When image size change, how do you calculate to counter the real-size coordinate value?

Question

I want to know the coordinates value when the image is stretched from the center.

I know one pixel coordinate in texture image, and I'm using ray cast by matching it to mobile screen.

But I don't know how the coordinate value changes when the image grows.

When images grow, how do you calculate to counter the real-size coordinate value?

The image will increase to 1.33f size.

Answer 1

There may be simpler ways in Unity3D - I don't have any experience there - but this sounds like a fairly simple scaling problem.

You'll need to know the following:

• The image coordinates of the centre of the image
  This is the vector (width/2, height/2)
• The screen coordinates of the centre of the image
  Where the center of the image is on the screen
• The scaling factor ( 1.33f in this example)

Given the above you can calculate the pixel being touched using simple math:

public Vector2Int ScaleTouch(Vector2Int imgCentre, Vector2Int dispCentre, float scale, Vector2Int touch)
{
    var x = imgCentre.x + (touch.x - dispCentre.x) * scale;
    var y = imgCentre.y + (touch.y - dispCentre.y) * scale;
    return Vector2Int.RoundToInt(new Vector2(x, y));
}

Or using the methods in Vector2 and Vector2Int you might be able to do this:

public Vector2Int ScaleTouch(Vector2Int imgCentre, Vector2Int dispCentre, float scale, Vector2Int touch)
{
    var offset = Vector2.Scale(touch - dispCentre, new Vector2(scale, scale));
    return offset + imgCentre;
}

Both assume that your scale is homogeneous in x and y . You could provide a scale vector if you want it to be flexible about scaling in different axes.