Develop Reference

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;
}
}
}

Color picker not working with undo and redo

This is the code for implementing undo and redo in Android Canvas and is working fine.
package com.example.canva;
import java.util.ArrayList;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.view.MotionEvent;
import android.view.View;
public class MainView extends View {
private Canvas mCanvas;
private Path mPath;
private Paint mPaint;
private ArrayList<Path> paths = new ArrayList<Path>();
private ArrayList<Path> undonePaths = new ArrayList<Path>();
public MainView(Context context)
{
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(0xFFFFFFFF);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(6);
mCanvas = new Canvas();
mPath = new Path();
}
// im=BitmapFactory.decodeResource(context.getResources(),R.drawable.ic_launcher);
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}
#Override
protected void onDraw(Canvas canvas) {
//mPath = new Path();
//canvas.drawPath(mPath, mPaint);
for (Path p : paths){
canvas.drawPath(p, mPaint);
}
canvas.drawPath(mPath, mPaint);
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;
private void touch_start(float x, float y) {
undonePaths.clear();
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
paths.add(mPath);
mPath = new Path();
}
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
}
#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;
}
}
But in my app I need to change color, stroke width, style etc. when I try to change the Color using the following method, entire thing in the Canvas is changing to that Color.
public void setColor(int color){
mPaint.setColor(color);}

Save the paths in array and perform operations on that array to undo or redo.

Android onDraw only take changes on second drawing

I am developing drawing module for my app. All features working fine. The problem is, everytime when I change the color, or set the brushSize or change to eraser, the first touch on the screen will draw with the previous settings. The second touch then will have the newest changes. Same goes to undo. Nothing change on first click. For second click and so on, it is working fine. This is my reference. The sample app in the reference also has the same problem. This is my code:
public class DrawingView extends View {
//drawing path
private Path drawPath;
private Point pointDraw;
//drawing and canvas paint
private Paint drawPaint, canvasPaint;
//initial color
private int paintColor;
//canvas
private Canvas drawCanvas;
//canvas bitmap
private Bitmap canvasBitmap;
//brush sizes
private float brushSize, lastBrushSize;
//private int defaultBrush = 10;
//erase flag
private boolean erase=false;
private int tempColor;
private boolean checkDraw = false;
private ArrayList<PathPoints> paths = new ArrayList<PathPoints>();
private ArrayList<PathPoints> undonePaths = new ArrayList<PathPoints>();
private ArrayList<Point> tempCanvas = new ArrayList<Point>();
private int countPoint = 0;
int x,y;
public DrawingView(Context context, AttributeSet attrs){
super(context, attrs);
setupDrawing();
}
//setup drawing
private void setupDrawing(){
//prepare for drawing and setup paint stroke properties
//brushSize = getResources().getInteger(R.integer.medium_size);
lastBrushSize = brushSize;
drawPath = 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);
paths.add(new PathPoints(drawPath, paintColor, brushSize, false));
drawCanvas = new Canvas();
}
//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) {
super.onDraw(canvas);
//canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
//canvas.drawPath(drawPath, drawPaint);
for (PathPoints p : paths) {
drawPaint.setColor(p.getColor());
drawPaint.setStrokeWidth(p.getStrokeSize());
canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
canvas.drawPath(p.getPath(), drawPaint);
}
setCheckDraw(true);
}
public int getArr()
{
return paths.size();
}
public boolean isCheckDraw() {
return checkDraw;
}
public void setCheckDraw(boolean checkDraw) {
this.checkDraw = checkDraw;
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 0;
private void touch_start(float x, float y) {
drawPath.reset();
drawPath.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) {
drawPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
mX = x;
mY = y;
}
}
private void touch_up() {
drawPath.lineTo(mX, mY);
// commit the path to our offscreen
drawCanvas.drawPath(drawPath, drawPaint);
// kill this so we don't double draw
drawPath = new Path();
paths.add(new PathPoints(drawPath, paintColor, brushSize, false));
}
//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:
touch_start(touchX, touchY);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
touch_move(touchX, touchY);
break;
case MotionEvent.ACTION_UP:
touch_up();
//invalidate();
break;
}
//redraw
invalidate();//do not call frequently
return true;
}
public void validateDraw()
{
invalidate();
}
//update color
public void setColor(String newColor){
//invalidate();
paintColor = Color.parseColor(newColor);
drawPaint.setColor(paintColor);
}
public void setColor(int newColor){
//invalidate();
paintColor = newColor;
drawPaint.setColor(paintColor);
tempColor = paintColor;
}
//set brush size
public void setBrushSize(float newSize){
float pixelAmount = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,
newSize, getResources().getDisplayMetrics());
brushSize=pixelAmount;
}
//get and set last brush size
public void setLastBrushSize(float lastSize){
lastBrushSize=lastSize;
}
public float getLastBrushSize(){
drawPath.reset();
return lastBrushSize;
}
//set erase true or false
public void setErase(boolean isErase)
{
//drawPath.reset();
erase=isErase;
if(erase)
this.setColor("#FFFFFFFF");
else
//drawPaint.setXfermode(null);
this.setColor(tempColor);
}
//// new drawing
public void startNew(){
//drawCanvas.drawColor(0, PorterDuff.Mode.CLEAR);
paths.clear();
undonePaths.clear();
invalidate();
}
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
}
Thank in advance

