I can't render a cube in OpenGL, in Windows, using MinGW - c

Question

I tried rendering a cube using OpenGL, in Windows. But the display window is black. I enabled the Z-Buffer, I clear the depth bit in the glClear function, etc. But no luck. And the problem is that every example or documentation I follow, is incomplete, or omit some information, and I'm very, very confused right now. I don't know what am I doing right and what am I doing wrong.
All I want is to display a cube, to know that the renderer is ready for 3D graphics (I can display 2D graphics with no problems). Nothing else.
This is the code of my main program:
#include "demo.h"
#include "renderfunc.c"
HDC hDC;
HGLRC hRC;
void enableGL(HWND hWnd)
{
hDC = GetDC(hWnd);
int nPixelFormat;
static PIXELFORMATDESCRIPTOR pfd = {
sizeof(PIXELFORMATDESCRIPTOR),
1,
PFD_DRAW_TO_WINDOW |
PFD_SUPPORT_OPENGL |
PFD_DOUBLEBUFFER,
PFD_TYPE_RGBA,
24,
0,0,0,0,0,0,
0,0,
0,0,0,0,0,
32,
0,
0,
PFD_MAIN_PLANE,
0,
0,0,0 };
if(!hDC)
{
MessageBox(hWnd,L"Can't Create A GL Device Context.",L"ERROR",MB_OK|MB_ICONEXCLAMATION);
return;
}
nPixelFormat = ChoosePixelFormat(hDC, &pfd);
if(!nPixelFormat)
{
MessageBox(hWnd,L"Can't find a proper Pixel Format.",L"ERROR",MB_OK|MB_ICONEXCLAMATION);
return;
}
SetPixelFormat(hDC, nPixelFormat, &pfd);
/* Those lines has to be here*/
hRC = wglCreateContext(hDC);
wglMakeCurrent(hDC,hRC);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
/* UNCOMMENT THIS SECTION FOR 3D */
glClearDepth(1.0f);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_EQUAL); //In some examples this is GL_LESS
glDepthMask(GL_TRUE);
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST); //Accurate perspective calculations
return;
}
GLvoid ChangeSize(GLsizei width, GLsizei height)
{
if(height==0)
height=1;
glViewport(0,0,width,height);
//glLoadIdentity();
/* THIS SECTION IS FOR 3D GRAPHICS */
/* Comment glLoadIdentity above, and uncomment this section */
/* If you enable Z-buffer */
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f, (GLfloat)width/(GLfloat)height,0.1f,100.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
return;
}
LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch (msg)
{
case WM_CREATE:
enableGL(hWnd);
return 0;
case WM_CLOSE:
PostQuitMessage(0);
return 0;
case WM_DESTROY:
ReleaseDC(hWnd,hDC);
wglMakeCurrent(hDC, NULL);
wglDeleteContext(hRC);
PostQuitMessage(0);
return 0;
case WM_KEYDOWN:
switch(wParam)
{
case VK_ESCAPE:
PostQuitMessage(0);
return 0;
}
return 0;
case WM_PAINT:
glClearColor( 0.0f, 0.0f, 0.0f, 1.0f );
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
/* GL ANIMATION GOES HERE */
//Change this for whatever you want to render
renderCubeTest();
/* -------------------- */
SwapBuffers(hDC);
ValidateRect(hWnd, NULL);
return 0;
case WM_SIZE:
ChangeSize(LOWORD(lParam), HIWORD(lParam));
return 0;
default:
return DefWindowProc(hWnd, msg, wParam, lParam);
}
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int iCmdShow)
{
WNDCLASS wc;
HWND hWnd;
MSG msg;
//String with the name of the class of our window
LPCTSTR classname = L"OpenGL";
//String with the title of our window
