Develop Reference

Combine Images in Canvas and then view it through ImageView using Android Studio

I want to combine images by putting them on top of eachother in Canvas and then view the combination using ImageView. What I know is if you set the first Bitmap into the Canvas everything else you do will be added to that first Bitmap. I only get the error:
PointerException: Attempt to invoke virtual method 'int android.graphics.Bitmap.getWidth()' on a null object reference
ImageView mainImage = (ImageView) view.findViewById(R.id.mainImage);
Bitmap bottomImage = BitmapFactory.decodeFile("image1.png");
Bitmap topImage = BitmapFactory.decodeFile("image2.png");
Bitmap tempBitmap = Bitmap.createBitmap(bottomImage.getWidth(), bottomImage.getHeight(), Bitmap.Config.RGB_565);
Canvas tempCanvas = new Canvas(tempBitmap);
tempCanvas.drawBitmap(bottomImage, 0, 0, null);
tempCanvas.drawBitmap(topImage, 0, 0, null);
mainImage.setImageBitmap(bitmap);

Try Below Code
public Bitmap drawImageOnImage(Bitmap background, Bitmap pic, int x_to_draw, int y_to_draw, int width, int height)
{
try
{
Canvas newCanvas = new Canvas(background);
Bitmap img_bitmap = Bitmap.createScaledBitmap(pic, width, height, true);
newCanvas.drawBitmap(img_bitmap, x_to_draw, y_to_draw,new Paint());
}catch (Exception e)
{
System.out.println("Error Occured=>");
e.printStackTrace();
}
return background;
}
Here function takes 2 input bitmaps, Background bitmap and another image bitmap to draw over background bitmap. You will get combined bitmap to set for ImageView. X and Y are the co-rdinates where top image bitmap start paint. Same for height and width

After some experiments this code worked perfectly. And I added multiple top images.
private void drawAndView(ImageView imgView, Bitmap bottomImage, Bitmap[] topImages){
Bitmap tempBitmap = Bitmap.createBitmap(bottomImage.getWidth(), bottomImage.getHeight(), Bitmap.Config.RGB_565);
Canvas tempCanvas = new Canvas(tempBitmap);
tempCanvas.drawBitmap(bottomImage, 0, 0, null);
for (Bitmap bitmap : topImages){
tempCanvas.drawBitmap(bitmap, 0, 0, null);
}
imgView.setImageBitmap(tempBitmap);
}

Create new bitmap with black remain region issue

I have to create new bitmap from an original image after user do somethings with it like zooming, rotating, dragging. And i have a frame border, and only part of original image lay on frame is picked. Issue is that remain region of frame is black, and i want it could be transparent or white. How to do that? Thanks in advance.
public Bitmap createBitmap(final Matrix pMatrix, final Bitmap pSourceBitmap){
Bitmap bmp = Bitmap.createBitmap(width, height, pSourceBitmap.getConfig());
Canvas canvas = new Canvas(bmp);
canvas.drawBitmap(pSourceBitmap, pMatrix, new Paint());
return bmp;
}

To make the remaining portion transparent
use the following code
public Bitmap createBitmap(final Matrix pMatrix, final Bitmap pSourceBitmap)
{
Bitmap.Config conf = Bitmap.Config.ARGB_8888;
Bitmap bmp= Bitmap.createBitmap(width, height, conf);
Canvas canvas = new Canvas(bmp);
canvas.drawBitmap(pSourceBitmap, pMatrix, new Paint());
return bmp;
}

Android water mark

I have some question about water mark within android code!
Following code showed my idea about WaterMark!
However,It does not work normally.
e.g. only the image end with .png can be watered mark
Is there a scheme about water mark(.jpeg, .jpg, .wbmp, .bmp, .png or others)
protected static Bitmap getDrmPicture(Context context,String path){
BitmapFactory.Options options = new BitmapFactory.Options();
options.inPreferredConfig = Bitmap.Config.ARGB_8888;
Bitmap originMap = BitmapFactory.decodeFile (path,options);
Bitmap waterMark = BitmapFactory.decodeResource(context.getResources(), R.drawable.close);
InputStream input;
byte[] b;
Bitmap waterMark = null;
try {
input = context.getResources().openRawResource(R.drawable.lock);
b = new byte[input.available()];
input.read(b);
waterMark = DecodeUtils.requestDecode(jc, b, null);
}catch(IOException e){
}
int w = originMap.getWidth();
int h = originMap.getHeight();
int ww = waterMark.getWidth();
int wh = waterMark.getHeight();
Bitmap newb = Bitmap.createBitmap(w, h,Bitmap.Config.ARGB_8888;);
Canvas cv = new Canvas(newb);
cv.drawBitmap(originMap, 0, 0, null);
cv.drawBitmap(waterMark, w - ww, h - wh, null);
cv.save(Canvas.ALL_SAVE_FLAG);
cv.restore();
return newb;
}
Thanks !

