Implement 4-View Foveated ISR Pipeline with Game Integration Template

FOVEATED_RENDERING.md

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+# 4-View Foveated ISR Pipeline Implementation
+
+This implementation provides a complete 4-View Foveated Instanced Stereo Rendering (ISR) pipeline for VR applications, along with an example game integration template.
+
+## Overview
+
+The foveated rendering system enables high-quality VR rendering by using four views:
+- **Foveal views** (left/right): High resolution, narrow field of view for central vision
+- **Peripheral views** (left/right): Lower resolution, wide field of view for peripheral vision
+
+This approach optimizes rendering performance by allocating more resources to the user's central vision while maintaining a wide field of view.
+
+## Architecture
+
+### Core Components (`src/mods/foveated/`)
+
+#### 1. StereoEmulator (203 lines)
+Manages 4 emulated views with projection matrices and frustum culling data.
+
+**Key Features:**
+- Configurable FOV for foveal (default 40°) and peripheral (default 110°) views
+- Per-view projection and view matrices
+- Frustum plane computation for culling
+- Integration with VRRuntime for IPD and pose data
+
+**Usage:**
+```cpp
+auto& emulator = foveated::StereoEmulator::get();
+emulator.initialize(vrRuntime);
+emulator.configureFOV(40.0f, 110.0f);
+emulator.beginFrame(frameIndex);
+```
+
+#### 2. FoveatedAtlas (218 lines)
+Creates and manages the double-height render target atlas for 4-view output.
+
+**Atlas Layout:**
+```
++-------------------+-------------------+
+| Foveal Left       | Foveal Right      |  <- High resolution
+| (1440x1600)       | (1440x1600)       |
++-------------------+-------------------+
+| Peripheral Left   | Peripheral Right  |  <- Lower resolution
+| (720x800)         | (720x800)         |
++-------------------+-------------------+
+Total: 2880x2400
+```
+
+**Key Features:**
+- Configurable resolution per view type
+- Automatic descriptor heap creation (RTV/DSV)
+- Resource state tracking and transitions
+- Depth buffer support
+
+**Usage:**
+```cpp
+auto& atlas = foveated::FoveatedAtlas::get();
+foveated::AtlasConfig config{};
+config.fovealWidth = 1440;
+config.fovealHeight = 1600;
+atlas.initialize(device, config);
+```
+
+#### 3. ViewInjector (140 lines)
+Hooks D3D12 rendering pipeline to redirect output to the atlas.
+
+**Key Features:**
+- Viewport injection for 4-view rendering
+- Render target redirection to atlas
+- Integration with D3D12Hook callback system
+- Separate rendering passes for foveal and peripheral pairs
+
+**Usage:**
+```cpp
+auto& injector = foveated::ViewInjector::get();
+injector.install(d3d12Hook);
+injector.setAtlasRT(atlas.getTexture(), atlas.getRTV());
+```
+
+#### 4. VisibilityCache (158 lines)
+Optimizes rendering by sharing culling results between view pairs.
+
+**Key Features:**
+- Per-view visibility bitmask storage
+- 3-frame history for temporal coherence
+- Thread-safe operations with shared_mutex
+- Visibility sharing: Foveal → Peripheral for same eye
+
+**Usage:**
+```cpp
+auto& cache = foveated::VisibilityCache::get();
+cache.initialize(maxPrimitives);
+cache.beginFrame(frameIndex);
+cache.recordVisibility(viewIdx, visibilityBits, count);
+if (cache.canShare(0, 2)) {
+    cache.copyVisibility(0, 2); // Left foveal → Left peripheral
+}
+```
+
+## Game Integration Template (`src/games/ExampleUE/`)
+
+This template demonstrates how to integrate the foveated rendering system into an Unreal Engine-based game.
+
+### Structure
+
+```
+src/games/ExampleUE/
+├── ExampleUEEntry.h/cpp           # Mod entry point
+├── ExampleUERendererModule.h/cpp  # Frame/render lifecycle hooks
+├── ExampleUECameraModule.h/cpp    # Camera transform hooks
+├── memory/
+│   └── offsets.h                  # Pattern-based function location
+└── sdk/
+    └── ExampleUESDK.h            # Reversed engine structures
+```
+
+### Integration Points
+
+#### 1. ExampleUEEntry (44 lines)
+Main mod entry point that inherits from `Mod`.
+
+**Features:**
+- Module initialization and hook installation
+- UI configuration (HUD scale, decoupled pitch)
+- Follows vrframework mod pattern
+
+#### 2. ExampleUERendererModule (87 lines)
+Hooks game rendering lifecycle events.
+
+**Key Hook Points:**
+- `BeginFrame`: Frame counter synchronization
+- `BeginRender`: VR state update, HMD tracking
+
+**Frame Synchronization:**
+For Unreal Engine specifically, the frame counter is read directly from the engine's `GFrameNumber` global variable rather than manually incrementing. This ensures perfect synchronization with the engine's frame lifecycle and avoids being one frame behind or out of sync.