Overwriting onDraw on EditText

I'm writing a subclass of EditText that allows the user to draw with his finger on it. For that, I created a boolean called drawing, that if it's true put the EditText on drawing mode and the keyboard it's not opened, and if it's false allow the user to open the keyboard and write on keeping his drawing that he does with the drawing mode.
The code for the drawing is based on the Google Android Example called FingerPaint. Before this intent to implement this into an EditText, the code was implemented on a subclass of view, and worked perfectly, but the problem was that combining an EditText and that view in a layout reduces the performance was really bad.
There's a lot of code to do this, because can be used to implement two different mask filters that add some lines to this code that are not used locally in this class.
My problem is that when I override the onDraw(), and drawing is false, the texts it's not showed to ther user, but the keyboard and the writing line (|) are showed.
Here my code:
import android.content.Context;
import android.graphics.*;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.EditText;
public class DrawEditText extends EditText {
private Bitmap mBitmap;
private Canvas mCanvas;
private Path mPath;
private Paint mBitmapPaint;
private Paint mPaint;
private MaskFilter mEmboss;
private MaskFilter mBlur;
private Boolean drawing;
public DrawEditText(Context c) {
super(c);
//This initializes all the objects
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
mPaint = new Paint();
mPaint.setColor(Color.BLACK);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeWidth(5);
mPaint.setAntiAlias(true);
mEmboss = new EmbossMaskFilter(new float[] { 1, 1, 1 },
0.4f, 6, 3.5f);
mBlur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
drawing = true;
}
public DrawEditText(Context c, AttributeSet attrs) {
super(c, attrs);
//This initializes all the objects
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
mPaint = new Paint();
mPaint.setColor(Color.BLACK);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeWidth(5);
mPaint.setAntiAlias(true);
mEmboss = new EmbossMaskFilter(new float[] { 1, 1, 1 },
0.4f, 6, 3.5f);
mBlur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
drawing = true;
}
#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) {
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();
//This conditional makes that if not it's drawing no points are saved and no points are drawed
if (drawing){
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;
} else {
return super.onTouchEvent(event);
}
}
public void changePaint(int stroke, int color){
mPaint.setColor(color);
mPaint.setStrokeWidth(stroke);
}
public void clear(){
mCanvas.drawColor(0x00AAAAAA);
mCanvas.drawColor( 0, PorterDuff.Mode.CLEAR );
}
public void changeBrush(int id){
//String[] ids={"emboss", "blur", "another"};
switch (id) {
case 0:
mPaint.setMaskFilter(mEmboss);
break;
case 1:
mPaint.setMaskFilter(mBlur);
break;
case 2:
mPaint.setMaskFilter(null);
break;
default:
mPaint.setMaskFilter(null);
break;
}
}
public void eraser(){
mPaint.setMaskFilter(null);
mPaint.setColor(0x00AAAAAA);
}
public void setDrawing(Boolean drawing){
this.drawing = drawing;
}
public Boolean isDrawing(){
return drawing;
}
}

Just give the EditText a chance to draw its own content:
#Override
protected void onDraw(Canvas canvas) {
if(drawing) {
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
canvas.drawPath(mPath, mPaint);
} else {
super.onDraw(canvas);
}
}

