Discretize ISO and shutter speed to common values

app/src/main/java/eu/wa5p/lightmeter/MainActivity.kt

@@ -27,17 +27,20 @@ import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
 import eu.wa5p.lightmeter.ui.theme.LightMeterTheme
-import kotlin.math.roundToInt
+import kotlin.math.abs
 
 const val TAG: String = "lightmeter MainActivity"
 
+private val commonIsoValues = listOf(50, 100, 200, 400, 800, 1600, 3200, 6400)
+private val commonApertureValues = listOf(0.85, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11.0, 16.0, 22.0)
+
 class MainActivity : ComponentActivity(), SensorEventListener {
     private lateinit var sensorManager: SensorManager
     private var illuminanceSensor: Sensor? = null
     private var lightmeterState = mutableStateOf(
         LightmeterState(
             illuminance = 0.0,
-            aperture = 1.8,
+            aperture = 2.8,
             iso = 100,
             shutterSpeed = 0.01
         )
@@ -150,6 +153,14 @@ fun LightmeterListItemPreview() {
 
 @Composable
 fun IsoSlider(state: MutableState<LightmeterState>, recalculateShutterSpeed: () -> Unit) {
+    // Convert common ISO values to the range used by the slider
+    val minIso = commonIsoValues.first().toFloat()
+    val maxIso = commonIsoValues.last().toFloat()
+
+    // Find the closest ISO value to the slider's value
+    val isoValue = state.value.iso.toFloat()
+    val closestIso = commonIsoValues.minByOrNull { abs(it - isoValue) } ?: minIso
+
     Row(
         modifier = Modifier.padding(all = 8.dp),
         verticalAlignment = Alignment.CenterVertically
@@ -160,16 +171,17 @@ fun IsoSlider(state: MutableState<LightmeterState>, recalculateShutterSpeed: ()
         )
         Slider(
             modifier = Modifier.weight(0.7f),
-            value = state.value.iso.toFloat(),
+            value = closestIso.toFloat(),
             onValueChange = { value ->
-                state.value = state.value.copy(iso = value.roundToInt())
+                val newIso = commonIsoValues.minByOrNull { abs(it - value) } ?: minIso
+                state.value = state.value.copy(iso = newIso.toInt())
                 recalculateShutterSpeed()
             },
-            valueRange = 1f..2000f
+            valueRange = minIso..maxIso,
+            steps = (commonIsoValues.size - 1) * 10
         )
     }
 }
-
 val previewlightmeterState = mutableStateOf(
     LightmeterState(
         illuminance = 0.0,
@@ -197,6 +209,14 @@ fun ApertureSlider(
     state: MutableState<LightmeterState>,
     recalculateShutterSpeed: () -> Unit
 ) {
+    // Convert common aperture values to the range used by the slider
+    val minAperture = commonApertureValues.first().toFloat()
+    val maxAperture = commonApertureValues.last().toFloat()
+
+    // Find the closest aperture value to the slider's value
+    val apertureValue = state.value.aperture.toFloat()
+    val closestAperture = commonApertureValues.minByOrNull { abs(it - apertureValue) } ?: minAperture
+
     Row(
         modifier = Modifier.padding(all = 8.dp),
         verticalAlignment = Alignment.CenterVertically
@@ -207,16 +227,17 @@ fun ApertureSlider(
         )
         Slider(
             modifier = Modifier.weight(0.7f),
-            value = state.value.aperture.toFloat(),
+            value = closestAperture.toFloat(),
             onValueChange = { value ->
-                state.value = state.value.copy(aperture = value.toDouble())
+                val newAperture = commonApertureValues.minByOrNull { abs(it - value) } ?: minAperture
+                state.value = state.value.copy(aperture = newAperture.toDouble())
                 recalculateShutterSpeed()
             },
-            valueRange = 0.85f..22f
+            valueRange = minAperture..maxAperture,
+            steps = (commonApertureValues.size - 1) * 10
         )
     }
 }
-
 @Preview(showBackground = true)
 @Composable
 fun ApertureSliderPreview() {