+
+**Integration:**
+```cpp
+// Read frame directly from Unreal Engine's GFrameNumber global
+if (sdk::GFrameNumber != nullptr) {
+    vr->m_engine_frame_count = static_cast<int>(*sdk::GFrameNumber);
+} else {
+    // Fallback for unknown engines
+    vr->m_engine_frame_count++;
+}
+vr->m_render_frame_count = vr->m_engine_frame_count;
+vr->on_begin_rendering(vr->m_render_frame_count);
+vr->update_hmd_state(vr->m_render_frame_count);
+```
+
+#### 3. ExampleUECameraModule (87 lines)
+Hooks camera calculations for VR transform injection.
+
+**Key Hook Points:**
+- `CalcView`: Apply HMD pose to camera
+- `GetProjection`: Submit VR projection matrices
+
+**Integration:**
+```cpp
+auto eye = vr->get_current_eye_transform();
+auto hmd = vr->get_transform(0);
+GlobalPool::submit_projection(*outProj, vr->m_render_frame_count);
+```
+
+### Memory Offsets (40 lines)
+Pattern-based function location using signature scanning.
+
+**Example:**
+```cpp
+inline uintptr_t beginFrameAddr() {
+    return FuncRelocation("BeginFrame", 
+        "48 89 5C 24 ? 57 48 83 EC 20 48 8B D9 E8", 0x0);
+}
+
+inline uintptr_t getGFrameNumberAddr() {
+    // Locate GFrameNumber global variable for direct frame reading
+    return FuncRelocation("GFrameNumber", 
+        "48 8B 05 ?? ?? ?? ?? 48 85 C0", 0x0);
+}
+```
+
+### SDK Structures (50 lines)
+Reversed engine structures for camera and view data.
+
+**Example:**
+```cpp
+struct FMinimalViewInfo {
+    FVector Location;
+    FRotator Rotation;
+    float FOV;
+    float AspectRatio;
+};
+
+// Global frame counter pointer - read directly from engine
+extern uint64_t* GFrameNumber;
+```
+
+## Integration Checklist
+
+To integrate this system into a new game:
+
+1. **Create game folder**: `src/games/{GameName}/`
+2. **Define offsets**: Find function addresses via signature scanning
+   - **Critical for Unreal Engine**: Locate `GFrameNumber` (or equivalent) global variable to read frame counter directly from the engine
+3. **Implement modules**:
+   - Entry point (`{GameName}Entry`)
+   - Renderer hooks (`{GameName}RendererModule`)
+   - Camera hooks (`{GameName}CameraModule`)
+4. **Hook targets** (minimum required):
+   - Frame begin (grab engine frame counter if available)
+   - Render begin (call `VR::on_begin_rendering`)
+   - Projection matrix calc (inject VR projection)
+   - View matrix calc (inject HMD transform)
+
+### Important: Engine-Specific Frame Handling
+
+**For Known Engines (e.g., Unreal Engine):**
+- Read frame counter directly from the engine's global variable (`GFrameNumber` for UE)
+- This ensures perfect synchronization and avoids being one frame behind
+- Example: `vr->m_engine_frame_count = static_cast<int>(*sdk::GFrameNumber);`
+
+**For Unknown Engines:**
+- Fall back to manual frame counting: `vr->m_engine_frame_count++;`
+- This approach is less precise but works when the engine's internal frame counter is not accessible
+
+## Technical Details
+
+### Thread Safety
+- VisibilityCache uses `shared_mutex` for concurrent read access
+- StereoEmulator and FoveatedAtlas are designed for single-threaded access during frame rendering
+
+### Performance Considerations
+- Foveal views: Full resolution (e.g., 1440x1600)
+- Peripheral views: Half resolution (e.g., 720x800)
+- Visibility cache enables skipping redundant culling operations
+- Mega-frustum optimization shares culling between view pairs
+
+### Compatibility
+- Requires D3D12 for rendering
+- Integrates with existing vrframework VRRuntime abstraction
+- Compatible with OpenXR and OpenVR backends
+- Designed for Unreal Engine games but adaptable to other engines
+
+## Statistics
+
+- **Total Lines of Code**: 1,085
+- **Core Components**: 767 lines
+- **Game Integration Template**: 318 lines
+- **Files Created**: 16
+
+## References
+
+This implementation follows the integration pattern from the `mutars/acsvr` repository and implements the design specification. The frame synchronization approach for Unreal Engine (reading `GFrameNumber` directly) ensures proper lifecycle management without frame desynchronization issues.
+
+## Future Enhancements
+
+Potential improvements for production use:
+
+1. **Dynamic Resolution**: Adjust foveal/peripheral resolution based on performance
+2. **Gaze Tracking**: Real-time foveation based on eye tracking
+3. **Advanced Culling**: Hierarchical culling with mega-frustum
+4. **Multi-GPU**: Split foveal/peripheral rendering across GPUs
+5. **Shader Integration**: Coordinate with ISR shader passes

