Every tutorial I find Online uses SDL or GLAD or other libraries to initialize OpenGL. Is there a way of initializing OpenGL with no extra libraries (like DirectX)?
The reason for that, Is that I am building a Game Engine and I want to minimize the external libraries as possible and to be able to handle more error messages.
Initializing OpenGL differs from one operating system to another, that's why people made these libraries to ease other developers work.
Some tutorials that will help you.
For Windows (WGL)
For Linux (GLX)
There isn't much quality information about doing this. I found a great piece of code called windows_modern_opengl_context.c on github by the user nickrolfe. I thought I'd share it here to make it easier for others to find. If you link -lopengl32 and make sure you have -mwindows flag up it should compile fine with a modern c compiler. I'm using gcc -std=c11. If you want to use C++ you may have to edit the code to not use designated initializers when initializing the structs. I'm not sure.
EDIT:
This code creates an empty window using the win32 api with a modern opengl context (Version 3.3). You will still need to load the appropriate gl extensions in order to call functions such as glCreateShader(...); I recommend using glad to do this. If you use glad like I said you should use gladLoadGL() instead of gladLoadGLLoader() to load the extensions.
// Sample code showing how to create a modern OpenGL window and rendering context on Win32.
#include <windows.h>
#include <gl/gl.h>
#include <stdbool.h>
typedef HGLRC WINAPI wglCreateContextAttribsARB_type(HDC hdc, HGLRC hShareContext, const int *attribList);
wglCreateContextAttribsARB_type *wglCreateContextAttribsARB;
// See https://www.opengl.org/registry/specs/ARB/wgl_create_context.txt for all values
#define WGL_CONTEXT_MAJOR_VERSION_ARB 0x2091
#define WGL_CONTEXT_MINOR_VERSION_ARB 0x2092
#define WGL_CONTEXT_PROFILE_MASK_ARB 0x9126
#define WGL_CONTEXT_CORE_PROFILE_BIT_ARB 0x00000001
typedef BOOL WINAPI wglChoosePixelFormatARB_type(HDC hdc, const int *piAttribIList, const FLOAT *pfAttribFList, UINT nMaxFormats, int *piFormats, UINT *nNumFormats);
wglChoosePixelFormatARB_type *wglChoosePixelFormatARB;
// See https://www.opengl.org/registry/specs/ARB/wgl_pixel_format.txt for all values
#define WGL_DRAW_TO_WINDOW_ARB 0x2001
#define WGL_ACCELERATION_ARB 0x2003
#define WGL_SUPPORT_OPENGL_ARB 0x2010
#define WGL_DOUBLE_BUFFER_ARB 0x2011
#define WGL_PIXEL_TYPE_ARB 0x2013
#define WGL_COLOR_BITS_ARB 0x2014
#define WGL_DEPTH_BITS_ARB 0x2022
#define WGL_STENCIL_BITS_ARB 0x2023
#define WGL_FULL_ACCELERATION_ARB 0x2027
#define WGL_TYPE_RGBA_ARB 0x202B
static void
fatal_error(char *msg)
{
MessageBoxA(NULL, msg, "Error", MB_OK | MB_ICONEXCLAMATION);
exit(EXIT_FAILURE);
}
static void
init_opengl_extensions(void)
{
// Before we can load extensions, we need a dummy OpenGL context, created using a dummy window.
// We use a dummy window because you can only set the pixel format for a window once. For the
// real window, we want to use wglChoosePixelFormatARB (so we can potentially specify options
// that aren't available in PIXELFORMATDESCRIPTOR), but we can't load and use that before we
// have a context.
WNDCLASSA window_class = {
.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC,
.lpfnWndProc = DefWindowProcA,
.hInstance = GetModuleHandle(0),
.lpszClassName = "Dummy_WGL_djuasiodwa",
};
if (!RegisterClassA(&window_class)) {
fatal_error("Failed to register dummy OpenGL window.");
}
HWND dummy_window = CreateWindowExA(
0,
window_class.lpszClassName,
"Dummy OpenGL Window",
0,
CW_USEDEFAULT,
CW_USEDEFAULT,
CW_USEDEFAULT,
CW_USEDEFAULT,
0,
0,
window_class.hInstance,
0);
if (!dummy_window) {
fatal_error("Failed to create dummy OpenGL window.");
}
HDC dummy_dc = GetDC(dummy_window);
PIXELFORMATDESCRIPTOR pfd = {
.nSize = sizeof(pfd),
.nVersion = 1,
.iPixelType = PFD_TYPE_RGBA,
.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER,
.cColorBits = 32,
.cAlphaBits = 8,
.iLayerType = PFD_MAIN_PLANE,
.cDepthBits = 24,
.cStencilBits = 8,
};
int pixel_format = ChoosePixelFormat(dummy_dc, &pfd);
if (!pixel_format) {
fatal_error("Failed to find a suitable pixel format.");
}
if (!SetPixelFormat(dummy_dc, pixel_format, &pfd)) {
fatal_error("Failed to set the pixel format.");
}
HGLRC dummy_context = wglCreateContext(dummy_dc);
if (!dummy_context) {
fatal_error("Failed to create a dummy OpenGL rendering context.");
}
if (!wglMakeCurrent(dummy_dc, dummy_context)) {
fatal_error("Failed to activate dummy OpenGL rendering context.");
}
wglCreateContextAttribsARB = (wglCreateContextAttribsARB_type*)wglGetProcAddress("wglCreateContextAttribsARB");
wglChoosePixelFormatARB = (wglChoosePixelFormatARB_type*)wglGetProcAddress("wglChoosePixelFormatARB");
wglMakeCurrent(dummy_dc, 0);
wglDeleteContext(dummy_context);
ReleaseDC(dummy_window, dummy_dc);
DestroyWindow(dummy_window);
}
static HGLRC
init_opengl(HDC real_dc)
{
init_opengl_extensions();
// Now we can choose a pixel format the modern way, using wglChoosePixelFormatARB.