This is the code I use to apply watermark to a jpeg, it should work for you too,
public Bitmap applyWatermarkColorFilter(Drawable drawable) {
Bitmap image = ((BitmapDrawable)drawable).getBitmap();
Bitmap result = Bitmap.createBitmap(image.getWidth(), image.getHeight(), Config.ARGB_8888);
Canvas canvas = new Canvas(result);
canvas.drawBitmap(image, 0, 0, null);
Bitmap watermark = BitmapFactory.decodeResource(getResources(), R.drawable.watermark);
canvas.drawBitmap(watermark, image.getWidth()/2 - watermark.getWidth()/2,
image.getHeight()/2 - watermark.getHeight()/2,
null);
return result;
}
Basically after this u have to use Bitmap.compress(<arguments>) to get a jpg out of it.
Din't try for the other formats. May be it might be possible if you can extract the Bitmap out of them like how we do for jpg and png.

https://stackoverflow.com/questions/6756975/draw-multi-line-text-to-canvas
Measure height of multiline text
To center text vertically we need to know text height. Instantiate StaticLayout with text width according to your needs, for us it is simple the width of Bitmap/Canvas minus 16dp padding. The getHeight() then returns height of text.
Positioning text on Canvas
There are four simple steps to position text on Canvas:
Save the current matrix and clip with Canvas.save().
Apply translation to Canvas matrix with Canvas.translate(x,y).
Draw StaticLayout on Canvas with StaticLayout.draw(canvas).
Revert matrix translation with Canvas.restore() method.

Rotating a drawable in Android

How can a Drawable loaded from a resource be rotated when it is drawn? For example, I would like to draw an arrow and be able to rotate it to face in different directions when it is drawn?

You need to use Bitmap and Canvas Class functions to prepare drawable:
Bitmap bmpOriginal = BitmapFactory.decodeResource(this.getResources(), R.drawable.image2);
Bitmap bmResult = Bitmap.createBitmap(bmpOriginal.getWidth(), bmpOriginal.getHeight(), Bitmap.Config.ARGB_8888);
Canvas tempCanvas = new Canvas(bmResult);
tempCanvas.rotate(90, bmpOriginal.getWidth()/2, bmpOriginal.getHeight()/2);
tempCanvas.drawBitmap(bmpOriginal, 0, 0, null);
mImageView.setImageBitmap(bmResult);
In this code sample rotation for 90 degrees over image center occurs.

essentially it can be boiled down to: do a(n inverse) canvas transformation instead of transforming drawable
private BitmapDrawable drawable; // or Drawable
protected void onDraw(Canvas canvas) { // inherited from View
//...
canvas.save();
canvas.rotate(degrees, pivotX, pivotY);
drawable.draw(canvas);
canvas.restore();
//...
}
if you have BitmapDrawable it may be desirable to increase quality of the output by setting antialiasing
drawable.setAntialias(true);

Accepted answer doesn't work for me. I have non square image, so I changed his code a bit.
private Bitmap rotateDrawable(#DrawableRes int resId) {
Bitmap bmpOriginal = BitmapFactory.decodeResource(getResources(), resId);
Bitmap bmpResult = Bitmap.createBitmap(bmpOriginal.getHeight(), bmpOriginal.getWidth(), Bitmap.Config.ARGB_8888);
Canvas tempCanvas = new Canvas(bmpResult);
int pivot = bmpOriginal.getHeight() / 2;
tempCanvas.rotate(90, pivot, pivot);
tempCanvas.drawBitmap(bmpOriginal, 0, 0, null);
return bmpResult;
}
mImageView.setImageBitmap(rotateDrawable(R.drawable.some_image));

essentially this:
ImageView spaceshipImage = (ImageView) findViewById(R.id.spaceshipImage);
Animation hyperspaceJumpAnimation = AnimationUtils.loadAnimation(this, R.anim.hyperspace_jump);
spaceshipImage.startAnimation(hyperspaceJumpAnimation);
source link:
http://developer.android.com/guide/topics/graphics/2d-graphics.html#tween-animation

how to display complete Bitmap in android using Canvas?

friends,
i am using following onDraw method to display bitmap on screen.
#Override
public void onDraw(Canvas canvas) {
Bitmap _scratch = BitmapFactory.decodeResource(getResources(), R.drawable.icon2);
//ImageView img= new ImageView(Tutorial2D.this);
//img.setImageBitmap(_scratch);
canvas.drawColor(Color.BLACK);
canvas.drawBitmap(_scratch, 0, 0, null);
}
image is displayed on the screen but some part because android screen is small
how can i display complete image in whole android screen?
can i set ScaleType of image to fitxy in canvas ?
or
can i add android layout image to this canvas so that i could set fitxy property or image there as i have commented the code?
any help would be appreciated.

You can call Bitmap.createScaledBitmap(Bitmap src, int dstWidth, int dstHeight, boolean filter)

You can use a ImageView
iv = (ImageView) findViewById(R.id.ImageView01);
iv.setImageBitmap(getImageBitmap(myurl));