Develop Reference

Canvas bitmap is not being saved

i am new to android canvas and i failed to get solution of my problem,
the problem is:
I am using canvas in two modes AvoidXfermode.Mode.TARGET(to remove occurence of a single color) and PorterDuff.Mode.CLEAR(to erase a part of my canvas).
everything independently is working perfect
but in my code i want to use both of them in such a way that when i choose i want to erase a particular color it should erase it, and my code is doing so,
but after removing that particular color when i am switching my mode to eraser mode...everything which was deleted using AvoidXfermode comes back.
i am doing these things on a bitmap,
my onDraw method is:
#Override
protected void onDraw(Canvas canvas) {
canvas.drawBitmap(DrawBitmap, 0, 0, DrawBitmapPaint);
if (flag != 1) {
setDrawingCacheEnabled(true);
for (Path p : paths) {
canvas.drawPath(p, mPaint);
Bitmap bitmap = getDrawingCache();
DrawBitmap = bitmap;
//
}
//canvas.setBitmap(bitmap.isMutable() ? bitmap : bitmap.copy(Bitmap.Config.ARGB_8888,true));
} else if (flag == 1) {
if (touchx > mCanvas.getWidth() || touchy > mCanvas.getHeight() || touchx < 0 || touchy < 0) {
return;
}
for (Path p : paths) {
color = DrawBitmap.getPixel(touchx, touchy);
mPaint.setXfermode(new AvoidXfermode(color, 100, AvoidXfermode.Mode.TARGET));
mPaint.setColor(Color.TRANSPARENT);
canvas.drawPaint(mPaint);
setDrawingCacheEnabled(true);
Bitmap bitmap = getDrawingCache();
DrawBitmap = bitmap;
}
}
}
everything is declared in onDraw for now just for the this question,
and the code where i switch my mode is:
case R.id.erase:
mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
mPaint.setColor(Color.TRANSPARENT);
mPaint.setStrokeWidth(40);
flag = 0;
break;
case R.id.DELETE:
flag = 1;
break;
the code where i am creating my canvas is:
DrawBitmap = BitmapFactory.decodeResource(MainActivity.this.getResources(), R.drawable.sample);
DrawBitmap = DrawBitmap.copy(Bitmap.Config.ARGB_8888, true);
mCanvas = new Canvas(DrawBitmap);
mPath = new Path();
paths.add(mPath);
DrawBitmapPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
i am wrong somewhere,but i don't know where, any suggestions would be helpful, thanks in advance.

Bitmap bitmap = getDrawingCache();
DrawBitmap = bitmap;
Your logic is a lot complicated. I specifically mean the above lines of code. You have mCanvas that is backed up with the DrawBitmap bitmap. Then you have the canvas of onDraw() which is backed by it's own bitmap. The thing you need to understand is whatever you draw in DrawBitmap stays or as you would call it "saved". Anything that is drawn via canvas is subjected to change during the next call to onDraw().
So if you want to save something in DrawBitmap use the mCanvas. The moment you want to save the state of the user's drawing, draw it in mCanvas. You could just draw everything on mCanvas and at the end of onDraw(), you can call canvas.drawBitmap(DrawBitmap, 0, 0, DrawBitmapPaint); This way everything that is done by the user is saved every step of the way.

Android setBitmap to canvas

i want to convert canvas to image and save it on device. But when I set bitmap to canvas I get error java.lang.UnsupportedOperationException.
My full code:
public class SingleTouchEventView extends View {
private Paint paint = new Paint();
private Path path = new Path();
public SingleTouchEventView(Context context, AttributeSet attrs) {
super(context, attrs);
paint.setAntiAlias(true);
paint.setStrokeWidth(6f);
paint.setColor(Color.WHITE);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeJoin(Paint.Join.BEVEL);
}
#Override
protected void onDraw(Canvas canvas) {
canvas.drawPath(path, paint);
canvas.drawCircle(50, 50, 3, paint);
Bitmap bitmap = Bitmap.createBitmap(canvas.getWidth(), canvas.getHeight(), Bitmap.Config.ARGB_8888);
canvas.setBitmap(bitmap);
try {
File file = new File(Environment.getExternalStorageDirectory() + "/image.jpg");
bitmap.compress(Bitmap.CompressFormat.JPEG, 100, new FileOutputStream(file));
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
Maybe someone could help me to solve this problem?

That isn't how you draw to a bitmap. You do NOT use the canvas that draws to the screen. You create a second canvas, passing in the bitmap you want to draw to as a parameter in the constructor. Then any draw commands to that canvas will draw the bitmap. Then you draw that bitmap to the screen. Something like this:
Canvas myCanvas = new Canvas(myBitmap);
myCanvas.drawLine();
myCanvas.drawCircle();
//Insert all the rest of the drawing commands here
screenCanvas.drawBitmap(myBitmap, 0, 0);
I also would not write it to the file system in onDraw - I'd expect drawing performance to suffer badly if you do. A separate function call can do that. If you keep myBitmap around in a variable, you can just compress it anytime to write out the last draw to disk.

