Adapt: Desktop to Mobile

Expert guidance for porting desktop games to mobile platforms.

NEVER Do

• NEVER use mouse position directly — Touch has no "hover" state. Replace mouse_motion with screen_drag and check InputEventScreenTouch.pressed.
• NEVER keep small UI elements — Apple HIG requires 44pt minimum touch targets. Android Material: 48dp. Scale up buttons 2-3x.
• NEVER forget finger occlusion — User's finger blocks 50-100px radius. Position critical info ABOVE touch controls, not below.
• NEVER run at full performance when backgrounded — Mobile OSs kill apps that drain battery in background. Pause physics, reduce FPS to 1-5 when app loses focus.
• NEVER use desktop-only features — Mouse hover, right-click, keyboard shortcuts, scroll wheel don't exist on mobile. Provide touch alternatives.

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Available Scripts

MANDATORY: Read the appropriate script before implementing the corresponding pattern. Do not paste joystick/gesture/UI tutorials inline.

dynamic_joystick_spawner.gd

MANDATORY for move sticks — Joystick appears where the user touches the left half (prefer over fixed-position recipes).

virtual_joystick.gd

Fixed-base stick Control — use when UI art requires a static well; otherwise prefer dynamic_joystick_spawner.

gesture_combo_system.gd

MANDATORY for swipe/pinch — Duration/distance/multi-touch ratio → signals.

mobile_ui_adapter.gd

MANDATORY for Control remaps — Scales/reanchors desktop HUD for thumb reach + density.

resolution_scaler.gd

Adaptive scaling_3d_scale to hold 60FPS while keeping 2D UI sharp.

battery_saver_mode.gd

MANDATORY — NOTIFICATION_APPLICATION_PAUSED → Engine.max_fps = 1 + pause physics.

ui_safe_area_margins.gd

DisplayServer.get_display_safe_area() padding for notches / hole-punch.

touch_camera_pan_zoom.gd

1-finger pan + 2-finger pinch Camera2D.

haptic_feedback_manager.gd

Input.vibrate_handheld + iOS plugin hook pattern.

mobile_shader_fallback.gd

Strip SSS/clearcoat/heavy shading on weak mobile renderers.

on_screen_keyboard_handler.gd

Virtual keyboard occlusion → tween UI up. Use for LineEdit/TextEdit focus — not a substitute for HUD scaling.

mobile_ui_adapter.gd vs on_screen_keyboard_handler

offline_save_sync.gd

MANDATORY — Persist on App Pause (WM_CLOSE is unreliable on mobile kill).

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Touch Control Schemes

Decision Matrix

Port Procedure (ordered)

1. MANDATORY mobile-port-checklist.md — confirm pre-port inventory and gate rows before remapping controls.
2. Replace hover/right-click/scroll with touch equivalents (decision matrix).
3. MANDATORY safe-area + mobile_ui_adapter for 44–48dp targets; keep critical HUD above fingers.
4. Hook battery_saver_mode + offline_save_sync on pause/resume.
5. Enable resolution_scaler + mobile_shader_fallback until device FPS is stable.
6. Deep Android/iOS IAP/permissions → godot-platform-mobile (Do NOT Load full platform skill until control/UI/perf gates pass).

Edge Cases (checklist)

• Multi-touch index conflicts on dual sticks — track event.index per stick
• OSK covering LineEdit → on_screen_keyboard_handler.gd
• Background kill without save → offline_save_sync.gd (WM_CLOSE unreliable on mobile)
• Notch clipping → ui_safe_area_margins.gd
• Palm touches screen edge — ignore ~50px border taps
• Desktop test builds: handle both InputEventMouseButton and InputEventScreenTouch

Device testing (before ship)

• 44–48dp touch targets on real hardware
• HUD above fingers (50–100px occlusion)
• Pause drops FPS + saves on background
• Stable FPS after resolution_scaler.gd + mobile_shader_fallback.gd
• Portrait + landscape safe areas

Full port recipes → mobile-port-deep.md.

