maui-linux/Xamarin.Forms.ControlGallery.GTK/BasicOpenGLView.cs

using System;
using OpenTK.Graphics.OpenGL;

namespace Xamarin.Forms.ControlGallery.GTK
{
    public class BasicOpenGLApp : Application
    {
        public BasicOpenGLApp()
        {
            MainPage = new BasicOpenGLView();
        }
    }

    public class BasicOpenGLView : ContentPage
    {
        private bool _initGl = false;
        private int _viewportWidth;
        private int _viewportHeight;
        private uint _mProgramHandle;
        private OpenGLView _openGLView = null;

        public BasicOpenGLView()
        {
            Title = "Basic OpenGLView Sample";

            var titleLabel = new Label
            {
                Text = "OpenGLView",
                FontSize = 36
            };

            _openGLView = new OpenGLView
            {
                HeightRequest = 300,
                WidthRequest = 300,
                HasRenderLoop = true
            };

            _openGLView.OnDisplay = r =>
            {
                if (!_initGl)
                {
                    double width_in_pixels = 300;
                    double height_in_pixels = 300;

                    InitGl((int)width_in_pixels, (int)height_in_pixels);
                }

                Render();
            };

            var stack = new StackLayout
            {
                Padding = new Size(12, 12),
                Children = { titleLabel, _openGLView }
            };

            Content = stack;
        }

        void InitGl(int width, int height)
        {
            _viewportHeight = width;
            _viewportWidth = height;

            _mProgramHandle = (uint)GL.CreateProgram();
            if (_mProgramHandle == 0)
                throw new InvalidOperationException("Unable to create program");

            GL.BindAttribLocation(_mProgramHandle, 0, "vPosition");
            GL.LinkProgram(_mProgramHandle);

            GL.Viewport(0, 0, _viewportWidth, _viewportHeight);

            GL.UseProgram(_mProgramHandle);

            _initGl = true;
        }


        void Render()
        {
            GL.ClearColor(0, 0, 0, 0);
            GL.Clear(ClearBufferMask.ColorBufferBit);

            GL.Color3(1.0f, 0.85f, 0.35f);
            GL.Begin(BeginMode.Triangles);

            GL.Vertex3(0.0, 0.6, 0.0);
            GL.Vertex3(-0.2, -0.3, 0.0);
            GL.Vertex3(0.2, -0.3, 0.0);

            GL.End();

            GL.Flush();
        }
    }
}