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SDL3 Migration Plan

Version: 0.4.0 Target Author: imgui-frontend-engineer agent Date: 2025-11-23 Status: Planning Phase

Executive Summary

This document outlines the migration strategy from SDL2 (v2.30.0) to SDL3 for the YAZE project. SDL3 was released as stable in January 2025 and brings significant architectural improvements, particularly in audio handling and event processing. The YAZE codebase is well-positioned for this migration due to existing abstraction layers for audio, input, and rendering.

Current SDL2 Usage Inventory

Core Application Files

Category	Files	SDL2 APIs Used
Window Management	`src/app/platform/window.h`, `window.cc`	`SDL_Window`, `SDL_CreateWindow`, `SDL_DestroyWindow`, `SDL_GetCurrentDisplayMode`, `SDL_PollEvent`, `SDL_GetMouseState`, `SDL_GetModState`
Main Controller	`src/app/controller.h`, `controller.cc`	`SDL_Delay`, `SDL_WINDOW_RESIZABLE`
Timing	`src/app/platform/timing.h`	`SDL_GetPerformanceCounter`, `SDL_GetPerformanceFrequency`

Graphics Subsystem

Category	Files	SDL2 APIs Used
Renderer Interface	`src/app/gfx/backend/irenderer.h`	`SDL_Window*`, `SDL_Rect`, `SDL_Color`
SDL2 Renderer	`src/app/gfx/backend/sdl2_renderer.h`, `sdl2_renderer.cc`	`SDL_Renderer`, `SDL_CreateRenderer`, `SDL_CreateTexture`, `SDL_UpdateTexture`, `SDL_RenderCopy`, `SDL_RenderPresent`, `SDL_RenderClear`, `SDL_SetRenderTarget`, `SDL_LockTexture`, `SDL_UnlockTexture`
Bitmap	`src/app/gfx/core/bitmap.h`, `bitmap.cc`	`SDL_Surface`, `SDL_CreateRGBSurfaceWithFormat`, `SDL_FreeSurface`, `SDL_SetSurfacePalette`, `SDL_DEFINE_PIXELFORMAT`
Palette	`src/app/gfx/types/snes_palette.cc`	`SDL_Color`
Resource Arena	`src/app/gfx/resource/arena.cc`	`SDL_Surface`, texture management
Utilities	`src/util/sdl_deleter.h`	`SDL_DestroyWindow`, `SDL_DestroyRenderer`, `SDL_FreeSurface`, `SDL_DestroyTexture`

Emulator Subsystem

Category	Files	SDL2 APIs Used
Audio Backend	`src/app/emu/audio/audio_backend.h`, `audio_backend.cc`	`SDL_AudioSpec`, `SDL_OpenAudioDevice`, `SDL_CloseAudioDevice`, `SDL_PauseAudioDevice`, `SDL_QueueAudio`, `SDL_ClearQueuedAudio`, `SDL_GetQueuedAudioSize`, `SDL_GetAudioDeviceStatus`, `SDL_AudioStream`, `SDL_NewAudioStream`, `SDL_AudioStreamPut`, `SDL_AudioStreamGet`, `SDL_FreeAudioStream`
Input Backend	`src/app/emu/input/input_backend.h`, `input_backend.cc`	`SDL_GetKeyboardState`, `SDL_GetScancodeFromKey`, `SDLK_*` keycodes, `SDL_Event`, `SDL_KEYDOWN`, `SDL_KEYUP`
Input Handler UI	`src/app/emu/ui/input_handler.cc`	`SDL_GetKeyName`, `SDL_PollEvent`
Standalone Emulator	`src/app/emu/emu.cc`	Full SDL2 initialization, window, renderer, audio, events

ImGui Integration

Category	Files	Notes
Platform Backend	`ext/imgui/backends/imgui_impl_sdl2.cpp`, `imgui_impl_sdl2.h`	Used for platform/input integration
Renderer Backend	`ext/imgui/backends/imgui_impl_sdlrenderer2.cpp`, `imgui_impl_sdlrenderer2.h`	Used for rendering
SDL3 Backends (Available)	`ext/imgui/backends/imgui_impl_sdl3.cpp`, `imgui_impl_sdl3.h`, `imgui_impl_sdlrenderer3.cpp`, `imgui_impl_sdlrenderer3.h`	Ready to use

Test Files

Files	Notes
`test/yaze_test.cc`	SDL initialization for tests
`test/test_editor.cc`	SDL window for editor tests
`test/integration/editor/editor_integration_test.cc`	Integration tests with SDL

SDL3 Breaking Changes Affecting YAZE

Critical Changes (Must Address)

