20. OpenGL MipMap Generation

Mipmaps are a group of the same image, scaled to different sizes which are then selected according to how far away the viewer is.
 Instead of resizing the texture to fit the object on the fly,
 opengl will pick the mipmap that best fits the shape and textures
 it with that. This fixes dodgy looking textures, and smooths
 out the overall effect. Making a better looking image.

 To do this all we need is this line in our LoadTexture function:
 gluBuild2DMipmaps( GL_TEXTURE_2D, 3, width, height, GL_RGB, GL_UNSIGNED_BYTE, data );
 Instead of the line:
 glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
 The ‘data’ being the texture, the width and height being the width and height
 of the texture file.

Then you just bind it like you would a normal texture.

But because we are now using mipmaps, we also want to change:
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
 To
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_LINEAR );

Simply so that we can get better looking textures.

 And wasn’t that simple, we now have mipmaps :-D
 If you have any questions, please email me at swiftless@gmail.com

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  #include <GL/gl.h>
#include <GL/glut.h>
#include <windows.h>
#include <stdio.h>

GLuint texture; //the array for our texture

GLfloat angle = 0.0;

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

    //The following code will read in our RAW 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 
the loaded data

    glBindTexture( GL_TEXTURE_2D, texture ); //bind the texture
 to it’s array

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

    //here we are setting what textures to use and when. The MIN 
filter is which quality to show

    //when the texture is near the view, and the MAG filter is which
 quality to show when the texture

    //is far from the view.

    //The qualities are (in order from worst to best)
    //GL_NEAREST
    //GL_LINEAR
    //GL_LINEAR_MIPMAP_NEAREST
    //GL_LINEAR_MIPMAP_LINEAR

    //And if you go and use extensions, you can use Anisotropic 
filtering textures which are of an

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

    //Here we are setting the parameter to repeat the texture 
instead of clamping 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 with mipmaps
    gluBuild2DMipmaps( GL_TEXTURE_2D, 3, width, height, 
GL_RGB, GL_UNSIGNED_BYTE, data );
    free( data ); //free the texture
    return texture; //return whether it was successfull
}

void FreeTexture( GLuint texture )
{
  glDeleteTextures( 1, &texture );
}

void square (void) {
    glBindTexture( GL_TEXTURE_2D, texture ); //bind our texture

    glPushMatrix();
    glRotatef( angle, 1.0f, 1.0f, 1.0f );
    glBegin (GL_QUADS);
    glTexCoord2d(0.0,0.0); glVertex2d(-1.0,-1.0);
    glTexCoord2d(1.0,0.0); glVertex2d(+1.0,-1.0);
    glTexCoord2d(1.0,1.0); glVertex2d(+1.0,+1.0);
    glTexCoord2d(0.0,1.0); glVertex2d(-1.0,+1.0);
    glEnd();
    glPopMatrix();
    glPushMatrix();
    glTranslatef( 0,0,-5 );
    glBegin (GL_QUADS);
    glTexCoord2d(0.0,0.0); glVertex2d(-1.0,-1.0);
    glTexCoord2d(1.0,0.0); glVertex2d(+1.0,-1.0);
    glTexCoord2d(1.0,1.0); glVertex2d(+1.0,+1.0);
    glTexCoord2d(0.0,1.0); glVertex2d(-1.0,+1.0);
    glEnd();
    glPopMatrix();
}

void display (void) {
    glClearColor (0.0,0.0,0.0,1.0);
    glClear (GL_COLOR_BUFFER_BIT);
    glLoadIdentity();  
    glEnable( GL_TEXTURE_2D ); //enable texturing
    gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    square();
    glutSwapBuffers();
    angle ++;
}
void reshape (int w, int h) {
    glViewport (0, 0, (GLsizei)w, (GLsizei)h);
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    gluPerspective (60, (GLfloat)w / (GLfloat)h, 1.0, 100.0);
    glMatrixMode (GL_MODELVIEW);
}

int main (int argc, char **argv) {
    glutInit (&argc, argv);
    glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowSize (500, 500);
    glutInitWindowPosition (100, 100);
    glutCreateWindow (“A basic OpenGL Window);
    glutDisplayFunc (display);
    glutIdleFunc (display);
    glutReshapeFunc (reshape);

    texture = LoadTexture( “texture.raw”, 256, 256 ); //load our texture

    glutMainLoop ();

    FreeTexture( texture );

    return 0;
}

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