Develop Reference

How would you do this in canvas drawing

How would you draw something like this programmatically in a ondraw method? I know how to draw lines or squares, but to have an image inside a squarebox that has an arrow, is kind of confusing for me
Thank you

Just break the drawing up in different elements:
a gray box
a white rounded rectangle
a white rectangle
a blue rectangle
a blue rounded rectangle
a blue triangle
a red heart (I would just try to find a font with a nice heart)
the text in white.
Draw it all to the canvas in this order and you are fine.

Semi transparent bitmap overlay renders wrong colour

I have a stack of bitmaps that I need to render one above the other. I achieve this with a relative layout and several ImageViews on top of each other which all have a Bitmap assigned to it.
This works great, but when the top layers is semi-transparent, the colours of the lower bitmap are off.
All my bitmaps use Config.ARGB_8888.
Say the top layer is red with an alpha of 50% and the bottom layer is green with an alpha of 100%.
I can either set the colour of the bitmap to red, then the alpha of the ImageView to 0.5f and it will render the green colour below fine (darker green with some red mixed in).
If I set the bitmap pixels to a 50% red like this: bmp.eraseColor(0x7Fff0000); and leave the imageView alpha on 100%, the green below will be displayed as yellow, mixing red and green, rather than overlaying it.
Unfortunately I can not use the (working) fist version because the alpha on the Bitmap above is not going to be uniform.
Is there a blend mode setting to use true colours when using semi transparent pixels in a Bitmap?
EDIT: I have also tried to set several PorterDuffXfermodes to the ImageViews but none gives the right result.
Paint paint = new Paint();
paint.setXfermode(new PorterDuffXfermode(Mode.MULTIPLY)); //OVERLAY//ADD//SCREEN//DARKEN//LIGHTEN
imageView.setLayerType(View.LAYER_TYPE_SOFTWARE, paint);

Got it, needed to premultiply the alpha to get the desired result.

Draw smooth transparent line

I am trying to draw smooth line following my finger. The problem is in superposition. Left example is array of drawLine, and right is drawPath. Is it way to make it like smooth left example?

Construct the line as a solid color, then wrap that line inside of a drawable. Turn this drawable transparent, and then draw it to the screen.

How to correctly extract highlights and shadows from a grayscale image

I am drawing some buttons on the screen. Each with a different color, but the same shape, designed in Photoshop with all sort of reflections and shines.
I want to use a single bitmap of the shape and change its color programmatically, preserving all the reflections and shadows. This is what I do right now:
Get the shape into a ARRGB_8888 bitmap (even though all colors are shades of gray)
Copy the bitmap pixels to 3 buffers: Image, Highlights, Shadows
The reference grayshade is RGB[128,128,128]
In the Highlights buffer, zero all pixels below the reference (+ threshold)
In the Shadows buffer, zero all pixels above the reference (- threshold)
From the Highlights and Shadow buffers create Highlights and Shadow Bitmaps
Draw the original grayscale image using a PorterDuffColorFilter on mode MULTIPLY
Draw on top the shadows, using the Shadows bitmap and XferMode DARKEN
Draw on top the highlights, using the Highlights bitmap and XferMode LIGHTEN
I do get a result, but I realize that the final button color is not the target color, but a darker shade of it, because the MULTIPLY mode with a reference of 128 cuts all components in half.
I tried to set the reference to a whiter shade of gray, but then the highlights get saturated.
I tried to use SRC_IN on step 7 above, and I get the target color only on areas that are neither highlights nor shadows.
See the results:
Not sure what I need to ask, but I want to get the buttons with the exact target color and its highlights and shadows. Maybe I am generating the Highlights and Shadows masks wrong, or maybe I am using the wrong blending modes. Or maybe it is something else.

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.