Develop Reference

Motion to draw numbers on android

im new to this android things. And i have to develop an application that can help an autism to learn numbers. I have a few ideas and I've been trying to learn and implement the code. But it's failed. The question is how can i apply the motion code or sprite to draw a numbers or letter? For example like this, i wanna make the penguin move through the line and draw a number nine.
There is example from mybringback.com which is the image move to draw a rectangle. How can i implement it to draw a number? Im sorry if i asking too much, i just trying to get some ideas.

I think that you should first build an utility program, in order to create the "path vector".
What I mean by path vector is simply a vector of Points (where a point has x value, and y value). And your utility should let you draw whatever you want, with a simple pen. You should draw on surface and store points when mouse is down, and ignore points when mouse is up.
Then, in the main program, you will just have to read at the path of your number/letter.
I've tried to implement something like this for the Sugar OLPC platform, without serializing path into files : I was able to draw, and to view the animation. And I used the process I've just described you.
Hope it can help you.
P.S : I used the word mouse, but you guessed that I talk about finger ...

There are various ways to achieve animation effects. One approach that is quite versatile involves creating a custom View or SurfaceView in which you Override the onDraw method. Various tutorials can be found on this; the official Android discussion of it is here:
http://developer.android.com/guide/topics/graphics/2d-graphics.html#on-view
Your implementation will look something like this:
// Find elapsed time since previous draw
// Compute new position of drawable/bitmap along figure
// Draw bitmap in appropriate location
// Add line to buffer containing segments of curve drawn so far
// Render all segments in curve buffer
// Take some action to call for the rendering of the next frame (this may be done in another thread)
Obviously a simplification. For a very simplistic tutorial, see here:
http://www.techrepublic.com/blog/software-engineer/bouncing-a-ball-on-androids-canvas/1733/
Note that different implementations of this technique will require different levels of involvement by you; for example, if you use a SurfaceView, you are in charge of calling the onDraw method, whereas subclassing the normal View lets you leave Android in charge of redrawing (at the expense of limiting your ability to draw on a different thread). In this respect, Google remains your friend =]

Moving between two points in canvas

I have 2 points(x1,y1) and (x2,y2). I need to move the image from (x1,y1) to (x2,y2). Please let me know if there is any methods in android SDK to achieve this.

If you are doing a custom view that handles it's on onDraw method you could:
Create a path object:
Move to position 1 using the moveTo method
line to position 2 using the line2 method
Create a path measure object.
User the path measure object to animate to the position.(Here is an example of that--note you will have to do it a little differently as the code doesn't show View.onDraw & View.invalidate being called).
Alternatively if you aren't handling your own on draw, you might be able to simply use a TranslateAnimation.

Looks like all you need is an animation.
Search this site for Animation Drawable and you'll get tons of examples :)

Drawing curved lines in AndEngine

I am new to AndEngine and very happy that it's very easy and exciting thing to do. Unfortunately I am unable to draw a curved line in AndEngine.
Actually my scenario is that I have an animated sprite say Object. I want to move this object on a Line with the points given onToucing and dragging it. Now the problem is that I can't find any method to draw a line on points in a way that it does not produce corners. I want a smooth line with no corners.
Suppose I touch the object and drag it on the screen with the points of a square type region. But I don't want the corners in it. I want curves. Previously I am doing this by using quadTo(..) function of android to do this. All I want is a complete alternative to quadto function in AndEngine but with same functionality.

You have to stitch together the curved line from many many small straight lines.
Moving an object along a line is a very different task though. You'd want to have a look at CubicBezierMoveModifier and QuadraticBezierMoveModifier for those.
Maybe you can actually use the code in those modifiers to create your 'smooth' line.

Trying to modify simple Android shape tutorial to use images, having trouble

I am following the below tutorial:
http://www3.ntu.edu.sg/home/ehchua/programming/android/Android_2D.html
In it,
Canvas canvas.drawOval();
is called in order to have a default circle drawn, that bounces around. My normal way of learning a new graphics framework is to build on this, and then upgrade to images. Normally, this is very simple, but I"m having trouble here. There is no equivalent "drawImage" to the drawOval command (which I'm more used to).
Instead, I'm trying to figure out "drawables".
So, following another tutorial (specifically the default Android "snake" game), I tried doing:
Resources r = this.getContext().getResources();
in my view, then passed the resource object to my ball object, to get:
img = r.getDrawable(R.drawable.ball);
where ball is a file stored in /res/drawable/ball.png
In the ball objects draw method (which I call in the view's onDraw method), I have:
img.draw(canvas);
canvas is passed from onDraw, which is itself passed a canvas. I don't really understand who is calling onDraw (I assume some internal process), but this differs from the snake example where they make their own canvas?
Either way, this doesn't seem to work. I am not getting any image, or any errors. I know that img is at least populated (its not null or anything), but other than that I don't really know what to do...
If this were Ruby (my most familiar language), I'd call inspect on the img to see if actually has anything in it...is there an equivalent for Java (or should I fool around with break points)?
Is there anything obvious that I'm doing wrong? Can I not use the default canvas I'm being passed, even though I clearly can for drawing simple shapes?

