Wrong result when using setPixel() - unity3d

Question

I'm dealing with a problem for a few days now with setPixel() on Texture2D.
What i'm doing is getting mouse position or touch position(on android), then using that in setPixel() with transparent color. But the result i'm getting occur elsewhere instead of exactly where the mouse is...
public class EarshPic : MonoBehaviour {
public SpriteRenderer sr;
public SpriteRenderer srO;
public Camera c;
// Use this for initialization
void Start () {
CreateCover();//This method is working fine
}
private void CreateCover()
{
Color color = new Color(0.5F, 0.5f, 0.5F, 1.0F);
int x = srO.sprite.texture.width;
int y = srO.sprite.texture.height;
Texture2D tmpTexture = new Texture2D(srO.sprite.texture.width,
srO.sprite.texture.height);
for (int i = 0; i < tmpTexture.width; i++)
{
for (int j = 0; j < tmpTexture.height; j++)
{
tmpTexture.SetPixel(i, j, color);
}
}
tmpTexture.Apply(true);
sr.sprite = Sprite.Create(tmpTexture, srO.sprite.rect,
new Vector2(0.5f, 0.5f),srO.sprite.pixelsPerUnit);
}
// I have problem in that method
// Vector2 v = mousePostion or touchpostion
void Eraser(Vector2 v)
{
Color color = new Color(0.5F, 0.5f, 0.5F, 0.0F);
sr.sprite.texture.SetPixel(v.x, v.y, color);
sr.sprite.texture.Apply(true);
}
// Update is called once per frame
void Update () {
if(Input.mousePosition!=null)
{
Eraser(Input.mousePosition);
}
if (Input.touchCount == 1)
{
Touch touch = Input.GetTouch(0);
switch (touch.phase)
{
case TouchPhase.Moved:
Eraser(touch.position);
break;
}
}
}
}

Answer 1

Problem
You are mixing different coordinates. This is the case if the texture is not perfectly screen sized. Your click is in screen coordinates and you are using it to set the transparency in texture coordinates.
Solution
This one requires the use of 3D models with colliders and textures on them. For 2D scenario you can use a box and set its texture to your 2D sprite. I don't know any easier method, but hopefully there is.
You have to first convert the screen position to world coordinate ray. This can be done with Camera.ScreenPointToRay.
Then you need to Physics.Raycast that ray to chech which position of the 3d model's collider it is intersecting with.
The intersection point can be changed to texture coordinates with RaycastHit.textureCoord. In the previous link, you can find a complete code example of the whole process.