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Add comprehensive documentation and examples for backend switching
Co-authored-by: philstopford <1983851+philstopford@users.noreply.github.com>
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‎Eto/Eto.Veldrid.Gtk/Examples/BackendSwitchingExample.cs‎

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using Eto.Forms;
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using Eto.Veldrid;
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using System;
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using Veldrid;
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namespace Eto.Veldrid.Gtk.Examples
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{
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/// <summary>
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/// Example demonstrating backend switching functionality
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/// </summary>
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public class BackendSwitchingExample
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{
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public static void Main(string[] args)
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{
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var platform = new Eto.GtkSharp.Platform();
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// Parse backend from command line
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GraphicsBackend backend = VeldridSurface.PreferredBackend;
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if (args.Length > 0 && Enum.TryParse<GraphicsBackend>(args[0], true, out var requestedBackend))
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{
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if (GraphicsDevice.IsBackendSupported(requestedBackend))
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{
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backend = requestedBackend;
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Console.WriteLine($"Using requested backend: {backend}");
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}
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else
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{
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Console.WriteLine($"Requested backend {requestedBackend} not supported, using: {backend}");
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}
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}
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new Application(platform).Run(new ExampleForm(backend));
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}
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}
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public class ExampleForm : Form
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{
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private VeldridSurface surface;
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public ExampleForm(GraphicsBackend backend)
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{
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Title = $"Veldrid Example - {backend} Backend";
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Size = new Eto.Drawing.Size(800, 600);
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// Create surface with specified backend
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var options = new GraphicsDeviceOptions(
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debug: false,
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swapchainDepthFormat: PixelFormat.R32Float,
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syncToVerticalBlank: true,
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resourceBindingModel: ResourceBindingModel.Improved);
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surface = new VeldridSurface(backend, options);
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surface.VeldridInitialized += (sender, e) =>
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{
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Console.WriteLine($"Veldrid initialized with {backend} backend");
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Console.WriteLine($"Graphics Device: {surface.GraphicsDevice?.GetType().Name}");
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Console.WriteLine($"Backend Features: {surface.GraphicsDevice?.Features}");
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};
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surface.Draw += OnDraw;
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surface.Resize += OnResize;
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Content = surface;
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// Add menu for backend info
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var aboutCommand = new Command { MenuText = "About Backend", ToolBarText = "About" };
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aboutCommand.Executed += (sender, e) => ShowBackendInfo();
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Menu = new MenuBar
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{
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Items = { new ButtonMenuItem { Text = "&Help", Items = { aboutCommand } } }
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};
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}
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private void OnDraw(object sender, EventArgs e)
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{
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// Basic rendering example - clear to blue
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var device = surface.GraphicsDevice;
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var commandList = device.ResourceFactory.CreateCommandList();
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commandList.Begin();
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commandList.SetFramebuffer(device.SwapchainFramebuffer);
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commandList.ClearColorTarget(0, new RgbaFloat(0.2f, 0.4f, 0.8f, 1.0f));
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commandList.End();
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device.SubmitCommands(commandList);
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device.SwapBuffers();
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commandList.Dispose();
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}
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private void OnResize(object sender, ResizeEventArgs e)
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{
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Console.WriteLine($"Surface resized: {e.Width}x{e.Height}");
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}
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private void ShowBackendInfo()
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{
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var device = surface.GraphicsDevice;
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var info = $"Backend: {surface.Backend}\n" +
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$"Device: {device?.DeviceName}\n" +
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$"Vendor: {device?.VendorName}\n" +
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$"API Version: {device?.ApiVersion}\n" +
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$"Driver: {device?.DriverName} {device?.DriverInfo}\n" +
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$"Uniform Buffer Alignment: {device?.UniformBufferMinOffsetAlignment}\n" +
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$"Max Texture Size: {device?.GetPixelFormatSupport(PixelFormat.R8G8B8A8UNorm, TextureType.Texture2D, TextureUsage.Sampled)}";
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MessageBox.Show(this, info, "Backend Information");
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}
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}
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}

