ok in the android cube example, it shows the draw() function wrapped in the runnable run(), and handler callbacks, etc are used.
public class CubeWallpaper1 extends WallpaperService {
private final Handler mHandler = new Handler();
@Override
public void onCreate() {
super.onCreate();
}
@Override
public void onDestroy() {
super.onDestroy();
}
@Override
public Engine onCreateEngine() {
return new CubeEngine();
}
class CubeEngine extends Engine {
private final Paint mPaint = new Paint();
private float mOffset;
private float mTouchX = -1;
private float mTouchY = -1;
private long mStartTime;
private float mCenterX;
private float mCenterY;
private final Runnable mDrawCube = new Runnable() {
public void run() {
drawFrame();
}
};
private boolean mVisible;
CubeEngine() {
// Create a Paint to draw the lines for our cube
final Paint paint = mPaint;
paint.setColor(0xffffffff);
paint.setAntiAlias(true);
paint.setStrokeWidth(2);
paint.setStrokeCap(Paint.Cap.ROUND);
paint.setStyle(Paint.Style.STROKE);
mStartTime = SystemClock.elapsedRealtime();
}
@Override
public void onCreate(SurfaceHolder surfaceHolder) {
super.onCreate(surfaceHolder);
// By default we don't get touch events, so enable them.
setTouchEventsEnabled(true);
}
@Override
public void onDestroy() {
super.onDestroy();
mHandler.removeCallbacks(mDrawCube);
}
@Override
public void onVisibilityChanged(boolean visible) {
mVisible = visible;
if (visible) {
drawFrame();
} else {
mHandler.removeCallbacks(mDrawCube);
}
}
@Override
public void onSurfaceChanged(SurfaceHolder holder, int format, int width, int height) {
super.onSurfaceChanged(holder, format, width, height);
// store the center of the surface, so we can draw the cube in the right spot
mCenterX = width/2.0f;
mCenterY = height/2.0f;
drawFrame();
}
@Override
public void onSurfaceCreated(SurfaceHolder holder) {
super.onSurfaceCreated(holder);
}
@Override
public void onSurfaceDestroyed(SurfaceHolder holder) {
super.onSurfaceDestroyed(holder);
mVisible = false;
mHandler.removeCallbacks(mDrawCube);
}
@Override
public void onOffsetsChanged(float xOffset, float yOffset,
float xStep, float yStep, int xPixels, int yPixels) {
mOffset = xOffset;
drawFrame();
}
/*
* Store the position of the touch event so we can use it for drawing later
*/
@Override
public void onTouchEvent(MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_MOVE) {
mTouchX = event.getX();
mTouchY = event.getY();
} else {
mTouchX = -1;
mTouchY = -1;
}
super.onTouchEvent(event);
}
/*
* Draw one frame of the animation. This method gets called repeatedly
* by posting a delayed Runnable. You can do any drawing you want in
* here. This example draws a wireframe cube.
*/
void drawFrame() {
final SurfaceHolder holder = getSurfaceHolder();
Canvas c = null;
try {
c = holder.lockCanvas();
if (c != null) {
// draw something
drawCube(c);
drawTouchPoint(c);
}
} finally {
if (c != null) holder.unlockCanvasAndPost(c);
}
// Reschedule the next redraw
mHandler.removeCallbacks(mDrawCube);
if (mVisible) {
mHandler.postDelayed(mDrawCube, 1000 / 25);
}
}
/*
* Draw a wireframe cube by drawing 12 3 dimensional lines between
* adjacent corners of the cube
*/
void drawCube(Canvas c) {
c.save();
c.translate(mCenterX, mCenterY);
c.drawColor(0xff000000);
drawLine(c, -400, -400, -400, 400, -400, -400);
drawLine(c, 400, -400, -400, 400, 400, -400);
drawLine(c, 400, 400, -400, -400, 400, -400);
drawLine(c, -400, 400, -400, -400, -400, -400);
drawLine(c, -400, -400, 400, 400, -400, 400);
drawLine(c, 400, -400, 400, 400, 400, 400);
drawLine(c, 400, 400, 400, -400, 400, 400);
drawLine(c, -400, 400, 400, -400, -400, 400);
drawLine(c, -400, -400, 400, -400, -400, -400);
drawLine(c, 400, -400, 400, 400, -400, -400);
drawLine(c, 400, 400, 400, 400, 400, -400);
drawLine(c, -400, 400, 400, -400, 400, -400);
c.restore();
}
/*
* Draw a 3 dimensional line on to the screen
*/
void drawLine(Canvas c, int x1, int y1, int z1, int x2, int y2, int z2) {
long now = SystemClock.elapsedRealtime();
float xrot = ((float)(now - mStartTime)) / 1000;
float yrot = (0.5f - mOffset) * 2.0f;
float zrot = 0;
// 3D transformations
// rotation around X-axis
float newy1 = (float)(Math.sin(xrot) * z1 + Math.cos(xrot) * y1);
float newy2 = (float)(Math.sin(xrot) * z2 + Math.cos(xrot) * y2);
float newz1 = (float)(Math.cos(xrot) * z1 - Math.sin(xrot) * y1);
float newz2 = (float)(Math.cos(xrot) * z2 - Math.sin(xrot) * y2);
// rotation around Y-axis
float newx1 = (float)(Math.sin(yrot) * newz1 + Math.cos(yrot) * x1);
float newx2 = (float)(Math.sin(yrot) * newz2 + Math.cos(yrot) * x2);
newz1 = (float)(Math.cos(yrot) * newz1 - Math.sin(yrot) * x1);
newz2 = (float)(Math.cos(yrot) * newz2 - Math.sin(yrot) * x2);
// 3D-to-2D projection
float startX = newx1 / (4 - newz1 / 400);
float startY = newy1 / (4 - newz1 / 400);
float stopX = newx2 / (4 - newz2 / 400);
float stopY = newy2 / (4 - newz2 / 400);
c.drawLine(startX, startY, stopX, stopY, mPaint);
}
/*
* Draw a circle around the current touch point, if any.
*/
void drawTouchPoint(Canvas c) {
if (mTouchX >=0 && mTouchY >= 0) {
c.drawCircle(mTouchX, mTouchY, 80, mPaint);
}
}
}
}
but should not the draw() method be replaced in areas like onVisibilityChanged with
handler.post(mDrawCube);
because it seems to me that the cube is being written outside of the thread. i'm sure i'm wrong but would like verification : ). is the only function of the thread to cover the destruction of the app, and not for calling in onVisibilityChanged, onSurfaceChanged, onOffsetsChanged?
ah! now i get it. the thread is also run under the draw() method itself. i totally missed that. so whenever drawFrame is called the thread is called through the handler. crazy it seems very loopy.