Develop Reference

Why does drawing a shape to a bitmap reduce quality?

Why does drawing a shape to a bitmap cause the shape to be blurry versus drawing the shape straight to the canvas?

Bitmap is a rasterized computer image, consisting of points (pixels).
The Canvas class holds the "draw" calls.
A shape is an abstract definition of shape (vector-like).
drawing the shape straight to the canvas
That's not accurate, maybe you mean straight to the screen of device, which is Bitmap too.
To use Canvas for drawing, you need the canvas to host the calls, some bitmap as target, and some drawing primitive (shape is one), and Paint (contains information how to paint the drawing primitive).
Once you draw some shape into the target bitmap, it will be aliased to the pixels of target bitmap. Ie. an circle will turn into some approximation created by rectangular pixels of target bitmap.
What you probably see in your particular case is, that your Bitmap has lower resolution than screen, and when you draw that low-res bitmap to the target screen bitmap, it is upscaled by some filter which makes the upscaled picture a bit blurry to avoid big rectangular pixelation (or it may be also other way, downscaling hi-res bitmap, which contains too sharp/thin contours, which will be aliased second time when downscaled, and even with anti-aliasing filtering it will get blurred a bit). Or maybe you use some paint with settings causing blur (unlikely, can't think of creating one by accident, you would knew).
If you will use for both targets Bitmap of identical density (resolution of single pixel), and the same paint method, then the result will be same, and also drawing the shape from bitmap to bitmap as long as you will use whole pixel coordinates/size, and no filtering, again the result will be same as drawing directly to screen bitmap.
So start first by checking the size of your bitmap vs screen bitmap, and then check paint settings and additional canvas arguments to draw the bitmap, whether you don't upscale/downscale it with some kind of filtering.

How to make circle drawable in Android custom canvas?

I want to make in my app possibilty to draw circles by user. The drawing is quite simple - user just press on canvas somewhere and then predefined circle
The difficult part here is to draw it with some drawable (picture) as a fill. It is quite simple when it is about rectangle. Then you just need to write:
Drawable drawable = getResources().getDrawable(R.drawable.my_background_picture);
drawable.setBounds(myRectangle);
drawable.draw(myCanvas);
Everything is done on onDraw() method of my custom view.
Unfortunatelly there isn't such simple method to make it with circle. The one that I've found is slight modification from Vogella's tutorial:
InputStream resource = getResources().openRawResource(R.drawable.sand);
Bitmap bitmap = BitmapFactory.decodeStream(resource);
BitmapShader shader;
shader = new BitmapShader(bitmap, Shader.TileMode.CLAMP,Shader.TileMode.CLAMP);
paint = new Paint();
paint.setAntiAlias(true);
paint.setShader(shader);
myCanvas.drawRoundRect(myRectangle, 120, 120, paint);
At first sight it looks ok, but it's not. This commands make just something like frame on a picture below, so you move hollow circle on a picture and that's all. Not as with rectangle where you actually move rectangular bitmap.
So, my question is - Is there a way to make circle drawable that can be also moved/resized?

Why make a drawable? You can easily draw a circle via the canvas.drawCircle command. You can also easily make one via a Path object.
Edit:
If you need a drawable, try making a ShapeDrawable based off an OvalShape.

Android custom brush pattern/image

I have an 8x8 Image. (bitmap - can be changed)
What I want to do is be able to draw a shape, given a Path and Paint object onto my SurfaceView.
At the moment all I can do is fill the shape with solid colour. How can I draw it with a pattern.
In the image you can see the brush pattern (The cross). It can be anything from a cross to a donut or an elf.
How would I go about drawing this pattern background.
I also eventually want to apply colours to it.
So far, my theory is to create a clip area of the shape, and tile the bitmaps until area is covered, but this is extreme overkill in processing. Nor sound ideal.
In terms of colouring, I can edit the brushes to be alpha, fill the same with background colour, then draw the images on top. The real issue it the tiling of such patterns.
Ive found a few questions of a similar nature, all unanswered, and/or not applicable to my situation. (use of xmls on views etc)

