Develop Reference

Android canvas load bmp on click button

i have a layout for drawing content_designer.xml
<Button
android:id="#+id/loadBMP"
android:layout_width="match_parent"
android:layout_height="100dp"
android:text="Load"/>
<com.system.v.construct.Drawing
android:id="#+id/canvasDraw"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
In my activity i set the view and whe user click the button bmp must be loaded.
setContentView(R.layout.content_designer);
Button load=(Button)findViewById(R.id.loadBMP);
final Drawing drawing=new Drawing(this);
load.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Toast.makeText(getApplicationContext(),"Click",Toast.LENGTH_LONG).show();
drawing.looadBMP();
}
});
In drawing class i have a method looadBMP()
But the image doesnt load, i'm beginner in drawing, so sorry for mistake
Here is a full Drawin class seems like method on Draw is executed first, i need bmp image load on button click:
public class Drawing extends View implements OnTouchListener {
private Canvas mCanvas;
private Path mPath;
public Paint mPaint;
private ArrayList<Path> paths = new ArrayList<Path>();
Bitmap bmp;
public static Canvas myCanvas;
public Drawing(Context context) {
super(context);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}
public void looadBMP()
{
setFocusable(true);
setFocusableInTouchMode(true);
bmp = BitmapFactory.decodeResource(getResources(), R.drawable.simple);
this.setOnTouchListener(this);
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(Color.BLUE);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(6);
mCanvas = new Canvas(bmp);
mPath = new Path();
paths.add(mPath);
mCanvas.drawBitmap(bmp, 0, 0, mPaint);
for (Path p : paths) {
mCanvas.drawPath(p, mPaint);
}
}
#Override
protected void onDraw(Canvas canvas) {
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 0;
//Drawing dw = new Drawing();
private void touch_start(float x, float y) {
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
mX = x;
mY = y;
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
// commit the path to our offscreen
mCanvas.drawPath(mPath, mPaint);
// kill this so we don't double draw
mPath = new Path();
paths.add(mPath);
}
#Override
public boolean onTouch(View arg0, 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:
touch_move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
}

Erase drawing in canvas

I have written an Android application with a Canvas for drawing with a stylus. It works well. When I'm pushing the upper function key of my stylus I would like to erase the drawing by brushing over the text. The normal drawing is in black, so I thought to do the erase with white (on top of the black line). My problem is that all lines change the color when I press the upper function key of the stylus (i.e. all lines are then white) instead of just painting the new draw line in white.
Another option would be to delete elements from the path for the erase. If somebody has a solution for this, I would be happy too.
The layout looks as follows:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#ffffff"
tools:context="StylusBaselineA">
<inf.ethz.ch.affectivestudy.CanvasView
android:id="#+id/baselineACanvas"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:textColor="#FFFFFF" />
</android.support.constraint.ConstraintLayout>
The CanvasView class look as follows:
public class CanvasView extends View {
public int width;
public int height;
private Bitmap mBitmap;
private Canvas mCanvas;
private Path mPath;
private Path mPathErase;
Context context;
private Paint mPaint;
private Paint mPaintErase;
private float mX, mY;
private static final float TOLERANCE = 5;
private boolean erase = false;
public CanvasView(Context c, AttributeSet attrs) {
super(c, attrs);
context = c;
// we set a new Path
mPath = new Path();
mPathErase = new Path();
// and we set a new Paint with the desired attributes
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setColor(Color.BLACK);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeWidth(4f);
mPaintErase = new Paint();
mPaintErase.setAntiAlias(true);
mPaintErase.setColor(Color.WHITE);
mPaintErase.setStyle(Paint.Style.STROKE);
mPaintErase.setStrokeJoin(Paint.Join.ROUND);
mPaintErase.setStrokeWidth(4f);
}
// override onSizeChanged
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
// your Canvas will draw onto the defined Bitmap
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
}
// override onDraw
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
// draw the mPath with the mPaint on the canvas when onDraw
if (erase) {
canvas.drawPath(mPathErase, mPaintErase);
} else {
canvas.drawPath(mPath, mPaint);
}
}
// when ACTION_DOWN start touch according to the x,y values
private void startTouch(float x, float y) {
if (erase) {
mPathErase.moveTo(x, y);
} else {
mPath.moveTo(x, y);
}
mX = x;
mY = y;
}
// when ACTION_MOVE move touch according to the x,y values
private void moveTouch(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOLERANCE || dy >= TOLERANCE) {
if (erase) {
mPathErase.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
} else {
mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
}
mX = x;
mY = y;
}
}
public void clearCanvas() {
mPath.reset();
mPathErase.reset();
invalidate();
}
// when ACTION_UP stop touch
private void upTouch() {
if (erase) {
mPathErase.lineTo(mX, mY);
} else {
mPath.lineTo(mX, mY);
}
}
#Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
if (event.getToolType(0) == MotionEvent.TOOL_TYPE_ERASER) {
// Upper function key of stylus
erase = true;
} else if (event.getToolType(0) == MotionEvent.TOOL_TYPE_FINGER) {
// Touch input
erase = false;
return false;
} else {
erase = false;
}
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
startTouch(x, y);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
moveTouch(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
upTouch();
invalidate();
break;
}
return true;
}
}

