Selection-Delete Mode

Overview

Selection-Delete Mode is a gesture that enables text selection by swiping and holding on the backspace key. When activated, horizontal finger movement selects characters (left/right), vertical movement selects lines (up/down), and releasing the finger deletes all selected text. This provides a single fluid gesture for rapid text correction.

Key Files

File	Class/Function	Purpose
src/main/kotlin/tribixbite/cleverkeys/Pointers.kt	handleSelectionDeleteRepeat()	Main selection logic, repeat handler
src/main/kotlin/tribixbite/cleverkeys/Pointers.kt	FLAG_P_SELECTION_DELETE_MODE	Mode state flag (value: 128)
src/main/kotlin/tribixbite/cleverkeys/Config.kt	selection_delete_vertical_threshold	Vertical activation threshold
src/main/kotlin/tribixbite/cleverkeys/Config.kt	selection_delete_vertical_speed	Vertical speed multiplier
src/main/kotlin/tribixbite/cleverkeys/SettingsActivity.kt	Settings UI	Threshold and speed sliders

Architecture

User Input (backspace key short swipe + hold)
       |
       v
+------------------+
| onTouchDown()    | -- Defers backspace for gesture detection
+------------------+
       |
       v
+------------------+
| Short Swipe      | -- Detects initial swipe direction
| Detection        |
+------------------+
       |
       v (if hold detected after swipe)
+------------------+
| FLAG_P_SELECTION | -- Sets mode flag, records activation center
| _DELETE_MODE     |
+------------------+
       |
       v
+------------------+
| handleSelection  | -- Timer-based repeat, sends Shift+Arrow keys
| DeleteRepeat()   |
+------------------+
       |
       v (on finger release)
+------------------+
| Delete selected  | -- Sends DEL key to remove selection
| text             |
+------------------+

Data Flow

• 1. Activation: Short swipe on backspace key, then hold (don't lift finger)
• 2. Selection: Finger movement from activation center determines direction

- Horizontal (dx): Shift+Left or Shift+Right for character selection

- Vertical (dy): Shift+Up or Shift+Down for line selection (if threshold met)

• 3. Speed Scaling: Further from center = faster selection rate
• 4. Release: Sends DEL key to delete all selected text

Configuration

Key	Type	Default	Range	Description
selection_delete_vertical_threshold	Int	40	20-80	% of horizontal distance required for vertical selection
selection_delete_vertical_speed	Float	0.4	0.1-1.0	Speed multiplier for vertical selection

Public API

Pointers.kt

// State flag constant
private const val FLAG_P_SELECTION_DELETE_MODE = 128

// Timer identifier for repeat handler
private val selectionDeleteWhat = Any()

// Main selection handler - called repeatedly while mode active
private fun handleSelectionDeleteRepeat(ptr: Pointer) {
    val dx = ptr.currentX - ptr.selectionCenterX
    val dy = ptr.currentY - ptr.selectionCenterY

    // Horizontal selection (character by character)
    if (abs(dx) > threshold) {
        val key = if (dx > 0) DPAD_RIGHT else DPAD_LEFT
        sendShiftArrow(key)
    }

    // Vertical selection (line by line) with configurable threshold
    if (abs(dy) > verticalThreshold) {
        val key = if (dy > 0) DPAD_DOWN else DPAD_UP
        sendShiftArrow(key, speedMultiplier = verticalSpeed)
    }
}

// Helper to send Shift+Arrow for selection
private fun sendShiftArrow(keyCode: Int, speedMultiplier: Float = 1.0f)

// Helper to add Shift modifier to key
private fun with_extra_mod(value: KeyValue, extra: Modifier): KeyValue

Implementation Details

Activation Sequence

• 1. User touches backspace key
• 2. User performs short swipe (any direction except center)
• 3. User holds finger without lifting
• 4. After LONGPRESS_TIMEOUT (600ms default), mode activates
• 5. FLAG_P_SELECTION_DELETE_MODE flag set on pointer
• 6. selectionCenterX/Y records activation point
• 7. Repeat timer starts calling handleSelectionDeleteRepeat()

Bidirectional Movement

Selection direction changes dynamically based on current finger position relative to activation center:

// Direction determined each repeat cycle
val direction = when {
    dx > 0 -> DPAD_RIGHT  // Finger right of center
    dx < 0 -> DPAD_LEFT   // Finger left of center
    else -> null
}

This means:

• • Move finger left → select backwards
• • Move finger right → select forwards
• • Return to center and go opposite direction → select opposite direction

Independent Axis Handling

X and Y axes fire independently, allowing diagonal selection:

// Both axes checked independently each repeat
if (abs(dx) > horizontalThreshold) {
    sendShiftArrow(horizontalKey)
}
if (abs(dy) > verticalThreshold) {
    sendShiftArrow(verticalKey)
}

Shift State Management

Selection requires holding Shift while sending arrow keys:

private fun sendShiftArrow(keyCode: Int) {
    // Create internal Shift modifier
    val shift = makeInternalModifier(Modifier.SHIFT)

    // Apply Shift to arrow key
    val arrowKey = KeyValue.getKeyByCode(keyCode)
    val shiftedArrow = with_extra_mod(arrowKey, Modifier.SHIFT)

    // Send the combined key event
    sendKeyEvent(shiftedArrow)
}

Vertical Threshold Calculation

Vertical movement requires meeting a threshold relative to horizontal movement:

val verticalThreshold = config.selectionDeleteVerticalThreshold / 100f
val horizontalDistance = abs(dx)
val verticalDistance = abs(dy)

// Vertical only fires if it exceeds threshold percentage of horizontal
val shouldFireVertical = verticalDistance > (horizontalDistance * verticalThreshold)

Error Handling

• • Invalid threshold values: Clamped to 20-80%
• • Invalid speed values: Clamped to 0.1-1.0
• • No text to select: Selection commands sent but have no effect (harmless)