Develop Reference

Drawing animate line on Canvas of a View

I simply need to draw a line which moves from one coordinate of a canvas to another. I am having troubles with synchronizing my drawing code with time.\
public class CustomMYChart extends View {
float x=0,y=0;
Canvas canvas;
Paint paint;
public CustomMYChart(Context context) {
super(context);
// TODO Auto-generated constructor stub
paint = new Paint();
paint.setColor(Color.GREEN);
}
#Override
protected void onDraw(final Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
this.canvas=canvas;
for(int i=0; i<1000; i++){
canvas.drawCircle(x, y, 5, paint);
x+=1;
y+=1;
invalidate();
}
}
}

Just remove the for statement in onDraw, with just one for iteration you call 1000 times invalidate() and then you get x and y out of the screen.
#Override
protected void onDraw(final Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
this.canvas=canvas;
canvas.drawCircle(x, y, 5, paint);
x+=1;
y+=1;
invalidate();
}

animate a Rectangle moving smoothly android view

I have multiple rectangles in the middle of the view (canvas). I want to move them all to the edges of the screen smoothly simultaneously. This is not a jump, i need to see the between positions from start to end so it appear as a smooth transition.
Whats the best way to do that?

Try this code :
public class animatedView extends View {
Bitmap i;
int x=0;
int y=0;
public animatedView(Context context) {
super(context);
// TODO Auto-generated constructor stub
i = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);
}
#Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
Rect bk = new Rect();
bk.set(0, 0, canvas.getWidth(), canvas.getHeight());
Paint pBk = new Paint();
pBk.setStyle(Paint.Style.FILL);
pBk.setColor(Color.BLUE);
canvas.drawRect(bk, pBk);
canvas.drawBitmap(i, x, y, pBk);
x+=10;
invalidate();
}
}
Hope it helps !

How to draw a circle in android?

I'm using this method to draw a circle in my app:
public void drawCircle(){
paint.setColor(Color.rgb(52, 73, 94));
paint.setFlags(Paint.ANTI_ALIAS_FLAG);
canvas.drawCircle(100, 200, 60, paint);
}
The problem is that the circle appears kind of oval and with pixellated edges.
I used the ANTI_ALIAS_FLAG but it didn't work.
How to draw a circle with smooth edges?
EDIT
I using a framework for games. from this book: http://www.amazon.com/Beginning-Android-Games-Mario-Zechner/dp/1430246774

Try This
#Override
public void onDraw(Canvas canvas){
super.onDraw(canvas);
canvas.drawCircle(x, y, radius, paint);
}
For a better reference on drawing custom views check out the official Android documentation
Good Luck!

#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new MyView(this));
}
public class MyView extends View {
public MyView(Context context) {
super(context);
// TODO Auto-generated constructor stub
}
#Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
int x = getWidth();
int y = getHeight();
int radius;
radius = 100;
Paint paint = new Paint();
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.WHITE);
canvas.drawPaint(paint);
// Use Color.parseColor to define HTML colors
paint.setColor(Color.parseColor("#CD5C5C"));
canvas.drawCircle(x / 2, y / 2, radius, paint);
}
}

Android: Canvas not scaling

I have a custom View which draw some bitmaps on canvas in onDraw(). The drawing is working. Look at the code snippet:
#Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
canvas.save();
if(appInitialized) {
hsSide.draw(canvas);
scaleA.draw(canvas);
scaleB.draw(canvas);
}
canvas.scale(mScaleFactor, mScaleFactor, pivotX, pivotY);
canvas.restore();
}
I have implemented a ScaleGestureListener which scale the canvas when pinch zoom is applied on screen. The problem is that canvas is not scaling. if I put canvas.scale(mScaleFactor, mScaleFactor, pivotX, pivotY); before if(appInitialized) { it scales the canvas but after it the drawing i.e. hsSide.draw(canvas); is not scaling. It draws on its normal scale.
Here are draw methods:
hsDide.draw:
#Override
public void draw(Canvas canvas) {
// TODO Auto-generated method stub
canvas.drawBitmap(mBitmap, canvas.getWidth()/2 - mBitmap.getWidth()/2, 0, null);
}
scaleA.draw:
#Override
public void draw(Canvas canvas) {
// TODO Auto-generated method stub
canvas.drawBitmap(mBitmap, canvas.getWidth()/2 - mBitmap.getWidth()/2, canvas.getHeight()/2 - mBitmap.getHeight()/2, null);
}
scaleB.draw:
#Override
public void draw(Canvas canvas) {
// TODO Auto-generated method stub
canvas.save();
mMatrix.setRotate(currentAngle, canvas.getWidth()/2, canvas.getHeight()/2);
canvas.setMatrix(mMatrix);
canvas.drawBitmap(mBitmap, canvas.getWidth()/2 - mBitmap.getWidth()/2, canvas.getHeight()/2 - mBitmap.getHeight()/2, null);
canvas.restore();
}
Any idea where I am going wrong...???

Looking at your code infact, you should scale the canvas before drawing onto it, then restore it once drawn. So move your canvas scale as follows:
#Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
canvas.save();
canvas.scale(mScaleFactor, mScaleFactor, pivotX, pivotY); // MOVED HERE.
if(appInitialized) {
hsSide.draw(canvas);
scaleA.draw(canvas);
scaleB.draw(canvas);
}
canvas.restore();
}
You are then basing the draw size on the canvas size. So when you scale the canvas, you are still drawing it to its entire size, then resizing back to normal size. Hence not getting any effect.
What you need do is take the canvas size BEFORE scaling, then pass this to your draw method too. Then use those sizes to draw onto canvas.

android: How do you scale a circle using a seekbar?

I've drawn a circle programmatically to act as a paint brush, but I'm having trouble scaling it. I've connected the values of the radius to progress in the seekbar methods and they scale numerically, but when I touch my tablet, the brush is still the same size. How do I get the brush to redraw itself constantly scaling while I'm sliding the seekbar?

Here is the code to change the radius of circle on seek bar progress
private class test extends View {
private int radius;
public test(Context context) {
super(context);
// TODO Auto-generated constructor stub
}
#Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
Paint paint = new Paint();
paint.setAntiAlias(false);
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.RED);
// RectF rect = new RectF(100, 100, 200, 200);
// canvas.drawRect(rect, paint);
canvas.drawCircle(50, 50, getRadius(), paint);
canvas.drawLine(10, 10, 10, 10 + 15, paint);
}
/**
* #param radius the radius to set
*/
public void setRadius(int radius) {
this.radius = radius;
}
/**
* #return the radius
*/
public int getRadius() {
return radius;
}
}
in your activity
LinearLayout layout = new LinearLayout(this);
layout.setLayoutParams(new LayoutParams(320, 420));
layout.setOrientation(LinearLayout.VERTICAL);
tt = new test(this);
tt.setLayoutParams(new LayoutParams(100, 200));
layout.addView(tt);
SeekBar bar = new SeekBar(this);
bar.setMax(40);
bar.setOnSeekBarChangeListener(new OnSeekBarChangeListener() {
#Override
public void onStopTrackingTouch(SeekBar seekBar) {
// TODO Auto-generated method stub
}
#Override
public void onStartTrackingTouch(SeekBar seekBar) {
// TODO Auto-generated method stub
}
#Override
public void onProgressChanged(SeekBar seekBar, int progress,
boolean fromUser) {
// TODO Auto-generated method stub
tt.setRadius(progress);
tt.invalidate();
}
});
layout.addView(bar);
setContentView(layout);
Hope useful to you.