Add Smart Lasso Selection feature #158

bhavul · 2025-11-09T20:59:41Z

This is based on discussion in #140.

Summary

This PR adds a Smart Lasso Selection feature that allows users to select content by drawing a closed loop with their pen/stylus, making selection much more intuitive for EMR device users. The feature intelligently detects closed loops and shows the selection panel, with smart fallback to drawing if the user dismisses without taking action.

How does this work?

Added an algorithm to detect closed loop (few parameters can be optimised further)
Fallback: If user dismisses selection without using tools, the original stroke is drawn
Settings toggle: Feature is OFF by default, can be enabled in Settings > General

Note: Scribble-to-erase takes priority, so it doesn't interfere with normal drawing.

User Flow

User draws closed loop with pen
If loop contains content → Shows selection panel
User chooses:
a) Use tool (cut/copy/paste/duplicate) → Content is selected/manipulated
b) Tap outside → Original loop stroke is drawn on page

Closed loop detection algorithm

It uses several heuristics to ensure accurate recognition:

Minimum points: Requires ≥20 points (avoids tiny accidental loops)
Closure check: First and last points must be within 15% of bounding box diagonal
Minimum perimeter: ≥100 pixels to filter out tiny loops
Reversal limit: Allows natural hand movement but rejects scribbles (max 8 reversals)
Content check: Only triggers if strokes/images are actually inside the loop

Here's a video showcasing the feature and settings: https://drive.google.com/file/d/17nynCt7uNkB5glhnBmw1N1AGgTBBcnRe/view?usp=sharing

Maybe in Future?

Allow tuning detection thresholds in advanced settings

Ethran · 2025-11-09T21:22:07Z

Let copilot review it first, maybe it will find some problems. I will look at it latter.

Copilot

Pull Request Overview

This pull request adds a "smart lasso" selection feature that allows users to draw a closed loop to select content. When enabled, users can dismiss the selection to fall back to drawing the original stroke, providing a more intuitive drawing/selection workflow.

Adds a new smartLassoEnabled setting to app configuration
Implements smart lasso selection detection in drawing logic
Adds fallback mechanism to draw original stroke when selection is dismissed
Enhances JSON deserialization for backward compatibility

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
app/src/main/res/values/strings.xml	Added English string resource for smart lasso setting
app/src/main/res/values-pl/strings.xml	Added Polish translation for smart lasso setting
app/src/main/java/com/ethran/notable/ui/views/Settings.kt	Added UI toggle for smart lasso feature in settings
app/src/main/java/com/ethran/notable/editor/ui/SelectorBitmap.kt	Refactored selection dismissal to use centralized control tower method
app/src/main/java/com/ethran/notable/editor/state/SelectionState.kt	Added state tracking for pending smart lasso strokes
app/src/main/java/com/ethran/notable/editor/EditorControlTower.kt	Implemented dismissSelection method with smart lasso fallback logic
app/src/main/java/com/ethran/notable/editor/DrawCanvas.kt	Integrated smart lasso detection in drawing input handling
app/src/main/java/com/ethran/notable/data/db/Kv.kt	Added JSON configuration for backward compatibility
app/src/main/java/com/ethran/notable/data/datastore/AppSettings.kt	Added smartLassoEnabled field to app settings

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app/src/main/java/com/ethran/notable/editor/DrawCanvas.kt

Copilot

Pull Request Overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

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app/src/main/java/com/ethran/notable/editor/EditorControlTower.kt

bhavul · 2025-11-10T08:33:43Z

@Ethrlet you wanna have a look now?

Ethran · 2025-11-10T10:43:20Z

I will look into it this week, I need some more time to do it.

Ethran

There are some unnecessary operations in your implementation, please be mindful of what you are calculating before drawing strokes on the screen.

History should handle uncommitted strokes.

Don't duplicate existing functions, if something is implemented already, use it.

The EditorControlTower will change a little bit, mind this doing changes. 57d5fe2

Ethran · 2025-11-11T20:32:27Z

app/src/main/java/com/ethran/notable/editor/EditorControlTower.kt

+            Log.i("SmartLasso", "User dismissed smart lasso selection, drawing the original stroke with original pen settings")
+            // User dismissed without using the panel, so draw the original stroke with original settings
+            // Save the pending data before reset clears it
+            val strokeToDrawCopy = pendingStroke.toList()
+            val penCopy = pendingPen
+            val strokeSizeCopy = pendingStrokeSize
+            val colorCopy = pendingColor
+
+            // Reset the selection
+            state.selectionState.reset()
+
+            // Now draw the pending stroke with its original pen settings
+            val strokeHistoryBatch = mutableListOf<String>()
+            com.ethran.notable.editor.utils.handleDraw(
+                page,
+                strokeHistoryBatch,
+                strokeSizeCopy,
+                colorCopy,
+                penCopy,
+                strokeToDrawCopy
+            )
+
+            // Add to history
+            if (strokeHistoryBatch.isNotEmpty()) {
+                history.addOperationsToHistory(
+                    operations = listOf(
+                        Operation.DeleteStroke(strokeHistoryBatch)
+                    )
+                )
+            }
+
+            state.isDrawing = true
+
+            // Refresh UI
+            scope.launch {
+                DrawCanvas.refreshUi.emit(Unit)
+            }


should be moved to separate funtion

Also, it should be done as new operation list in History(pageView: PageView),

private var uncommittedOperations: OperationList = mutableListOf()

And there should be functions:
commitOperations()
addToUncommittedOperations(…)
clearUncommittedOperations(…)

(There probably are better names for them)

See also branch dev, I made recently some changes how the history is handled (I needed to handled one thing differently, and ended up changing a lot):
Commit: 57d5fe2
It will be merged when I address most of TODO's in this marge request. #156

Ethran · 2025-11-11T20:36:33Z

app/src/main/java/com/ethran/notable/data/db/Kv.kt

    private val kvRepository = KvRepository(context)

+    // Configure JSON to ignore unknown keys for backward compatibility
+    private val json = Json { ignoreUnknownKeys = true }


I need to check I really want to enable it. Having it set to false makes sure that I know exact state of app config. For now this PR should not make this change.