Try this.
public class CanvasActivity extends AppCompatActivity {
private Paint mPaint;
View mView;
Button clear;
private Canvas mCanvas;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_canvas);
RelativeLayout layout = (RelativeLayout) findViewById(R.id.Linear_layout);
mView = new DrawingView(this);
layout.addView(mView, new LayoutParams(
RelativeLayout.LayoutParams.MATCH_PARENT,
RelativeLayout.LayoutParams.MATCH_PARENT));
clear= (Button) findViewById(R.id.clear);
clear.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
mCanvas.drawColor(Color.WHITE);
}
});
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(Color.GREEN);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(12);
}
public class DrawingView extends View {
public int width;
public int height;
private Bitmap mBitmap;
private Path mPath;
private Paint mBitmapPaint;
Context context;
private Paint circlePaint;
private Path circlePath;
public DrawingView(Context c) {
super(c);
context=c;
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
circlePaint = new Paint();
circlePath = new Path();
circlePaint.setAntiAlias(true);
circlePaint.setColor(Color.BLUE);
circlePaint.setStyle(Paint.Style.STROKE);
circlePaint.setStrokeJoin(Paint.Join.MITER);
circlePaint.setStrokeWidth(4f);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawBitmap( mBitmap, 0, 0, mBitmapPaint);
canvas.drawPath( mPath, mPaint);
canvas.drawPath( circlePath, circlePaint);
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;
private void touch_start(float x, float y) {
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
mX = x;
mY = y;
circlePath.reset();
circlePath.addCircle(mX, mY, 30, Path.Direction.CW);
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
circlePath.reset();
// commit the path to our offscreen
mCanvas.drawPath(mPath, mPaint);
// kill this so we don't double draw
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:
touch_move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
}
}

