GLUT(freeglut)으로 간단한 OpenGL 예제 만들기

freeglut을 설치하고 간단한 OpenGL 예제를 만들어 보자.

http://freeglut.sourceforge.net/ 에서 MSVC용 Prepackaged Release 를 다운 받아 원하는 폴더에 설치 한다.

빈 Console 프로젝트를 만든다.

freeglut 라이브러리의 dll 파일이 있는 폴더를 Environment에 지정 한다.

Include 디렉토리를 지정 한다.

sprintf() 사용을 위해 SDL checks를 No로 바꾼다. Yes로 된 경우 비표준 함수인 sprintf_s()를 써야 한다.

SDL checks: Adds recommended Security Development Lifecycle (SDL) checks. These checks include extra security-relevant warnings as errors, and additional secure code-generation features.

Library 디렉토리를 지정 한다.

외부 라이브러리 사용시 위 사진과 같이 라이브러리 파일들을 추가해야 하지만 freeglut_std.h에 필요한 라이브러리가 모두 추가 되어 있으므로 하지 않아도 된다.

<freeglut_std.h>

#   include <windows.h>
 
/* Windows static library */
#   ifdef FREEGLUT_STATIC
 
#error Static linking is not supported with this build. Please remove the FREEGLUT_STATIC preprocessor directive, or download the source code from http://freeglut.sf.net/ and build against that.
 
/* Windows shared library (DLL) */
#   else
 
#       define FGAPIENTRY __stdcall
#       if defined(FREEGLUT_EXPORTS)
#           define FGAPI __declspec(dllexport)
#       else
#           define FGAPI __declspec(dllimport)
 
            /* Link with Win32 shared freeglut lib */
#           if FREEGLUT_LIB_PRAGMAS
#             pragma comment (lib, "freeglut.lib")
#           endif
 
#       endif
 
#   endif
 
/* Drag in other Windows libraries as required by FreeGLUT */
#   if FREEGLUT_LIB_PRAGMAS
#       pragma comment (lib, "glu32.lib")    /* link OpenGL Utility lib     */
#       pragma comment (lib, "opengl32.lib") /* link Microsoft OpenGL lib   */
#       pragma comment (lib, "gdi32.lib")    /* link Windows GDI lib        */
#       pragma comment (lib, "winmm.lib")    /* link Windows MultiMedia lib */
#       pragma comment (lib, "user32.lib")   /* link Windows user lib       */
#   endif
 
#else
 
/* Non-Windows definition of FGAPI and FGAPIENTRY  */
#        define FGAPI
#        define FGAPIENTRY
 
#endif

windows.h 도 포함 되어 있다.

#include <gl/glut.h>
#include <cstdio>
 
GLfloat locationX = 0.0f, locationY = 0.0f;
const GLfloat step = 0.02f;
const GLfloat size = 0.2f;
int winId;
 
void Menu(int value);
void Keyboard(unsigned char key, int x, int y);
void Special(int key, int x, int y);
void Mouse(int button, int state, int x, int y);
void Display();
 
int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    
    winId = glutCreateWindow("OpenGL");
 
    glutKeyboardFunc(Keyboard);
    glutSpecialFunc(Special);
    glutMouseFunc(Mouse);
 
    // Sub menu
    GLint SubMenu = glutCreateMenu(Menu);
    glutAddMenuEntry("Red", 4);
    glutAddMenuEntry("Green", 5);
    glutAddMenuEntry("Blue", 6);
 
    // Menu
    glutCreateMenu(Menu);
    glutAddMenuEntry("White", 1);
    glutAddMenuEntry("Black", 2);
    glutAddMenuEntry("Gray", 3);
 
    // Add sub menu
    glutAddSubMenu("Triangle Color", SubMenu);
    glutAttachMenu(GLUT_RIGHT_BUTTON);
 
    glutDisplayFunc(Display);
 
    glutMainLoop();
 
    return 0;
}
 
void Menu(int value)
{
    switch (value) {
    case 1:
        glClearColor(1.0f, 1.0f, 1.0f, 1.0f);    // 배경 흰색
 
        break;
    case 2:
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);    // 배경 검정색
 
