1. ## Weired results

Hi, I've been looking through stuff on OpenGL for a little while now, and am trying to create my first game, old school PONG. I have gotten everything done with it, collision detection and all, but then I found a flaw that has rendered my project useless.

I made the ball go on a random trajectory by getting a random number between 0 and 359 degrees. No problem there, except the ball doesn't take the given course.

I did some experimenting, and found out that all the degree system I was using was lopsided, literally. I set the ball angle manually to 0 degrees, and it went off to the right. Well, I ended up scrapping the game and starting fresh, but not before I find something to correct the problem. Here is the source for a small program I made from a template that is still having the same problem, it draws a line from the center, to supposidly 270 degrees.

I have no clue what it is, but if I were to put any money on it, it would be in the trig I did to find the ending point of the line.

Any help is appreciated

Code:
```// Include headers
#include <windows.h>
#include <gl/gl.h>
#include <math.h>

#define PI 3.14159265

// Declare functions
LRESULT CALLBACK WndProc (HWND hWnd, UINT message,		// Windows procedure
WPARAM wParam, LPARAM lParam);							// Windows procedure contd..
void EnableOpenGL (HWND hWnd, HDC *hDC, HGLRC *hRC);	// Initialize OpenGL
void DisableOpenGL (HWND hWnd, HDC hDC, HGLRC hRC);		// DisableOpenGL
void draw_scene();										// Draw OpenGL Scene

// Declare global variables
char class_name[] = "OpenGL 2D Pong";					// Windows class name
char window_name[] = "Pong";							// Window title name
int window_width = 500;									// Window width
int window_height = 500;								// Window height

WNDCLASS wc;											// Windows class handle
HWND hWnd;												// Window Handle
HDC hDC;												// Device context handle
HGLRC hRC;												// Rendering context handle
MSG msg;												// Message handle
bool bQuit = FALSE;										// Quit the loop
bool keys[256];											// Array for the keypress routine

// Windows Main function
int WINAPI WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int iCmdShow)
{
// register window class
wc.style = CS_OWNDC;										// Window style - own decive context
wc.lpfnWndProc = WndProc;									// Which windows procedure to use
wc.cbClsExtra = 0;											// Extra parameters, 0
wc.cbWndExtra = 0;											// Extra parameters, 0
wc.hInstance = hInstance;									// Program instance handle
wc.hIcon = LoadIcon (NULL, IDI_APPLICATION);				// Program icon
wc.hCursor = LoadCursor (NULL, IDC_ARROW);					// Mouse cursor
wc.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);		// Background color of our screen
wc.lpszClassName = class_name;								// Name of our class
RegisterClass (&wc);										// Register the class

// Create the window
hWnd = CreateWindow (
class_name, window_name,
WS_CAPTION | WS_POPUPWINDOW | WS_VISIBLE,
0, 0, window_width, window_height,
NULL, NULL, hInstance, NULL);

// Enable OpenGL
EnableOpenGL(hWnd, &hDC, &hRC);

// Main Program Loop
while (!bQuit)
{
// Check for messages in the queue
if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
{
// Handle or dispatch messages
if (msg.message == WM_QUIT)
{
bQuit = TRUE;
}
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
else
{
// Draw the OpenGL Scene
draw_scene();
}
}

// Shutdown OpenGL
DisableOpenGL(hWnd, hDC, hRC);

// Destroy the window
DestroyWindow(hWnd);

return msg.wParam;
}

// Windows Procedure
LRESULT CALLBACK WndProc(HWND hWnd, UINT message,
WPARAM wParam, LPARAM lParam)
{

switch (message)
{
case WM_CREATE:
return 0;
break;
case WM_CLOSE:
PostQuitMessage(0);
return 0;
break;

case WM_DESTROY:
return 0;
break;
case WM_KEYDOWN:
keys[wParam] = true;
switch (wParam)
{
case VK_ESCAPE:
PostQuitMessage(0);
return 0;
break;
}
return 0;
break;
case WM_KEYUP:
keys[wParam] = false;
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
}

// Enable OpenGL
void EnableOpenGL(HWND hWnd, HDC *hDC, HGLRC *hRC)
{
PIXELFORMATDESCRIPTOR pfd;
int iFormat;

// Get the device context for the window
*hDC = GetDC(hWnd);

// Set PFD
ZeroMemory (&pfd, sizeof(pfd));
pfd.nSize = sizeof(pfd);
pfd.nVersion = 1;
pfd.dwFlags = PFD_DRAW_TO_WINDOW |
PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;
pfd.iPixelType = PFD_TYPE_RGBA;
pfd.cColorBits = 24;
pfd.cDepthBits = 16;
pfd.iLayerType = PFD_MAIN_PLANE;
iFormat = ChoosePixelFormat(*hDC, &pfd);
SetPixelFormat (*hDC, iFormat, &pfd);

// Create the RC and make it current
*hRC = wglCreateContext(*hDC);
wglMakeCurrent(*hDC, *hRC);

}

// Disable OpenGL
void DisableOpenGL(HWND hWnd, HDC hDC, HGLRC hRC)
{
wglMakeCurrent(NULL, NULL);
wglDeleteContext(hRC);
ReleaseDC(hWnd, hDC);
}

// Draw OpenGL Scene
void draw_scene()
{
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);

glPushMatrix();
glColor3f(0.2f, 1.0f, 0.2f);
glBegin(GL_LINES);
//for (int i = 0; i < 360; i++)
//{
glVertex2f(0.0f, 0.0f);
glVertex2f(cos((270 * (PI / 180)) * 0.9f), sin((270 * (PI / 180)) * 0.9f));
//}
glEnd();
glPopMatrix();

SwapBuffers(hDC);
}```

2. From what I'm taking...you're trying to draw the line to be 0.9 units long?

I think you have to move the 0.9f outside of the brackets it is in, i.e.:
Code:
`glVertex2f(cos((270 * (PI / 180)) * 0.9f), sin((270 * (PI / 180)) * 0.9f));`
becomes
Code:
`glVertex2f(cos((270 * (PI / 180))) * 0.9f, sin((270 * (PI / 180))) * 0.9f);`
Right now you're multiplying the rotation angle by 0.9, which would be throwing your degrees off....but that change will take the sin/cos of your angle, and then size it appropriately by your 0.9 value.

3. ## re:

Wow, what a way to screw up. It works perfectly, thank you.