SDL + GLAD + OpenGL + NanoVG Example in C++

sdl_nanovg_example.cpp

#include <SDL.h>
#include <glad\glad.h>
#include <nanovg.h>
#define NANOVG_GL3_IMPLEMENTATION
#include <nanovg_gl.h>
#include <nanovg_gl_utils.h> // For framebuffer utilities not shown in this code
#include <string>
#include <iostream>
#include <iomanip> // for setw

int main(int argc, char *argv[])
{
    int screen_width = 640, screen_height = 480;
    SDL_Window * main_window = nullptr;
    SDL_GLContext gl_context = nullptr;
    NVGcontext * nvg_context = nullptr;
    SDL_Event event = { 0 };
    bool should_quit = false;

    // TRY-CATCH TO FACILITATE COMMON CLEAN-UP CODE
    try {

        // INITIALIZE SDL:
        if (SDL_Init(SDL_INIT_EVENTS) < 0) {
            throw(std::string("Failed to initialize SDL: ") + SDL_GetError());
        }

        // CONFIGURE OPENGL ATTRIBUTES USING SDL:
        int context_flags = SDL_GL_CONTEXT_FORWARD_COMPATIBLE_FLAG;
#ifdef _DEBUG
        context_flags |= SDL_GL_CONTEXT_DEBUG_FLAG;
#endif
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, context_flags);
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);
        SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
        SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
        SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
        SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
        SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
        SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
        SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);

        // CREATE AND SDL WINDOW CONFIGURED FOR OPENGL:
        if (0 == (main_window = SDL_CreateWindow("OpenGL Init Example", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, screen_width, screen_height, SDL_WINDOW_OPENGL))) {
            throw(std::string("Failed to create window: ") + SDL_GetError());
        }

        // CREATE THE OPENGL CONTEXT AND MAKE IT CURRENT:
        if(NULL == (gl_context = SDL_GL_CreateContext(main_window))) {
            throw(std::string("Failed to create OpenGL context"));
        }
        else SDL_GL_MakeCurrent(main_window, gl_context);

        // INITIALIZE GLAD:
        if (!gladLoadGLLoader((GLADloadproc)SDL_GL_GetProcAddress)) {
            throw(std::string("Failed to initialize GLAD"));
        }

        // LOG OPENGL VERSION, VENDOR (IMPLEMENTATION), RENDERER, GLSL, ETC.:
        std::cout << std::setw(34) << std::left << "OpenGL Version: " << GLVersion.major << "." << GLVersion.minor << std::endl;
        std::cout << std::setw(34) << std::left << "OpenGL Shading Language Version: " << (char *)glGetString(GL_SHADING_LANGUAGE_VERSION) << std::endl;
        std::cout << std::setw(34) << std::left << "OpenGL Vendor:" << (char *)glGetString(GL_VENDOR) << std::endl;
        std::cout << std::setw(34) << std::left << "OpenGL Renderer:" << (char *)glGetString(GL_RENDERER) << std::endl;

        // INITIALIZE NANOVG:
        int flags = NVG_STENCIL_STROKES | NVG_ANTIALIAS;
#ifdef _DEBUG
        flags |= NVG_DEBUG;
#endif
        if (NULL == (nvg_context = nvgCreateGL3(flags))) {
            throw(std::string("Failed to create NVG Context"));
        }

        // GAME LOOP:
        while (!should_quit) {
            // EVENT LOOP:
            while (SDL_PollEvent(&event)) {
                switch (event.type) {
                case SDL_QUIT:
                    should_quit = true;
                    break;
                case SDL_KEYDOWN:
                    switch (event.key.keysym.sym) {
                    case SDLK_ESCAPE:
                        should_quit = true;
                        break;
                    }
                    break;
                }
            }

            // RENDERING GOES HERE:
            // ...
            
            // Clear the screen to WHITE:
            glClearColor(1.f, 1.f, 1.f, 1.f);
            glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

            // BEGIN NANOVG DRAWING:
            nvgBeginFrame(nvg_context, screen_width, screen_height, 1.f);

            // DRAW A ROUND RECTANGLE WITH AN OUTLINE:
            float rect_w = 250.f, rect_h = 250.f;
            NVGcolor nvg_stroke_color = nvgRGBAf(0.f, 0.f, 0.f, 1.f);
            NVGcolor nvg_fill_color = nvgRGBAf(0.f, 1.f, 0.1f, 1.f);

            nvgBeginPath(nvg_context); 

            nvgRoundedRectVarying(
                nvg_context,
                (float)screen_width / 2.f - rect_w / 2.f, screen_height / 2.f - rect_h / 2.f, 
                rect_w, rect_h,
                30.f, 8.f, 30.f, 8.f
            );

            nvgFillColor(nvg_context, nvg_fill_color);
            nvgFill(nvg_context);
            nvgStrokeWidth(nvg_context, 2.f);
            nvgStrokeColor(nvg_context, nvg_stroke_color);
            nvgStroke(nvg_context);

            // END NANOVG DRAWING:
            nvgEndFrame(nvg_context);

            // PRESENT BACKBUFFER:
            SDL_GL_SwapWindow(main_window);
        }
    }
    catch (std::string e) {
        std::cout << e << std::endl;;
    }
    catch (...) {
        std::cout << "Unknown exception caught!" << std::endl;
    }

    if (nvg_context) nvgDeleteGL3(nvg_context);
    if (gl_context) SDL_GL_DeleteContext(gl_context);
    if (main_window) SDL_DestroyWindow(main_window);
    SDL_Quit();

    return 0;
}