Triangle

using CImGui
using CImGui.CSyntax
using CImGui.CSyntax.CStatic
using CImGui.GLFWBackend
using CImGui.OpenGLBackend
using CImGui.GLFWBackend.GLFW
using CImGui.OpenGLBackend.ModernGL
 
include("Frame02.jl")
 
window = GLFW.CreateWindow(600,600,"App")
GLFW.MakeContextCurrent(window)
 
# get version info
renderer = unsafe_string(glGetString(GL_RENDERER))
version = unsafe_string(glGetString(GL_VERSION))
@info "Renderder: $renderer"
@info "OpenGL version supported: $version"
 
# enable depth test
glEnable(GL_DEPTH_TEST)
glDepthFunc(GL_LESS)
 
ctx =  CImGui.CreateContext()
ImGui_ImplGlfw_InitForOpenGL(window,true)
ImGui_ImplOpenGL3_Init(130)
 
while !GLFW.WindowShouldClose(window)
    glClearColor(0.2,0.2,0.2,1)
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
    GLFW.PollEvents()
    ImGui_ImplOpenGL3_NewFrame()
    ImGui_ImplGlfw_NewFrame()
    CImGui.NewFrame()
    
    Frame02.Frame()
    CImGui.Render()
    ImGui_ImplOpenGL3_RenderDrawData(CImGui.GetDrawData())
    GLFW.MakeContextCurrent(window)
    GLFW.SwapBuffers(window)
end
 
CImGui.DestroyContext(ctx)
GLFW.DestroyWindow(window)

module Frame02
    using CImGui
    using CImGui.CSyntax
    using CImGui.CSyntax.CStatic
    using CImGui.GLFWBackend
    using CImGui.OpenGLBackend
    using CImGui.GLFWBackend.GLFW
    using CImGui.OpenGLBackend.ModernGL
 
    # print errors in shader compilation
    function shader_info_log(shader::GLuint)
        max_length = GLint(0)
        @c glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &max_length)
        actual_length = GLsizei(0)
        log = Vector{GLchar}(undef, max_length)
        @c glGetShaderInfoLog(shader, max_length, &actual_length, log)
        @info "shader info log for GL index $shader: $(String(log))"
    end
 
    const vert_source = """
    #version 410 core
    in vec3 vp;
    void main(void){
        gl_Position = vec4(vp,1.0);
    }
    """
 
    const frag_source = """
    #version 410 core
    out vec4 frag_colour;
    void main(void){
        frag_colour = vec4(0.5,0.0,0.5,1.0);
    }
    """
 
    # vertex data
    const points = GLfloat[ 0.0,  0.5, 0.0,
                      0.5, -0.5, 0.0,
                     -0.5, -0.5, 0.0]
 
    function CompileShader(type,source)
        vert_shader = glCreateShader(type)
        glShaderSource(vert_shader,1,Ptr{GLchar}[pointer(source)],C_NULL)
        glCompileShader(vert_shader)
        shader_info_log(vert_shader)
        return vert_shader
    end
 
    function CreateShader(vertex_shader,fragment_shader)
        program = glCreateProgram()
 
        vs = CompileShader(GL_VERTEX_SHADER,vertex_shader)
        fs = CompileShader(GL_FRAGMENT_SHADER,fragment_shader)
 
        glAttachShader(program,vs)
        glAttachShader(program,fs)
 
        glLinkProgram(program)
 
        # create buffer located in the memory of graphic card
        vbo = GLuint(0)
        @c glGenBuffers(1,&vbo)
        glBindBuffer(GL_ARRAY_BUFFER,vbo)
        glBufferData(GL_ARRAY_BUFFER,sizeof(points),points,GL_DYNAMIC_DRAW)
 
        #crate array
        global vao = GLuint(0)
        @c glGenBuffers(1,&vao)
        glBindVertexArray(vao)
        glBindBuffer(GL_ARRAY_BUFFER,vbo)
        glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,0,C_NULL)
        glEnableVertexAttribArray(0)
        return program
    end
 
    function Frame()     
        shader = CreateShader(vert_source,frag_source)
        glUseProgram(shader)
        glBindVertexArray(vao)
        glDrawArrays(GL_TRIANGLES, 0, 3)
    end
end