Fix system gesture triggering when editing quad corners.

app/src/main/java/org/fairscan/app/ui/screens/crop/CropScreen.kt

@@ -27,6 +27,7 @@ import androidx.compose.foundation.gestures.waitForUpOrCancellation
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.WindowInsets
 import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.mandatorySystemGestures
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.safeDrawing
 import androidx.compose.foundation.layout.windowInsetsPadding
@@ -81,6 +82,10 @@ fun CropScreen(
     BackHandler { navigation.back() }
 
     val isLandscape = isLandscape(LocalConfiguration.current)
+    val density = LocalDensity.current
+    val bottomInsetForSystemGestures = with(density) {
+        WindowInsets.mandatorySystemGestures.getBottom(density).toDp()
+    }
 
     MyScaffold(
         navigation = navigation,
@@ -102,6 +107,7 @@ fun CropScreen(
                         contentDescription = "Image to edit",
                         modifier = Modifier
                             .fillMaxSize()
+                            .padding(bottom = bottomInsetForSystemGestures)
                             .onGloballyPositioned { coordinates ->
                                 state.containerSize = coordinates.size
                             },

app/src/main/java/org/fairscan/app/ui/screens/crop/QuadOverlay.kt

@@ -16,14 +16,18 @@ package org.fairscan.app.ui.screens.crop
 
 import androidx.compose.foundation.Canvas
 import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.systemGestureExclusion
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.geometry.Rect
 import androidx.compose.ui.unit.IntSize
 import org.fairscan.imageprocessing.Point
 import org.fairscan.imageprocessing.Quad
 import org.fairscan.imageprocessing.scaledTo
+import kotlin.math.max
+import kotlin.math.min
 
 @Composable
 fun QuadOverlay(
@@ -35,7 +39,15 @@ fun QuadOverlay(
     val quadColor = MaterialTheme.colorScheme.primary
     val handleColor = quadColor.copy(alpha = 0.5f)
 
-    Canvas(modifier = modifier.fillMaxSize()) {
+    Canvas(modifier = modifier
+        .fillMaxSize()
+        // Android limits the exclusion areas, so we cannot simply exclude the whole quad/image.
+        // Instead, the corners must get excluded individually.
+        .systemGestureExclusion { cornerExclusionRect(quad.topLeft, containerSize, displaySize) }
+        .systemGestureExclusion { cornerExclusionRect(quad.topRight, containerSize, displaySize) }
+        .systemGestureExclusion { cornerExclusionRect(quad.bottomRight, containerSize, displaySize) }
+        .systemGestureExclusion { cornerExclusionRect(quad.bottomLeft, containerSize, displaySize) }
+    ) {
         val scaledQuad = quad.scaledTo(
             fromWidth = 1,
             fromHeight = 1,
@@ -74,3 +86,17 @@ fun QuadOverlay(
 }
 
 fun Point.toOffset() = Offset(x.toFloat(), y.toFloat())
+
+private fun cornerExclusionRect(
+    corner: Point,
+    containerSize: IntSize,
+    displaySize: IntSize
+): Rect {
+    val pos = QuadCoordinateUtils.normalizedToScreen(corner, containerSize, displaySize)
+    val r = QuadEditingHandler.CORNER_TOUCH_RADIUS
+    return Rect(max(.0f, pos.x - r),
+                max(.0f, pos.y - r),
+                min(containerSize.width.toFloat(), pos.x + r),
+                min(containerSize.height.toFloat(), pos.y + r)
+    )
+}