1. Audio API Overhaul

SDL2 Code:

SDL_AudioSpec want, have;
want.callback = nullptr;  // Queue-based
device_id_ = SDL_OpenAudioDevice(nullptr, 0, &want, &have, 0);
SDL_QueueAudio(device_id_, samples, size);
SDL_PauseAudioDevice(device_id_, 0);

SDL3 Equivalent:

SDL_AudioSpec spec = { SDL_AUDIO_S16, 2, 48000 };
SDL_AudioStream* stream = SDL_OpenAudioDeviceStream(
    SDL_AUDIO_DEVICE_DEFAULT_PLAYBACK, &spec, nullptr, nullptr);
SDL_PutAudioStreamData(stream, samples, size);
SDL_ResumeAudioDevice(SDL_GetAudioStreamDevice(stream));

Impact: SDL2AudioBackend class needs complete rewrite. The existing IAudioBackend interface isolates this change.

2. Window Event Restructuring

SDL2 Code:

case SDL_WINDOWEVENT:
    switch (event.window.event) {
        case SDL_WINDOWEVENT_CLOSE: ...
        case SDL_WINDOWEVENT_RESIZED: ...
    }

SDL3 Equivalent:

case SDL_EVENT_WINDOW_CLOSE_REQUESTED: ...
case SDL_EVENT_WINDOW_RESIZED: ...

Impact: window.cc HandleEvents() needs event type updates.

3. Keyboard Event Changes

SDL2 Code:

event.key.keysym.sym  // SDL_Keycode
SDL_GetKeyboardState(nullptr)  // Returns Uint8*

SDL3 Equivalent:

event.key.key  // SDL_Keycode (keysym removed)
SDL_GetKeyboardState(nullptr)  // Returns bool*

Impact: SDL2InputBackend keyboard handling needs updates.

4. Surface Format Changes

SDL2 Code:

surface->format->BitsPerPixel

SDL3 Equivalent:

SDL_GetPixelFormatDetails(surface->format)->bits_per_pixel

Impact: Bitmap class surface handling needs updates.

Moderate Changes

5. Event Type Renaming

SDL2	SDL3
`SDL_KEYDOWN`	`SDL_EVENT_KEY_DOWN`
`SDL_KEYUP`	`SDL_EVENT_KEY_UP`
`SDL_MOUSEMOTION`	`SDL_EVENT_MOUSE_MOTION`
`SDL_MOUSEWHEEL`	`SDL_EVENT_MOUSE_WHEEL`
`SDL_DROPFILE`	`SDL_EVENT_DROP_FILE`
`SDL_QUIT`	`SDL_EVENT_QUIT`

6. Function Renames

SDL2	SDL3
`SDL_GetTicks()`	`SDL_GetTicks()` (now returns Uint64)
`SDL_GetTicks64()`	Removed (use `SDL_GetTicks()`)
N/A	`SDL_GetTicksNS()` (new, nanoseconds)

7. Audio Device Functions

SDL2	SDL3
`SDL_OpenAudioDevice()`	`SDL_OpenAudioDeviceStream()`
`SDL_QueueAudio()`	`SDL_PutAudioStreamData()`
`SDL_GetQueuedAudioSize()`	`SDL_GetAudioStreamQueued()`
`SDL_ClearQueuedAudio()`	`SDL_ClearAudioStream()`
`SDL_PauseAudioDevice(id, 0/1)`	`SDL_ResumeAudioDevice(id)` / `SDL_PauseAudioDevice(id)`

Low Impact Changes

8. Initialization

// SDL2
SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)

// SDL3 - largely unchanged
SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_EVENTS)

9. Renderer Creation

// SDL2
SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED)

// SDL3
SDL_CreateRenderer(window, nullptr)  // Name string instead of index

Existing Abstraction Layers

Strengths - Ready for Migration

IAudioBackend Interface (src/app/emu/audio/audio_backend.h)
- Complete abstraction for audio operations
- Factory pattern with BackendType::SDL3 placeholder already defined
- Only SDL2AudioBackend implementation needs updating
IInputBackend Interface (src/app/emu/input/input_backend.h)
- Platform-agnostic controller state management
- Factory pattern with BackendType::SDL3 placeholder already defined
- Only SDL2InputBackend implementation needs updating
IRenderer Interface (src/app/gfx/backend/irenderer.h)
- Abstract texture and rendering operations
- SDL2Renderer implementation isolated
- Ready for SDL3Renderer implementation
util::SDL_Deleter (src/util/sdl_deleter.h)
- Centralized resource cleanup
- Easy to add SDL3 variants

