1.c

//BEGIN HEAD
#include <stdio.h>
#include <stdlib.h>

#ifdef _WIN32
	#include <SDL.h>
	#include <SDL_opengl.h>
	#include <SDL_image.h>
	#include <SDL_ttf.h>
#else
	#include <SDL2/SDL.h>
	#include <SDL2/SDL_opengl.h>
	#include <SDL2/SDL_image.h>
	#include <SDL2/SDL_ttf.h>
#endif

#define NANOVG_GL3_IMPLEMENTATION
#include "nanovg.h"
#include "nanovg_gl.h"
#include "nanovg_gl_utils.h"
//END HEAD

//BEGIN MAIN
int main(int argc, char **argv)
{

(void)argc;
(void)argv;

if (SDL_Init(SDL_INIT_EVERYTHING) < 0){
	return EXIT_FAILURE;
}

SDL_GLContext 	context;
SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 		8);

SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 	2);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 	0);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, 	SDL_GL_CONTEXT_PROFILE_CORE);

SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 		1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 		1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, 		8);

SDL_Window 	*window = NULL;
window = SDL_CreateWindow("SDL2/OpenGL/Nanovg", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 1024, 800,
SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_SHOWN | SDL_WINDOW_ALLOW_HIGHDPI);//only SDL_WINDOW_OPENGL may suffice
if (!window){
	SDL_Log("fallback");
	SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 0);
	SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, 0);
	window = SDL_CreateWindow("SDL2/OpenGL/Nanovg", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 1024, 800,
		SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_SHOWN | SDL_WINDOW_ALLOW_HIGHDPI);//same as above
		if (!window){
			return EXIT_FAILURE;
		}
}

context = SDL_GL_CreateContext(window);
SDL_GL_MakeCurrent(window, context);

NVGcontext	*vg 	= NULL;
vg = nvgCreateGL3(NVG_ANTIALIAS | NVG_STENCIL_STROKES | NVG_DEBUG);
if (vg == NULL){
	return EXIT_FAILURE;
}

int winWidth, winHeight;
int fbWidth, fbHeight;
float pxRatio;

SDL_GetWindowSize(window, &winWidth, &winHeight);
fbWidth=winWidth; fbHeight=winHeight;

pxRatio = (float)fbWidth / (float)winWidth;

SDL_Event 	event;

int running=1;
//BEGIN MAIN LOOP
while (running){
	    //BEGIN EVENT LOOP
	    while(SDL_PollEvent(&event)){
		    if(event.type == SDL_QUIT){
			    running =0;
		    }
		    if(event.type == SDL_MOUSEMOTION){
			    ;
		    }
		    if(event.type == SDL_MOUSEBUTTONDOWN){
			    if(event.button.button == SDL_BUTTON_RIGHT){
				    ;
			    }
			    if(event.button.button == SDL_BUTTON_MIDDLE){
				    ;
			    }
			    if(event.button.button==SDL_BUTTON_LEFT){
				    break;
			    }
		    }
		    if(event.type == SDL_KEYDOWN ){
			    switch(event.key.keysym.sym ){
				    case SDLK_ESCAPE:
					    running =0;
					    break;
					    
				    case SDLK_r:
				    case SDLK_BACKSPACE:
					    break;
					    
				    case SDLK_p:	
				    case SDLK_SPACE:
					    break;
					    
				    default:
					    break;
			    }
		    }
	    }
	    //END   EVENT LOOP
        nvgBeginFrame(vg, winWidth, winHeight, pxRatio);

        nvgBeginPath(vg);
		nvgRect(vg, 300,100, 120,30);
		nvgFillColor(vg, nvgRGBA(255,192,0,255));
		nvgFill(vg);
	nvgEndFrame(vg);

	SDL_GL_SwapWindow(window);
    }
//END 	MAIN LOOP
return EXIT_SUCCESS;

}
//END 	MAIN