OpenGL texture mapping blank screen

Question

So I've been running through a tutorial on texture mapping in OpenGL and I'm using the function from the tutorial to attempt to map a texture in my own program.

I think I must be missing some necessary calls to something or going horribly wrong somewhere, but at the moment, I'm managing to achieve the black screen effect as per usual.

I've ran through this code and to my knowledge I see no reason why i should be getting a blank screen and was hoping anybody around here could spot where I'm going wrong

I'm using SDL just to clarify which I think might have some relevance to the problem maybe:

#include <iostream>
#include <SDL/SDL.h>
#include <SDL/SDL_opengl.h>
#include <GL/glu.h>

void Draw()

{

glTranslatef(320,240,0);
glBegin(GL_QUADS);
glColor3f(1,0,0);

    glTexCoord2f(0,0); glVertex2f(0,0);
    glTexCoord2f(100,0); glVertex2f(100,0);
    glTexCoord2f(100,100); glVertex2f(100,100);
    glTexCoord2f(0,100); glVertex2f(0,100);

glEnd();

glLoadIdentity();

}

void Init(void)

{

SDL_Init(SDL_INIT_EVERYTHING);
SDL_SetVideoMode(640,480,32,SDL_OPENGL);
SDL_WM_SetCaption("Texture Test", NULL);

}

void Set_States(void)

{

glClearColor(0,0,0,0);
glViewport(0, 0, 640, 480);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, 640, 0, 480, -1, 1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

}

GLuint LoadTextureRAW( const char * filename, int wrap )

{
GLuint texture;
int width, height;
BYTE * data;
FILE * file;

// open texture data
file = fopen( filename, "rb" );
if ( file == NULL ) return 0;

// allocate buffer
width = 256;
height = 256;
data = (BYTE*)malloc( width * height * 3 );

// read texture data
fread( data, width * height * 3, 1, file );
fclose( file );

// allocate a texture name
glGenTextures( 1, &texture );

// select our current texture
glBindTexture( GL_TEXTURE_2D, texture );

// select modulate to mix texture with color for shading
glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE );

// when texture area is small, bilinear filter the closest mipmap
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
                 GL_LINEAR_MIPMAP_NEAREST );
// when texture area is large, bilinear filter the first mipmap
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );

// if wrap is true, the texture wraps over at the edges (repeat)
//       ... false, the texture ends at the edges (clamp)
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,
                 wrap ? GL_REPEAT : GL_CLAMP );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,
                 wrap ? GL_REPEAT : GL_CLAMP );

// build our texture mipmaps
gluBuild2DMipmaps( GL_TEXTURE_2D, 3, width, height,
                   GL_RGB, GL_UNSIGNED_BYTE, data );

// free buffer
free( data );

return texture;

}

int main (int argc, char ** argv)

{

GLuint texture;
SDL_Event event;
Init();
Set_States();
bool running = true;
glEnable( GL_TEXTURE_2D );
texture = LoadTextureRAW("texture.raw", 1);
glBindTexture( GL_TEXTURE_2D, texture );

while (running == true)

{

    while (SDL_PollEvent(&event))

    {

        switch (event.type)

        {

            case SDL_QUIT: running = false; break;

        }

        glClear(GL_COLOR_BUFFER_BIT);
        Draw();
        SDL_GL_SwapBuffers();

    }

}

SDL_Quit();
glDeleteTextures( 1, &texture );
return 0;

}

Answer 1

Give this a shot (texturing removed for brevity and lack of referenced file):

#include <SDL/SDL.h>
#include <SDL/SDL_opengl.h>

void Draw()
{
    glClear(GL_COLOR_BUFFER_BIT);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0, 640, 0, 480, -1, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glPushMatrix();
    glTranslatef(320,240,0);
    glScalef( 100, 100, 0 );
    glBegin(GL_QUADS);
    glColor3f(1,0,0);
    glTexCoord2f(0,0); glVertex2f(0,0);
    glTexCoord2f(1,0); glVertex2f(1,0);
    glTexCoord2f(1,1); glVertex2f(1,1);
    glTexCoord2f(0,1); glVertex2f(0,1);
    glEnd();
    glPopMatrix();
}

int main (int argc, char ** argv)
{
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_SetVideoMode(640,480,32,SDL_OPENGL);
    SDL_WM_SetCaption("Texture Test", NULL);

    glClearColor(0,0,0,0);
    glViewport(0, 0, 640, 480);

    bool running = true;
    while (running == true)
    {
        SDL_Event event;
        while (SDL_PollEvent(&event))
        {
            switch (event.type)
            {
                case SDL_QUIT: running = false; break;
            }
        }

        Draw();
        SDL_GL_SwapBuffers();
    }

    SDL_Quit();
    return 0;
}

Answer 2

Well one problem is that you're not resetting your model-view matrix each time, so your quad gets quickly translated out of view (assuming it was in view to start with, which I haven't checked).