Gaps - Need New Abstractions

Window Management
- core::Window struct directly exposes SDL_Window*
- CreateWindow() and HandleEvents() have inline SDL2 code
- Recommendation: Create IWindow interface or wrapper class
Event Handling
- Event processing embedded in window.cc
- SDL2 event types used directly
- Recommendation: Create event abstraction layer or adapter
Timing
- TimingManager uses SDL2 functions directly
- Recommendation: Create ITimer interface (low priority - minimal changes)
Bitmap/Surface
- Bitmap class directly uses SDL_Surface
- Tight coupling with SDL2 surface APIs
- Recommendation: Create ISurface wrapper or use conditional compilation

Migration Phases

Phase 1: Preparation (Estimated: 1-2 days)

1.1 Add SDL3 Build Configuration

# cmake/dependencies/sdl3.cmake (new file)
option(YAZE_USE_SDL3 "Use SDL3 instead of SDL2" OFF)

if(YAZE_USE_SDL3)
  CPMAddPackage(
    NAME SDL3
    VERSION 3.2.0
    GITHUB_REPOSITORY libsdl-org/SDL
    GIT_TAG release-3.2.0
    OPTIONS
      "SDL_SHARED OFF"
      "SDL_STATIC ON"
  )
endif()

1.2 Create Abstraction Headers

Create src/app/platform/sdl_compat.h for cross-version macros
Define version-agnostic type aliases

// src/app/platform/sdl_compat.h
#pragma once

#ifdef YAZE_USE_SDL3
#include <SDL3/SDL.h>
#define YAZE_SDL_KEYDOWN SDL_EVENT_KEY_DOWN
#define YAZE_SDL_KEYUP SDL_EVENT_KEY_UP
#define YAZE_SDL_WINDOW_CLOSE SDL_EVENT_WINDOW_CLOSE_REQUESTED
// ... etc
#else
#include <SDL.h>
#define YAZE_SDL_KEYDOWN SDL_KEYDOWN
#define YAZE_SDL_KEYUP SDL_KEYUP
#define YAZE_SDL_WINDOW_CLOSE SDL_WINDOWEVENT // (handle internally)
// ... etc
#endif

1.3 Update ImGui CMake

# cmake/dependencies/imgui.cmake
if(YAZE_USE_SDL3)
  set(IMGUI_SDL_BACKEND "imgui_impl_sdl3.cpp")
  set(IMGUI_RENDERER_BACKEND "imgui_impl_sdlrenderer3.cpp")
else()
  set(IMGUI_SDL_BACKEND "imgui_impl_sdl2.cpp")
  set(IMGUI_RENDERER_BACKEND "imgui_impl_sdlrenderer2.cpp")
endif()

Phase 2: Core Subsystem Migration (Estimated: 3-5 days)

2.1 Audio Backend (Priority: High)

Create SDL3AudioBackend class in audio_backend.cc
Implement using SDL_AudioStream API
Update AudioBackendFactory::Create() to handle SDL3

Key changes:

class SDL3AudioBackend : public IAudioBackend {
  SDL_AudioStream* stream_ = nullptr;

  bool Initialize(const AudioConfig& config) override {
    SDL_AudioSpec spec;
    spec.format = SDL_AUDIO_S16;
    spec.channels = config.channels;
    spec.freq = config.sample_rate;

    stream_ = SDL_OpenAudioDeviceStream(
        SDL_AUDIO_DEVICE_DEFAULT_PLAYBACK, &spec, nullptr, nullptr);
    return stream_ != nullptr;
  }

  bool QueueSamples(const int16_t* samples, int num_samples) override {
    return SDL_PutAudioStreamData(stream_, samples,
        num_samples * sizeof(int16_t));
  }
};

2.2 Input Backend (Priority: High)

Create SDL3InputBackend class in input_backend.cc
Update keyboard state handling for bool* return type
Update event processing for new event types

Key changes:

class SDL3InputBackend : public IInputBackend {
  ControllerState Poll(int player) override {
    const bool* keyboard_state = SDL_GetKeyboardState(nullptr);
    // Note: SDL3 returns bool* instead of Uint8*
    state.SetButton(SnesButton::B, keyboard_state[SDL_SCANCODE_Z]);
    // ...
  }
};

2.3 Window/Event Handling (Priority: Medium)

Update HandleEvents() in window.cc
Replace SDL_WINDOWEVENT with individual event types
Update keyboard modifier handling

Before (SDL2):

case SDL_WINDOWEVENT:
    switch (event.window.event) {
        case SDL_WINDOWEVENT_CLOSE:
            window.active_ = false;