LPCTSTR windowtitle = L"Cubes Demo By Ninjihaku Software";
wc.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
wc.lpfnWndProc = (WNDPROC) WndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hInstance;
//wc.hIcon = (HICON) LoadImage(hInstance, MAKEINTRESOURCE(IDI_APPICON), IMAGE_ICON, 0, 0, LR_DEFAULTSIZE | LR_DEFAULTCOLOR | LR_SHARED);
wc.hIcon = NULL;
wc.hCursor = (HCURSOR) LoadImage(NULL, IDC_ARROW, IMAGE_CURSOR, 0, 0, LR_SHARED);
wc.hbrBackground = NULL;
wc.lpszMenuName = NULL;
wc.lpszClassName = classname;
if(RegisterClass(&wc) == 0)
return false;
//hWnd = CreateWindow(classname, windowtitle, WS_OVERLAPPEDWINDOW | WS_CLIPCHILDREN | WS_CLIPSIBLINGS, 100, 100, 640, 480, NULL, NULL, hInstance, NULL);
hWnd = CreateWindowEx(WS_EX_APPWINDOW | WS_EX_WINDOWEDGE, classname, windowtitle, WS_OVERLAPPEDWINDOW | WS_CLIPSIBLINGS | WS_CLIPCHILDREN, 0, 0, 640, 480, NULL, NULL, hInstance, NULL);
if(hWnd == NULL)
return FALSE;
ShowWindow(hWnd, SW_SHOW);
UpdateWindow(hWnd);
while(GetMessage(&msg, NULL, 0,0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
DestroyWindow(hWnd);
return (int) msg.wParam;
}
Then the renderCubeTest() function included in renderfunc.c:
void renderCubeTest()
{
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPushMatrix();
glTranslatef(1.5f, 0.0f, -7.0f); // Move right and into the screen
glBegin(GL_QUADS); // Begin drawing the color cube with 6 quads
// Top face (y = 1.0f)
// Define vertices in counter-clockwise (CCW) order with normal pointing out
glColor3f(0.0f, 1.0f, 0.0f); // Green
glVertex3f( 1.0f, 1.0f, -1.0f);
glVertex3f(-1.0f, 1.0f, -1.0f);
glVertex3f(-1.0f, 1.0f, 1.0f);
glVertex3f( 1.0f, 1.0f, 1.0f);
// Bottom face (y = -1.0f)
glColor3f(1.0f, 0.5f, 0.0f); // Orange
glVertex3f( 1.0f, -1.0f, 1.0f);
glVertex3f(-1.0f, -1.0f, 1.0f);
glVertex3f(-1.0f, -1.0f, -1.0f);
glVertex3f( 1.0f, -1.0f, -1.0f);
// Front face (z = 1.0f)
glColor3f(1.0f, 0.0f, 0.0f); // Red
glVertex3f( 1.0f, 1.0f, 1.0f);
glVertex3f(-1.0f, 1.0f, 1.0f);
glVertex3f(-1.0f, -1.0f, 1.0f);
glVertex3f( 1.0f, -1.0f, 1.0f);
// Back face (z = -1.0f)
glColor3f(1.0f, 1.0f, 0.0f); // Yellow
glVertex3f( 1.0f, -1.0f, -1.0f);
glVertex3f(-1.0f, -1.0f, -1.0f);
glVertex3f(-1.0f, 1.0f, -1.0f);
glVertex3f( 1.0f, 1.0f, -1.0f);
// Left face (x = -1.0f)
glColor3f(0.0f, 0.0f, 1.0f); // Blue
glVertex3f(-1.0f, 1.0f, 1.0f);
glVertex3f(-1.0f, 1.0f, -1.0f);
glVertex3f(-1.0f, -1.0f, -1.0f);
glVertex3f(-1.0f, -1.0f, 1.0f);
// Right face (x = 1.0f)
glColor3f(1.0f, 0.0f, 1.0f); // Magenta
glVertex3f(1.0f, 1.0f, -1.0f);
glVertex3f(1.0f, 1.0f, 1.0f);
glVertex3f(1.0f, -1.0f, 1.0f);
glVertex3f(1.0f, -1.0f, -1.0f);
glEnd(); // End of drawing color-cube
glFlush();
glPopMatrix();
return;
}
I hope someone can help me and tell me what's wrong with this.

Answer 1

glDepthFunc(GL_EQUAL);
I suspect this is the problem - what it basically does is tell OpenGL that pixels should only be rendered to the screen if the new pixel's depth value is equal to the current pixel's depth value. This is most certainly not what you want.
Instead, you should use either GL_LEQUAL (note the "L" before "EQUAL") or GL_LESS, as these are the normal comparison functions.