Android Drawing View is very slow

I got this code from a answer in one of the questions that was asking how to draw in Android, but then when using it and testing it in my app, I found out that it's not efficient when drawing big things or many paths. The problem comes from the code inside onDraw because each time invalidate() is called onDraw is called which contains a loop that draws all paths again to the canvas, and by adding more paths to it, it gets very very slow.
Here is the Class:
public class DrawingView extends View implements OnTouchListener {
private Canvas m_Canvas;
private Path m_Path;
private Paint m_Paint;
ArrayList<Pair<Path, Paint>> paths = new ArrayList<Pair<Path, Paint>>();
ArrayList<Pair<Path, Paint>> undonePaths = new ArrayList<Pair<Path, Paint>>();
private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;
public static boolean isEraserActive = false;
private int color = Color.BLACK;
private int stroke = 6;
public DrawingView(Context context, AttributeSet attr) {
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
setBackgroundColor(Color.WHITE);
this.setOnTouchListener(this);
onCanvasInitialization();
}
public void onCanvasInitialization() {
m_Paint = new Paint();
m_Paint.setAntiAlias(true);
m_Paint.setDither(true);
m_Paint.setColor(Color.parseColor("#000000"));
m_Paint.setStyle(Paint.Style.STROKE);
m_Paint.setStrokeJoin(Paint.Join.ROUND);
m_Paint.setStrokeCap(Paint.Cap.ROUND);
m_Paint.setStrokeWidth(2);
m_Canvas = new Canvas();
m_Path = new Path();
Paint newPaint = new Paint(m_Paint);
paths.add(new Pair<Path, Paint>(m_Path, newPaint));
}
#Override
public void setBackground(Drawable background) {
mBackground = background;
super.setBackground(background);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}
public boolean onTouch(View arg0, 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:
touch_move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
#Override
protected void onDraw(Canvas canvas) {
for (Pair<Path, Paint> p : paths) {
canvas.drawPath(p.first, p.second);
}
}
private void touch_start(float x, float y) {
if (isEraserActive) {
m_Paint.setColor(Color.WHITE);
m_Paint.setStrokeWidth(50);
Paint newPaint = new Paint(m_Paint); // Clones the mPaint object
paths.add(new Pair<Path, Paint>(m_Path, newPaint));
} else {
m_Paint.setColor(color);
m_Paint.setStrokeWidth(stroke);
Paint newPaint = new Paint(m_Paint); // Clones the mPaint object
paths.add(new Pair<Path, Paint>(m_Path, newPaint));
}
m_Path.reset();
m_Path.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
m_Path.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
mX = x;
mY = y;
}
}
private void touch_up() {
m_Path.lineTo(mX, mY);
// commit the path to our offscreen
m_Canvas.drawPath(m_Path, m_Paint);
// kill this so we don't double draw
m_Path = new Path();
Paint newPaint = new Paint(m_Paint); // Clones the mPaint object
paths.add(new Pair<Path, Paint>(m_Path, newPaint));
}
public void onClickUndo() {
if (!paths.isEmpty()) {//paths.size() > 0) {
undonePaths.add(paths.remove(paths.size() - 1));
undo = true;
invalidate();
}
}
public void onClickRedo() {
if (!undonePaths.isEmpty()){//undonePaths.size() > 0) {
paths.add(undonePaths.remove(undonePaths.size() - 1));
undo = true;
invalidate();
}
}}
But I searched on the internet again to find a better way for drawing, so I found the following:
1 Add the following to the constructor:
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
2 Override onSizeChanged with the following code:
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_4444);
m_Canvas = new Canvas(mBitmap);
}
3 put this in onDraw:
protected void onDraw(Canvas canvas) {
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
if (!paths.isEmpty())
canvas.drawPath(paths.get(paths.size() - 1).first, paths.get(paths.size() - 1).second);
}
This approach works and it doesn't slow down the view, but the problem with this approach is that I can't have undo and redo functionalities.
I tried many many things to do the undo and redo with the second approach, but I couldn't do it. So what I'm asking here is one of three things:
1. A way to do undo and redo with the second approach
2. Another approach that makes it possible to do undo and redo
3. A whole new class that has everything already done, like an open source library or something.
Please help if you can.
Thanks
EDIT 1
OK, so I limited it down to this and then I couldn't do anything more, I have been trying for over 8 hours now. It works up until undo (you can undo as many paths as you want), then when drawing again all remaining paths disappear, I don't know what makes it do that.
#Override
protected void onDraw(Canvas canvas) {
if (mBitmap != null)
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
if (!paths.isEmpty() && !undo)
canvas.drawPath(paths.get(paths.size() - 1).first, paths.get(paths.size() - 1).second);
if (undo) {
setBackground(mBackground);
for (Pair<Path, Paint> p : paths)
canvas.drawPath(p.first, p.second);
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_4444);
m_Canvas = new Canvas(mBitmap);
undo = false;
}
}
so basically what I did is use the first approach at first (before undo is called), then if undo is clicked, undo is set to true and the code under if (undo) is executed which is actually the first approach (calculating all paths again), then I draw the result of calculating all paths again into mBitmap so whenever the onDraw is called again it draws on top of that, but that part is still needs working, I hope someone can help with that part.

The way to handle such a case is to have a Bitmap that has the size of the view. On touch events, draw into the bitmap's canvas. in onDraw, just draw the bitmap into the canvas at 0,0. For undo/redo,. you can erase the bitmap and re-draw all the paths. It make take a bit longer, but it happens only once per undo/redo.
If users typically do one undo/redo. you can optimize by having another bitmap for just one step back.

Ok, here is what I came up with at the end, the problem was that I draw the paths to the canvas before creating the bitmap on undo, which lead to loss of the paths onDraw after undo:
#Override
protected void onDraw(Canvas canvas) {
if (mBitmap != null)
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
if (!paths.isEmpty()) {
canvas.drawPath(paths.get(paths.size() - 1).first, paths.get(paths.size() - 1).second);
}
}
public void onClickUndo() {
if (paths.size() >= 2) {
undonePaths.add(paths.remove(paths.size() - 2));
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
m_Canvas = new Canvas(mBitmap);
for (Pair<Path, Paint> p : paths)
m_Canvas.drawPath(p.first, p.second);
invalidate();
}
}
public void onClickRedo() {
if (undonePaths.size() >= 2){
paths.add(undonePaths.remove(undonePaths.size() - 2));
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
m_Canvas = new Canvas(mBitmap);
for (Pair<Path, Paint> p : paths)
m_Canvas.drawPath(p.first, p.second);
invalidate();
}
}
Drawing all paths again and again is still there but not in onDraw(), which improves the performance of drawing quite very much.
But the user might experience little bit of delay in onClickUndo() and onClickRedo() if he has drawn a lot of paths because there where the paths are getting drawn again from scratch, but just one time per click.

