Very basic SDL2 OpenGL application (C++1y)

sdl2_opengl.cpp

#include <iostream>

#define _USE_MATH_DEFINES
#include <cmath>

#include <SDL2/SDL.h>
#include <SDL2/SDL_opengl.h>

constexpr int SCREEN_WIDTH = 800;
constexpr int SCREEN_HEIGHT = 600;

constexpr int OPENGL_MAJOR_VERSION = 2;
constexpr int OPENGL_MINOR_VERSION = 1;

constexpr SDL_GLprofile OPENGL_PROFILE = SDL_GLprofile::SDL_GL_CONTEXT_PROFILE_CORE;

/*
 * http:*nehe.gamedev.net/article/replacement_for_gluperspective/21002/
 *
 * Replaces gluPerspective. Sets the frustum to perspective mode.
 * fovY     - Field of vision in degrees in the y direction
 * aspect   - Aspect ratio of the viewport
 * zNear    - The near clipping distance
 * zFar     - The far clipping distance
 */

void perspectiveGL(GLdouble fovY, GLdouble aspect, GLdouble zNear, GLdouble zFar) {

	GLdouble fW, fH;

	fH = tan(fovY / 360 * M_PI) * zNear;
	fW = fH * aspect;

	glFrustum(-fW, fW, -fH, fH, zNear, zFar);

}

void Display_InitGL() {

	/* Enable smooth shading */
	glShadeModel( GL_SMOOTH);

	/* Set the background red */
	glClearColor(1.0f, 0.0f, 0.0f, 0.0f);

	/* Depth buffer setup */
	glClearDepth(1.0f);

	/* Enables Depth Testing */
	glEnable( GL_DEPTH_TEST);

	/* The Type Of Depth Test To Do */
	glDepthFunc( GL_LEQUAL);

	/* Really Nice Perspective Calculations */
	glHint( GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
}

/* function to reset our viewport after a window resize */
int Display_SetViewport(int width, int height) {

	/* Height / width ration */
	GLfloat ratio;

	/* Protect against a divide by zero */
	if (height == 0) {
		height = 1;
	}

	ratio = (GLfloat) width / (GLfloat) height;

	/* Setup our viewport. */
	glViewport(0, 0, (GLsizei) width, (GLsizei) height);

	/* change to the projection matrix and set our viewing volume. */
	glMatrixMode( GL_PROJECTION);
	glLoadIdentity();

	/* Set our perspective */
	perspectiveGL(45.0f, ratio, 0.1f, 100.0f);

	/* Make sure we're chaning the model view and not the projection */
	glMatrixMode( GL_MODELVIEW);

	/* Reset The View */
	glLoadIdentity();

	return 1;
}

void Display_Render(SDL_Window* displayWindow) {

	/* Clear The Screen And The Depth Buffer */
	glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glColor4f(0, 0, 0, 1.0);

	/* Move Left 1.5 Units And Into The Screen 6.0 */
	glLoadIdentity();
	glTranslatef(-1.5f, 0.0f, -6.0f);

	glBegin( GL_TRIANGLES); /* Drawing Using Triangles */
	glVertex3f(0.0f, 1.0f, 0.0f); /* Top */
	glVertex3f(-1.0f, -1.0f, 0.0f); /* Bottom Left */
	glVertex3f(1.0f, -1.0f, 0.0f); /* Bottom Right */
	glEnd(); /* Finished Drawing The Triangle */

	/* Move Right 3 Units */
	glTranslatef(3.0f, 0.0f, 0.0f);

	glBegin( GL_QUADS); /* Draw A Quad */
	glVertex3f(-1.0f, 1.0f, 0.0f); /* Top Left */
	glVertex3f(1.0f, 1.0f, 0.0f); /* Top Right */
	glVertex3f(1.0f, -1.0f, 0.0f); /* Bottom Right */
	glVertex3f(-1.0f, -1.0f, 0.0f); /* Bottom Left */
	glEnd(); /* Done Drawing The Quad */

	SDL_GL_SwapWindow(displayWindow);

}

int main(int argc, char *argv[]) {

	if (SDL_Init( SDL_INIT_VIDEO) < 0) {
		std::cerr << "There was an error initing SDL2: " << SDL_GetError() << std::endl;
		return 1;
	}

	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, OPENGL_PROFILE);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, OPENGL_MAJOR_VERSION);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, OPENGL_MINOR_VERSION);

	SDL_Window* displayWindow = SDL_CreateWindow("Very basic SDL2 OpenGL application", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_OPENGL);

	if (displayWindow == nullptr) {
		std::cerr << "There was an error creating the window: " << SDL_GetError() << std::endl;
		return 1;
	}

	SDL_GLContext context = SDL_GL_CreateContext(displayWindow);

	if (context == nullptr) {
		std::cerr << "There was an error creating OpenGL context: " << SDL_GetError() << std::endl;
		return 1;
	}

	const unsigned char *version = glGetString(GL_VERSION);
	if (version == nullptr) {
		std::cerr << "There was an error with OpenGL configuration:" << std::endl;
		return 1;
	}

	SDL_GL_MakeCurrent(displayWindow, context);

	Display_InitGL();

	Display_SetViewport(SCREEN_WIDTH, SCREEN_HEIGHT);

	Display_Render(displayWindow);

	SDL_Delay(5000);

	SDL_GL_DeleteContext(context);

	SDL_DestroyWindow(displayWindow);

	SDL_Quit();

	return 0;
}

a) #define _USE_MATH_DEFINES before #define <cmath> is needed for many platforms to be able to use M_PI
b) at least C++11 is needed for compilation (constexpr used)

apart from that, +1 for fixing the original code.

Thanks for tips, cheers

Thank you so much. You are my hero.