Develop Reference

How to draw alpha on an image / setting pixels invisible - on fingertouch

I want to create a little scratch game. The problem is, that I can't figure out how to erase pixels from an image in android (like the eraser in gimp / photoshop).
The image is an .png with alpha channel.

AIUI, drawing operations on a canvas blend a transparent pixel with the prior value of the pixel. This is by default, and you can see it by setting a canvas to black and drawing a fully transparent shape onto it, and then drawing the underlying bitmap over an image of another canvas (result: a fully black canvas), or by setting a canvas to a partially transparent color and, drawing a shape of another partially transparent color, and then drawing this over an image (result: the original image is tinted by the first color, outside the shape; within the shape, it's tinted by both transparent colors). I don't know the blending method used by default, and looking through the docs just makes me wish I knew what book to buy so I can understand how to use what's available.
So I would set pixels to transparent by setting them 'directly', with Bitmap methods, rather than with canvas operations. Although if you need to punch a transparent shape into an overlay, you can draw the shape with a solid non-transparent color, and then manipulate the bitmap directly, mapping this color to the transparent color.
Bitmap docs. Prefer getPixels() and setPixels() to a method-call per pixel.
EDIT: ...er, did I misunderstand? You want to 'erase' pixels as in a paint program? Then just draw whatever the background color is. There's no erasure involved.

What does 'Paint' parameter do in android.graphics.Canvas.drawBitmap()?

I have a question about drawBitmap.
android.graphics.Canvas.drawBitmap(Bitmap bitmap, float left, float top, Paint paint)
What does that Paint paint? For example I have a picture.jpg and I make
Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.picture);
paint = new Paint();
paint.setColor(Color.BLUE);
canvas.drawBitmap(bitmap, 0, 0, paint);
What can I do with that "paint" when I have a real picture not some canvas.drawCircle. Is there any way I can change pictures color or something like that?
Yes and another question. For example I draw circle in mspaint in 80x80 size and my background stays plain white. When I use that drawing in my program it shows circle + that white background. Is there any way that there will be displayed only circle without background. Maybe somebody can suggest some program in which I can make that happen or which code should I use in my program? (circle is just example, there can be anything)
Yes and excuse to use circle's background same as program's background is not appropriate, because my program's background isn't white or black or any other color, it is picture.

Paint objects can affect the rendering of the Bitmap. For example, they be used to mask the drawing of the Bitmap.
Save your circle as a PNG or GIF, and set the background as transparent (I do not know if MS Paint can do this).

i suggest gimp for image editing with transparency.
start a new image, delete the default layer, add a transparent layer, then paste your image over that. you can use the fuzzy select tool to trim any white space, then save as .png and you have a transparent image!

Android: how to simply draw a bitmap on another bitmap

I'm new to Android dev and I'm having a hard time trying to do something which seems obvious to me: drawing little images on top of a bigger image.
Let's say that I have a 500x500 image and I want to draw icons at different locations. Icons are png files that I load with:
Bitmap img =
BitmapFactory.decodeResource(getResources(),
R.drawable.idIcon1)
My "background image" is a LayerDrawable.
Then, I am totally lost... Do I have to create a canvas ? How to draw on my "background image" my icons at different positions?

int positionLeft=0;
int positionTop=0;
Bitmap newBitmap =Bitmap.createBitmap(backgroundBitmap.getWidth(),bitmap.getHeight(),Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(newBitmap);
canvas.drawBitmap(backgroundBitmap, positionLeft, positionTop,null);
positionLeft=100;
positionTop=100;
canvas.drawBitmap(iconBitmap,positionLeft,positionTop,null);
imageView.setImageBitmap(newBitmap);

You're making simple things difficult. Just use a layout with android:background attribute, and then add ImageViews dynamically with the necessary bitmaps inside.

How do you tint a bitmap in Android?

I draw a bitmap onto a canvas using the following call:
_playerImage = BitmapFactory.decodeResource(getResources(), R.drawable.player);
How can I now tint this image white?
I'm trying to make the image flash white like in top-scrollers when an enemy is hit by a bullet.
Do I need to use something other than BitmapFactory?

You can use a ColorFilter on your Paint when you draw the bitmap.

Android : Make image opaque / transparent

Greetings,
I would like to place an image over a surfaceview. However I would like the image to be transparent so you can see the image and also the undlying surfaceview. Can anyone suggest how I could do this?

This is how I do it before drawing my shapes.
Bitmap buffer = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_4444);
buffer.eraseColor(Color.TRANSPARENT);