Develop Reference

Android how to stretch a particular section of a Image?

I am developing a photography app in which I want to select a particular section of a photo and stretch that portion only. How to do that?
I have tried to stretch a photo using Canvas but failed to do so. Is it possible from android.graphics.NinePatch class?
Any suggestions?

You can use matrix to apply new dimension to your bitmap.
you could use setscale/postScale methods of a matrix object.

A rather ugly solution would be using a image cropping library. You can use it to temporarily crop a portion of the image and load it into another ImageView and then scaling it up.
Also, you can get things done without using that CropImageView. The idea is whenever user touches the original image view, you will be given a (x, y) at which user's finger resides. So, you can extract a bitmap image centered at (x, y) and with a given radius.
For applying a magnifier effect you could use a round/circular ImageView for showing magnified portion of the image.
Something like this:

Finally i found a solution of my problem below :
Bitmap stretchImage = Bitmap.createBitmap(w, h+progress, Bitmap.Config.ARGB_8888 );
c = new Canvas(stretchImage);
//draw top bit
c.drawBitmap(normalImage, new Rect(0,0,w,75), new Rect(0,0,w,75), null);
//draw middle bit
c.drawBitmap(normalImage, new Rect(0,75,w, 150), new Rect(0,75,w,150+progress), null);
//draw right bit
c.drawBitmap(normalImage, new Rect(0 ,150,w,225), new Rect(0 ,150+progress,w,225+progress), null);
myImage.setImageBitmap(stretchImage);

Android: drawing on large bitmap, 2 layers, best way?

im working on an app, that displays large(around 2000x2000px) bitmap in imageview. This image has to be that large since user can pinch to zoom it in order to see some details. App has to be able to draw circles on that image, and also to display image alone, without circles on it. I was using 2 layers but the problem is memory since 2k x 2k px is around 16mb of memory, and creating another bitmap(another 16mb), just to draw a few circles, is pointless in my opinion. Is there any way, that you can draw simple primitives on image, and also be able to display it without primitives(circles in my case)?
Maybe somehow to store only modified pixels or sth?
Thanks!

You don't need to make another 2000x2000 Bitmap to draw those circles on. Just 'prerender' a circle, and then choose where you draw it.
I'm working under the assumption that you're drawing your 'big' image on a Canvas, since you have zooming features etc.
If you're not, you'll need to override your SurfaceView's onDraw(Canvas canvas) method so that you can access the SurfaceView Canvas. I won't go into depth about that part since again I'm assuming you have it, but if not the implementation of that function would look like this:
//Overriding SurfaceView onDraw(Canvas canvas)
#Override
protected void onDraw(Canvas surfaceCanvas) {
if(canvas == null) return; //No Canvas? No point in drawing then.
surfaceCanvas.drawColor(Color.BLACK);
//Draw your 'big' image on the SurfaceView Canvas
insertYourBigImageDrawingFunctionHere(surfaceCanvas);
//Now draw your circles at their correct positions...
insertCircleDrawingFunctionHere(surfaceCanvas);
}
Now that you have access to the SurfaceView Canvas, you can choose precisely how things are drawn on it. Like circles for example...
I want to draw your attention to the multiple Canvas' being used below (surfaceCanvas vs. circleCanvas). I once thought that Canvas was a kind-of 'one Canvas for the whole app/activity' implementation, but it isn't. You are free to create Canvas' as you please. It is merely an instance of a tool to draw onto Bitmaps. This was a HUGE revelation for me, and gave me much more robust control over how Bitmaps are composed.
public void myCircleDrawingFunction(Canvas surfaceCanvas){
//Make a new Bitmap for your circle
Bitmap.Config conf = Bitmap.Config.ARGB_4444;
tinyCircleBMP = Bitmap.createBitmap(10,10, conf);
//Make a new canvas using that Bitmap as the source...
Canvas circleCanvas = new Canvas(cacheBmp);
//Now, perform your drawing on the `Canvas`...
Paint p = new Paint();
circleCanvas.drawCircle(5, 5, 5, p);
//Now the `Bitmap` has a circle on it, draw the `Bitmap` on the `SufaceView Canvas`
surfaceCanvas.drawBitmap(tinyCircleBMP, 10, 10, p);
//Replace the '10's in the above function with relevant coordinates.
}
Now obviously, your circles will zoom/pan differently to your 'big' image, since they are no longer being drawn at the same size/position of the 'big' image. You will need to consider how to translate the positions of each circle taking into account the current scale and position of the 'big' image.
For example, if your image is zoomed in to 200%, and a circle is supposed to appear 100px from the left of the big image, then you should multiply the pixel values to take into account the zoom, like this
(PsuedoCode):
drawCircleAtX = Bitmap.left * BitmapZoomFactor

