How to get all points in Motion event

Question

I'm developing finger paint type of application for erasing . I m using stroke deletion (not points deletion) for this I m collecting whole stroke objects stored in array-list when stroke deletion , I just compared for each stroke and delete the particular stroke. While re-rendering whole strokes in canvas after deletion ,I m missing many points even though I m collecting my historical points event

Answer 1

In apiDemos, in android there is "FingerPaint" demo inside "Graphics" folder. The demo also has option for erase (click the sub menu to see the option). You can refer that.

In case you dont have the source code of android, refer code below:

FingerPaint.java

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.apis.graphics;

import android.content.Context;
import android.graphics.*;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;

public class FingerPaint extends GraphicsActivity
        implements ColorPickerDialog.OnColorChangedListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new MyView(this));

        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(0xFFFF0000);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(12);

        mEmboss = new EmbossMaskFilter(new float[] { 1, 1, 1 },
                                       0.4f, 6, 3.5f);

        mBlur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
    }

    private Paint       mPaint;
    private MaskFilter  mEmboss;
    private MaskFilter  mBlur;

    public void colorChanged(int color) {
        mPaint.setColor(color);
    }

    public class MyView extends View {

        private static final float MINP = 0.25f;
        private static final float MAXP = 0.75f;

        private Bitmap  mBitmap;
        private Canvas  mCanvas;
        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);
        }

        @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;
        }
    }

    private static final int COLOR_MENU_ID = Menu.FIRST;
    private static final int EMBOSS_MENU_ID = Menu.FIRST + 1;
    private static final int BLUR_MENU_ID = Menu.FIRST + 2;
    private static final int ERASE_MENU_ID = Menu.FIRST + 3;
    private static final int SRCATOP_MENU_ID = Menu.FIRST + 4;

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        super.onCreateOptionsMenu(menu);

        menu.add(0, COLOR_MENU_ID, 0, "Color").setShortcut('3', 'c');
        menu.add(0, EMBOSS_MENU_ID, 0, "Emboss").setShortcut('4', 's');
        menu.add(0, BLUR_MENU_ID, 0, "Blur").setShortcut('5', 'z');
        menu.add(0, ERASE_MENU_ID, 0, "Erase").setShortcut('5', 'z');
        menu.add(0, SRCATOP_MENU_ID, 0, "SrcATop").setShortcut('5', 'z');

        /****   Is this the mechanism to extend with filter effects?
        Intent intent = new Intent(null, getIntent().getData());
        intent.addCategory(Intent.CATEGORY_ALTERNATIVE);
        menu.addIntentOptions(
                              Menu.ALTERNATIVE, 0,
                              new ComponentName(this, NotesList.class),
                              null, intent, 0, null);
        *****/
        return true;
    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        super.onPrepareOptionsMenu(menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        mPaint.setXfermode(null);
        mPaint.setAlpha(0xFF);

        switch (item.getItemId()) {
            case COLOR_MENU_ID:
                new ColorPickerDialog(this, this, mPaint.getColor()).show();
                return true;
            case EMBOSS_MENU_ID:
                if (mPaint.getMaskFilter() != mEmboss) {
                    mPaint.setMaskFilter(mEmboss);
                } else {
                    mPaint.setMaskFilter(null);
                }
                return true;
            case BLUR_MENU_ID:
                if (mPaint.getMaskFilter() != mBlur) {
                    mPaint.setMaskFilter(mBlur);
                } else {
                    mPaint.setMaskFilter(null);
                }
                return true;
            case ERASE_MENU_ID:
                mPaint.setXfermode(new PorterDuffXfermode(
                                                        PorterDuff.Mode.CLEAR));
                return true;
            case SRCATOP_MENU_ID:
                mPaint.setXfermode(new PorterDuffXfermode(
                                                    PorterDuff.Mode.SRC_ATOP));
                mPaint.setAlpha(0x80);
                return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

Hope it helps...

Answer 2

check this link for Getting All x and y coordinates from a motion event in android.

OR

try this code

 void printSamples(MotionEvent ev) {
 final int historySize = ev.getHistorySize();
 final int pointerCount = ev.getPointerCount();
 for (int h = 0; h < historySize; h++) {
     System.out.printf("At time %d:", ev.getHistoricalEventTime(h));
     for (int p = 0; p < pointerCount; p++) {
         System.out.printf("  pointer %d: (%f,%f)",
             ev.getPointerId(p), ev.getHistoricalX(p, h), ev.getHistoricalY(p, h));
     }
 }
 System.out.printf("At time %d:", ev.getEventTime());
 for (int p = 0; p < pointerCount; p++) {
     System.out.printf("  pointer %d: (%f,%f)",
         ev.getPointerId(p), ev.getX(p), ev.getY(p));
 }
 }

From this link for Motion Events.

Hope this helps you.