Develop Reference

Clear canvas and draw again inside it

I'm trying to create a "clear all" button in my app, but it doesn't work. This is the code I use to create and use the canvas:
public DrawingView(Context context, AttributeSet attrs) {
super(context, attrs);
setLayerType(LAYER_TYPE_HARDWARE, null);
startActivity = System.currentTimeMillis();
setupDrawing();
}
public void setDimension (DisplayMetrics displaymetrics) {
height = displaymetrics.heightPixels;
width = displaymetrics.widthPixels;
diameter = width;
if (height < width){
diameter = height;
}
offset = (int) (0.32*diameter);
diameter -= offset;
String imageName = protocol+draw;
}
//setup drawing
private void setupDrawing(){
//prepare for drawing and setup paint stroke properties
drawPath = new Path();
drawPaint = new Paint();
drawPaint.setColor(paintColor);
drawPaint.setAntiAlias(true);
drawPaint.setStrokeWidth(5);
drawPaint.setStyle(Paint.Style.STROKE);
drawPaint.setStrokeJoin(Paint.Join.ROUND);
drawPaint.setStrokeCap(Paint.Cap.ROUND);
canvasPaint = new Paint(Paint.DITHER_FLAG);
}
//size assigned to view
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
drawCanvas = new Canvas(canvasBitmap);
}
//draw the view - will be called after touch event
#Override
protected void onDraw(Canvas canvas) {
canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
canvas.drawPath(drawPath, drawPaint);
canvas.drawRect(width/2 - diameter/2 ,
(70),
width/2 + diameter/2,
1100, drawPaint);
}
And this is the code I used to clear the screen, but pressing the button nothing showed up:
public void restoreDraw () {
drawPath = null;
canvasBitmap = Bitmap.createBitmap(width, 350, Bitmap.Config.ARGB_8888);
drawPath = new Path();
}
Should I clear the bitmap canvas, right?

You have to add requestLayout() inside restoreDraw() method.
public void restoreDraw () {
drawPath = null;
canvasBitmap = Bitmap.createBitmap(width, 350, Bitmap.Config.ARGB_8888);
drawPath = new Path();
requestLayout();
}

Draw line on canvas and modify the position after it's been drawn

I need help with this thing
I draw line on canvas and i need to be able to modify the position after it's been drawn. I search and try a lot of things, but no one seems that it works
I want to select one of the ends of the line and dragging them in another position
Can someone give me and advice?

Please try this.In this you can draw and edit the line.
class Drawing extends View{
private Canvas mCanvas = null;
private Path mPath = null;
private Paint mBitmapPaint = null;
private Bitmap mBitmap = null;
private Bitmap bit=null;
private Paint mPaint = null;
private MainActivity baseMainActivity = null;
public interface onDrawingViewSingleTap{
void onDrawingViewTap(float x , float y);
}
public Drawing(Context c) {
super(c);
baseMainActivity=(MainActivity) c;
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(Color.YELLOW);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(6);//This sets the width of signature
Display display =baseMainActivity.getWindowManager().getDefaultDisplay();
mBitmap = Bitmap.createBitmap(display.getWidth(), display.getHeight(), Bitmap.Config.ARGB_8888);// 320*480 // For setting size of screen to draw Bitmap
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
mCanvas = new Canvas(mBitmap);
onDraw(mCanvas);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}
#Override
protected void onDraw(Canvas canvas) {
try{
canvas.drawColor(Color.TRANSPARENT);//Color.WHITE //To change background color of Application
if(bit!=null)
canvas.drawBitmap(bit, 0, 0, mBitmapPaint);
else
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
}catch(Exception e){}
if(bit==null)
canvas.drawPath(mPath, mPaint);
bit=null;
}
private float mX, mY;
private void touch_start(float x, float y) {
mPath.reset();
mPath.moveTo(x, y);
mX = x+1;
mY = y+1;
}
private void touch_upline(float x,float y) {
mPath.lineTo(mX, mY);
mCanvas.drawLine(mX, mY, x, y, mPaint);
mPath.reset();
}
#Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
touch_start(x, y);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
eraseAll();
touch_upline(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_upline(x,y);
invalidate();
break;
}
return true;
}
public void eraseAll()
{
mBitmap.eraseColor(android.graphics.Color.TRANSPARENT);
mCanvas = new Canvas(mBitmap);
}
public class MainActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
RelativeLayout relativeLayout= (RelativeLayout) (findViewById(R.id.mainLayout));
relativeLayout.addView(new Drawing(this));
}
}

