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texture.cpp

//FILE:         texture.cpp
//AUTHOR:       Nathan Cournia <nathan@cournia.com>

#ifdef WIN32
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#endif

#include <GL/glu.h>
#include "image_loader.h"
#include "texture.h"

GLenum gl::texture::s_greyscale_format = GL_LUMINANCE;

gl::texture
gl::texture::load( const std::string& filename, bool build_mipmaps, 
        GLfloat min_filter, GLfloat max_filter )
{
        //texture handle to return
        texture tex;
        
        //load image
        image::image_t *img = image::load( filename );

        //was the image loaded successfully
        if( !img ) {
                //could not load image, set error
                tex.m_handle = 0;
                return tex;
        }

        //flip the image
        img->flip_horizontal( );

        //send the image to opengl
        tex = load( img, build_mipmaps, min_filter, max_filter );

        //delete local copy of image
        delete img;

        //return handle
        return tex;
}

gl::texture
gl::texture::load( std::istream& stream, bool build_mipmaps, 
        GLfloat min_filter, GLfloat max_filter )
{
        //texture handle to return
        texture tex;

        //load image
        image::image_t *img = image::load( stream );

        //was the image loaded successfully
        if( !img ) {
                //could not load image, set error
                tex.m_handle = 0;
                return tex;
        }

        //flip the image
        img->flip_horizontal( );
        
        //send the image to opengl
        tex = load( img, build_mipmaps, min_filter, max_filter );

        //delete local copy of image
        delete img;

        //return handle
        return tex;
}

//this is the actual workhorse function to send images to the open subsystem
gl::texture
gl::texture::load( image::image_t* img, bool build_mipmaps, 
        GLfloat min_filter, GLfloat max_filter )
{
        //texture handle to return
        texture tex;
        
        //make sure img is valid
        if( !img ) {
                //image pointer is null
                tex.m_handle = 0;
                return tex;
        }

        //determine format of image
        GLenum format;
        if( img->get_format( ) == image::image_t::RGB ) {
                format = GL_RGB;
        } else if( img->get_format( ) == image::image_t::RGBA ) {
                format = GL_RGBA;
        } else if( img->get_format( ) == image::image_t::GREYSCALE ) {
                format = s_greyscale_format;
        } else {
                //unknown format
                tex.m_handle = 0;
                return tex;
        }

        //determine how the image data is stored
        GLenum type;
        if( img->get_bpc( ) == image::image_t::BYTE ) {
                glPixelStorei( GL_UNPACK_ALIGNMENT, 1 );
                type = GL_UNSIGNED_BYTE;
        } else {
                //TODO WORD and DWORD types
                //unknown type
                tex.m_handle = 0;
                return tex;
        }

        //get a handle from opengl
        GLuint handle;
        glGenTextures( 1, &handle );
        glBindTexture( GL_TEXTURE_2D, handle );

        //should we generate mipmaps
        if( build_mipmaps ) {
                glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, min_filter );
                glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, max_filter );
                glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP );
                glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP );
                gluBuild2DMipmaps( GL_TEXTURE_2D, format, img->get_width( ), 
                        img->get_height( ), format, type, img->get_pixels( ) );
        } else {
                //don't build mipmaps
                //TODO  We need a mechanism to support npot images and 
                //      defining mipmapping levels.
                //      This shouldn't be too hard to do but probably not 
                //      worth the effort.
                glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, min_filter );
                glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, max_filter );
                glTexImage2D( GL_TEXTURE_2D, 0, format, img->get_width( ), 
                        img->get_height( ), 0, format, type, img->get_pixels( ) ); 
        }

        //set the aspect ratio
        tex.m_aspect = static_cast<real_t>( img->get_width( ) ) / 
                static_cast<real_t>( img->get_height( ) );

        //set the handle and return
        tex.m_handle = handle;
        return tex;
}

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