How can I tell how much of a "scratch card" has been revealed?

Question

I have developed scratch card effect.I am now working on reward system, so my question is how will I go on and implement logic which will let me know that the object behind scratch card is now visible??

Answer 1

I agree with Superdoggy's answer, but I believe there is a better way to go about this. If you know the area of the scratch card collision box you are wanting to reveal, you could go about it by: Get the Total Pixel amount of the object(width*height). When the mouse is pressed: check the pixels around the mouse in a radius of your choice, and if it is within the area of the object, and the pixel is currently opaque, set to transparent and ++ a 'revealed pixel' counter. To check how much of the scratch card is currently visible, just divide 'Revealed Pixels' by 'Total Pixels.'

Unfortunately I don't know how to program in Unity, so here's some pseudo code!

    Initializer:
      set object = {x1, y1, x2, y2}
      set revelead_pixels = 0
      set radius = (number greater than 0)
      set bool object_pixels[object.x2 - object.x1][object.y2 - object.y1] = 1
      set percent_visible = (percentage of object to be visible before coninuing, 0 to 1)

    On mouse press:
      --mouse.x and mouse.y are coordinates of mouse

      FOR x, radius * 2 DO


        FOR y, radius * 2 DO

          --only run if x and y are within circle around mouse
          IF ((x - radius) * (y - radius) > radius) THEN 
            continue 
          ENDIF

          --if mouse + 'for variables' is within object
          IF ((x + mouse.x >= object.x1) AND (x + mouse.x < object.x2) AND (y + mouse.y >= object.y1) AND (y + mouse.y < object.y2)) THEN

            --if the current pixel is set to 1 (or opaque)
            IF (object_pixels[x + mouse.x - object.x1][y + mouse.y - object.y1] == 1) THEN
              object_pixels[x + mouse.x][y + mouse.y] = 0
              revealed_pixels += 1
            ENDIF

          ENDIF

        ENDFOR

      ENDFOR


      IF revealed_pixels >= ((object.x2 - object.x1) * (object.y2 - object.y1)) / percent_visible THEN
        --This statement runs if over preferred amount of pixels are visible
      END

Answer 2

I would add up all of the alpha values of the scratch card pixels that are overlapping the object pixels. Then if "A" < some value you can assume that the user has cleared enough pixels that they can see the object.

You can find a really good tutorial on per-pixel collision detection in C# here: Linkylink. It's made for C# with XNA, but the concept isn't too hard to adapt to C# with Unity, I would assume. Simply just modify the code a bit to count alpha values of colliding pixels instead of just checking for collision.

Hope this helps!