Mobile Platform Support (iOS & Android)

[jdolan]

Overview

ObjectivelyMVC is built on SDL3, which ships first-class iOS and Android support. SDL3 already emulates SDL_EVENT_MOUSE_* from single-finger touch by default, and WindowController already handles SDL_EVENT_WINDOW_SAFE_AREA_CHANGED — so basic tap interaction likely works today without any changes. The gaps are multi-touch gestures, virtual keyboard, responsive layout, and touch-sized hit targets.

This is a prerequisite for any engine using ObjectivelyMVC as its UI framework (e.g. Quetoo) to run on mobile platforms.

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What Works Today (via SDL3 mouse emulation)

• Single-finger tap → SDL_EVENT_MOUSE_BUTTON_DOWN/UP → Button, Checkbox, Select all fire correctly
• Single-finger drag → SDL_EVENT_MOUSE_MOTION → Panel drag, Slider works
• Safe area inset handling already present in WindowController
• SDL_EVENT_WINDOW_RESIZED / orientation change already triggers layout

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Work Items

1. Multi-Touch Gesture Support

SDL3 delivers raw touch as SDL_EVENT_FINGER_DOWN/UP/MOTION. Two-finger gestures are not currently routed through the event system.

• Add SDL_EVENT_FINGER_* to WindowController::respondToEvent and View::didReceiveEvent
• Implement a gesture recognizer abstraction (tap, long-press, two-finger scroll/swipe, pinch-to-zoom) so consumers can override per-view
• Wire two-finger scroll to ScrollView and CollectionView in place of SDL_EVENT_MOUSE_WHEEL
• Wire pinch-to-zoom where applicable (e.g. ImageView)

2. Virtual Keyboard Integration

TextView currently relies on SDL_EVENT_TEXT_INPUT which requires SDL_StartTextInput() to be called first. On mobile this also raises the software keyboard.

• Call SDL_StartTextInput(window) when a TextView gains focus
• Call SDL_StopTextInput(window) when it loses focus
• Handle SDL_EVENT_WINDOW_RESIZED triggered by the keyboard appearing/disappearing (layout must reflow)
• Optionally suppress the software keyboard when a physical keyboard is detected

3. Touch Target Sizing

Apple HIG and Android Material both specify 44pt / 48dp minimum tap targets. ObjectivelyMVC's default control sizes are desktop-tuned and often smaller.

• Add a minimumTouchTarget concept to Control that pads the hit-test rect without affecting visual layout
• Default to 44pt on mobile (could be driven by a theme / stylesheet variable)
• Audit Button, Checkbox, Slider, Select for compliance

4. Responsive Layout & Orientation

Portrait/landscape orientation changes require layout to adapt. Safe area insets (notch, home indicator, rounded corners) must be respected.

• Ensure all pixel constants in built-in themes are DPI-independent (points, not pixels)
• Verify pixelDensity / SDL_GetWindowPixelDensity path is used consistently (partially done)
• Add orientation-aware layout hooks to ViewController so subclasses can rearrange on rotation
• Test against multiple screen aspect ratios (16:9, 19.5:9, 4:3 tablets)

5. Keyboard-Free Navigation

Several components assume keyboard availability:

• Select / dropdown: relies on keyboard to confirm selection — needs tap-to-select fallback
• TextView: relies on keyboard shortcuts (select-all, copy, paste) — needs long-press context menu
• Tab-stop focus traversal is irrelevant on touch — hide/skip gracefully
• Remove assumption of cursor (hover states) in Control highlight logic

6. Build System

ObjectivelyMVC currently uses autotools. Mobile targets need CMake (iOS) or Gradle/CMake (Android).

• Add CMakeLists.txt alongside existing autotools build
• iOS: CMake toolchain for xcrun/iphoneos SDK
• Android: CMakeLists.txt compatible with Android NDK's CMake integration

7. OpenGL ES Rendering Path

The Renderer currently uses OpenGL 4.1 Core Profile. Mobile requires OpenGL ES 3.0 or Metal.

• Abstract GL calls behind a thin compatibility layer or use SDL3's SDL_gpu API for rendering primitives (2D ortho, texture blits)
• GLSL 4.10 shaders → GLSL ES 3.0 (version header + precision qualifiers + minor syntax changes)
• This is a shared prerequisite with the Quetoo iOS/Android renderer port

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Notes

• Objectively (the base OOP framework) is pure portable C and requires no mobile-specific changes
• SDL3 handles the platform event loop, window lifecycle, and audio on both iOS and Android
• The SDL_EVENT_TERMINATING, SDL_EVENT_LOW_MEMORY, SDL_EVENT_WILL_ENTER_BACKGROUND, and SDL_EVENT_DID_ENTER_FOREGROUND lifecycle events should be forwarded through WindowController for apps to respond to