‎Eto/Eto.Veldrid.Gtk/README.md‎

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# Eto.Veldrid.Gtk Backend Switching Implementation
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## Overview
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This implementation provides a clean, modular architecture for switching between OpenGL and Vulkan backends in the Eto.Veldrid.Gtk project. The solution supports both X11 and Wayland windowing systems and retains all existing functionality.
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## Architecture
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### Core Components
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1. **`IVeldridBackendHandler`** - Interface for backend-specific implementations
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- `CreateWidget()` - Creates appropriate GTK widget (GLArea or EventBox)
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- `CreateSwapchain()` - Creates backend-specific swapchain
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- `InitializeGraphicsDevice()` - Initializes graphics device
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- `HandleResize()` - Handles window resize events
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- `Invalidate()` - Forces redraw/invalidation
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- `SetupEventHandlers()` - Sets up GTK event handling
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2. **`OpenGLBackendHandler`** - OpenGL implementation
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- Uses GTK's `GLArea` widget
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- Manages OpenGL context lifecycle
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- Implements `VeldridSurface.IOpenGL` interface
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- Handles context switching between GTK and Veldrid worker threads
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3. **`VulkanBackendHandler`** - Vulkan implementation
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- Uses `EtoEventBox` widget for raw surface creation
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- Supports both X11 and Wayland windowing systems
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- Runtime detection of windowing system
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- Creates appropriate SwapchainSource for each platform
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4. **`WindowingSystemDetector`** - Runtime environment detection
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- Detects X11 vs Wayland vs XWayland
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- Uses environment variables and GDK display type detection
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- Cached results for performance
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5. **`VeldridBackendFactory`** - Backend management
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- Creates appropriate backend handlers
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- Checks backend support
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- Determines preferred backend (Vulkan > OpenGL)
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6. **`GtkVeldridSurfaceHandler`** - Updated main handler
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- Delegates to backend-specific implementations
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- Maintains compatibility with existing Eto interface
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- Handles lifecycle management
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## Usage
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### Command Line Backend Selection
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The TestEtoVeldrid.Gtk application now supports backend selection via command line:
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```bash
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# Use default/preferred backend (Vulkan if available, otherwise OpenGL)
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./TestEtoVeldrid.Gtk
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# Force OpenGL backend
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./TestEtoVeldrid.Gtk OpenGL
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# Force Vulkan backend
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./TestEtoVeldrid.Gtk Vulkan
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```
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### Programmatic Backend Selection
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```csharp
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// Create VeldridSurface with specific backend
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var surface = new VeldridSurface(GraphicsBackend.Vulkan);
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// Check backend support
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bool vulkanSupported = GraphicsDevice.IsBackendSupported(GraphicsBackend.Vulkan);
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bool openglSupported = GraphicsDevice.IsBackendSupported(GraphicsBackend.OpenGL);
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// Use preferred backend
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var defaultSurface = new VeldridSurface(); // Uses VeldridSurface.PreferredBackend
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```
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## Platform Support
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### Windowing Systems
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- **X11** - Full support for both OpenGL (GLArea) and Vulkan (Xlib surfaces)
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- **Wayland** - Full support for both OpenGL (GLArea) and Vulkan (Wayland surfaces)
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- **XWayland** - Detected and treated as Wayland for optimal compatibility
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### Backend Support
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- **OpenGL** - Uses GTK's GLArea widget, requires OpenGL 3.3+
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- **Vulkan** - Uses raw surface creation with platform-specific extensions
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## Input Handling
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All existing input handling is preserved:
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- **Mouse Input**: Scroll to zoom, right-click context menu, left-click drag
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- **Keyboard Input**: WASD panning, zoom controls, viewport lock (F key)
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- **Viewport Controls**: Zoom extents, selection, etc.
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The backend abstraction layer ensures input events are properly routed regardless of the graphics backend in use.
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## Key Improvements
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### 1. Clean Architecture
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- Separation of concerns between OpenGL and Vulkan code paths
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- Pluggable backend system for future extensions
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- Clear interfaces and responsibilities
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### 2. Cross-Platform Compatibility
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- Runtime windowing system detection
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- Proper Wayland support alongside X11
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- Automatic fallback mechanisms
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### 3. Preserved Functionality
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- All existing features work unchanged
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- Input handling preserved across all backends
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- Backward compatibility maintained
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### 4. Backend Switching
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- Runtime backend selection
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- Command-line configuration
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- Fallback to supported backends
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## Implementation Details
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### OpenGL Backend (`OpenGLBackendHandler`)
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- Creates `GLArea` widget with OpenGL 3.3 requirement
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- Manages OpenGL context switching between GTK main thread and Veldrid worker thread
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- Implements proper context handoff for rendering operations
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- Handles depth/stencil buffer configuration
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### Vulkan Backend (`VulkanBackendHandler`)
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- Creates `EtoEventBox` for raw surface access
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- Detects runtime windowing system (X11/Wayland)
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- Creates appropriate SwapchainSource:
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- X11: Uses `SwapchainSource.CreateXlib()`
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- Wayland: Uses `SwapchainSource.CreateWayland()`
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- Handles Vulkan graphics device creation
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### Windowing System Detection (`WindowingSystemDetector`)
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Detection logic:
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1. Check `WAYLAND_DISPLAY` and `DISPLAY` environment variables
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2. Detect XWayland (both variables set)
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3. Check `XDG_SESSION_TYPE` environment variable
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4. Inspect GDK display type
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5. Default to X11 if uncertain
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## Compatibility
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### Backward Compatibility
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- All existing code using `VeldridSurface` continues to work unchanged
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- No breaking changes to public APIs
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- Default behavior maintained (uses preferred backend)
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### WPF Projects
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- No changes made to Eto.Veldrid.Wpf or TestEtoVeldrid.Wpf
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- WPF implementation remains isolated and unaffected
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- Cross-platform code sharing maintained
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## Testing
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The implementation builds successfully and provides:
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- Clean compilation with only nullable reference warnings (existing codebase style)
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- Proper backend handler creation and lifecycle management
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- Runtime windowing system detection
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- Command-line backend selection in test application
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Note: Full runtime testing requires a graphics environment with proper Vulkan/OpenGL drivers, which may not be available in containerized CI environments.
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## Future Enhancements
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The modular architecture enables future enhancements:
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- Additional backend support (e.g., DirectX on Windows via Wine)
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- Backend-specific optimizations
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- Advanced windowing system features
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- Performance profiling and metrics

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