, we
know that the context has been re-created and thus is missing all the states that we might have
set before. We can also put
glEnable()
and the texture-binding call into the
resume()
method.
After all, we want texturing to be enabled all the time, and we also only want to use that single
texture containing Bob's image. For good measure, we also call
texture.reload()
in the
resume()
method, so that our texture image data is also reloaded in the case of a context loss.
Here are our modified
present()
and
resume()
methods:
@Override
public void
resume() {
GL10 gl = glGraphics.getGL();
gl.glViewport(0, 0, glGraphics.getWidth(), glGraphics.getHeight());
gl.glClearColor(1, 0, 0, 1);
gl.glMatrixMode(GL10.
GL_PROJECTION
);
gl.glLoadIdentity();
gl.glOrthof(0, 320, 0, 480, 1, -1);