Undo and Redo Functionality in android drawing app using Canvas

i'm working on a project where i create mirror of drawing. my main logic is working fine.Only thing causing Problem is Redo and undo functionality.
i have searched a lot. implement may methods but couldn't get success. Following is my Drawing Class.
DrawingView.java
private ArrayList<Path> paths = new ArrayList<Path>();
private ArrayList<Path> undonePaths = new ArrayList<Path>();
public DrawingView(Context context, AttributeSet attrs){
super(context, attrs);
this.context=context;
setupDrawing();
}
//setup drawing
private void setupDrawing(){
//prepare for drawing and setup paint stroke properties
brushSize = getResources().getInteger(R.integer.small_size);
lastBrushSize = brushSize;
drawPath = new Path();
drawPath1 = new Path();
drawPaint = new Paint();
drawPaint.setColor(paintColor);
drawPaint.setAntiAlias(true);
drawPaint.setStrokeWidth(brushSize);
drawPaint.setStyle(Paint.Style.STROKE);
drawPaint.setStrokeJoin(Paint.Join.ROUND);
drawPaint.setStrokeCap(Paint.Cap.ROUND);
canvasPaint = new Paint(Paint.DITHER_FLAG);
}
//size assigned to view
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
width=w;
height=h;
Log.d("width,height", w + " , " + h);
drawCanvas = new Canvas(canvasBitmap);
}
//draw the view - will be called after touch event
#Override
protected void onDraw(Canvas canvas) {
for (Path p : paths){canvas.drawPath(p, drawPaint);}
canvas.drawPath(drawPath, drawPaint);
Log.i("OnDRAWING", "REACH ON DRAW");
/*canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
canvas.drawPath(drawPath, drawPaint);
canvas.drawPath(drawPath1, drawPaint);*/
}
//register user touches as drawing action
#Override
public boolean onTouchEvent(MotionEvent event) {
float touchX = event.getX();
float touchY = event.getY();
//respond to down, move and up events
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
drawPath.reset();
undonePaths.clear();
drawPath.moveTo(touchX, touchY);
undonePaths.clear();
break;
case MotionEvent.ACTION_MOVE:
drawPath.lineTo(touchX, touchY);
break;
case MotionEvent.ACTION_UP:
drawPath.lineTo(touchX, touchY);
drawCanvas.drawPath(drawPath, drawPaint);// commit the path to our offscreen
paths.add(drawPath);
drawCanvas.drawPath(drawPath, drawPaint);
drawPath.reset();
drawCanvas.drawPath(drawPath1, drawPaint);
drawPath1.reset();
break;
default:
return false;
}
//redraw
invalidate();
return true;
}
What i am missing here?
Any suggestions/ideas/examples which is the best way to implement this kind of functionality on my project?

Canvas drawing is sort of hierarchal in that drawing happens in the order that you do them.
So all drawing should be done in onDraw and only here.
Your draw events should be pushed on a draw stack. You do not store a canvas. You just store the operations that are supposed to happen when the drawing eventually occurs (coordinates, width, and color of a path for example).
An "undo" operation can be done by popping from the drawing stack and pushing the event to a "redo" stack. The "redo" event can be done by popping from the "redo" stack and pushing back on to the "drawing" stack.
In onDraw method of your View, just scan through the drawing events and draw on the canvas.
EDIT:
The onDraw() method would just iterate through your drawing operations. So first you could have an interface called DrawEvent like so:
public interface DrawEvent {
void draw(Canvas c);
}
Then in your View class have your collection of DrawEvents and iterate through them in onDraw(Canvas c).
public class MyView extends View {
Deque<DrawEvent> drawEvents = new LinkedList<DrawEvent>();
#Override
public void onDraw(Canvas c) {
for (DrawEvent e : drawEvents) {
e.draw(c);
}
}
}

