make a photoshop like lasso tool in unity

Im looking to build a tool to cut out a portion of a photo by letting the user create a closed shape. The user should be able to start drawing lines. From point a to point b, to c, e, d, e, f … to eventually point a again to close the shape.
like in photoshop .

the goal of this will ultimatly be to know what is the portion of the image that was selected , the pourcentage of the image that was selected , in other terms , the area in pixel?? or else , of the selected portion of the picture

i would appreciate any advice , for the coding part i would prefer it to be in javascript as it is easier for me

thanks a lot , i am sorry to ask this question without having anithing to present myself
but i have been thinking about this for days and have not been able to come with idea on how to do that in unity

i can’t help you with code, but as i was working in flash before and there is possible to work with bitmaps in unity almost like in flash so i suggest to

  1. use ortographic camera
  2. put 2d object with texture (sprite or quad or plane probably but can be any geometry) to scene facing camera
  3. on update track mouse position and through raycast get the mouse position on the 2d object and compute where is this position on bitmap and add all those positions into list Unity - Scripting API: RaycastHit (the textureCoord)
  4. then you just need to get all pixels inside the polygon by Unity - Scripting API: Texture2D.GetPixel or Unity - Scripting API: Texture2D.GetPixels (there is plenty of help you can google to get the formula unity bitmap - Google Search)