Why does the drawBitmap method in Canvas class distorts the image

Why does the drawBitmap() method in Canvas class distorts the image?
When I use setImageBitmap() function of ImageView to set the bitmap on a subclass of ImageView, the image is rendered perfectly.
Now there is a bug in Android 4.x and this setImageBitmap causes problem for extra menu items. The extra menu items (generally beyond six menu items that are displayed using More...) looses touch listener.
I have following code that shows how the image is rendered using two different method.
/**
* draws bitmap icons
*/
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if(bitmap == null){
bitmap = AppMain.getItemIcon(thisItem);
}
//drawBitmap(canvas, bitmap); //distorts image
drawBitmap(bitmap); //works perfect
}
//draw using setImageBitmap
private void drawBitmap(Bitmap bitmap){
if(bitmap != null){
this.setImageBitmap(bitmap);
Matrix m = this.getImageMatrix();
m.setRectToRect(new RectF(0, 0, bitmap.getWidth(), bitmap.getHeight()),
new RectF(0, 0, this.getWidth(), this.getHeight()),
Matrix.ScaleToFit.CENTER);
this.setImageMatrix(m);
}
}
//draw using canvas.drawBitmap()
private void drawBitmap(Canvas canvas, Bitmap bitmap){
if(bitmap != null){
Matrix m = new Matrix();
m.setRectToRect(new RectF(0, 0, bitmap.getWidth(), bitmap.getHeight()),
new RectF(0, 0, this.getWidth(), this.getHeight()),
Matrix.ScaleToFit.CENTER);
canvas.drawBitmap(bitmap, m, null);
}
}

Probably it is just scaled up. By default ImageView draws scaled bitmaps using bilinear filtering. You can try enabling it when calling Canvas.drawBitmap. You need to create new Paint object with corresponding flag (but don't do this in onDraw method):
Paint mPaint = new Paint(Paint.FILTER_BITMAP_FLAG);
And then supply this Paint object to the Canvas.drawBitmap method:
canvas.drawBitmap(bitmap, m, mPaint);

How to work with finger eraser in android?

I have prepared one paint app.In my app we can draw any thing.It is working fine.Here i want prepare finger erase for erase paint.Eraser is working,but it is eraser all the drawn paint.I want to eraser only where i touch if drawn paint is there for that i wrote some code,
this my ondraw method,
public void onDraw(Canvas canvas) {
if (myDrawBitmap == null) {
myDrawBitmap = Bitmap.createBitmap(480, 800,
Bitmap.Config.ARGB_8888);
mBmpDrawCanvas = new Canvas(myDrawBitmap);
mIntDrawArray = new int[myDrawBitmap.getWidth()
* myDrawBitmap.getHeight()];
}
if (mBmpDrawCanvas != null) {
myDrawBitmap.getPixels(mIntDrawArray, 0, myDrawBitmap.getWidth(),
0, 0, myDrawBitmap.getWidth(), myDrawBitmap.getHeight());
for (Path path : ILearnPaintActivity.mArryLstPath) {
if (ILearnPaintActivity.mArryLstPath.contains(path)
&& ILearnPaintActivity.paintAndEraserFlag == 1) {
mPaint.setXfermode(new PorterDuffXfermode(
PorterDuff.Mode.CLEAR));
mBmpDrawCanvas.drawPath(ILearnPaintActivity.mPath, mPaint);
} else {
mBmpDrawCanvas.drawPath(ILearnPaintActivity.mPath, mPaint);
}
}
if (myDrawBitmap != null)
canvas.drawBitmap(myDrawBitmap, 0, 0, null);
}
}
draw paint is working fine.In same activity i have one button "Eraser". when we click on eraser button i assign flag for difference.Please help me how to do this...

first u need to make clear what erase.
for vector base canvas it's delete vector element.
for pixel base canvas it's mean draw with backgournd color. (or make it's transparency)
so in my point of view. when erase. you can change a Paint with backgournd color. and continue draw a very bold line on bitmap by touch.

try like this
mBitmap.eraseColor(Color.TRANSPARENT); // Bitmap erase color
mPath.reset(); // your path
mView.invalidate(); // your View Path

Adding an Image to a Canvas in Android

Good Day Everyone
I was hoping if you could help me understand the concepts of understanding how to add an image into a canvas on a OnTouchEvent implemented on a View. So far, this is what i've come up with.
parent is the Activity where in this customized view is instantiated and is added into.
#Override
protected void onDraw(Canvas canvas)
{
// TODO Auto-generated method stub
super.onDraw(canvas);
}
public void insertImage()
{
if (parent.selected_icon.contentEquals("image1"))
{
image = getResources().getDrawable(R.drawable.image1);
}
else if (parent.selected_icon.contentEquals("image1"))
{
image = getResources().getDrawable(R.drawable.image2);
}
else if (parent.selected_icon.contentEquals("iamge3"))
{
image = getResources().getDrawable(R.drawable.image3);
}
Rect srcRect = new Rect(0, 0, image.getIntrinsicWidth(),
image.getIntrinsicHeight());
Rect dstRect = new Rect(srcRect);
Bitmap bitmap = Bitmap.createBitmap(image.getIntrinsicWidth(),
image.getIntrinsicHeight(), Bitmap.Config.ALPHA_8);
Canvas canvas = new Canvas();
canvas.drawBitmap(bitmap, srcRect, dstRect, null);
invalidate();
}

When you want to draw over a view, you have to do that in onDraw(), using the Canvas passed there. That Canvas is already bound to the Bitmap that is the actual drawing of your view.
I had to do something similar and my approach was like this:
I had a list of "things to be drawn over the view" as a member of the class.
whenever I added something to that list, I called invalidate(), so that onDraw() would get called.
My onDraw() looked like this:
...
protected void onDraw(Canvas canvas) {
super.onDraw(canvas); // the default drawing
for(ThingToBeDrawn thing : mListOfThingsToBeDrawn) {
thing.drawThing(canvas); // draw each thing over the view
}
}
A Canvas is just a tool used to draw a Bitmap, and it works quite differently than SurfaceView.