I am not sure if this is the best way for undo and redo. However the below worked on my device (Samsung galaxy s3). The Draw seems to be fast and the undo works fine. I do think the below can be modified to further enhance performance.
public class MainActivity extends Activity {
MyView mv;
LinearLayout ll;
private ArrayList<Path> undonePaths = new ArrayList<Path>();
private ArrayList<Path> paths = new ArrayList<Path>();
Button b;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mv= new MyView(this);
mv.setDrawingCacheEnabled(true);
ll= (LinearLayout) findViewById(R.id.ll);
ll.addView(mv);
b= (Button) findViewById(R.id.button1);
b.setOnClickListener(new OnClickListener()
{
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
if (paths.size() > 0) {
undonePaths.add(paths
.remove(paths.size()-2));
mv.invalidate();
}
}
});
}
public class MyView extends View implements OnTouchListener {
private Canvas mCanvas;
private Path mPath;
private Paint mPaint;
// private ArrayList<Path> undonePaths = new ArrayList<Path>();
private float xleft, xright, xtop, xbottom;
public MyView(Context context) {
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setColor(Color.RED);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(6);
mCanvas = new Canvas();
mPath = new Path();
paths.add(mPath);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}
#Override
protected void onDraw(Canvas canvas) {
for (Path p : paths) {
canvas.drawPath(p, mPaint);
}
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 0;
private void touch_start(float x, float y) {
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
mX = x;
mY = y;
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
// commit the path to our offscreen
mCanvas.drawPath(mPath, mPaint);
// kill this so we don't double draw
mPath = new Path();
paths.add(mPath);
}
#Override
public boolean onTouch(View arg0, 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:
touch_move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<LinearLayout
android:id="#+id/ll"
android:layout_width="match_parent"
android:layout_height="fill_parent"
android:layout_weight="1"
android:orientation="vertical" >
</LinearLayout>
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="Undo" />
</LinearLayout>

Android FingerPaint Undo/Redo implementation

I'm working on a test project which is something similar to FingerPaint example in Android SDK Demos. I was trying to implement undo/redo functionality in my project,but the things that I tried didn't work as I expect. I find some questions similar to this over internet and here,but they didn't help me, that's why I'm asking a new question.
Here is some idea what I'm doing actually :
public class MyView extends View {
//private static final float MINP = 0.25f;
//private static final float MAXP = 0.75f;
private Path mPath;
private Paint mBitmapPaint;
public MyView(Context c) {
super(c);
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
mCanvas.drawColor(Color.WHITE);
}
#Override
protected void onDraw(Canvas canvas) {
canvas.drawColor(Color.WHITE);
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
canvas.drawPath(mPath, mPaint);
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;
private void touch_start(float x, float y) {
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
mX = x;
mY = y;
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
// commit the path to our offscreen
mCanvas.drawPath(mPath, mPaint);
// kill this so we don't double draw
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:
touch_move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
}
Any suggestions/ideas/examples which is the best way to implement this kind of functionality on my project?