Erasing bitmap contents on canvas

'I want to remove contents of the image that has been drawn on canvas like finger eraser but drawCircle is not removing.Here my code
'
public class PaintView extends View {
Canvas c1;
Paint mPaintt;
Bitmap mBitmap;
Matrix mMatrix;
RectF mSrcRectF;
RectF mDestRectF;
boolean mPause;
Bitmap bit;
Path path;
int X = -100;
int Y = -100;
Paint mPaint;
Bitmap mBitmaps;
public PaintView(Context context, AttributeSet attributeSet){
super(context,attributeSet);
mPaintt=new Paint();
mMatrix = new Matrix();
mSrcRectF = new RectF();
mDestRectF = new RectF();
mPause = false;
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_OUT));
mPaint.setAlpha(0);
mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
mPaint.setAntiAlias(true);
mPaint.setColor(Color.TRANSPARENT);
mPaint.setMaskFilter(new BlurMaskFilter(15, BlurMaskFilter.Blur.NORMAL));
}
public void addBitmap(Bitmap bitmap){
mBitmap = bitmap;
}
public Bitmap getBitmap(){
return mBitmap;
}
#Override
public boolean onTouchEvent(MotionEvent ev) {
switch (ev.getAction()) {
case MotionEvent.ACTION_DOWN: {
X = (int) ev.getX();
Y = (int) ev.getY();
invalidate();
break;
}
case MotionEvent.ACTION_MOVE: {
X = (int) ev.getX();
Y = (int) ev.getY();
invalidate();
break;
}
case MotionEvent.ACTION_UP:
break;
}
return true;
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if(!mPause){
if(mBitmap!=null){
canvas.drawColor(0, PorterDuff.Mode.CLEAR);
//mPaint.setColor(Color.TRANSPARENT);
// Setting size of Source Rect
mSrcRectF.set(0, 0,mBitmap.getWidth(),mBitmap.getHeight());
// Setting size of Destination Rect
mDestRectF.set(0, 0, getWidth(), getHeight());
// Scaling the bitmap to fit the PaintView
mMatrix.setRectToRect( mSrcRectF , mDestRectF, Matrix.ScaleToFit.CENTER);
canvas.drawBitmap(mBitmap, mMatrix,mPaintt);
canvas.drawCircle(X,Y,30,mPaint);
}
}
// Redraw the canvas
invalidate();
}
// Pause or resume onDraw method
public void pause(boolean pause){
mPause = pause;
}
}

How to draw on Canvas in another thread?

I have been developing the application, and I need that drawingg is executed in another thread. Now my code is:
public class PainterView extends View implements DrawingListener {
//private GestureDetector detector;
private Context context;
private Painter painter;
private Bitmap background;
private Bitmap bitmap;
private Paint bitmapPaint;
private Path path;
private Paint paint;
private float x;
private float y;
private boolean isErasing=false;
private boolean isTextDrawing=false;
private ExecutorService pool;
public PainterView(Context context, Painter painter) {
super(context);
this.context = context;
this.painter = painter;
pool=Executors.newFixedThreadPool(3);
//detector = new GestureDetector(context, new GestureListener());
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}
#Override
protected void onDraw(final Canvas canvas) {
if (bitmap != null) {
pool.submit(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
synchronized (PainterView.this) {
canvas.drawBitmap(background, 0, 0, bitmapPaint);
canvas.drawBitmap(bitmap, 0, 0, bitmapPaint);
canvas.drawPath(path, paint);
}
}
});
}
}
#Override
public boolean onTouchEvent(MotionEvent event) {
//detector.onTouchEvent(event);
x = event.getX();
y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
painter.touchStart(x, y);
break;
case MotionEvent.ACTION_MOVE:
painter.touchMove(x, y);
break;
case MotionEvent.ACTION_UP:
painter.touchUp();
break;
}
return true;
}
#Override
public void onPictureUpdate(Bitmap background, Bitmap bitmap, Paint bitmapPaint, Path path, Paint paint) {
this.background=background;
this.bitmap = bitmap;
this.bitmapPaint = bitmapPaint;
this.path = path;
this.paint = paint;
invalidate();
}
public void setPainter(Painter painter) {
this.painter = painter;
}
}
I thought that if I uses ExecutorService then the application can draw in another thread, but it doesn't work - when I draw the screen of device blinkes. So, please, tell me, how can I use multithreading for drawing using SurfaceHolder and other elements? I need to make as few as possible changes in my code.

You can only draw in the main UI thread. You should use SurfaceView, since it was made specifically to support drawing from secondary threads.
One of the purposes of this class is to provide a surface in which a
secondary thread can render into the screen. If you are going to use
it this way, you need to be aware of some threading semantics.
source
See also this video: Learn Android Tutorial 1.28- Introduction to the SurfaceView