CODEWITHSUNDEEP
androidmatrixcanvasbitmapcontour
Anonim
Anonim

Reputation: 37

Draw outline from image

I wanted to draw a contour around the picture by drawing and expanding a second picture in the Background, but I wasn't very successful, how can I draw a regular stroke?

The contour I drew: Click to see the picture

The contour I want to draw: Click to see the picture

My Code;

private Bitmap ContourBitmap() {
int strokeWidth = 8;
Bitmap originalBitmap =  BitmapFactory.decodeResource(getResources(), R.drawable.flower_icon);
Bitmap newStrokedBitmap = Bitmap.createBitmap(originalBitmap.getWidth() + 2 * strokeWidth, 
originalBitmap.getHeight() + 2 * strokeWidth, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(newStrokedBitmap);
float scaleX = (originalBitmap.getWidth() + 2.0f * strokeWidth) / originalBitmap.getWidth();
float scaleY = (originalBitmap.getHeight() + 2.0f * strokeWidth) / originalBitmap.getHeight();
Matrix matrix = new Matrix();
matrix.setScale(scaleX, scaleY);
canvas.drawBitmap(originalBitmap, matrix, null);
canvas.drawColor(Color.WHITE, PorterDuff.Mode.SRC_ATOP); //Color.WHITE is stroke color
canvas.drawBitmap(originalBitmap, strokeWidth, strokeWidth, null);
}

Upvotes: 2

Views: 922

Answers (1)

Helder Sepulveda
Helder Sepulveda

Reputation: 17594

I think you are on the right track...

Here is a strategy, instead of scaling just draw the same original picture a few times each time slightly offset, see sample below: 

var canvas = document.getElementById('canvas')
var ctx = canvas.getContext('2d')
var img = new Image;
img.onload = draw;
img.src = "https://i.sstatic.net/UFBxY.png";

var s = 10, // thickness scale
  x = 15, // final position
  y = 15;

function draw() {
  ctx.globalAlpha = 0.2
  ctx.filter = 'brightness(0%)'
  for (i = 0; i < 360; i++)
    ctx.drawImage(img, x + Math.sin(i) * s, y + Math.cos(i) * s);
  ctx.globalAlpha = 1
  ctx.filter = 'none'
  ctx.drawImage(img, x, y);
}
<canvas id=canvas width=350 height=600></canvas>

I applied a filter = 'brightness(0%)' but there are many more you can apply:
https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/filter

I'm using HTML canvas but that same idea should "translate" nicely to an android canvas.

Upvotes: 1

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