Is there a way to detect the touch offset of the original bitmap not the `Image()` Composable itself...

# compose

[AmrJyniat]

Is there a way to detect the touch offset of the original bitmap not the Image() Composable itself?

[AmrJyniat]

I'm using pointerInput with detectTapGestures to get the offset for the user clicked on an Image() Composable as following:

Image(
   bitmap = imageBitmap,
   contentDescription = "",
   modifier = Modifier.pointerInput(Unit){
        detectTapGestures { offset ->
           //This offset related to Image() composable          
        }
   }
)

I can get the bitmap offset only when its size of it equals the Image() size, but when Image() size becomes different than the original bitmap, I get the Image() offset not the bitmap offset.

How I can get the offset of the original bitmap?

[Daniele Segato]

You have the bitmap size and you know how it will be used (cropped / center inside etc). The rest is just math

[AmrJyniat]

I don't set any specific scale type, however, the only thing that may change the Image size is Modifier.weight(), I think the full code will elaborate more:

Column(
  verticalArrangement = Arrangement.spacedBy(12.dp),
  modifier = Modifier.fillMaxSize()
) {
   Image(
      bitmap = bitmap,
      contentDescription = "",
      modifier = Modifier
           .weight(1f)
           .pointerInput(Unit) {
                 detectTapGestures { offset -> }
            }
    )

    Divider(Modifier.background(LightGray))

    Text(text = pageNum.toString())
}

[Daniele Segato]

The default ContentScale is Fit. You have the size of the input area from the PointerInputScope the bitmap has width and height. That's all you need

[AmrJyniat]

Can you elaborate more please?
Yes, I have the bitmap and Image() sizes, but my question is how to get the bitmap offset while detectTapGestures gives me the Image() offset

[Kirill Grouchnikov]

Let’s say your Image is 400x400, and your bitmap is 1000x2000. If the scale is fit, you compute the scale factor yourself, which is 0.2 in this case, which then used to determine the position of the bitmap inside your image - the bitmap is 200x400, offset horizontally by 100. And that would give you the next step, translating coordinates of the click from image to bitmap.