Deep Recipes

MANDATORY when porting beyond the decision matrix: read mobile-port-deep.md. Do NOT Load it for a first-pass control remap.

Expert Techniques (short)

• Capture store screenshots via await RenderingServer.frame_post_draw + viewport image.
• Debug overlay: OS.get_memory_info() — do not spam heavy allocs while monitoring.

Reference

Progressive disclosure: open Official Documentation links only when researching a specific API; load Related Skills when routing work to a peer domain — do not preload the whole lattice.

Official Documentation

• Using InputEvent — Event pipeline and why InputEventScreenTouch / InputEventScreenDrag replace hover/mouse-motion assumptions on mobile.
• Mouse and input coordinates — Viewport vs canvas transforms so touch positions land on the same UI/game space as desktop mouse tests.
• Input examples — Practical multi-touch and drag patterns that map to virtual joysticks, swipes, and pinch gestures.
• Multiple resolutions — Stretch modes, aspect, and content scale so phone/tablet layouts keep touch targets readable.
• Resolution scaling — scaling_3d_scale / FSR tradeoffs used by adaptive quality when mobile GPUs miss frame budget.
• Introduction to the 3 rendering methods — Why ports should prefer Mobile or Compatibility over Forward+ for fill-rate and feature set.
• Handling quit requests — NOTIFICATION_APPLICATION_PAUSED / resume lifecycle that mobile OSes use instead of reliable window-close saves.
• DisplayServer — get_display_safe_area(), virtual keyboard APIs, and screen metrics behind notches and OSK occlusion.
• Using Containers — Margin/Box/Grid container contracts for safe-area padding and large touch targets.
• TouchScreenButton — Built-in on-screen buttons that emit Input actions without custom hit-testing.
• Exporting for Android — Permissions, APK/AAB, and device testing gates after the control/UI port is ready.
• Exporting for iOS — Xcode export, capabilities, and App Store constraints that catch desktop leftovers late.

Related Skills

Prerequisites

• godot-input-handling — Shared InputEvent buffering, deadzones, and multi-touch gesture foundations before building virtual joysticks or swipe combos.
• godot-ui-containers — Anchors, containers, and minimum sizes so 44–48px touch targets and safe-area margins stay layout-correct.
• godot-project-foundations — Feature tags (mobile/android/ios), display stretch, and renderer defaults that every port branch depends on.

Complements

• godot-platform-mobile — Deeper Android/iOS platform APIs (permissions, IAP, thermal) once the desktop→touch control remap is in place.
• godot-performance-optimization — Profiling and CPU/GPU cuts when adaptive scaling_3d_scale and material fallbacks are not enough.
• godot-save-load-systems — Durable save ownership that hooks pause/resume instead of desktop-only quit notifications.
• godot-camera-systems — Camera2D/3D follow and zoom contracts used by one-finger pan + two-finger pinch controllers.
• godot-shaders-basics — Cheaper CanvasItem/Spatial shader paths when stripping desktop-only visual features for mobile GPUs.
• godot-3d-materials — StandardMaterial3D feature flags (SSS, clearcoat) that mobile_shader_fallback disables on weak renderers.
• godot-tweening — Smooth UI lifts when the OS virtual keyboard covers LineEdits/TextEdits.
• godot-autoload-architecture — Singleton homes for haptic feedback, battery saver, and offline save sync managers.

Downstream / consumers

• godot-export-builds — Packaging, signing, and CI export presets after touch/UI/perf gates pass on devices.
• godot-platform-desktop — Keep desktop mouse/keyboard paths working when the same project remains dual-input after the mobile adapt.
• godot-genre-puzzle — Tap/swipe/pinch control schemes that consume the gesture and UI scaling patterns from this skill.

Master

• godot-master — Library router and mirrored module entry for discovering this adapt skill beside sibling domains.