Ground.cpp

/*
 * Ground.cpp: A class for drawing the ground.
 *
 * (c) 2001-2002: Stephen Chenney, University of Wisconsin at Madison.
 */


#include "Ground.h"
#include "libtarga.h"
#include <stdio.h>
#include <GL/glu.h>

// Destructor
Ground::~Ground(void)
{
    if ( initialized )
    {
        glDeleteLists(display_list, 1);
        glDeleteTextures(1, &texture_obj);
    }
}


// Initializer. Returns false if something went wrong, like not being able to
// load the texture.
bool
Ground::Initialize(void)
{
    ubyte   *image_data;
    int     image_height, image_width;

    // Load the image for the texture. The texture file has to be in
    // a place where it will be found.
    if ( ! ( image_data = (ubyte*)tga_load("grass.tga", &image_width,
                                           &image_height, TGA_TRUECOLOR_24) ) )
    {
        fprintf(stderr, "Ground::Initialize: Couldn't load grass.tga\n");
        return false;
    }

    // This creates a texture object and binds it, so the next few operations
    // apply to this texture.
    glGenTextures(1, &texture_obj);
    glBindTexture(GL_TEXTURE_2D, texture_obj);

    // This sets a parameter for how the texture is loaded and interpreted.
    // basically, it says that the data is packed tightly in the image array.
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

    // This sets up the texture with high quality filtering. First it builds
    // mipmaps from the image data, then it sets the filtering parameters
    // and the wrapping parameters. We want the grass to be repeated over the
    // ground.
    gluBuild2DMipmaps(GL_TEXTURE_2D,3, image_width, image_height, 
                      GL_RGB, GL_UNSIGNED_BYTE, image_data);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
                    GL_NEAREST_MIPMAP_LINEAR);

    // This says what to do with the texture. Modulate will multiply the
    // texture by the underlying color.
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE); 

    // Now do the geometry. Create the display list.
    display_list = glGenLists(1);
    glNewList(display_list, GL_COMPILE);
        // Use white, because the texture supplies the color.
        glColor3f(1.0, 1.0, 1.0);

        // The surface normal is up for the ground.
        glNormal3f(0.0, 0.0, 1.0);

        // Turn on texturing and bind the grass texture.
        glEnable(GL_TEXTURE_2D);
        glBindTexture(GL_TEXTURE_2D, texture_obj);

        // Draw the ground as a quadrilateral, specifying texture coordinates.
        glBegin(GL_QUADS);
            glTexCoord2f(100.0, 100.0);
            glVertex3f(50.0, 50.0, 0.0);
            glTexCoord2f(-100.0, 100.0);
            glVertex3f(-50.0, 50.0, 0.0);
            glTexCoord2f(-100.0, -100.0);
            glVertex3f(-50.0, -50.0, 0.0);
            glTexCoord2f(100.0, -100.0);
            glVertex3f(50.0, -50.0, 0.0);
        glEnd();

        // Turn texturing off again, because we don't want everything else to
        // be textured.
        glDisable(GL_TEXTURE_2D);
    glEndList();

    // We only do all this stuff once, when the GL context is first set up.
    initialized = true;

    return true;
}


// Draw just calls the display list we set up earlier.
void
Ground::Draw(void)
{
    glPushMatrix();
    glCallList(display_list);
    glPopMatrix();
}