Did you checked this blog. Its using BitmapShader
Example:
//Initialize the bitmap object by loading an image from the resources folder
fillBMP = BitmapFactory.decodeResource(m_context.getResources(), R.drawable.cross);
//Initialize the BitmapShader with the Bitmap object and set the texture tile mode
fillBMPshader = new BitmapShader(fillBMP, Shader.TileMode.REPEAT, Shader.TileMode.REPEAT);
fillPaint.setStyle(Paint.Style.FILL);
//Assign the 'fillBMPshader' to this paint
fillPaint.setShader(fillBMPshader);
//Draw the fill of any shape you want, using the paint object.
canvas.drawCircle(posX, posY, 100, fillPaint);

Tiling a Bitmap on a Canvas

I would like to create a 'graph paper' look to the Bitmap I am drawing via a Canvas, and trying to figure out the best way to do this.
I can't pass a source Bitmap containing the graph paper background to the Canvas constructor, as I am getting the Canvas in a SurfaceView via the .lockCanvas() call.
Some solutions I've tried:
I've tried implementing this solution in my SurfaceView's Thread.run(), but the issue I believe is when the BitmapDrawable is converted to a Bitmap... it loses the tiling properties.
canvas = mSurfaceHolder.lockCanvas(null);
BitmapDrawable TileMe = new BitmapDrawable(BitmapFactory.decodeResource(getResources(), R.drawable.editor_graph));
TileMe.setTileModeX(Shader.TileMode.REPEAT);
TileMe.setTileModeY(Shader.TileMode.REPEAT);
Bitmap b = TileMe.getBitmap();
canvas.drawBitmap(b, 0, 0, null);
If I use the Canvas.drawBitmap method that takes a destination RectF as a parameter, it looks like the bitmap will be tiled to fill the RectF... but how do I declare a RectF reliably that fills the entire view area?
Setting the Activities background to the desired graph paper look also doesn't work, as the bitmap/canvas layout is opaque and blocks that from being seen.
Any ideas how to achieve this?

You have two easy solutions:
Either use a BitmapDrawable, but instead of extracting the Bitmap, just call BitmapDrawable.draw(Canvas). Don't forget to set the drawable's bounds to fill your drawing area.
Create a Paint with a BitmapShader and draw a rectangle with it (this is basically what BitmapDrawable does).

I'm sure there is a way to get a tiled effect using a SurfaceView. Unfortunately, it looks like you can't use the BitmapDrawable with a canvas. So you would probably have to implement you own custom tiling method by creating your own series of Rect's on the Canvas and drawing a scaled bitmap to each one.
It honestly wouldn't be that hard. Just get the width/height of the view, and create an array of Rect's based on this data that you will draw the Bitmap to.
Alternatively, if you don't need to make modifications to the actual tiled background on the fly, just draw it as a background and draw the SurfaceView on top of it. That post you linked provided multiple solutions to tiling a BitmapDrawable that you could implement.

Android: adding a bitmap texture to a non rectangular item

I have a widget which looks like this:
Every cone is a "touchable element". Now I want to put a bitmap texture above each cone. However, bitmap images are all rectangular, so a bitmap texture above one cone would interfere with the bitmap texture above another cone.
I'm wondering what is the best solution to this approach. Should I just create an image which fits (as a rectangle) exactly above the cone and make the non used areas transparent?
A second question is, how do bitmap textures work with stretching? Because this whole circle draws itself to fit the whole screen size, while bitmap textures are pretty much one size.

Offhand I can't think of a better way to draw bitmaps over those cones than your own suggestion of using transparent zones.
However, I can help with your second question as stretching bitmaps is not hard. You've got a few options in the Canvas class. For example:
canvas.save();
canvas.scale(xRatio, yRatio);
canvas.drawBitmap(....);
canvas.restore();
You can also use a Matrix, using matrix.postScale(xRatio, yRatio), to then generate either a larger bitmap and draw it normally, or pass the matrix in to your canvas.drawBitmap(....) command to make it scale while it draws.
All of these methods assume you have access to the drawing canvas itself. If you are using a view, you can subclass it and override the onDraw(Canvas canvas) method to grab the canvas before it starts drawing it. If you're using a SurfaceHolder, then you should already know how to get the canvas.
Edit: I forgot the third method I was going to describe. You can use the canvas.drawBitmap(bitmap, srcRect, dstRect, paint) to also make the canvas scale the bitmap to fit the destination rectangle. In short, there are lots of methods to do this - pick the one that's easiest based on your application!