I don't know if this is what you had in mind but it's how i am doing it. Instead of storing it in only one path, you store an array with all the paths, like this the user can draw many lines, with a small modification you can add multi touch too.
To make the undo and redo, just remove or add the last path path from the paths variable
and store them in a new array. Something like:
public void onClickUndo () {
if (paths.size()>0) {
undonePaths.add(paths.remove(paths.size()-1))
invalidate();
}
else
//toast the user
}
public void onClickRedo (){
if (undonePaths.size()>0) {
paths.add(undonePaths.remove(undonePaths.size()-1))
invalidate();
}
else
//toast the user
}
Here is my modified panel, I cant try it right now but the methods above should work! Hope it helps! (there are few extra variables just remove them :)
private ArrayList<Path> undonePaths = new ArrayList<Path>();
public class DrawingPanel extends View implements OnTouchListener {
private Canvas mCanvas;
private Path mPath;
private Paint mPaint,circlePaint,outercirclePaint;
private ArrayList<Path> paths = new ArrayList<Path>();
private ArrayList<Path> undonePaths = new ArrayList<Path>();
private float xleft,xright,xtop,xbottom;
public DrawingPanel(Context context) {
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
circlePaint = new Paint();
mPaint = new Paint();
outercirclePaint = new Paint();
outercirclePaint.setAntiAlias(true);
circlePaint.setAntiAlias(true);
mPaint.setAntiAlias(true);
mPaint.setColor(0xFFFFFFFF);
outercirclePaint.setColor(0x44FFFFFF);
circlePaint.setColor(0xAADD5522);
outercirclePaint.setStyle(Paint.Style.STROKE);
circlePaint.setStyle(Paint.Style.FILL);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(6);
outercirclePaint.setStrokeWidth(6);
mCanvas = new Canvas();
mPath = new Path();
paths.add(mPath);
cx = 400*DrawActivity.scale;
cy = 30*DrawActivity.scale;
circleRadius = 20*DrawActivity.scale;
xleft = cx-10*DrawActivity.scale;
xright = cx+10*DrawActivity.scale;
xtop = cy-10*DrawActivity.scale;
xbottom = cy+10*DrawActivity.scale;
}
public void colorChanged(int color) {
mPaint.setColor(color);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}
#Override
protected void onDraw(Canvas canvas) {
for (Path p : paths){
canvas.drawPath(p, mPaint);
}
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 0;
private void touch_start(float x, float y) {
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
mX = x;
mY = y;
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
// commit the path to our offscreen
mCanvas.drawPath(mPath, mPaint);
// kill this so we don't double draw
mPath = new Path();
paths.add(mPath);
}
#Override
public boolean onTouch(View arg0, MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
if (x <= cx+circleRadius+5 && x>= cx-circleRadius-5) {
if (y<= cy+circleRadius+5 && cy>= cy-circleRadius-5){
paths.clear();
return true;
}
}
touch_start(x, y);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
touch_move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
}

The best solution is that you implement your own Undo / Redo engine.
Save into an array every single action you perform in an array (ie. [0] circle in position x1, y1, [1] line from x2, y2 to x3, y3, etc)
draw
if you need to undo, clear the canvas and repaint all the n - 1 actions from [0] to [n - 1]
if you undo more just have to to paint from [0] to [n - 2] etc
I hope it gives you a hint
Cheers!

One way to implement a do/redo functionality is to encapsulate a method call and all info needed for the call in an object so that you can store it and call it later - the Command Pattern.
In this pattern, each action has its own object: DrawCircleCommand, DrawPathCommand, FillColorCommand, etc. In each object the draw() method is implemented in a unique way but is always called as draw(Canvas canvas) which allows the CommandManager to iterate through the commands. To undo you iterate over the objects calling the undo() method;
Each command object implements an Interface
public interface IDrawCommand {
public void draw(Canvas canvas);
public void undo();
}
An object would look like:
public class DrawPathCommand implements IDrawCommand{
public Path path;
public Paint paint;
public void setPath(path){
this.path = path
}
public void draw(Canvas canvas) {
canvas.drawPath( path, paint );
}
public void undo() {
//some action to remove the path
}
}
Your commands are added to the CommandManager:
mCommandManager.addCommand(IDrawCommand command)
and to undo a command you just call:
mCommandManager.undo();
The CommandManager stores the commands in a data structure e.g. list that allows it to iterative over the command objects.
You can find a complete tutorial here on how to implement the Command Pattern with do/undo for Canvas drawing on Android.
Here is a another tutorial on how implement the Command Pattern in Java;

Fortunately,I solved this today. I find a way to do this.Something like:
private ArrayList<Path> paths = new ArrayList<>();
private ArrayList<Path> undonePaths = new ArrayList<>();
public void undo() {
if (paths.size() > 0) {
LogUtils.d("undo " + paths.size());
clearDraw();
undonePaths.add(paths.remove(paths.size() - 1));
invalidate();
}
}
public void redo() {
if (undonePaths.size() > 0) {
LogUtils.d("redo " + undonePaths.size());
clearDraw();
paths.add(undonePaths.remove(undonePaths.size() - 1));
invalidate();
}
}
public void clearDraw() {
mBitmap = Bitmap.createBitmap(mWidth, mHeight, Bitmap.Config.ARGB_8888);
mCanvas.setBitmap(mBitmap);
invalidate();
}
public void clear() {
paths.clear();
undonePaths.clear();
invalidate();
}
in Activity.
private DrawView mDrawView;
if (v == mIvUndo) {
mDrawView.undo();
} else if (v == mIvRedo) {
mDrawView.redo();
in xml
<com.cinread.note.view.DrawView
android:id="#+id/paintView"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
If you have a better solution you can contact me.
[here is my blog that I write in
http://blog.csdn.net/sky_pjf/article/details/51086901]

I think that in this case you can use two canvases. You know when user starts drawing and when finishes. So, in touch_start you can create copy of your current canvas. When user clicks undo you replace your current canvas with previously saved.
This should guarantee that you will have previous state of picture, but I am not sure about performance.

