[QUESTION] Minimal WebAssembly example with NativeAOT-LLVM

[yowl]

Hi,

I'm trying to see if its possible to use SkiaSharp with NativeAOT-LLVM (https://github.com/dotnet/runtimelab/tree/feature/NativeAOT-LLVM). I've created what I think is a pretty small example (https://github.com/yowl/wskia) . You can build it with the command line (assuming you have SkiaSharp 2.0.12)

dotnet publish /p:SelfContained=true -r browser-wasm -c Debug /p:TargetArchitecture=wasm /p:PlatformTarget=AnyCPU /p:MSBuildEnableWorkloadResolver=false  --self-contained /p:EmccExtraArgs=.packages\skiasharp.nativeassets.webassembly\2.80.3\build\netstandard1.0\libSkiaSharp.a\2.0.12\libSkiaSharp.a

It attempts to fill the canvas with white and draws some rectangles, there's no errors but nothing appears on the canvas, it stays black. Is the set up code ok? Copied below (and removed the debug that's in the original for clarity):

        [UnmanagedCallersOnly(EntryPoint = "MainLoop")]
        static void MainLoop()
        {
            SKCanvas canvas = surface.Canvas;

            canvas.Clear(SKColors.White);

            // configure our brush
            var redBrush = new SKPaint
            {
                Color = new SKColor(0xff, 0, 0),
                IsStroke = true
            };
            var blueBrush = new SKPaint
            {
                Color = new SKColor(0, 0, 0xff),
                IsStroke = true
            };

            for (int i = 0; i < 64; i += 8)
            {
                var rect = new SKRect(i, i, 256 - i - 1, 256 - i - 1);
                canvas.DrawRect(rect, (i % 16 == 0) ? redBrush : blueBrush);
            }
        }
        static SKSurface surface;

        static void Main()
        {
            EmscriptenWebGLContextAttributes attrs;
            emscripten_webgl_init_context_attributes(&attrs);

            attrs.stencil = 8;
            // attrs.majorVersion = 2;
            fixed (byte* n = &(s[0]))
            {
                glContext = emscripten_webgl_create_context(n, &attrs); // this is "#canvas"
            }

            emscripten_webgl_make_context_current(glContext);

            GRGlInterface grGlInterface = GRGlInterface.Create();

            GRContext grContext = GRContext.CreateGl(grGlInterface);

            emscripten_set_main_loop(&MainLoop, 0, 0);

            const SKColorType colorType = SKColorType.Rgba8888;

            int width, height;
            fixed (byte* n = &(s[0]))
            {
                emscripten_get_canvas_element_size(n, &width, &height);
            }

            var info = new GRGlFramebufferInfo(0, colorType.ToGlSizedFormat());

            surface = SKSurface.Create(grContext, new GRBackendRenderTarget(width, height, 0, 8, info),
                colorType);
            if (surface != null)
            {
                Console.WriteLine("got a surface");
            }
            else
            {
                Console.WriteLine("Failed to create surface");
            }

            surface.Canvas.DrawColor(SKColors.White);
    }

[mattleibow]

I wonder if you are just missing a canvas and grcontext Flush()? That has gotten me numerous times.