Create CLAUDE.md

Author: wtholliday

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+vger is a GPU-accelerated vector graphics renderer written in C with Swift bindings, designed for iOS and macOS. It renders primitives analytically in fragment shaders rather than using CPU tessellation, achieving high performance for immediate-mode UIs.
+
+## Architecture
+
+### Core Components
+
+- **C Core (`Sources/vger/`)**: The main rendering engine written in C/C++/Objective-C++ with Metal shaders
+  - `vger.h`: Main API interface - review this for all available rendering functions
+  - `vger.mm`: Core implementation with Metal rendering logic
+  - `vgerRenderer.mm`: Main renderer class handling Metal command encoding
+  - `vgerPathScanner.mm`: Path processing and horizontal slab decomposition for fills
+  - `vgerGlyphCache.mm`: Text rendering with glyph atlas management
+  - `vger.metal`: Fragment shaders for primitive rendering
+
+- **Swift Layer (`Sources/vgerSwift/`)**: SwiftUI integration and higher-level APIs
+  - `VgerView.swift`: SwiftUI view wrapper for Metal rendering
+  - `Renderer.swift`: Metal rendering coordinator
+  - `TextureRenderer.swift`: Additional texture rendering utilities
+
+- **Demo App (`Demo/`)**: Complete iOS/macOS SwiftUI application demonstrating usage
+  - Cross-platform implementation showing VgerView integration
+  - Examples of text, shapes, SVG rendering, and various primitives
+
+### Key Design Patterns
+
+- **Immediate Mode**: All drawing commands are recorded per frame, no retained geometry
+- **GPU-Centric**: Fragment shaders handle primitive evaluation, minimal CPU work
+- **Instanced Rendering**: Each primitive renders as a quad with shader-computed geometry
+- **Paint System**: Separate paint objects for colors, gradients, textures, and patterns
+- **Transform Stack**: Standard graphics transform state with save/restore
+
+## Development Commands
+
+### Building
+```bash
+# Build the project
+./build.sh
+
+# Or use xcodebuild directly
+xcodebuild -scheme vger -sdk macosx -destination "name=My Mac"
+```
+
+### Testing
+```bash
+# Run all tests
+./test.sh
+
+# Or use xcodebuild directly
+xcodebuild test -scheme vger -sdk macosx -destination "name=My Mac"
+```
+
+### Swift Package Manager
+This project uses SPM and can be built with:
+```bash
+swift build
+swift test
+```
+
+## Usage Patterns
+
+### Basic C API Usage
+```c
+vgerContext vg = vgerNew(0, MTLPixelFormatBGRA8Unorm);
+vgerBegin(vg, width, height, devicePixelRatio);
+
+// Create paint and draw primitives
+vgerPaintIndex paint = vgerColorPaint(vg, (vector_float4){1,0,0,1});
+vgerFillCircle(vg, center, radius, paint);
+
+vgerEncode(vg, commandBuffer, renderPassDescriptor);
+```
+
+### SwiftUI Integration
+```swift
+VgerView(renderCallback: { vger, size in
+    let paint = vgerColorPaint(vger, SIMD4<Float>(1,0,1,1))
+    vgerFillRect(vger, min, max, cornerRadius, paint)
+})
+```
+
+## Key Implementation Details
+
+- **Path Fills**: Uses reverse Loop-Blinn technique in fragment shader to avoid solving quadratic equations
+- **Text Rendering**: Glyph atlas with SDF-based rendering for scalable text
+- **Buffering**: Supports double/triple buffering schemes via creation flags
+- **Layers**: Multi-layer rendering support (up to 4 layers)
+- **Transform Stack**: Full 2D transformation support with save/restore
+
+## Test Structure
+
+Tests are in `Tests/vgerTests/` and include:
+- Basic primitive rendering tests with reference images
+- Path scanning and fill algorithm tests  
+- Glyph cache and text rendering tests
+- SDF computation tests
+- Texture management tests
+
+Reference images in `Tests/vgerTests/images/` are used for visual regression testing.