After placing a texture2D's pixel alpha value into an int[] array, later change that value without knowing xy coordinates?

I am trying to figure out something I have had problems with in the past, but unfortunately I cannot find the answer I had found before...

Anyway, I take a Texture2D with some transparent pixels, and create an int array (which I init by doing int[someTexture2D.GetPixels32().Length] & then assign the int value to match the alpha value) and with that array I have every pixels alpha value, which is either completely transparent or completely solid. This seems to work no problem for me and I can tell which are solid, which are not...

Now the problem is that later, I need to take specific pixels, and change them to transparent or solid, and then have the values in this array match. I just need to find the same individual value in the int array to change, based on a Vector 2 I need to change.

So I would like to utilize some poor developer testing art to help describe my problems:

Here you can see that the top left of the purple sprite (0, 64 in unity, 0, 0 in photoshop) and surrounding it is transparent, which I take this sprites texture2d, and assign all the alpha values to the int array (which again is either transparent or solid) and later I am planning on removing certain pixels somewhere from the sprite, so how can I then take the 1 dimensional int array (same length as there are pixels) and find that one exact pixel?... lets say 30, 34 - which is near the center. I can't just take x y because, well that would be wrong! Whats the math magic that is slipping my mind? Is there something as simple as counting how many times its gone over the width/height of the images pixels, maybe like x y / width, take remainder as x, or y...? I have a feeling this is one of those questions I will refer to later... many many times...

ADDITIONAL INFO:

-to assign alpha to the ints, I try to iterate through x, and then y within that iteration, and take x, y values a, assign to the int... hope that makes sense to you. Problem is I don't know which int[number] to assign, based on an x, y value!

• wish I knew a better way to store the alpha value without referring to the texture2d itself (for speed reasons), and thought an int array would be faster, if I could just compare the int array with the vector2's of the texture2d...

• come up with incredibly complex ways to ask simple questions.

• found this page about a similar issue, does this comment apply to my problem:

  SniperED007 said... Looks confusing, but its pretty simple:

  Say you have an array of 5 wide and 3 down, this would be:

  When creating the arry [width * height] = [5*3] = 15.

  So now we want to compare the very first pixel which is [x=0,y=0]

  This would be [x+y*width] = [0+0*5] = 0

  The next pixel would be [x=1, y=0] This would then be [x+y*width] = [1+0*width] = 1 (remember BODMAS, so the Multiplication happens before the addition)

  Hope that makes more sense? Basically you getting rid of the Y co-ordinate and making one array with the total number of pixels and then just finding the position in that array by using x + (y * width) July 5, 2008 11:51 AM