Implement OSC snap to grid functionality

app/src/main/java/emu/skyline/input/onscreen/OnScreenButton.kt

@@ -179,8 +179,40 @@ abstract class OnScreenButton(
      * Moves this button to the given coordinates
      */
     open fun move(x : Float, y : Float) {
-        relativeX = x / width
-        relativeY = (y - heightDiff) / adjustedHeight
+        var adjustedX = x
+        var adjustedY = y
+
+        if (editInfo.snapToGrid) {
+            val centerX = width / 2f
+            val centerY = height / 2f
+            val gridSize = editInfo.gridSize
+            // The coordinates of the first grid line for each axis, because the grid is centered and might not start at [0,0]
+            val startX = centerX % gridSize
+            val startY = centerY % gridSize
+
+            /**
+             * The offset to apply to a coordinate to snap it to the grid is the remainder of
+             * the coordinate divided by the grid size.
+             * Since the grid is centered on the screen and might not start at [0,0] we need to
+             * subtract the grid start offset, otherwise we'd be calculating the offset for a grid that starts at [0,0].
+             *
+             * Example: Touch event X: 158 | Grid size: 50 | Grid start X: 40 -> Grid lines at 40, 90, 140, 190, ...
+             * Snap offset: 158 - 40 = 118 -> 118 % 50 = 18
+             * Apply offset to X: 158 - 18 = 140 which is a grid line
+             *
+             * If we didn't subtract the grid start offset:
+             * Snap offset: 158 % 50 = 8
+             * Apply offset to X: 158 - 8 = 150 which is not a grid line
+             */
+            val snapOffsetX = (x - startX) % gridSize
+            val snapOffsetY = (y - startY) % gridSize
+
+            adjustedX = x - snapOffsetX
+            adjustedY = y - snapOffsetY
+        }
+
+        relativeX = adjustedX / width
+        relativeY = (adjustedY - heightDiff) / adjustedHeight
     }
 
     /**

app/src/main/java/emu/skyline/input/onscreen/OnScreenControllerView.kt

@@ -69,6 +69,7 @@ class OnScreenControllerView @JvmOverloads constructor(context : Context, attrs
     lateinit var vibrator : Vibrator
     private val effectClick = VibrationEffect.createPredefined(VibrationEffect.EFFECT_CLICK)
 
+    // Ensure controls init happens after editInfo is initialized so that the buttons have a valid reference to it
     private val controls = Controls(this)
 
     override fun onDraw(canvas : Canvas) {
@@ -263,8 +264,7 @@ class OnScreenControllerView @JvmOverloads constructor(context : Context, attrs
 
     fun setEditMode(editMode : EditMode) {
         editInfo.editMode = editMode
-        setOnTouchListener(if (editMode == EditMode.None) playingTouchHandler else editingTouchHandler)
-        invalidate()
+        setOnTouchListener(if (isEditing) editingTouchHandler else playingTouchHandler )
     }
 
     fun resetControls() {
@@ -286,6 +286,10 @@ class OnScreenControllerView @JvmOverloads constructor(context : Context, attrs
         invalidate()
     }
 
+    fun setSnapToGrid(snap : Boolean) {
+        editInfo.snapToGrid = snap
+    }
+
     fun increaseOpacity() {
         controls.alpha = (controls.alpha + ALPHA_STEP).coerceIn(ALPHA_RANGE)
         invalidate()

app/src/main/java/emu/skyline/input/onscreen/OnScreenEditActivity.kt

@@ -12,6 +12,7 @@ import android.os.VibratorManager
 import android.view.*
 import androidx.appcompat.app.AppCompatActivity
 import androidx.core.content.ContextCompat
+import androidx.core.view.isGone
 import com.google.android.material.dialog.MaterialAlertDialogBuilder
 import com.google.android.material.floatingactionbutton.FloatingActionButton
 import dagger.hilt.android.AndroidEntryPoint
@@ -108,12 +109,26 @@ class OnScreenEditActivity : AppCompatActivity() {
         }
     }
 
