shared handler backcall error

[htrlq]

code for #2675
cefsharp version branch cefsharp/73

#define USE_SHARED_TEXTURE
#define RESET_WINDOWLESSFRAMERATE_ON_LOAD
using System;
using System.Diagnostics;
using System.IO;
using System.Threading;
using CefSharp.OffScreen;
using System.Threading.Tasks;
using CefSharp.Structs;
using CefSharp;
using CefSharp.Example.Handlers;

namespace ConsoleApp1
{
    public class Program
    {
        public static void Main(string[] args)
        {
            const string testUrl = "https://github.com/cefsharp/CefSharp/issues/2675";

            CefSharpSettings.SubprocessExitIfParentProcessClosed = true;

            // Initialize CEF.
            Cef.Initialize(new CefSettings
            {
                CachePath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "CefSharp\\Cache"),
                CefCommandLineArgs =
                {
                    { "disable-gpu-shader-disk-cache", null },
                    { "show-fps-counter", null },
                    { "use-angle", "d3d11" },
                },
                WindowlessRenderingEnabled = false
            }, performDependencyCheck: true, browserProcessHandler: null);

            // Create the browser.
            var browser = new ChromiumWebBrowser(testUrl, new BrowserSettings
            {
                WindowlessFrameRate = 60,
            }, automaticallyCreateBrowser: false)
            {
                Size = new System.Drawing.Size(1280, 720),
            };

            // Create and assign the render handler.
            var customRenderHandler = new CustomRenderHandler(browser);
            browser.RenderHandler = customRenderHandler;

#if RESET_WINDOWLESSFRAMERATE_ON_LOAD
            browser.BrowserInitialized += delegate
            {
                browser.GetBrowserHost().WindowlessFrameRate = 60;
            };
#endif

            // Create the browser.
            var windowInfo = new WindowInfo
            {
#if USE_SHARED_TEXTURE
                SharedTextureEnabled = true,
                ExternalBeginFrameEnabled = true
#endif
            };
            windowInfo.SetAsWindowless(IntPtr.Zero);
            windowInfo.WindowlessRenderingEnabled = false;

            browser.CreateBrowser(windowInfo);

            // Compute frame rate in a separate thread.
            new Thread(() =>
            {
                var stopwatch = Stopwatch.StartNew();
                for (; ; )
                {
                    browser.StartBeginFrame();

                    Thread.Sleep(1000);
                    var elapsed = stopwatch.Elapsed;
                    stopwatch.Restart();
                    var frameCount = Interlocked.Exchange(ref customRenderHandler.FrameCount, 0);
                    var frameRate = frameCount / elapsed.TotalSeconds;
#if USE_SHARED_TEXTURE
                    Console.WriteLine($"OnAcceleratedPaint rate: {frameRate:0.##}");
#else
                    Console.WriteLine($"OnPaint rate: {frameRate:0.##}");
#endif
                }
            })
            {
                IsBackground = true
            }.Start();

            // Wait until user presses a key.
            Console.ReadKey();

            // Shutdown CEF.
            Cef.Shutdown();
        }

        private sealed class CustomRenderHandler : DefaultRenderHandler
        {
            public int FrameCount;

            public CustomRenderHandler(ChromiumWebBrowser browser) : base(browser) { }

#if !USE_SHARED_TEXTURE
            public override void OnPaint(PaintElementType type, Rect dirtyRect, IntPtr buffer, int width, int height) => Interlocked.Increment(ref FrameCount);
#else
            public override void OnAcceleratedPaint(PaintElementType type, Rect dirtyRect, IntPtr sharedHandle) => Interlocked.Increment(ref FrameCount);
#endif
        }
    }
}

console write Crash reporting enabled for process: browser, not run CustomRenderHandler.OnAcceleratedPaint

[amaitland]

OnAcceleratedPaint is not supported. Once CEF re-adds support we can look at implementing it. Your welcome to try get it working with an old unsupported version, you will need to debug any issues you have yourself.

#2770 tracks adding support, I don't anticipate CEF adding support anything soon as there's some technical challenges that are yet to be resolved.

Upstream PR https://bitbucket.org/chromiumembedded/cef/pull-requests/285
You can build CEF from source and manually apply the PR if you wish to participate in debugging.