Ah, I figured it out:
With the draw oval method, I needed to set the bounds like so:
RectF bounds.set(ballX-ballRadius, ballY-ballRadius, ballX+ballRadius, ballY+ballRadius);
But for the drawable object, I have to go one step further and say
img.setBounds(bounds);
and make bounds be a Rect instead of a RectF.
Once that is done, voila, things are rendering.
It didn't occur to me at first that the bounds are how things know where to render themselves, and while you pass the bounds to an oval, you have to SET them to a drawable.

Android: tween animation of a bitmap

My app implements its own sprites by calling the following in my view's onDraw() method:
canvas.drawBitmap(sprite.getBitmap(), sprite.getX(), sprite.getY(), null);
The app is a physics simulation, and so far this has worked out great. But now I'd like to enhance the animation by morphing between images for the sprites when certain events occur.
For example- when a collision happens, I would like to play an animation of an explosion. My idea was to replace the usual sprite bitmap with that of an explosion PNG, and use Android "tween animation" to make the explosion grow larger.
But the Android tween animation example assumes that you have an ImageView defined somewhere statically in your XML configuration.
Is there a way to animate a bitmap as drawn in onDraw() using tween animation? Or do I need to convert my sprites to use some sort of ImageView? If the latter, can you point me to an example of proper sprite animation in Android?
Thanks

I built a generic Tween Engine in java that you can use to animate anything, including your sprites. It's optimized for Android and games because it does not allocate anything at runtime, to avoid any garbage collection. Moreover, Tweens are pooled, so really: no garbage collection at all!
You can see a complete demo here as an android application, or here as a WebGL html page (requires Chrome)!
All you have to do is implement the TweenAccessor interface to add Tween support to all your sprites. You don't even have to change your Sprite class, just create a SpriteTweenAccessor class that implements TweenAccessor<Sprite>, and register it to the engine at initialization. Just have a look at the GetStarted wiki page ;)
http://code.google.com/p/java-universal-tween-engine/
I'm also building a visual timeline editor that can be embedded in any application. It will feature a timeline similar to the Flash authoring tool and Expression Blend (a Silverlight dev tool).
The whole engine is heavily documented (all public methods and classes have detailed javadoc), and the syntax is quite similar to Greensock's TweenMax/TweenLite engine that is used in the Flash world. Note that it supports every Robert Penner easing equation.
// Arguments are (1) the target, (2) the type of interpolation,
// and (3) the duration in seconds. Additional methods specify
// the target values, and the easing function.
Tween.to(mySprite, Type.POSITION_XY, 1.0f).target(50, 50).ease(Elastic.INOUT);
// Possibilities are:
Tween.to(...); // interpolates from the current values to the targets
Tween.from(...); // interpolates from the given values to the current ones
Tween.set(...); // apply the target values without animation (useful with a delay)
Tween.call(...); // calls a method (useful with a delay)
// Current options are:
yourTween.delay(0.5f);
yourTween.repeat(2, 0.5f);
yourTween.repeatYoyo(2, 0.5f);
yourTween.pause();
yourTween.resume();
yourTween.setCallback(callback);
yourTween.setCallbackTriggers(flags);
yourTween.setUserData(obj);
// You can of course chain everything:
Tween.to(...).delay(1.0f).repeat(2, 0.5f).start();
// Moreover, slow-motion, fast-motion and reverse play is easy,
// you just need to change the speed of the update:
yourTween.update(delta * speed);
Of course, no tween engine would be complete without providing a way to build powerful sequences :)
Timeline.createSequence()
// First, set all objects to their initial positions
.push(Tween.set(...))
.push(Tween.set(...))
.push(Tween.set(...))
// Wait 1s
.pushPause(1.0f)
// Move the objects around, one after the other
.push(Tween.to(...))
.push(Tween.to(...))
.push(Tween.to(...))
// Then, move the objects around at the same time
.beginParallel()
.push(Tween.to(...))
.push(Tween.to(...))
.push(Tween.to(...))
.end()
// And repeat the whole sequence 2 times
// with a 0.5s pause between each iteration
.repeatYoyo(2, 0.5f)
// Let's go!
.start();
I hope you're convinced :) There are a lot of people already using the engine in their games or for android UI animation.

You can do the tween animation without the ImageView coming from an xml file, but it does need to actually be a View in your view hierarchy.
The drawing you're doing in your Canvas is opaque to the view hierarchy. I think you have two options:
Overlay an ImageView on top of your custom view and animate that using tween animations.
Use Canvas draw routines to animate your explosion.
I'd say that using Canvas routines, along with their maxtrix transformations, makes sense given that you probably already have an animation thread in your app.

You could draw and animate your explosion in Adobe Flash, export the sprite images using swfSheet or similar and then use Frame animation

If you are creating a game, you can use Vectors(Mathematical) to update the position of your images and then draw then with getX and getY. You should iterate and update this vector in some direction through some speed.
Those Vectors are not native (Game APIs has).
You need have a loop to iterate and update the position, then redraw.
For games, it's not a good idea to have components such ImageViews to make animations. They need the system to calc all the layout again and again over time.