        break;
    case 3:
        glClearColor(0.5f, 0.5f, 0.5f, 1.0f);    // 배경 회색
 
        break;
    case 4:
        glColor3f(1.0f, 0.0f, 0.0f);            // 삼감형 빨간색
 
        break;
    case 5:
        glColor3f(0.0f, 1.0f, 0.0f);            // 삼감형 녹색
 
        break;
    case 6:
        glColor3f(0.0f, 0.0f, 1.0f);            // 삼감형 파란색
 
        break;
    default:
 
        break;
    }
 
    glutPostRedisplay();
}
 
void Keyboard(unsigned char key, int x, int y)
{
    switch (key) {
    case 'r':
    case 'R':
        glClearColor(1.0f, 0.0f, 0.0f, 1.0f);    // 배경 빨간색
 
        break;
    case 'g':
    case 'G':
        glClearColor(0.0f, 1.0f, 0.0f, 1.0f);    // 배경 녹색
 
        break;
    case 'b':
    case 'B':
        glClearColor(0.0f, 0.0f, 1.0f, 1.0f);    // 배경 파란색
 
        break;
    case 27:
        glutDestroyWindow(winId);                // ESC키 프로그램 종료
        exit(0);
 
        break;
    default:
 
        break;
    }
 
    glutPostRedisplay();
}
 
void Special(int key, int x, int y)
{
    switch (key) {
    case GLUT_KEY_LEFT:        // step 만큼 x감소
        locationX -= step;
 
        break;
    case GLUT_KEY_RIGHT:    // step 만큼 x증가
        locationX += step;
 
        break;
    case GLUT_KEY_UP:        // step 만큼 y증가
        locationY += step;
 
        break;
    case GLUT_KEY_DOWN:        // step 만큼 y감소
        locationY -= step;
 
        break;
    }
    char title[128] = {0,};
    sprintf(title, "Triangle location (%.2f, y=%.2f)", locationX, locationY);
    glutSetWindowTitle(title); // 제목표시줄에 삼각형 좌표 표시
 
    glutPostRedisplay();
}
 
void Mouse(int button, int state, int x, int y)
{
    if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
        glColor3f(0.0f, 1.0f, 1.0f);    // 삼각형 하늘색
        char title[128] = { 0, };
        sprintf(title, "Click (x: %d, y: %d)", x, y);
        glutSetWindowTitle(title); // 제목표시줄에 클릭 좌표 표시
 
        glutPostRedisplay();
    }
    else if (button == GLUT_LEFT_BUTTON && state == GLUT_UP){
        glColor3f(1.0f, 1.0f, 0.0f);    // 삼각형 노란색
 
        glutPostRedisplay();
    }
}
 
 
void Display()
{
    glClear(GL_COLOR_BUFFER_BIT);
        
    glBegin(GL_TRIANGLES);
    glVertex2f(locationX, locationY + size);
    glVertex2f(locationX - size, locationY - size);
    glVertex2f(locationX + size, locationY - size);
    glEnd();
 
    glFinish();
}

코드를 입력하고 실행 한다.

오른쪽 버튼을 클릭하면 메뉴가 나온다.

삼각형이 빨간색으로 바뀌었다.

r,g,b, 방향키, ESC키 등을 눌러 본다.

SubSystem을Console에서 Widows로 바꾼다.

#include <gl/glut.h>
 
void Menu(int value)
{
    switch (value) {
    case 1:
        glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
 
        break;
    case 2:
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
 
        break;
    case 3:
        glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
 
        break;
    case 4:
        glColor3f(1.0f, 0.0f, 0.0f);
 
        break;
    case 5:
        glColor3f(0.0f, 1.0f, 0.0f);
 
        break;
    case 6:
        glColor3f(0.0f, 0.0f, 1.0f);
 
        break;
    default:
 
        break;
    }
 
    glutPostRedisplay();
}
 
void display() {
    glClear(GL_COLOR_BUFFER_BIT);
 
    glBegin(GL_TRIANGLES);
    glVertex2f(0.0f, 0.5f);
    glVertex2f(-0.5f, -0.5f);
    glVertex2f(0.5f, -0.5f);
    glEnd();
 
    glFinish();
}
 
int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpszCmdParam, int nCmdShow)
{
    glutCreateWindow("OpenGL");
 
    // Sub menu
    GLint SubMenu = glutCreateMenu(Menu);
    glutAddMenuEntry("Red", 4);
    glutAddMenuEntry("Green", 5);
    glutAddMenuEntry("Blue", 6);
 
    // Menu
    glutCreateMenu(Menu);
    glutAddMenuEntry("White", 1);
    glutAddMenuEntry("Black", 2);
    glutAddMenuEntry("Gray", 3);
 
    // Add sub menu
    glutAddSubMenu("Triangle Color", SubMenu);
    glutAttachMenu(GLUT_RIGHT_BUTTON);
 
    glutDisplayFunc(display);
 
    glutMainLoop();
 
    return 0;
}

위 코드와 같이 Windows 프로그램에 맞게 바꾸고 빌드하면 에러없이 빌드는 되지만 아무것도 실행 되지는 않는다.