+    private val enableGridAction = {
+        appSettings.onScreenControlSnapToGrid = true
+        binding.onScreenControllerView.setSnapToGrid(true)
+        binding.alignmentGrid.isGone = false
+    }
+
+    private val disableGridAction = {
+        appSettings.onScreenControlSnapToGrid = false
+        binding.onScreenControllerView.setSnapToGrid(false)
+        binding.alignmentGrid.isGone = true
+    }
+
     private val actions : List<Pair<Int, () -> Unit>> = listOf(
         Pair(R.drawable.ic_palette, paletteAction),
         Pair(R.drawable.ic_restore) { binding.onScreenControllerView.resetControls() },
         Pair(R.drawable.ic_toggle, toggleAction),
         Pair(R.drawable.ic_move, moveAction),
         Pair(R.drawable.ic_resize, resizeAction),
+        Pair(R.drawable.ic_grid_on, enableGridAction),
+        Pair(R.drawable.ic_grid_off, disableGridAction),
         Pair(R.drawable.ic_zoom_out) { binding.onScreenControllerView.decreaseScale() },
         Pair(R.drawable.ic_zoom_in) { binding.onScreenControllerView.increaseScale() },
         Pair(R.drawable.ic_opacity_minus) { binding.onScreenControllerView.decreaseOpacity() },
@@ -147,6 +162,12 @@ class OnScreenEditActivity : AppCompatActivity() {
 
         binding.onScreenControllerView.recenterSticks = appSettings.onScreenControlRecenterSticks
 
+        val snapToGrid = appSettings.onScreenControlSnapToGrid
+        binding.onScreenControllerView.setSnapToGrid(snapToGrid)
+
+        binding.alignmentGrid.isGone = !snapToGrid
+        binding.alignmentGrid.gridSize = OnScreenEditInfo.GridSize
+
         actions.forEach { pair ->
             binding.fabParent.addView(LayoutInflater.from(this).inflate(R.layout.on_screen_edit_mini_fab, binding.fabParent, false).apply {
                 (this as FloatingActionButton).setImageDrawable(ContextCompat.getDrawable(context, pair.first))

app/src/main/java/emu/skyline/input/onscreen/OnScreenEditInfo.kt

@@ -5,6 +5,9 @@
 
 package emu.skyline.input.onscreen
 
+import android.util.TypedValue
+import emu.skyline.SkylineApplication
+
 enum class EditMode {
     None,
     Move,
@@ -26,5 +29,20 @@ class OnScreenEditInfo {
      */
     var editButton : OnScreenButton? = null
 
+    /**
+     * Whether the buttons should snap to a grid when in edit mode
+     */
+    var snapToGrid : Boolean = false
+
+    var gridSize : Int = GridSize
+
     val isEditing get() = editMode != EditMode.None
+
+    companion object {
+
+        /**
+         * The size of the grid, calculated from the value of 8dp
+         */
+        val GridSize = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 8f, SkylineApplication.context.resources.displayMetrics).toInt()
+    }
 }

app/src/main/java/emu/skyline/settings/AppSettings.kt

@@ -31,6 +31,7 @@ class AppSettings @Inject constructor(@ApplicationContext private val context :
     var onScreenControl by sharedPreferences(context, true)
     var onScreenControlFeedback by sharedPreferences(context, true)
     var onScreenControlRecenterSticks by sharedPreferences(context, true)
+    var onScreenControlSnapToGrid by sharedPreferences(context, false)
 
     // Other
     var romFormatFilter by sharedPreferences(context, 0)

