SDL + GLAD + OpenGL + NanoVG Example in C++ (Triangle)

sdl_nanovg_triangle_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

void nvgTriangle(NVGcontext * ctx, float x1, float y1, float x2, float y2, float x3, float y3);

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);

			float triW = 350.f, triH = 300.f;
			float triX = screen_width / 2 - triW / 2;
			float triY = screen_height / 2 - triH / 2;
			nvgTriangle(nvg_context, triX + triW / 2, triY + 0, triX + triW, triY + triH, triX + 0, triY + triH);

			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;
}

void nvgTriangle(NVGcontext * ctx, float x1, float y1, float x2, float y2, float x3, float y3)
{
	nvgMoveTo(ctx, x1, y1);
	nvgLineTo(ctx, x2, y2);
	nvgLineTo(ctx, x3, y3);
	nvgClosePath(ctx);
}