cap-rendering-skia

A new rendering backend for Cap using Skia, designed to replace the current wgpu-based renderer.

Status

This crate implements the basic infrastructure for Skia-based rendering with GPU acceleration support:

• ✅ Basic Skia context creation
• ✅ GPU acceleration via Metal (macOS)
• ✅ CPU fallback for other platforms
• ✅ Surface creation and management
• ✅ Basic rendering operations
• ✅ Pixel readback for frame export

Building and Testing

# Build the crate
cargo build -p cap-rendering-skia

# Run the test binary
cargo run -p cap-rendering-skia --bin test-skia

# Run tests
cargo test -p cap-rendering-skia

The test binary will:

• Create a Skia context (GPU-accelerated on macOS via Metal)
• Test surface creation with various sizes
• Render a gradient with a green circle
• Save the output as test_render.ppm

Architecture

GPU Support

• macOS: Uses Metal backend for GPU acceleration
• Other platforms: Falls back to CPU raster backend
• Future: Can add Vulkan/OpenGL support for Linux/Windows

Core Components

• SkiaRenderContext: Main context managing GPU/CPU backends
• Surface management with automatic format selection
• Simple API for creating and reading from surfaces

Migration Plan Progress

Phase 1: Setup and Infrastructure ✅

• Create new crate with Skia dependencies
• Basic GPU context initialization
• Surface creation and management
• Test binary to verify functionality

Phase 2: Core Components (In Progress)

• Frame pipeline implementation
• Canvas-based layer system
• Uniform/parameter structures

Phase 3: Layer Migration (Not Started)

• Background layer (gradients, solid colors, images)
• Display layer (video frames with effects)
• Cursor layer
• Camera layer
• Blur effects
• Caption/text rendering

Phase 4: Integration (Not Started)

• Update render_video_to_channel
• Migrate frame decoding
• Update export pipeline

Phase 5: Optimization and Cleanup (Not Started)

• Performance profiling
• Remove wgpu dependencies
• Clean up old shader files

Next Steps

1. Implement the frame pipeline for managing render passes
2. Create the layer system with Canvas-based rendering
3. Start migrating individual rendering layers from wgpu shaders to Skia operations
4. Integrate with the existing video processing pipeline

Benefits Over wgpu

• Simpler API - no manual shader management
• Built-in effects and filters
• Better cross-platform consistency
• Rich text rendering capabilities
• Extensive image format support
• Battle-tested 2D graphics performance