app/src/main/java/emu/skyline/views/AlignmentGridView.kt

@@ -0,0 +1,65 @@
+/*
+ * SPDX-License-Identifier: MPL-2.0
+ * Copyright © 2023 Skyline Team and Contributors (https://github.com/skyline-emu/)
+ */
+
+package emu.skyline.views
+
+import android.content.Context
+import android.graphics.Canvas
+import android.graphics.Color
+import android.graphics.Paint
+import android.util.AttributeSet
+import android.view.View
+
+/**
+ * A view that draws a grid, used for aligning on-screen controller buttons
+ */
+class AlignmentGridView @JvmOverloads constructor(context : Context, attrs : AttributeSet? = null, defStyleAttr : Int = 0) : View(context, attrs, defStyleAttr) {
+    var gridSize = 0
+        set(value) {
+            field = value
+            invalidate()
+        }
+
+    private val gridPaint = Paint().apply {
+        color = Color.WHITE
+        alpha = 135
+    }
+    private val gridCenterPaint = Paint().apply {
+        color = Color.WHITE
+        alpha = 55
+        strokeWidth = 10f
+    }
+
+    override fun onDraw(canvas : Canvas) {
+        super.onDraw(canvas)
+        drawGrid(canvas)
+    }
+
+    /**
+     * Draws a centered grid on the given canvas
+     */
+    private fun drawGrid(canvas : Canvas) {
+        val centerX = width / 2f
+        val centerY = height / 2f
+        val gridSize = gridSize
+        // Compute the coordinates of the first grid line for each axis, because we want a centered grid, which might not start at [0,0]
+        val startX = centerX % gridSize
+        val startY = centerY % gridSize
+
+        // Draw the center lines with a thicker stroke
+        canvas.drawLine(centerX, 0f, centerX, height.toFloat(), gridCenterPaint)
+        canvas.drawLine(0f, centerY, width.toFloat(), centerY, gridCenterPaint)
+
+        // Draw the rest of the grid starting from the start coordinates
+        // Draw vertical lines
+        for (i in 0..width step gridSize) {
+            canvas.drawLine(startX + i, 0f, startX + i, height.toFloat(), gridPaint)
+        }
+        // Draw horizontal lines
+        for (i in 0..height step gridSize) {
+            canvas.drawLine(0f, startY + i, width.toFloat(), startY + i, gridPaint)
+        }
+    }
+}

app/src/main/res/drawable/ic_grid_off.xml

@@ -0,0 +1,10 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:tint="#000000"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <path
+        android:fillColor="@android:color/white"
+        android:pathData="M8,4v1.45l2,2L10,4h4v4h-3.45l2,2L14,10v1.45l2,2L16,10h4v4h-3.45l2,2L20,16v1.45l2,2L22,4c0,-1.1 -0.9,-2 -2,-2L4.55,2l2,2L8,4zM16,4h4v4h-4L16,4zM1.27,1.27L0,2.55l2,2L2,20c0,1.1 0.9,2 2,2h15.46l2,2 1.27,-1.27L1.27,1.27zM10,12.55L11.45,14L10,14v-1.45zM4,6.55L5.45,8L4,8L4,6.55zM8,20L4,20v-4h4v4zM8,14L4,14v-4h3.45l0.55,0.55L8,14zM14,20h-4v-4h3.45l0.55,0.54L14,20zM16,20v-1.46L17.46,20L16,20z" />
+</vector>

app/src/main/res/drawable/ic_grid_on.xml

@@ -0,0 +1,10 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:tint="#000000"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <path
+        android:fillColor="@android:color/white"
+        android:pathData="M20,2L4,2c-1.1,0 -2,0.9 -2,2v16c0,1.1 0.9,2 2,2h16c1.1,0 2,-0.9 2,-2L22,4c0,-1.1 -0.9,-2 -2,-2zM8,20L4,20v-4h4v4zM8,14L4,14v-4h4v4zM8,8L4,8L4,4h4v4zM14,20h-4v-4h4v4zM14,14h-4v-4h4v4zM14,8h-4L10,4h4v4zM20,20h-4v-4h4v4zM20,14h-4v-4h4v4zM20,8h-4L16,4h4v4z" />
+</vector>

app/src/main/res/layout/on_screen_edit_activity.xml

@@ -4,6 +4,11 @@
     android:layout_height="match_parent"
     android:background="@android:color/black">
 
+    <emu.skyline.views.AlignmentGridView
+        android:id="@+id/alignment_grid"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent" />
+
     <emu.skyline.input.onscreen.OnScreenControllerView
         android:id="@+id/on_screen_controller_view"
         android:layout_width="match_parent"