src/games/ExampleUE/ExampleUECameraModule.cpp

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+#include "ExampleUECameraModule.h"
+#include "memory/offsets.h"
+#include "aer/ConstantsPool.h"
+#include <mods/VR.hpp>
+#include <spdlog/spdlog.h>
+
+ExampleUECameraModule* ExampleUECameraModule::get() {
+    static auto inst = new ExampleUECameraModule();
+    return inst;
+}
+
+void ExampleUECameraModule::installHooks() {
+    spdlog::info("ExampleUECameraModule::installHooks - Installing camera hooks");
+
+    auto calcViewFn = memory::calcViewAddr();
+    if (calcViewFn) {
+        m_calcViewHook = safetyhook::create_inline(reinterpret_cast<void*>(calcViewFn), 
+                                                    reinterpret_cast<void*>(&onCalcView));
+        spdlog::info("ExampleUECameraModule: CalcView hook installed");
+    } else {
+        spdlog::warn("ExampleUECameraModule: CalcView address not found");
+    }
+
+    auto getProjectionFn = memory::getProjectionAddr();
+    if (getProjectionFn) {
+        m_getProjectionHook = safetyhook::create_inline(reinterpret_cast<void*>(getProjectionFn), 
+                                                         reinterpret_cast<void*>(&onGetProjection));
+        spdlog::info("ExampleUECameraModule: GetProjection hook installed");
+    } else {
+        spdlog::warn("ExampleUECameraModule: GetProjection address not found");
+    }
+}
+
+void ExampleUECameraModule::onCalcView(sdk::APlayerCameraManager* camMgr, float dt, 
+                                        sdk::FMinimalViewInfo* outView) {
+    auto inst = get();
+    inst->m_calcViewHook.call<void>(camMgr, dt, outView);
+
+    auto vr = VR::get();
+    if (vr->is_hmd_active()) {
+        // Get VR transforms
+        auto eye = vr->get_current_eye_transform();
+        auto hmd = vr->get_transform(0);
+        auto offset = vr->get_transform_offset();
+
+        // Apply VR transform to outView->Location/Rotation
+        // Note: This is a simplified example. In a real implementation,
+        // you would properly transform the camera location and rotation
+        // based on the HMD pose and eye offset.
+
+        spdlog::debug("ExampleUECameraModule: Applied VR transforms to camera view");
+    }
+}
+
+void ExampleUECameraModule::onGetProjection(glm::mat4* outProj, float fov, float aspect, 
+                                             float nearZ, float farZ) {
+    auto inst = get();
+    inst->m_getProjectionHook.call<void>(outProj, fov, aspect, nearZ, farZ);
+
+    auto vr = VR::get();
+    if (vr->is_hmd_active()) {
+        // Submit projection matrix to global pool for VR rendering
+        GlobalPool::submit_projection(*outProj, vr->m_render_frame_count);
+        spdlog::debug("ExampleUECameraModule: Submitted projection matrix to pool");
+    }
+}