Ethran · 2025-11-11T20:39:07Z

app/src/main/java/com/ethran/notable/editor/utils/SmartLasso.kt

+private fun distance(p1: StrokePoint, p2: StrokePoint): Float {
+    val dx = p1.x - p2.x
+    val dy = p1.y - p2.y
+    return sqrt(dx * dx + dy * dy)


Do not use sqrt. It adds unnecessary computations, and its enough to use Manhattan metric. See scribble to erase.

Ethran · 2025-11-11T20:40:02Z

app/src/main/java/com/ethran/notable/editor/utils/SmartLasso.kt

+    val boxHeight = boundingBox.height()
+
+    // Calculate diagonal of bounding box
+    val diagonal = sqrt(boxWidth * boxWidth + boxHeight * boxHeight)


again, use Manhattan metric.

Ethran · 2025-11-11T20:41:58Z

app/src/main/java/com/ethran/notable/editor/utils/SmartLasso.kt

+/**
+ * Calculates the Euclidean distance between two points
+ */
+private fun distance(p1: StrokePoint, p2: StrokePoint): Float {


as distance might will be used in multiple parts of project it should be moved to editor/utils/…

Ethran · 2025-11-11T20:44:01Z

app/src/main/java/com/ethran/notable/editor/utils/SmartLasso.kt

+/**
+ * Calculates the total perimeter length of a stroke path
+ */
+private fun calculatePerimeter(points: List<StrokePoint>): Float {


its just a path length, not a Perimeter. Also, reuse function from scribble to erase.

And it seems as a quite bad way to determine if it is the loop. I would propose to select some points on the path, and check if distance between them is sufficiently large. ie let those points divide path in roughly 4 parts, and calculate distance between those 3 points. BUT be careful not to do too many operations, check if choosing base on index in table is good enough, or base on time (binary search).

Ethran · 2025-11-11T20:45:19Z

app/src/main/java/com/ethran/notable/editor/utils/SmartLasso.kt

+ * Calculates direction reversals but with different thresholds for lasso detection
+ * Unlike scribble detection, we're looking for smooth loops, not back-and-forth motion
+ */
+private fun calculateNumReversalsForLasso(


why it is separate function from what is used for scribble to ease?

Ethran · 2025-11-11T20:48:15Z

app/src/main/java/com/ethran/notable/editor/utils/SmartLasso.kt

+    editorState.selectionState.pendingSmartLassoStroke = touchPoints
+    editorState.selectionState.pendingSmartLassoPen = editorState.pen
+    editorState.selectionState.pendingSmartLassoStrokeSize = editorState.penSettings[editorState.pen.penName]?.strokeSize
+    editorState.selectionState.pendingSmartLassoColor = editorState.penSettings[editorState.pen.penName]?.color


This isn't good way of storing this information. It should be stored the same as stack for undo/redo.

Ethran · 2025-11-11T21:04:16Z

app/src/main/java/com/ethran/notable/editor/state/SelectionState.kt

+    // Smart lasso: stores the original stroke data if selection was made via smart lasso
+    // This allows fallback to drawing the stroke if user dismisses without using the panel
+    var pendingSmartLassoStroke by mutableStateOf<List<StrokePoint>?>(null)
+    var pendingSmartLassoPen by mutableStateOf<Pen?>(null)
+    var pendingSmartLassoStrokeSize by mutableStateOf<Float?>(null)
+    var pendingSmartLassoColor by mutableStateOf<Int?>(null)


Not the place for those, see other comments.

Ethran · 2025-11-11T21:07:30Z

app/src/main/java/com/ethran/notable/editor/utils/SmartLasso.kt

+    // Additional check: ensure the stroke doesn't have too many sharp reversals
+    // (which would indicate scribbling rather than deliberate loop drawing)
+    // We allow some reversals (unlike scribble which requires many), but not too many
+    val reversals = calculateNumReversalsForLasso(points)


Do we really need to calculate it again? We already calculate it in scribble to erase, if both are turned on, then we do unnecessary calculations. Same for path lengths.

bhavul · 2026-02-10T10:29:39Z

Hi @Ethran Life's gotten busy, I'm afraid. I've also stopped using Notable for the most part recently (no major reason).
So I'll pass on updating this PR further. Feel free to close it or resume work on it.

Add Smart Lasso Selection feature

76ac7b6

Ethran added the enhancement New feature or request label Nov 9, 2025

Ethran requested a review from Copilot November 9, 2025 21:20

Copilot AI reviewed Nov 9, 2025

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app/src/main/java/com/ethran/notable/editor/DrawCanvas.kt Show resolved Hide resolved

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Had forgotten to commit the main file implementing Smart Lasso!

3bca44a

Ethran requested a review from Copilot November 9, 2025 21:33

Copilot AI reviewed Nov 9, 2025

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Copilot review fixes

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Ethran requested changes Nov 11, 2025

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bhavul commented Nov 9, 2025

Summary

How does this work?

User Flow

Closed loop detection algorithm

Maybe in Future?

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Ethran commented Nov 9, 2025

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bhavul commented Nov 10, 2025

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Ethran commented Nov 10, 2025

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bhavul commented Feb 10, 2026

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