Develop Reference

Using NinePatch (.9.png) for making scaled Bitmaps

I need to draw a Bitmap for my new Android Application. Since my content view is set to a Game-Panel class I've created. I want to display images through Bitmap. Just because its more convenient, and easier to do then anything else.
From what I've gathered from researching, Nine Patch images (.9.png) are used in android to scale more properly then regular Drawable images. It also says "This can be used for scaling properly in backgrounds. For example a regular button background...". If Nine Patch images are made to scale better. Can You use a Nine Patch for making a Bitmap in a specific width and height because it would scale more properly? For example
Bitmap b = createBitmap(BitmapFactory.decodeResource(NinePatchImage), x, y, width, height);
Is this possible? Should I do it a different way? Should I create a bitmap first and then just scale the bitmap? Is this even necessary? Please help.

Bitmap bitmap = Bitmap.createBitmap(canvasWidth, canvasHeight, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
NinePatchDrawable drawable = (NinePatchDrawable) getResources().getDrawable(R.drawable.myDrawable);
drawable.setBounds(new Rect(x, y, width, height));
drawable.draw(canvas);

How to find center position of a bitmap that rotated and scaled with a matrix?

I want to calculate center of a bitmap that is drawn on a canvas with a matrix, it can be rotated, scaled or translated with a arbitrary value. What is the easiest way to find center of the this bitmap on canvas?

You need to apply the matrix to the coordinates of the center of bitmap.
If you use a canvas that has a transformation matrix, you can get the final matrix through Canvas.getMatrix()
If you draw the Bitmap on the Canvas with a Matrix : drawBitmap(bitmap, matrix, paint), then you you need to use that Matrix, or concatenate it to that of the Canvas (in the case it has one).
Then you can finally apply that matrix to the center of the matrix using Matrix.mapPoints.
Something like :
canvas.drawBitmap(bitmap, bitmap_transform, paint);
Matrix full_transform = new Matrix(canvas.getMatrix());
full_transform.postConcat(bitmap_transform);
float[] center = new float[] {bitmap.getHeight()/2.0, bitmap.getWidth()/2.0};
full_transform.mapPoints(center);
Alternatively, if you apply transformations to your bitmap without a matrix, you can use the full_transform.postRotate, full_transform.postScale, etc with the same values. In particular, if you draw your bitmap with drawBitmap(bitmap, left, top, paint) then you need to do a full_transform.postTranslate(left, top).

If you're looking for the "easiest" way then just sticking with the translate rotate and scale functions would solve the problem. The reason that those were developed was so developers wouldn't have to do vector calculus for simple animations. Also the only value you would have to actually calculate in that sense it is the translate value after you take into account the original coordinates.

Zoom in and rotate simultaneously on seekbar in Android

I am working on a project where I need to ZoomIn and rotate the image simultaneously on seekbar progress value.
I have tried below code. But this is not working. This is just rotating the image.
Matrix matrix = new Matrix();
matrix.postRotate(curValue);
//matrix.postScale(curValue, curValue);
Bitmap resizedBitmap = Bitmap.createBitmap(bitmaprotate, 0, 0, bmpWidth, bmpHeight, matrix, true);
mainImage.setImageBitmap(resizedBitmap);

For achieving this you better to use custom view and canvas. Using canvas you can easily rotate and scale the images. Please refer this links (resize the bitmap canvas ,Android Scaling Canvas Bitmap , http://www.barebonescoder.com/2010/06/android-development-simple-2d-graphics-part-1/)

Drawing mirrored bitmaps in android

I'm trying to learn how to make an animated sprite in android and couldn't figure out how to go about organising my bitmaps. I have a sprite sheet of my character walking to the Right: a bitmap of five copies of a character, equally spaced (every 45px), in a walk cycle.
I planned to draw each frame by drawing a tiny section of my sprite sheet bitmap at a time by going:
Rect sourceRect = new Rect(0, 0, 45, 75);
canvas.drawBitmap(spriteSheetBitmap, sourceRect, new Rect(0, 0, 45, 75), null);
Then for the next frames, increment "sourceRect.x" by 45, then redraw and so forth.
However, I'm now not sure how to go about making my sprite walk to the Left. I had initially thought I could just mirror my rectangle that I am drawing from to get a flipped picture. Something like:
sourceRect = new Rect(45, 0, 0, 75);
which doesn't seem to work (not sure what actually happens here, but nothing gets drawn to my surface).
Searching online, it seems I should make a copy of my original bitmap, mirror it with a transform matrix, then use that bitmap for drawing when walking to the left. However I've also found implementations where many smaller bitmap objects get created out of the original sprite sheet, stored (and transformed for the mirrored motion), then used as needed.
So I'm wondering what would be the best in this case or if there is really any difference (performance/memory):
Method 1: Load in my original sprite sheet, make a new bitmap instance, mirror it,, then calculate all the rectangles and use those + two entire sheets to draw from (admittedly there is some extra bitmap space where the sprite sheet is unused).
Method 2: Load in my original sprite sheet, for every frame create a new two bitmap objects (1 mirrored, 1 normal) and store those to draw from.
Method 3: Other better ways?

Method 2 would be way too expensive, and you don't need a canvas to flip a bitmap. Simply create another bitmap with a Matrix applied, like so:
BitmapDrawable flip(BitmapDrawable d)
{
Matrix m = new Matrix();
m.preScale(-1, 1);
Bitmap src = d.getBitmap();
Bitmap dst = Bitmap.createBitmap(src, 0, 0, src.getWidth(), src.getHeight(), m, false);
dst.setDensity(DisplayMetrics.DENSITY_DEFAULT);
return new BitmapDrawable(dst);
}

To mirror your sprite simply apply the following transform on the Canvas: scale(-1, 1). You will have to offset the sprite by its width too.

To draw a vertical mirrored bitmap bmp on a canvas:
Matrix m = new Matrix();
// Mirror is basically a rotation
m.setScale( -1 , 1 );
// so you got to move your bitmap back to it's place. otherwise you will not see it
m.postTranslate(canvas.getWidth(), 0);
canvas.drawBitmap(bmp, m, p);

Question about rotate bitmap with Canvas.rotate

As we know, we can rotate a bitmap through 2 ways.
The 1st way is:
Matrix mt = new Matrix();
mt.postRotate(degree);
Bitmap bitmap = CreateBitmap(src, 0, 0, w, h, mt, true);
canvs.drawBitmap(bitmap, 0, 0, paint);
In this way, we always need create new bitmap for every rotation, it is not good way for high performance game or app.
The 2nd way is:
canvas.save();
canvas.rotate(degree);
canvas.drawBitmap(bitmap, 0, 0, paint);
canvas.restore();
In this way, we avoid creating new bitmap frequently, but the rotation bitmap is distortion, the bitmap quality is worse than first way.
So, Is there 3rd way to rotate bitmap with high performance and good quality?
Your any comments are really appreciated!

Make sure that you providing Paint to canvas.drawBitmap(bitmap, 0, 0, paint).
And don't forget to use anti-alias and bitmap filtering:
paint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.FILTER_BITMAP_FLAG);

If you really want high speed graphical applications (even 2D) you should use OpenGL on Android.
I believe Replica Island uses OpenGL and VBO's (where available) for rendering it's 2D scene. But I can't find a reference.

this method should use the GPU to rotate the bitmap
Canvas.drawBitmap(android.graphics.Bitmap, android.graphics.Matrix, android.graphics.Paint)