src/games/ExampleUE/ExampleUECameraModule.h

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+#pragma once
+#include <safetyhook/inline_hook.hpp>
+#include <glm/glm.hpp>
+
+namespace sdk { 
+    struct FMinimalViewInfo; 
+    struct APlayerCameraManager; 
+}
+
+class ExampleUECameraModule {
+public: 
+    static ExampleUECameraModule* get();
+    void installHooks();
+
+private:
+    safetyhook::InlineHook m_calcViewHook{};
+    safetyhook::InlineHook m_getProjectionHook{};
+
+    static void onCalcView(sdk::APlayerCameraManager* camMgr, float dt, sdk::FMinimalViewInfo* outView);
+    static void onGetProjection(glm::mat4* outProj, float fov, float aspect, float nearZ, float farZ);
+};

src/games/ExampleUE/ExampleUEEntry.cpp

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+#include "ExampleUEEntry.h"
+#include "ExampleUERendererModule.h"
+#include "ExampleUECameraModule.h"
+#include <spdlog/spdlog.h>
+
+std::optional<std::string> ExampleUEEntry::on_initialize() {
+    spdlog::info("ExampleUEEntry::on_initialize - Installing hooks");
+
+    // Install renderer hooks for frame/render lifecycle
+    ExampleUERendererModule::get()->installHooks();
+
+    // Install camera hooks for view/projection matrix injection
+    ExampleUECameraModule::get()->installHooks();
+
+    spdlog::info("ExampleUEEntry::on_initialize - Complete");
+    return std::nullopt;
+}
+
+void ExampleUEEntry::on_draw_ui() {
+    if (!ImGui::CollapsingHeader(get_name().data())) {
+        return;
+    }
+
+    m_hudScale->draw("HUD Scale");
+    m_decoupledPitch->draw("Decoupled Pitch");
+}

src/games/ExampleUE/ExampleUEEntry.h

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+#pragma once
+#include "Mod.hpp"
+
+class ExampleUEEntry : public Mod {
+public: 
+    static std::shared_ptr<ExampleUEEntry>& get() {
+        static auto inst = std::make_shared<ExampleUEEntry>();
+        return inst;
+    }
+
+    std::string_view get_name() const override { return "ExampleUE VR"; }
+    std::optional<std::string> on_initialize() override;
+    void on_draw_ui() override;
+
+private:
+    ModSlider::Ptr m_hudScale = ModSlider::create("HudScale", 0.1f, 1.0f, 0.5f);
+    ModToggle::Ptr m_decoupledPitch = ModToggle::create("DecoupledPitch", false);
+};