Develop Reference

I'm trying to write a text on canvas but nothing happens

I'm tryin to write a text on canvas and set as GL10 object texture like this:
Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_4444);
bitmap.eraseColor(0);
Canvas canvas = new Canvas(bitmap);
canvas.translate(width, height);
canvas.drawColor(Color.WHITE);
Paint paint = new Paint();
paint.setStyle(Paint.Style.FILL);
paint.setColor(0xffffffff & Color.MAGENTA);
paint.setAlpha(255);
canvas.drawText("Hello world", 0, 30, paint);
the texture color is drawn if i change but the text not apears.
some one know why ?

It looks like the alpha setting is missing on the paint object that draws the text:
paint.setAlpha(255); //This line must be after paint.setColor(Color.MAGENTA);
or
paint.setColor(0xffffffff & Color.MAGENTA);

Android - use bitmap as a gradient mask

I have implemented a flood fill algorithm in an android app. The way I have implemented the algorithm doesn't actually change the source bitmap, but instead creates a new bitmap of the fill area. I.E.
Flood filling this circle with red
Would produce this bitmap (where everything else in the bitmap is transparent)
Which I then combine again into a single bitmap. This works great for solid colors, but I want to be able to implement a gradient flood fill so that if a user fills the same circle, choosing red and blue, the resulting bitmap would look like this
My question is, is there a way that I can use the red circle as some sort of mask to make the desired gradient? or do I have to write a gradient generator myself?

Thanks to pskink's hint, I was able to find an answer.
The idea is that you create a canvas, draw the mask to it, create the gradient that you want, then draw the gradient on top of it using the SRC_IN PorterDuffXfermode. Here's the code:
public Bitmap addGradient(Bitmap src, int color1, int color2)
{
int w = src.getWidth();
int h = src.getHeight();
Bitmap result = Bitmap.createBitmap(w,h, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(result);
canvas.drawBitmap(src, 0, 0, null);
Paint paint = new Paint();
LinearGradient shader = new LinearGradient(0,0,0,h, color1, color2, Shader.TileMode.CLAMP);
paint.setShader(shader);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
canvas.drawRect(0,0,w,h,paint);
return result;
}
In this instance, the DST(destination) is the red circle and the SRC(source) is the gradient. The SRC_IN PorterDuff mode means draw the SRC everywhere that it intersects with the DST.
Note that it really doesn't matter what color the mask is, because the PorterDuff mode only pays attention to whether the DST pixel is transparent or not. The color of the resulting bitmap will be a gradient between color1 and color2.

Crop/Cut the shape of a View in android dynamically

I currently have a button template (layout) as XML, where I load it off resources in my code and dynamically create the button.
So here's the question, is there any possible way to crop/cut the buttons' (or any view for that matter) into a specific shape?
Let's say I have a rectangle button, am I able to cut it to create some triangular form with it? here's an example:
What are the possibilities on there without having to create a custom Bitmap for it? (since the XML uses specific stroke/radius stuff which wouldn't work correctly on a Bitmap)
Is it possible for it to keep its size and margins even after the cuts? I'm really interested to know.
Thanks in advance to anyone willing to help!

You can use Canvas for what you want. It will allow you to modify the view by drawing shapes, erasing some area etc.
For example, following function will return a circular cropped bitmap of the initial bitmap provided:
public Bitmap getCroppedBitmap(Bitmap bitmap) {
Bitmap output = Bitmap.createBitmap(bitmap.getWidth(),
bitmap.getHeight(), Config.ARGB_8888);
Canvas canvas = new Canvas(output);
final int color = 0xff424242;
Paint paint = new Paint();
final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
paint.setAntiAlias(true);
canvas.drawARGB(0, 0, 0, 0);
paint.setColor(color);
canvas.drawCircle((bitmap.getWidth() / 2), (bitmap.getHeight() / 2),
(output.getWidth() / 2), paint);
paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
canvas.drawBitmap(bitmap, rect, rect, paint);
canvas = null;
paint = null;
// bitmap.recycle();
return output;
}
To convert view into bitmap, see this.

android custom view ondraw, get bitmap from canvas?

So I seem to have a conundrum. I need to add multiple custom views to a framelayout. The code for this is working just fine. However, I wish to access the underlying bitmap that the canvas uses in the views onDraw method. Like this one (in a class that extends View):
#Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
canvas.drawARGB(Color.alpha(bgColor), Color.red(bgColor),
Color.green(bgColor), Color.blue(bgColor));
m.reset();
m.setTranslate(imgPosX - ((float) userImage.getWidth() / 2.0f), imgPosY
- ((float) userImage.getHeight() / 2.0f));
m.postRotate(angle);
m.postScale(1.0f, 1.0f);
canvas.drawBitmap(userImage, m, null);
}
I wish to erase certain pixels essentially. Now, I know I can do this via the setPixel method which is fine but it is exceptionally slow and not satisfactory. I have a working ndk function that does exactly what I want, but it passes in a bitmap. I know I can use a SurfaceView instead of a View to access the bitmap like that, however as mentioned here multiple SurfaceViews in a FrameLayout isn't an option. So, I would think I need to manipulate the bitmap itself used by the canvas in the onDraw method. How would I go about doing this? or alternatively I don't mind creating another bitmap, passing it into the ndk function and returning/drawing that, however would I do a canvas.drawBitmap with transparent pixels?

Have you looked into setting the PorterDuff mode on a Paint object?
use paint.setXfermode(new PorterDuffXfermode(Mode.CLEAR)) then draw over the pixels that you want to erase
edit: What exactly are you trying to clear? There are multiple modes and you may need to select a different one depending on what you are trying to do. Here is an example of a function I currently use to crop Bitmaps to a circle.
public static Bitmap crop_circle_center(Bitmap bitmap) {
final int diameter = Math.min(bitmap.getWidth(), bitmap.getHeight());
Bitmap output = Bitmap.createBitmap(diameter,
diameter, Config.ARGB_8888);
Canvas canvas = new Canvas(output);
final int color = 0xff424242;
final Paint paint = new Paint();
final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
rect.offset(-(bitmap.getWidth()-diameter)/2, -(bitmap.getHeight()-diameter)/2);
paint.setAntiAlias(true);
canvas.drawARGB(0, 0, 0, 0);
paint.setColor(color);
canvas.drawCircle(diameter/ 2, diameter/ 2,
diameter / 2, paint);
paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
canvas.drawBitmap(bitmap, null, rect, paint);
return output;
}

Draw circle over the bitmap with the color same as the under bitmap

I have an image, I can draw an circle over it like the code below:
Bitmap bitmap = BitmapFactory.decodeResource(getResources(),
R.drawable.girl).copy(Bitmap.Config.ARGB_8888, true);
Canvas canvas = new Canvas(bitmap);
Paint paint = new Paint();
paint.setColor(Color.RED);
paint.setStrokeWidth(200);
paint.setStyle(Style.STROKE.FILL);
paint.setAntiAlias(true);
canvas.drawCircle(bitmap.getWidth() / 2, bitmap.getHeight() / 2, 100,
paint);
And the circle will be red color! But because of some reason, I want the color of circle same as its under bitmap. Can I do it? and how? Thanks everyone!
Edited: One more question, How I can get all the pixels inside circle?

why dont you simply remove the paint.setStyle(Style.STROKE.FILL); or try changing the paint.setColor(Color.RED); to Transparent color, that should be it

you can get the color of a specified pixel by the method in this article and then make a RGB Color then set this color instead of the color.RED you mentioned.