int pixel_format_attribs[] = {
WGL_DRAW_TO_WINDOW_ARB, GL_TRUE,
WGL_SUPPORT_OPENGL_ARB, GL_TRUE,
WGL_DOUBLE_BUFFER_ARB, GL_TRUE,
WGL_ACCELERATION_ARB, WGL_FULL_ACCELERATION_ARB,
WGL_PIXEL_TYPE_ARB, WGL_TYPE_RGBA_ARB,
WGL_COLOR_BITS_ARB, 32,
WGL_DEPTH_BITS_ARB, 24,
WGL_STENCIL_BITS_ARB, 8,
0
};
int pixel_format;
UINT num_formats;
wglChoosePixelFormatARB(real_dc, pixel_format_attribs, 0, 1, &pixel_format, &num_formats);
if (!num_formats) {
fatal_error("Failed to set the OpenGL 3.3 pixel format.");
}
PIXELFORMATDESCRIPTOR pfd;
DescribePixelFormat(real_dc, pixel_format, sizeof(pfd), &pfd);
if (!SetPixelFormat(real_dc, pixel_format, &pfd)) {
fatal_error("Failed to set the OpenGL 3.3 pixel format.");
}
// Specify that we want to create an OpenGL 3.3 core profile context
int gl33_attribs[] = {
WGL_CONTEXT_MAJOR_VERSION_ARB, 3,
WGL_CONTEXT_MINOR_VERSION_ARB, 3,
WGL_CONTEXT_PROFILE_MASK_ARB, WGL_CONTEXT_CORE_PROFILE_BIT_ARB,
0,
};
HGLRC gl33_context = wglCreateContextAttribsARB(real_dc, 0, gl33_attribs);
if (!gl33_context) {
fatal_error("Failed to create OpenGL 3.3 context.");
}
if (!wglMakeCurrent(real_dc, gl33_context)) {
fatal_error("Failed to activate OpenGL 3.3 rendering context.");
}
return gl33_context;
}
static LRESULT CALLBACK
window_callback(HWND window, UINT msg, WPARAM wparam, LPARAM lparam)
{
LRESULT result = 0;
switch (msg) {
case WM_CLOSE:
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
result = DefWindowProcA(window, msg, wparam, lparam);
break;
}
return result;
}
static HWND
create_window(HINSTANCE inst)
{
WNDCLASSA window_class = {
.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC,
.lpfnWndProc = window_callback,
.hInstance = inst,
.hCursor = LoadCursor(0, IDC_ARROW),
.hbrBackground = 0,
.lpszClassName = "WGL_fdjhsklf",
};
if (!RegisterClassA(&window_class)) {
fatal_error("Failed to register window.");
}
// Specify a desired width and height, then adjust the rect so the window's client area will be
// that size.
RECT rect = {
.right = 1024,
.bottom = 576,
};
DWORD window_style = WS_OVERLAPPEDWINDOW;
AdjustWindowRect(&rect, window_style, false);
HWND window = CreateWindowExA(
0,
window_class.lpszClassName,
"OpenGL",
window_style,
CW_USEDEFAULT,
CW_USEDEFAULT,
rect.right - rect.left,
rect.bottom - rect.top,
0,
0,
inst,
0);
if (!window) {
fatal_error("Failed to create window.");
}
return window;
}
int WINAPI
WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmd_line, int show)
{
HWND window = create_window(inst);
HDC gldc = GetDC(window);
HGLRC glrc = init_opengl(gldc);
ShowWindow(window, show);
UpdateWindow(window);
bool running = true;
while (running) {
MSG msg;
while (PeekMessageA(&msg, 0, 0, 0, PM_REMOVE)) {
if (msg.message == WM_QUIT) {
running = false;
} else {
TranslateMessage(&msg);
DispatchMessageA(&msg);
}
}
glClearColor(1.0f, 0.5f, 0.5f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Do OpenGL rendering here
SwapBuffers(gldc);
}
return 0;
}
