OpenGL Texture messed up - opengl

Question

Here is my code to load a texture. I have tried to load a file using this example; it is a gif file. Can I ask if gif files can be loaded, or is it only raw files can be loaded?
void setUpTextures()
{
printf("Set up Textures\n");
//This is the array that will contain the image color information.
// 3 represents red, green and blue color info.
// 512 is the height and width of texture.
unsigned char earth[512 * 512 * 3];
// This opens your image file.
FILE* f = fopen("/Users/Raaj/Desktop/earth.gif", "r");
if (f){
printf("file loaded\n");
}else{
printf("no load\n");
fclose(f);
return;
}
fread(earth, 512 * 512 * 3, 1, f);
fclose(f);
glEnable(GL_TEXTURE_2D);
//Here 1 is the texture id
//The texture id is different for each texture (duh?)
glBindTexture(GL_TEXTURE_2D, 1);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
//In this line you only supply the last argument which is your color info array,
//and the dimensions of the texture (512)
glTexImage2D(GL_TEXTURE_2D, 0, 3, 512, 512, 0, GL_RGB, GL_UNSIGNED_BYTE,earth);
glDisable(GL_TEXTURE_2D);
}
void Draw()
{
glEnable(GL_TEXTURE_2D);
// Here you specify WHICH texture you will bind to your coordinates.
glBindTexture(GL_TEXTURE_2D,1);
glColor3f(1,1,1);
double n=6;
glBegin(GL_QUADS);
glTexCoord2d(0,50); glVertex2f(n/2, n/2);
glTexCoord2d(50,0); glVertex2f(n/2, -n/2);
glTexCoord2d(50,50); glVertex2f(-n/2, -n/2);
glTexCoord2d(0,50); glVertex2f(-n/2, n/2);
glEnd();
// Do not forget this line, as then the rest of the colors in your
// Program will get messed up!!!
glDisable(GL_TEXTURE_2D);
}
And all I get is this:
Can I know why?

Answer 1

Basically, no, you can't just give arbitrary texture formats to GL - it only wants pixel data, not encoded files.
Your code, as posted, clearly declares an array for 24-bit RGB data, but then you open and attempt to read that much data from a GIF file. GIF is a compressed and palettised format, complete with header information etc., so that's never doing to work.
You need to use an image loader to decompress the file into raw pixels.
Also, your texture coordinates don't look right. There are four vertices, but only 3 distinct coordinates used, and 2 adjacent coordinates are diagonally opposite each other. Even if your texture was loaded correctly, that's unlikely to be what you want.