#include <Windows.h>
#include <gl/gl.h>
 
# pragma comment (lib, "opengl32.lib")
# pragma comment(lib, "glu32.lib")
 
HINSTANCE g_hInst;
HWND hWndMain;
LPCTSTR lpszClass = TEXT("OpenGL");
HDC hdc;
HGLRC hrc;
 
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
void Display();
 
int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpszCmdParam, int nCmdShow)
{
    HWND hWnd;
    MSG Message;
    WNDCLASS WndClass;
    g_hInst = hInstance;
 
    WndClass.cbClsExtra = 0;
    WndClass.cbWndExtra = 0;
    WndClass.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);
    WndClass.hCursor = LoadCursor(NULL, IDC_ARROW);
    WndClass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    WndClass.hInstance = hInstance;
    WndClass.lpfnWndProc = WndProc;
    WndClass.lpszClassName = lpszClass;
    WndClass.lpszMenuName = NULL;
    WndClass.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
    RegisterClass(&WndClass);
 
    hWnd = CreateWindow(lpszClass, lpszClass, WS_OVERLAPPEDWINDOW | WS_CLIPCHILDREN | WS_CLIPSIBLINGS,
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, (HMENU)NULL, hInstance, NULL);
    ShowWindow(hWnd, nCmdShow);
 
    while (GetMessage(&Message, NULL, 0, 0)) {
        TranslateMessage(&Message);
        DispatchMessage(&Message);
    }
 
    return (int)Message.wParam;
}
 
void Display()
{
    glClear(GL_COLOR_BUFFER_BIT);
 
    glBegin(GL_TRIANGLES);
    glVertex2f(0.0f, 0.5f);
    glVertex2f(-0.5f, -0.5f);
    glVertex2f(0.5f, -0.5f);
    glEnd();
 
    glFinish();
}
 
LRESULT CALLBACK WndProc(HWND hWnd, UINT iMessage, WPARAM wParam, LPARAM lParam)
{
    switch (iMessage) {
    case WM_CREATE:
        hWndMain = hWnd;
        PIXELFORMATDESCRIPTOR pfd;
        int nPixelFormat;
 
        hdc = GetDC(hWnd);
        memset(&pfd, 0, sizeof(pfd));
 
        pfd.nSize = sizeof(pfd);
        pfd.nVersion = 1;
        pfd.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL;
        pfd.iPixelType = PFD_TYPE_RGBA;
        pfd.cColorBits = 32;
 
        nPixelFormat = ChoosePixelFormat(hdc, &pfd);
        SetPixelFormat(hdc, nPixelFormat, &pfd);
 
        hrc = wglCreateContext(hdc);
        wglMakeCurrent(hdc, hrc);
 
        return 0;
 
    case WM_PAINT:
        Display();
 
        SetTextColor(hdc, RGB(255, 255, 0));
        SetBkMode(hdc, TRANSPARENT);
        TextOutA(hdc, 10, 10, "Windows OpenGL", 14);
        
        ValidateRect(hWnd, NULL);
 
        return 0;
 
    case WM_SIZE:
        glViewport(0, 0, LOWORD(lParam), HIWORD(lParam));
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
 
        glOrtho(-1, 1, -1, 1, 1, -1);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
 
        return 0;
    case WM_DESTROY:
        wglMakeCurrent(hdc, NULL);
        wglDeleteContext(hrc);
        ReleaseDC(hWnd, hdc);
        PostQuitMessage(0);
 
        return 0;
    }
 
    return(DefWindowProc(hWnd, iMessage, wParam, lParam));
}

glut을 사용하지 않고 Windows에서 지원하는 OpenGL 관련 wgl함수를 이용해 작성한 코드이다.

※ Reference

http://soen.kr/lecture/library/opengl/opengl-5.htm