系列三：OPENGL我来了

完成系列二后，心里相当激动，如果能看到精美的游戏动画多好......

这不是做梦，有梦想就能实现，但是我们还是一步一步来，先来看一下显示普通的图形

注：在此版本里，用了最容易的老式OPENGL，后面接下来用的是新式的moden opengl

MainGame.h

#pragma once
#include <SDL/SDL.h>
#include <GL/glew.h>

enum class GameState{PLAY, EXIT};

class MainGame
{
public:
    MainGame();
    ~MainGame();

    void run();
    

private:
    void initSystems();
    void gameLoop();
    void processInput();
    void drawGame();

    SDL_Window* m_pWindow;
    int m_nScreenWidth;
    int m_nScreenHeight;
    GameState m_gameState;
};

MainGame.cpp

#include "MainGame.h"
#include <iostream>
#include <string>
void faterError(const std::string& errorString)
{
    std::cout << errorString << std::endl;
    std::cout << "Enter any key to quit...";
    std::cin.get();
    SDL_Quit();
}

MainGame::MainGame() :m_pWindow(nullptr), m_nScreenWidth(1024), m_nScreenHeight(768), m_gameState(GameState::PLAY)
{

}


MainGame::~MainGame()
{
}

void MainGame::run()
{
    initSystems();

    gameLoop();
}

void MainGame::initSystems()
{
    //Initialize SDL
    SDL_Init(SDL_INIT_EVERYTHING);
    m_pWindow = SDL_CreateWindow("GraphicToturial", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, m_nScreenWidth, m_nScreenHeight, SDL_WINDOW_OPENGL);
    if (nullptr == m_pWindow)
    {
        faterError("SDL Window could not be created!");
    }

    SDL_GLContext glContext = SDL_GL_CreateContext(m_pWindow);
    if (nullptr == glContext)
    {
        faterError("SDL_GL context could not be created!");
    }

    GLenum result = glewInit();
    if (GLEW_OK != result)
    {
        faterError("Could not initialize glew!");
    }

    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);

    glClearColor(0, 0, 1, 1);
}

void MainGame::gameLoop()
{
    while (m_gameState != GameState::EXIT)
    {
        processInput();
        drawGame();
    }
}

void MainGame::processInput()
{
    SDL_Event evnt;
    while (SDL_PollEvent(&evnt))
    {
        switch (evnt.type)
        {
        case SDL_QUIT:
            m_gameState = GameState::EXIT;
            break;
        case SDL_MOUSEMOTION:
            std::cout << evnt.motion.x << " " << evnt.motion.y << std::endl;
            break;
        }
    }
}

void MainGame::drawGame()
{
    glClearDepth(1.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glEnableClientState(GL_COLOR_ARRAY);
    glColor3f(1.0f, 0.0f, 0.0f);
    glBegin(GL_TRIANGLES);
    glVertex2f(0.0f, 0.0f);
    glVertex2f(0.0f, 500.0f);
    glVertex2f(500.f, 500.0f);
    glEnd();

    SDL_GL_SwapWindow(m_pWindow);
}