Android Canvas Redo and Undo Operation

I am working on a drawing project. My code is working perfectly other than canvas redo and undo operations. My undo operation removes paths from the paths ArrayList and saves to the undonePaths ArrayList, and the redo operation removes the last element from undonePaths and saves to paths.
Here's my code:
import java.util.ArrayList;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
public class DrawView extends View implements OnTouchListener {
private Canvas mCanvas;
private Path mPath;
private Paint mPaint;
private ArrayList<Path> paths = new ArrayList<Path>();
private ArrayList<Path> undonePaths = new ArrayList<Path>();
private Bitmap im;
public DrawView(Context context)
{
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(0xFFFFFFFF);
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);
im=BitmapFactory.decodeResource(context.getResources(),R.drawable.ic_launcher);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}
#Override
protected void onDraw(Canvas canvas) {
//mPath = new Path();
//canvas.drawPath(mPath, mPaint);
for (Path p : paths){
canvas.drawPath(p, 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 = new Path();
paths.add(mPath);
}
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
}
#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;
}
}
This code is working perfectly for drawing but not working perfectly for undo and redo operations. What's wrong with my code?
Here's my full source code:
http://www.4shared.com/rar/8PQQEZdH/test_draw.html
UPDATED:
Finally my problem was solved; here's my drawing class:
import java.util.ArrayList;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
public class DrawView extends View implements OnTouchListener {
private Canvas mCanvas;
private Path mPath;
private Paint mPaint;
private ArrayList<Path> paths = new ArrayList<Path>();
private ArrayList<Path> undonePaths = new ArrayList<Path>();
private Bitmap im;
public DrawView(Context context)
{
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(0xFFFFFFFF);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(6);
mCanvas = new Canvas();
mPath = new Path();
im=BitmapFactory.decodeResource(context.getResources(),R.drawable.ic_launcher);
}
#Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}
#Override
protected void onDraw(Canvas canvas) {
//mPath = new Path();
//canvas.drawPath(mPath, mPaint);
for (Path p : paths){
canvas.drawPath(p, mPaint);
}
canvas.drawPath(mPath, mPaint);
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;
private void touch_start(float x, float y) {
undonePaths.clear();
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
paths.add(mPath);
mPath = new Path();
}
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
}
#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;
}
}
That code is working perfectly...!

At first glance I see the following problems:
By adding your empty Path to paths as soon as you make it, you're going to have a problem as soon as you undo: you're popping that empty Path first, making the first undo not seem to work. Then if you draw into that Path, it's not added to paths. The solution is to add the completed Path to paths in touch_up() before creating a new one.
That is, remove
paths.add(mPath);
from the constructor, and in touch_up(), change
mPath = new Path();
paths.add(mPath);
to
paths.add(mPath);
mPath = new Path();
You'll also want to add
canvas.drawPath(mPath, mPaint);
after your for loop in onDraw() in order to draw the in-progress Path.
You're not emptying undonePaths when the user starts drawing again.

Please check below code it is working..
package com.testpath;
import java.util.ArrayList;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.View.OnTouchListener;
import android.widget.Button;
import android.widget.LinearLayout;
public class TesUndoPaintActivity extends Activity {
/** Called when the activity is first created. */
LinearLayout linearLayout2;
private ArrayList<Path> undonePaths = new ArrayList<Path>();
private ArrayList<Path> paths = new ArrayList<Path>();
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
linearLayout2 = (LinearLayout) findViewById(R.id.linearLayout2);
final DrawingPanel dp = new DrawingPanel(this);
linearLayout2.addView(dp);
((Button) findViewById(R.id.button1))
.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
if (paths.size() > 0) {
undonePaths.add(paths
.remove(paths.size() - 1));
dp.invalidate();
}
}
});
((Button) findViewById(R.id.button2))
.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
if (undonePaths.size()>0) {
paths.add(undonePaths.remove(undonePaths.size()-1));
dp.invalidate();
}
}
});
}
public class DrawingPanel extends View implements OnTouchListener {
private Canvas mCanvas;
private Path mPath;
private Paint mPaint, circlePaint, outercirclePaint;
// 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);
}
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;
}
}
}
And Below XML File.
<?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/linearLayout1"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Undo" />
<Button
android:id="#+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Redo" />
</LinearLayout>
<LinearLayout
android:id="#+id/linearLayout2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
</LinearLayout>
</LinearLayout>
Please check it.

Problem
The path is only shown when you finish drawing it which leaves the user clueless as to what he is drawing
Solution
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
for (Path p : paths){
canvas.drawPath(p, mPaint);
}
//Draw path along with the finger
canvas.drawPath(mPath, mPaint);
}
Add canvas.drawPath(mPath,mPaint) to onDraw() so the user gets a feeling of actually painting on the canvas.