Question

I cannot find any decent tutorials on how to load a PNG file and use it as a texture to bind it to a sphere. Are there any library functions to do this?
How would i go about binding it to a sphere?
I’ve had a go with this and it hasnt worked, there are no errors but the texture is not loaded onto the sphere.
I call the LoadTexture with the particular file, before glutMainLoop()

Here is my code for the loading of a file:

GLuint LoadTexture( const char * filename, int width, int height )
    {
GLuint texture;
unsigned char * data;
FILE * file;

//The following code will read in our PNG file
file = fopen( filename, "rb" );
if ( file == NULL ) return 0;
data = (unsigned char *)malloc( width * height * 3 );
fread( data, width * height * 3, 1, file );
fclose( file );

glGenTextures( 1, &texture ); //generate the texture with 

glBindTexture( GL_TEXTURE_2D, texture ); //bind the texture

glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, 
GL_MODULATE ); //set texture environment parameters



//even better quality, but this will do for now.
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
 GL_LINEAR );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,
 GL_LINEAR );

//Here we are setting the parameter to repeat the texture 
//to the edge of our shape. 
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, 
 GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, 
 GL_REPEAT );

//Generate the texture
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0,
 GL_RGB, GL_UNSIGNED_BYTE, data);
free( data ); //free the texture
return texture; //return whether it was successfull

}

and here is where i create the sphere

void renderScene(void) {

// Clear Color and Depth Buffers
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

 glEnable( GL_TEXTURE_2D );
// Reset transformations
glLoadIdentity();
glBindTexture( GL_TEXTURE_2D, texture );
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

glPushMatrix();
glTranslatef(0.0,2.0,-6);
glRotatef(angle, 0.0f, 2.0, -6.0f);
glutSolidSphere(1,50,50);
glPopMatrix();


angle+=0.4f;
glDisable(GL_TEXTURE_2D);
glutSwapBuffers();
 }

Have i done any of it right?

Answer 1

PNGs are compressed files, you can’t just read them in and expect OpenGL to know how to decode them. The recommended way to load a PNG is with libpng.

Here’s an example of using libpng which demonstrates synchronously reading in a PNG file into a 2D array. OpenGL expects a flat 1D array, so you’ll need to flatten it yourself, but that’s pretty straightforward.