After (SDL3):

case SDL_EVENT_WINDOW_CLOSE_REQUESTED:
    window.active_ = false;

Phase 3: Graphics Migration (Estimated: 2-3 days)

3.1 Renderer Backend

Create SDL3Renderer class implementing IRenderer
Update renderer creation (string name instead of index)
Handle coordinate system changes (float vs int)

Key changes:

class SDL3Renderer : public IRenderer {
  bool Initialize(SDL_Window* window) override {
    renderer_ = SDL_CreateRenderer(window, nullptr);
    return renderer_ != nullptr;
  }
};

3.2 Surface/Bitmap Handling

Update pixel format access in Bitmap class
Handle palette creation changes
Update SDL_DEFINE_PIXELFORMAT macros if needed

Key changes:

// SDL2
int depth = surface->format->BitsPerPixel;

// SDL3
const SDL_PixelFormatDetails* details =
    SDL_GetPixelFormatDetails(surface->format);
int depth = details->bits_per_pixel;

3.3 Texture Management

Update texture creation in SDL3Renderer
Handle any lock/unlock API changes

Phase 4: ImGui Integration (Estimated: 1 day)

4.1 Update Backend Initialization

// SDL2
ImGui_ImplSDL2_InitForSDLRenderer(window, renderer);
ImGui_ImplSDLRenderer2_Init(renderer);

// SDL3
ImGui_ImplSDL3_InitForSDLRenderer(window, renderer);
ImGui_ImplSDLRenderer3_Init(renderer);

4.2 Update Frame Processing

// SDL2
ImGui_ImplSDLRenderer2_NewFrame();
ImGui_ImplSDL2_NewFrame();
ImGui_ImplSDL2_ProcessEvent(&event);

// SDL3
ImGui_ImplSDLRenderer3_NewFrame();
ImGui_ImplSDL3_NewFrame();
ImGui_ImplSDL3_ProcessEvent(&event);

Phase 5: Cleanup and Testing (Estimated: 2-3 days)

5.1 Remove SDL2 Fallback (Optional)

Once stable, consider removing dual-support code
Keep SDL2 code path for legacy support if needed

5.2 Update Tests

Update test initialization for SDL3
Verify all test suites pass with SDL3

5.3 Documentation Updates

Update build instructions
Update dependency documentation
Add SDL3-specific notes to CLAUDE.md

Effort Estimates

Phase	Task	Estimated Time	Complexity
Phase 1	Build configuration	4 hours	Low
	Abstraction headers	4 hours	Low
	ImGui CMake updates	2 hours	Low
Phase 2	Audio backend	8 hours	High
	Input backend	4 hours	Medium
	Window/Event handling	6 hours	Medium
Phase 3	Renderer backend	8 hours	Medium
	Surface/Bitmap handling	6 hours	Medium
	Texture management	4 hours	Low
Phase 4	ImGui integration	4 hours	Low
Phase 5	Cleanup and testing	8-12 hours	Medium
Total		~58-62 hours

Risk Assessment

High Risk

Risk	Impact	Mitigation
Audio API complexity	Emulator audio may break	Start with audio migration; extensive testing
Cross-platform differences	Platform-specific bugs	Test on all platforms early
ImGui backend compatibility	UI rendering issues	Use official SDL3 backends from Dear ImGui

Medium Risk

Risk	Impact	Mitigation
Performance regression	Slower rendering/audio	Benchmark before and after
Build system complexity	Build failures	Maintain dual-build support initially
Event timing changes (ns vs ms)	Input lag or timing issues	Careful timestamp handling

Low Risk

Risk	Impact	Mitigation
Function rename compilation errors	Build failures	Mechanical fixes with search/replace
Minor API differences	Runtime bugs	Comprehensive test coverage

Testing Strategy

Unit Tests

Audio backend: Test initialization, queue, playback control
Input backend: Test keyboard state, event processing
Renderer: Test texture creation, rendering operations

Integration Tests

Full emulator loop with SDL3
Editor UI responsiveness
Graphics loading and display

Manual Testing Checklist

Application launches without errors
ROM loading works correctly
All editors render properly
Emulator audio plays without glitches
Keyboard input responsive in emulator
Window resize works correctly
Multi-monitor support (if applicable)
Performance comparable to SDL2

Dependencies

Required

SDL 3.2.0 or later
Updated ImGui with SDL3 backends (already available in ext/imgui)

Optional

SDL3_gpu for modern GPU rendering (future enhancement)
SDL3_mixer for enhanced audio (if needed)

Rollback Plan

If SDL3 migration causes critical issues:

Keep SDL2 build option available (-DYAZE_USE_SDL3=OFF)
Document known SDL3 issues in issue tracker
Maintain SDL2 compatibility branch if needed

