convert drawable xml containing a gradient to bitmap

Issue

I want to apply a gradient to a bitmap. So far I'm using this technique. here is my code in the onCreate method of MainActivity.class.

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        double angle = Math.toRadians(135);
        double length = 100;
        int x = (int) (Math.cos(angle) * length);
        int y = (int) (Math.sin(angle) * length);


        int[] colors = new int[3];
        colors[0] = Color.parseColor("#FF4081");
        colors[1] = Color.parseColor("#3F51B5");

        Bitmap bitmap = Bitmap.createBitmap(1080, 1080, Bitmap.Config.ARGB_8888);

        Canvas canvas = new Canvas(bitmap);

        LinearGradient linearGradient =
                new LinearGradient(0, 0, x, y, colors[1], colors[0], Shader.TileMode.CLAMP);

        Paint paint = new Paint();
        paint.setDither(true);
        paint.setShader(linearGradient);

        canvas.drawRect(new RectF(0, 0, 1080, 1080), paint);

        ImageView imageView = findViewById(R.id.iv);
        imageView.setImageBitmap(bitmap);
    }
}

which results in this

but I want to get an effect like this

image 2 results were achieved by simply creating a drawable XML file with the following code

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">

    <gradient
        android:angle="45"
        android:endColor="@color/colorPrimary"
        android:startColor="@color/colorAccent" />
</shape>

and setting it as a background for an ImageView, but I want this effect on the bitmap because I want to save that bitmap locally as an Image. I have tried creating a GradientDrawable instance in the MainActivity and calling onDraw(canvas) on the GradientDrawable as mentioned in the post

Solution

As I see, you calculated the angle incorrect.

Instead of this

 LinearGradient linearGradient =
            new LinearGradient(0, 0, x, y, colors[1], colors[0], Shader.TileMode.CLAMP);

Use this

LinearGradient linearGradient =
            new LinearGradient(1080, 0, 0, 1080, colors[1], colors[0], Shader.TileMode.CLAMP);

x0 is gradient start X, y0 is gradient start Y, x1 is gradient end X and y1 is gradient end Y.

Hope I helped you.

Answered By - Artur Akhnoyan