If you are using the canvas API (if not I would suggest to)? if so you are just draw your image on the canvas and then the primitive shapes on top of the same canvas before display. This way you just keep a reference of the circles position in some basic data types and scale them as the user moves around and zooms, so you know where to draw them each frame.

rotating and cropping a bitmap accurately and effiently in android

I'm writing an android application.By using it,a user can crop the bitmap image.But I want to add more function,that is to rotate the image before cropping.
I followed the below steps to accomplish this purpose.
built a custom view.
initialized BitmapDrawable() and a cropping rectangle(Rect()) [the rectangle determines where to cop in the bitmap]
override onTouch(MotionEvent) method for two functions
a. user can move the bitmap over the screen
b. user can transform the cropping rectangle
override onDraw(Canvas) method to update the screen.This code is for showing bitmap.
bitmap_drawable.draw(canvas,_bitmap_paint);
Problem:1
This step ,that I don't know how to do, is to show a rotated properly. I used this code to rotate the canvas in the onDraw(Canvas) method.
canvas.rotate(_angle);
But it makes all the things on the screen (including the cropping rectangle) to rotate.
Question:2
Is it a wise way to initialize my own Canvas() object to draw the bitmap on?
Note:
Here,the rotation that I want,is very accurate up to 1 degree and is performed by two-finger rotation gesture so that performance is very important and the following code(using matrix) is bad.
Matrix mat = new Matrix();
mat.preRotate(_degree, _one_finger_x, _one_finger_y);
Bitmap _new_bitmap = Bitmap.createBitmap(_old_bitmap, 0, 0, bmWidth, bmHeight, mat, true);
Therefore,I think initializing a separate Canvas() and using canvas.rotate(_degree) is very appropriate.However,this makes controlling touch events quite difficult.Any ideas?Please help.
Problem:2
Suppose that I can now rotate the bitmap separately from all objects,i.e. the cropping rectangle,etc.This step is to crop the bitmap and show the cropped result to the user efficiently.When rotate function is not included, I simply copy the color bytes within the cropping rectangle on the old bitmap as follow.
Bitmap _new_bitmap = Bitmap.createBitmap( _old_bitmap, _cropRectx, _cropRecty, _cropRectWidth, _cropRectHeight, null);
But here,from a rotated bitmap, how can I clone the color bytes through a crossing crop rectangle?
Question:2
How can I crop a rotated bitmap?

Android - Extend a Bitmap to use as MapMarker

I want to use downloaded images as markers on a MapView. I images are all squares but I would like the bottom to also extend to form a triangle marking the exact point.
My approach was to create a canvas which is slightly larger than the image. Then, draw the bitmap on to the canvas and then somehow pick the color from the bottom of the bitmap and draw a triangular shape from the horizontal center of the image to the bottom of the canvas. Something like this...
As you might guess I'm stuck with the last part. So far I have....
Bitmap canvasBitmap = Bitmap.createBitmap(markerBitmap.getWidth(), markerBitmap.getHeight()+10, Bitmap.Config.ARGB_8888);
// The 10 pixels will be the so called "pin"
Canvas canvas = new Canvas(canvasBitmap);
canvas.drawBitmap(markerBitmap, 0.0f, 0.0f, null);
// Can figure out how to draw the 10 px bottom using the color from markerBitmap
Help !!

Is there any specific reason why you want to create the images dynamically? If not, why don't you create them using a graphics editing program, save them as png's or 9-patch images and then simply assign it to the Drawable that's used for the marker.

Android: building a composite image

Im porting an app from Flex to Android and wondering about how to build a composite image and display it.
Specifically I have a map (PNG or JPG) of a house and Im placing different markers in various locations. I've implemented this in HTML using DIV and in Flex using a canvas. Each marker has an X,Y pair based on the original size of the image. Ideally I'd like to display the image, place the markers and then support resize, drag (of the image, not the markers), etc.
There is info about 'multi-touch' available here though its a bit dated.
Suggestions on where to start?

You have to watch out for non-mutable bitmaps. When you load your bitmap, you have to create a copy which will be mutable. Then just apply your overlay using a Canvas.
Bitmap tempBitmap = BitmapFactory.decodeResource(getResources(), R.id.background, options);
Bitmap overlay = BitmapFactory.decodeResource(getResources(), R.id.overlay, options);
Bitmap finalBitmap = Bitmap.createBitmap(tempBitmap.getWidth(), tempBitmap.getHeight(), tempBitmap.getConfig());
Canvas canvas = new Canvas(finalBitmap);
canvas.drawBitmap(tempBitmap, new Matrix(), null);
canvas.drawBitmap(badge, new Matrix(), null);
// finalBitmap will contain your background and its overlay
-I_Artist