问题
I have already seen fingurePaint.java from API demos. I want to implement touch smooth eraser to erase parts of the image by touch move in android.
fingurePaint told me to implement this
mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
But this is not working to erase the image. It is working to erase something which is drawn by touch.
public class SandboxView extends View implements OnTouchListener {
public final Bitmap bitmap;
private final int width;
private final int height;
private Matrix transform = new Matrix();
private Vector2D position = new Vector2D();
private float scale = 1;
private float angle = 0;
public boolean isInitialized = false;
private TouchManager touchManager = new TouchManager(2);
final GestureDetector mGesDetect;
// Debug helpers to draw lines between the two touch points
private Vector2D vca = null;
private Vector2D vcb = null;
private Vector2D vpa = null;
private Vector2D vpb = null;
private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;
private Path mPath;
private Canvas mCanvas;
private Paint mPaint;
private Paint mBitmapPaint;
public SandboxView(Context context, Bitmap bitmap) {
super(context);
this.bitmap = bitmap;
this.width = bitmap.getWidth();
this.height = bitmap.getHeight();
this.mGesDetect = new GestureDetector(context, new DoubleTapGestureDetector());
setOnTouchListener(this);
}
private float getDegreesFromRadians(float angle) {
return (float)(angle * 360.0 / Math.PI);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (!isInitialized) {
Bitmap mBitmap = bitmap.createBitmap(320, 480, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
mPaint = new Paint();
mPath = new Path();
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);
mPaint.setAlpha(0);
mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
mPaint.setAntiAlias(true);
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
int w = getWidth();
int h = getHeight();
position.set(w / 2, h / 2);
isInitialized = true;
}
if(isEraser==1){
canvas.drawColor(80000000);
canvas.drawBitmap(bitmap, transform, mBitmapPaint);
canvas.drawPath(mPath, mPaint);
}
else{
Paint paint = new Paint();
transform.reset();
transform.postTranslate(-width / 2.0f, -height / 2.0f);
transform.postRotate(getDegreesFromRadians(angle));
transform.postScale(scale, scale);
transform.postTranslate(position.getX(), position.getY());
canvas.drawBitmap(bitmap, transform, paint);
try {
/*paint.setColor(0xFF007F00);
canvas.drawCircle(vca.getX(), vca.getY(), 64, paint);
paint.setColor(0xFF7F0000);
canvas.drawCircle(vcb.getX(), vcb.getY(), 64, paint);
paint.setColor(0xFFFF0000);
canvas.drawLine(vpa.getX(), vpa.getY(), vpb.getX(), vpb.getY(), paint);
paint.setColor(0xFF00FF00);
canvas.drawLine(vca.getX(), vca.getY(), vcb.getX(), vcb.getY(), paint);*/
}
catch(NullPointerException e) {
// Just being lazy here...
}
}
}
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);
mCanvas.drawPath(mPath, mPaint);
mPath.reset();
}
@Override
public boolean onTouch(View v, MotionEvent event) {
if(isEraser ==1){
float x = event.getX();
float y = event.getY();
mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
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{
vca = null;
vcb = null;
vpa = null;
vpb = null;
mGesDetect.onTouchEvent(event);
try {
touchManager.update(event);
if (touchManager.getPressCount() == 1) {
vca = touchManager.getPoint(0);
vpa = touchManager.getPreviousPoint(0);
position.add(touchManager.moveDelta(0));
}
else {
if (touchManager.getPressCount() == 2) {
vca = touchManager.getPoint(0);
vpa = touchManager.getPreviousPoint(0);
vcb = touchManager.getPoint(1);
vpb = touchManager.getPreviousPoint(1);
Vector2D current = touchManager.getVector(0, 1);
Vector2D previous = touchManager.getPreviousVector(0, 1);
float currentDistance = current.getLength();
float previousDistance = previous.getLength();
if (previousDistance != 0) {
scale *= currentDistance / previousDistance;
}
angle -= Vector2D.getSignedAngleBetween(current, previous);
}
}
invalidate();
}
catch(Throwable t) {
// So lazy...
}
return true;
}
}
class DoubleTapGestureDetector extends GestureDetector.SimpleOnGestureListener {
@Override
public boolean onDoubleTap(MotionEvent e) {
colorseekbar.setVisibility(View.INVISIBLE);
opacityseekbar.setVisibility(View.INVISIBLE);
return true;
}
}
}
So please help me to erase the parts of image by using touch move.
Thanks in advance.
回答1:
First Declar your paint with all property in your constructor.
Write this code in your onDraw() method
@Override
protected void onDraw(Canvas canvas)
{
System.out.println("come in on draw......");
canvas.drawColor(Color.TRANSPARENT);
canvas.drawBitmap(mBitmap, 0, 0, mPaint);
if(eraser==true)
mPaint.setColor(Color.TRANSPARENT):
else
mPaint.setColor(Color.RED):
canvas.drawPath(mPath, mPaint);
super.dispatchDraw(canvas);
}
second solution:
call below method in your touch_move() method
mBitmap.setPixel(x, y, Color.TRANSPARENT); This method will change your bitmap you have to pass only X,Y & COLOR
public void changeBitmap(int x, int y, Bitmap mBitmap)
{
Bitmap tempBitmap = Bitmap.createBitmap(mBitmap); //Edited code
tempBitmap.setPixel(x, y, Color.TRANSPARENT);
}
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;
changeBitmap(x, y, your_bitmap)
}
}
回答2:
Isn't it better to invert this case ? Just paint on your image with background color and after all when saving, merge those layers if needed.
回答3:
Define a temporary canvas and bitmap then draw your path or line, circle, image anything on touch events and then pass this temporary bitmap to canvas in onDraw your work will done properly, and also if you want to do erasing then do your erasing on that temporary canvas.
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
TemporaryBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_4444);
TemporaryCanvas = new Canvas(TemporaryBitmap);
}
TemporaryCanvas.drawColor(0, PorterDuff.Mode.clear);
public void onDraw(Canvas canv){
canv.drawBitmap(TemporaryBitmap, matrix, paint);
来源：https://stackoverflow.com/questions/12297396/how-to-implement-touch-smooth-image-eraser-in-android