From e45344c18901cece9ccb491cbef4d00f52bdc55b Mon Sep 17 00:00:00 2001
From: Chris Bell <chrisbell@bellsworne.com>
Date: Thu, 16 Jan 2025 16:45:52 -0600
Subject: [PATCH] Render a triangle for testing purposes

---
 .../GLTFViewer/Engine/Rendering/Renderer.cs   | 113 +++++++++++++++++-
 1 file changed, 107 insertions(+), 6 deletions(-)

diff --git a/GLTFViewer/GLTFViewer/Engine/Rendering/Renderer.cs b/GLTFViewer/GLTFViewer/Engine/Rendering/Renderer.cs
index c0b1aff..a70f855 100644
--- a/GLTFViewer/GLTFViewer/Engine/Rendering/Renderer.cs
+++ b/GLTFViewer/GLTFViewer/Engine/Rendering/Renderer.cs
@@ -8,23 +8,125 @@ namespace GLTFViewer.Rendering;
 
 public class Renderer
 {
+    private int _vao;
+    private int _vbo;
+    private int _shaderProgram;
+
     public void Initialize(GlInterface gl)
     {
         GLLoader.LoadBindings(new AvaloniaBindingsContext(gl));
-        GL.ClearColor(1,1,1,1);
+        GL.ClearColor(1, 1, 1, 1);
+
+        // Vertex data for a triangle
+        float[] vertices = {
+            0.0f,  0.5f, 0.0f,  // Top vertex
+           -0.5f, -0.5f, 0.0f,  // Bottom left vertex
+            0.5f, -0.5f, 0.0f   // Bottom right vertex
+        };
+
+        // Create and bind the VAO
+        _vao = GL.GenVertexArray();
+        GL.BindVertexArray(_vao);
+
+        // Create and bind the VBO
+        _vbo = GL.GenBuffer();
+        GL.BindBuffer(BufferTarget.ArrayBuffer, _vbo);
+        GL.BufferData(BufferTarget.ArrayBuffer, vertices.Length * sizeof(float), vertices, BufferUsage.StaticDraw);
+
+        // Vertex shader source code
+        string vertexShaderSource = @"
+        #version 330 core
+        layout(location = 0) in vec3 aPos;
+        void main()
+        {
+            gl_Position = vec4(aPos, 1.0);
+        }";
+
+        // Fragment shader source code
+        string fragmentShaderSource = @"
+        #version 330 core
+        out vec4 FragColor;
+        void main()
+        {
+            FragColor = vec4(0.0, 0.0, 1.0, 1.0); // Blue color
+        }";
+
+        // Compile vertex shader
+        int vertexShader = GL.CreateShader(ShaderType.VertexShader);
+        GL.ShaderSource(vertexShader, vertexShaderSource);
+        GL.CompileShader(vertexShader);
+        CheckShaderCompileStatus(vertexShader);
+
+        // Compile fragment shader
+        int fragmentShader = GL.CreateShader(ShaderType.FragmentShader);
+        GL.ShaderSource(fragmentShader, fragmentShaderSource);
+        GL.CompileShader(fragmentShader);
+        CheckShaderCompileStatus(fragmentShader);
+
+        // Link shaders into a program
+        _shaderProgram = GL.CreateProgram();
+        GL.AttachShader(_shaderProgram, vertexShader);
+        GL.AttachShader(_shaderProgram, fragmentShader);
+        GL.LinkProgram(_shaderProgram);
+        CheckProgramLinkStatus(_shaderProgram);
+
+        // Clean up shaders as they are no longer needed
+        GL.DeleteShader(vertexShader);
+        GL.DeleteShader(fragmentShader);
+
+        // Specify the layout of the vertex data
+        GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 3 * sizeof(float), 0);
+        GL.EnableVertexAttribArray(0);
+
+        // Unbind the VAO
+        GL.BindVertexArray(0);
     }
-    
+
     public void Render(GlInterface gl, int width, int height, int fbo)
     {
         GL.Viewport(0, 0, width, height);
         GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
+
+        // Use the shader program
+        GL.UseProgram(_shaderProgram);
+
+        // Bind the VAO
+        GL.BindVertexArray(_vao);
+
+        // Draw the triangle
+        GL.DrawArrays(PrimitiveType.Triangles, 0, 3);
+
+        // Unbind the VAO
+        GL.BindVertexArray(0);
     }
-    
+
     public void Deinitialize(GlInterface gl)
     {
-        
+        GL.DeleteVertexArray(_vao);
+        GL.DeleteBuffer(_vbo);
+        GL.DeleteProgram(_shaderProgram);
     }
-    
+
+    private void CheckShaderCompileStatus(int shader)
+    {
+        GL.GetShaderi(shader, ShaderParameterName.CompileStatus, out int status);
+        if (status == (int)All.False)
+        { 
+            GL.GetShaderInfoLog(shader, out var infoLog);
+            throw new Exception($"Shader compilation failed: {infoLog}");
+        }
+    }
+
+    private void CheckProgramLinkStatus(int program)
+    {
+        GL.GetProgrami(program, ProgramProperty.LinkStatus, out int status);
+        if (status == (int)All.False)
+        {
+            GL.GetProgramInfoLog(program, out var infoLog);
+            throw new Exception($"Program linking failed: {infoLog}");
+        }
+    }
+
     private class AvaloniaBindingsContext : IBindingsContext
     {
         private readonly GlInterface _gl;
@@ -39,5 +141,4 @@ public class Renderer
             return _gl.GetProcAddress(procName);
         }
     }
-    
 }
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