[Feature] DS Dual-Screen: Touch coordinate translation for bottom screen

[github-actions]

Summary

DS bottom screen is a touchscreen. When a user taps the bottom-screen viewport in a dual-screen skin, the touch coordinates must be translated from skin-space into DS hardware coordinates (0–255 x, 0–191 y) before being forwarded to the core via PVDSSystemResponderClient.

Background

The existing PVDSSystemResponderClient protocol has:

func touchBegan(at point: CGPoint)
func touchMoved(at point: CGPoint)
func touchEnded()

Where point is expected in DS hardware coordinates (x: 0–255, y: 0–191).

Currently, touch events from the on-screen emulator view are passed directly to the core without any skin-aware coordinate mapping. With dual-screen skins, the bottom-screen output frame is a sub-region of the full view — touch points must be mapped:

viewTouchPoint → (normalize by bottomScreenOutputFrame) → dsX = normalizedX * 255, dsY = normalizedY * 191

Required Work

1. Detect bottom-screen touches — In DeltaSkinInputHandler or MultiTouchView, identify taps that fall within the bottom-screen output frame.

2. Coordinate transform:

   func mapToDS(touch: CGPoint, bottomScreenFrame: CGRect) -> CGPoint? {
       guard bottomScreenFrame.contains(touch) else { return nil }
       let normalizedX = (touch.x - bottomScreenFrame.minX) / bottomScreenFrame.width
       let normalizedY = (touch.y - bottomScreenFrame.minY) / bottomScreenFrame.height
       return CGPoint(x: normalizedX * 255, y: normalizedY * 191)
   }

3. Forward to core — Pass mapped coordinates to PVDSSystemResponderClient.touchBegan(at:) etc.

4. Block non-skin-aware path — Ensure the old direct-passthrough path is disabled when a dual-screen NDS skin is active (to avoid double-forwarding).

Files to Change

• PVUI/Sources/PVUIBase/SwiftUI/DeltaSkins/Models/DeltaSkinInputHandler.swift
• PVUI/Sources/PVUIBase/SwiftUI/DeltaSkins/Views/MultiTouchView.swift
• PVUI/Sources/PVUIBase/PVEmulatorVC/PVEmulatorViewController+DualScreen.swift

Acceptance Criteria

• Tapping the bottom screen viewport in an NDS skin sends correct DS coordinates to the core
• Tapping the top screen area does NOT trigger touchscreen events
• Touch tracking (began/moved/ended) is correctly forwarded
• Screen-swap mode (when active) swaps which viewport is treated as touch

Depends on

#[Metal sub-rectangle issue number] — touch regions are only meaningful once screens render at correct positions

Part of

Part of #2540 — DS Dual-Screen Skin System

[JoeMatt]

@claude please make a PR for this

Please implement DS dual-screen touch coordinate translation for the bottom screen. PR #3377 already enables DS skin loading — this follow-up adds the touch coordinate mapping.

Key tasks:

1. In the emulator view's touch handler, detect when a touch is on the bottom screen viewport (as defined by the skin's inputFrame for the DS bottom screen)
2. Map the touch from screen/SwiftUI coordinates to DS hardware coordinates (0–255 x, 0–191 y)
3. Forward the translated coordinates to the core's touch API (for MelonDS: touchScreen(x:y:), for DeSmuME: equivalent)
4. Handle touch down, move, and up events
5. Handle both portrait (stacked) and landscape (side-by-side) dual-screen layouts
6. Works in conjunction with PR [Agent] feat(ds): enable skin support for melonDS, desmume2015, and ThinLibretroCore DS (Phase 1) #3377's skin layout (DeltaSkinScreen inputFrame metadata)

[github-actions]

DS Touch Coordinate Translation - PR Created

Completed

• Agent started
• Read context and PR [Agent] feat(ds): enable skin support for melonDS, desmume2015, and ThinLibretroCore DS (Phase 1) #3377
• Explored touch handling code
• Implemented touch detection in DeltaSkinView
• Added touchScreenAtPoint to melonDS/Desmume2015 cores
• Created PR [Agent] feat(ds): DS bottom-screen touch coordinate translation (Phase 2) #3503
• Auto-merge enabled, AI review triggered

PR

#3503

[github-actions]

PR Created: #3503

I've implemented DS dual-screen touch coordinate translation. Here's what was done:

Changes

PVUI/Sources/PVUIBase/SwiftUI/DeltaSkins/Views/DeltaSkinView.swift

• Added touchToNDSScreenMap state to track which touch IDs are on the DS bottom screen
• Added mapToNDSBottomScreen(_:in:) helper that maps a view-space touch to normalized (0–1) bottom-screen coordinates using the skin's screenGroups outputFrame data
• In handleTouchAtLocation: detect NDS bottom-screen touches for both new touches and ongoing drag
• In .moved callback: treat NDS screen touches like D-pad (always process for smooth drag)
• In .ended/.cancelled: call ndsBottomScreenTouchReleased() when last screen touch lifts

Cores/melonDS/PVMelonDSCore/Core/PVMelonDSCore.swift
Cores/Desmume2015/PVDesmume2015Core/Core/PVDesmume2015Core.swift

• Added touchScreenAtPoint(_:) and releaseScreenTouch() that forward to the Obj-C bridge

Cores/melonDS/PVMelonDSCore/Core/PVMelonDSCore+Controls.mm
Cores/Desmume2015/PVDesmume2015Core/Core/PVDesmume2015Core+Controls.mm

• Implemented touchScreenAtPoint: (normalizes DS coords → libretro pointer state) and releaseScreenTouch on the ObjC bridge — same mechanism as PVThinLibretroCore

Note

This PR depends on #3377 (which enables supportsSkins = true for DS cores). The touch routing code is complete, but the skin must be loaded before it activates.

PR: #3503