References

Appendix A: Full File Impact List

Files Requiring Modification

src/app/platform/window.h          - SDL_Window type, event constants
src/app/platform/window.cc         - Event handling, window creation
src/app/platform/timing.h          - Performance counter functions
src/app/controller.cc              - ImGui backend calls
src/app/controller.h               - SDL_Window reference
src/app/gfx/backend/irenderer.h    - SDL types in interface
src/app/gfx/backend/sdl2_renderer.h/.cc - Entire file (create SDL3 variant)
src/app/gfx/core/bitmap.h/.cc      - Surface handling, pixel formats
src/app/gfx/types/snes_palette.cc  - SDL_Color usage
src/app/gfx/resource/arena.cc      - Surface/texture management
src/app/emu/audio/audio_backend.h/.cc - Complete audio API rewrite
src/app/emu/input/input_backend.h/.cc - Keyboard state, events
src/app/emu/ui/input_handler.cc    - Key name functions, events
src/app/emu/emu.cc                 - Full SDL initialization
src/util/sdl_deleter.h             - Deleter function signatures
test/yaze_test.cc                  - Test initialization
test/test_editor.cc                - Test window handling
cmake/dependencies/sdl2.cmake      - Build configuration
cmake/dependencies/imgui.cmake     - Backend selection

New Files to Create

src/app/platform/sdl_compat.h      - Cross-version compatibility macros
src/app/gfx/backend/sdl3_renderer.h/.cc - SDL3 renderer implementation
cmake/dependencies/sdl3.cmake      - SDL3 build configuration

Appendix B: Quick Reference - API Mapping

SDL2	SDL3	Notes
`SDL_INIT_TIMER`	Removed	Timer always available
`SDL_GetTicks()`	`SDL_GetTicks()`	Returns Uint64
`SDL_OpenAudioDevice()`	`SDL_OpenAudioDeviceStream()`	Stream-based
`SDL_QueueAudio()`	`SDL_PutAudioStreamData()`
`SDL_PauseAudioDevice(id, 0)`	`SDL_ResumeAudioDevice(id)`
`SDL_PauseAudioDevice(id, 1)`	`SDL_PauseAudioDevice(id)`
`SDL_CreateRenderer(w, -1, f)`	`SDL_CreateRenderer(w, name)`
`SDL_KEYDOWN`	`SDL_EVENT_KEY_DOWN`
`SDL_WINDOWEVENT`	Individual events
`event.key.keysym.sym`	`event.key.key`
`SDL_GetKeyboardState()`	`SDL_GetKeyboardState()`	Returns bool*

18 KiB Raw Blame History

SDL3 Migration Plan

Executive Summary

Current SDL2 Usage Inventory

Core Application Files

Graphics Subsystem

Emulator Subsystem

ImGui Integration

Test Files

SDL3 Breaking Changes Affecting YAZE

Critical Changes (Must Address)

1. Audio API Overhaul

2. Window Event Restructuring

3. Keyboard Event Changes

4. Surface Format Changes

Moderate Changes

5. Event Type Renaming

6. Function Renames

7. Audio Device Functions

Low Impact Changes

8. Initialization

9. Renderer Creation

Existing Abstraction Layers

Strengths - Ready for Migration

Gaps - Need New Abstractions

Migration Phases

Phase 1: Preparation (Estimated: 1-2 days)

1.1 Add SDL3 Build Configuration

1.2 Create Abstraction Headers

1.3 Update ImGui CMake

Phase 2: Core Subsystem Migration (Estimated: 3-5 days)

2.1 Audio Backend (Priority: High)

2.2 Input Backend (Priority: High)

2.3 Window/Event Handling (Priority: Medium)

Phase 3: Graphics Migration (Estimated: 2-3 days)

3.1 Renderer Backend

3.2 Surface/Bitmap Handling

3.3 Texture Management

Phase 4: ImGui Integration (Estimated: 1 day)

4.1 Update Backend Initialization

4.2 Update Frame Processing

Phase 5: Cleanup and Testing (Estimated: 2-3 days)

5.1 Remove SDL2 Fallback (Optional)

5.2 Update Tests

5.3 Documentation Updates

Effort Estimates

Risk Assessment

High Risk

Medium Risk

Low Risk

Testing Strategy

Unit Tests

Integration Tests

Manual Testing Checklist

Dependencies

Required

Optional

Rollback Plan

References

Appendix A: Full File Impact List

Files Requiring Modification

New Files to Create

Appendix B: Quick Reference - API Mapping

18 KiB

Raw Blame History