OpenGL Vala GTK3 example - opengl-es-2.0

Question

I'm trying to rewrite this first triangle example in vala and failing this is what I have so far:
public class MyApp : Gtk.Application {
private MyAppWindow? myAppWindow;
public string appName;
public MyApp () {
Object (
application_id: "com.github.myusername.myreponame",
flags: ApplicationFlags.FLAGS_NONE
);
appName = "My App";
}
protected override void activate () {
myAppWindow = new MyAppWindow (this);
add_window (myAppWindow);
myAppWindow.show_all ();
}
public static int main (string[] args) {
var myApp = new MyApp ();
return myApp.run (args);
}
}
public class MyAppWindow : Gtk.ApplicationWindow {
public MyApp myApp { get; construct set; }
private Gtk.HeaderBar headerBar;
private Gtk.GLArea glArea;
private Gtk.Frame frame;
// An array of 3 vectors which represents 3 vertices
private GLES2.GLfloat[] g_vertex_buffer_data = { -1.0f, -1.0f, 0.0f, 1.0f, -1.0f, 0.0f, 0.0f, 1.0f, 0.0f };
// This will identify our vertex buffer
private GLES2.GLuint vertexbuffer;
private GLES2.GLuint programID;
public MyAppWindow(MyApp myApp) {
Object(myApp: myApp);
}
construct {
set_default_size (480, 640);
headerBar = new Gtk.HeaderBar ();
headerBar.set_show_close_button (true);
headerBar.set_title (myApp.appName);
glArea = new Gtk.GLArea ();
glArea.margin = 10;
frame = new Gtk.Frame ("GL Area");
frame.margin = 10;
// Generate 1 buffer, put the resulting identifier in vertexbuffer
GLES2.glGenBuffers(1, &vertexbuffer);
// The following commands will talk about our 'vertexbuffer' buffer
GLES2.glBindBuffer(GLES2.GL_ARRAY_BUFFER, vertexbuffer);
// Give our vertices to OpenGL.
GLES2.glBufferData(GLES2.GL_ARRAY_BUFFER, 9*4, g_vertex_buffer_data, GLES2.GL_STATIC_DRAW);
LoadShaders (out programID);
GLES2.glClearColor (0.0f, 0.0f, 0.0f, 0.0f);
glArea.render.connect (() => {
GLES2.glClear (GLES2.GL_COLOR_BUFFER_BIT | GLES2.GL_DEPTH_BUFFER_BIT);
GLES2.glUseProgram(programID);
// 1st attribute buffer : vertices
GLES2.glEnableVertexAttribArray(0);
GLES2.glBindBuffer(GLES2.GL_ARRAY_BUFFER, vertexbuffer);
GLES2.glVertexAttribPointer(
0, // attribute 0. No particular reason for 0, but must match the layout in the shader.
3, // size
GLES2.GL_FLOAT, // type
GLES2.GL_FALSE, // normalized?
0, // stride
(void*)0 // array buffer offset
);
// Draw the triangle !
GLES2.glDrawArrays(GLES2.GL_TRIANGLES, 0, 3); // Starting from vertex 0; 3 vertices total -> 1 triangle
GLES2.glDisableVertexAttribArray(0);
GLES2.glFlush ();
return true;
});
set_titlebar (headerBar);
frame.add (glArea);
add (frame);
}
void LoadShaders(out GLES2.GLuint ProgramID) {
GLES2.GLint Result = GLES2.GL_FALSE;
int InfoLogLength = 0;
// create vertex shader
GLES2.GLuint VertexShaderID = GLES2.glCreateShader(GLES2.GL_VERTEX_SHADER);
string VertexSource = "#version 330 core
layout(location = 0) in vec3 vertexPosition_modelspace;
void main(){
gl_Position.xyz = vertexPosition_modelspace;
gl_Position.w = 1.0;
}";
// compile vertex shader
GLES2.glShaderSource(VertexShaderID, 1, out VertexSource, null);
GLES2.glCompileShader(VertexShaderID);
// check vertex shader
GLES2.glGetShaderiv(VertexShaderID, GLES2.GL_COMPILE_STATUS, &Result);
GLES2.glGetShaderiv(VertexShaderID, GLES2.GL_INFO_LOG_LENGTH, &InfoLogLength);
if ( InfoLogLength > 0 ) {
GLES2.GLchar[InfoLogLength+1] VertexShaderErrorMessage;
GLES2.glGetShaderInfoLog(VertexShaderID, InfoLogLength, null, &VertexShaderErrorMessage[0]);
}
// create fragment shader
GLES2.GLuint FragmentShaderID = GLES2.glCreateShader(GLES2.GL_FRAGMENT_SHADER);
string FragmentSource = "#version 330 core
out vec3 color;
void main(){
color = vec3(1,0,0);
}";
// compile fragment shader
GLES2.glShaderSource(FragmentShaderID, 1, out FragmentSource, null);
GLES2.glCompileShader(FragmentShaderID);
// check fragment shader
GLES2.glGetShaderiv(FragmentShaderID, GLES2.GL_COMPILE_STATUS, &Result);
GLES2.glGetShaderiv(FragmentShaderID, GLES2.GL_INFO_LOG_LENGTH, &InfoLogLength);
if ( InfoLogLength > 0 ){
GLES2.GLchar[InfoLogLength+1] FragmentShaderErrorMessage;
GLES2.glGetShaderInfoLog(FragmentShaderID, InfoLogLength, null, &FragmentShaderErrorMessage[0]);
}
ProgramID = GLES2.glCreateProgram();
GLES2.glAttachShader(ProgramID, VertexShaderID);
GLES2.glAttachShader(ProgramID, FragmentShaderID);
GLES2.glLinkProgram(ProgramID);
// Check the program
GLES2.glGetProgramiv(ProgramID, GLES2.GL_LINK_STATUS, &Result);
GLES2.glGetProgramiv(ProgramID, GLES2.GL_INFO_LOG_LENGTH, &InfoLogLength);
if ( InfoLogLength > 0 ){
GLES2.GLchar[InfoLogLength+1] ProgramErrorMessage;
GLES2.glGetProgramInfoLog(ProgramID, InfoLogLength, null, &ProgramErrorMessage[0]);
}
GLES2.glDetachShader(ProgramID, VertexShaderID);
GLES2.glDetachShader(ProgramID, FragmentShaderID);
GLES2.glDeleteShader(VertexShaderID);
GLES2.glDeleteShader(FragmentShaderID);
}
}
I compile it with valac --pkg gtk+-3.0 --vapidir=. --pkg gles2 valagl.vala -o valagl --Xcc=-lGLESv2. I have a gles2.vapi in the same folder.
There are 2 [-Wincompatible-pointer-types] warnings in glShaderSource for the shader source string at compile time. That could be where the problem is but I do not know how to fix it.
expected ‘const GLchar * const* {aka const char * const*}’ but argument is of type ‘gchar ** {aka char **}
The example has a step of glfwSwapBuffers(). I'm not sure what needs to be done there. I use GLES2.glFlush () but I do not understand how it connects to the GLArea I just created.
Also valadoc goes on about an on_realize signal where shaders need to be initialized, but I cant seem to find an on_realize signal at all
How do I draw a simple triangle in a GTK3 window using GLES2?
The program runs and shows a black GLArea. The only thing that works is the color of that area, I can change the color by changing GLES2.glClearColor (0.0f, 0.0f, 0.0f, 0.0f)