How to create a Scratch Card in Android?

I need to create a "Scratch Card" App for my final project in school and can't find the way how to implement the scratching event (How do I create background image and put Grey rectangles over it, so when I will scratch those rectangles I will see the picture under them)
The Implementation must be in Android because I don't how to develop In Objective-C yet.
I saw a reference for Objective-C Implementation, but it's no good as I don't understand it.
My Code is:
public class FingerPaint extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
try {
MyView myView = new MyView(this);
myView.requestFocus();
myView.PaintObjectInit();
// setContentView(myView);
LinearLayout upper = (LinearLayout) findViewById(R.id.LinearLayout01);
upper.addView(myView);
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}
// MyImageView myImageView = new MyImageView(this);
// setContentView(myImageView);
}
}
public class MyView extends View {
private Paint mPaint;
private Bitmap mBitmap;
private Canvas mCanvas;
private Path mPath;
private Paint mBitmapPaint;
public MyView(Context context) {
super(context);
this.mPaint = new Paint();
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
}
protected void PaintObjectInit() {
mPaint.setAntiAlias(true);
mPaint.setDither(true);
//mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
//mPaint.setColor(0xFFFF0000);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(12);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
try
{
//Bitmap bm1 = BitmapFactory.decodeResource(this.getResources(),R.drawable.scratch).copy(Bitmap.Config.ARGB_8888, true);;
//Bitmap bm2 = BitmapFactory.decodeResource(this.getResources(),R.drawable.main).copy(Bitmap.Config.ARGB_8888, true);;
//mBitmap = toTransparency(bm1, 0xFFAAAAAA, true, bm2);
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
}
catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}
}
#Override
protected void onDraw(Canvas canvas) {
canvas.drawColor(0xFFAAAAAA);
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
canvas.drawPath(mPath, mPaint);
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;
private void touch_start(float x, float y) {
// mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
mX = x;
mY = y;
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
// commit the path to our offscreen
mCanvas.drawPath(mPath, mPaint);
// kill this so we don't double draw
// 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:
touch_move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
}
Please help regarding this.

I come across this problem recently and then I created a library for this so everyone can have a quick implementation of scratch view, hope this can help those who still looking for answer
https://github.com/winsontan520/Android-WScratchView

I found this library very useful.
https://github.com/sharish/ScratchView
Very easy to integrate
<com.cooltechworks.views.ScratchImageView
android:id="#+id/sample_image"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="#android:color/white"
android:src="#drawable/img_sample2"
/>

you can make "Scratch Card" application like this way. you need to follow the below code which is working code. you just need to required understand and implement your own logic.
public class MainActJava extends AppCompatActivity {
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher);
setContentView(new MyView(this, bitmap));
}
public class MyView extends View implements View.OnTouchListener {
private static final float TOUCH_TOLERANCE = 4;
private Paint mPaint;
private Bitmap oBitmap;
private Bitmap holder;
private Canvas mCanvas;
private Path mPath;
private Paint mBitmapPaint;
private float mX, mY;
public MyView(Context context) {
super(context);
}
public MyView(Context context, Bitmap bitmap) {
super(context);
setOnTouchListener(this);
this.oBitmap = bitmap;
this.mPaint = new Paint();
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
init();
}
protected void init() {
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(35);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
holder = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(holder);
}
#Override
protected void onDraw(Canvas canvas) {
onDrawing(canvas);
}
private void onDrawing(Canvas canvas) {
mCanvas.drawColor(0xFFAAAAAA);
mCanvas.drawPath(mPath, mPaint);
canvas.drawBitmap(oBitmap, getWidth()/2, getHeight()/2, mBitmapPaint);
canvas.drawBitmap(holder, 0, 0, mBitmapPaint);
}
private void touch_start(float x, float y) {
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
mX = x;
mY = y;
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
mCanvas.drawPath(mPath, mPaint);
}
#Override
public boolean onTouch(View view, 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:
touch_move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
}
}
Output: