asscale.html

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## libAfterImage/tutorials/ASScale

SYNOPSIS

     Simple program based on libAfterImage to scale an image.

DESCRIPTION

     We will load image and scale it up to new size, specified as command
     line arguments
     We then display the result in simple window.
     After that we would want to wait, until user closes our window.

     In this tutorial we will only explain new steps, not described in
     previous tutorial. New steps described in this tutorial are :
     ASScale.1. Parsing geometry spec.
     ASScale.2. Scaling ASImage.

SEE ALSO

     Tutorial 1: ASView - explanation of basic steps needed to use
                          libAfterImage and some other simple things.

SOURCE

        #include <libAfterImage/afterbase.h>
        #include <libAfterImage/afterimage.h>
        #include "common.h"

        void usage()
        {
            printf( "Usage: asscale [-h]|[image [WIDTH[xHEIGHT]]]\n");
            printf( "Where: image - is image filename.\n");
            printf( "       WIDTH - width to scale image to.( Naturally :)\n");
            printf( "       HEIGHT- height to scale image to.\n");
        }

        int main(int argc, char* argv[])
        {
            char *image_file = "rose512.jpg" ;
            int dummy, geom_flags = 0;
            unsigned int to_width, to_height ;
            ASImage *im ;

            /* see ASView.1 : */
            set_application_name( argv[0] );

            if( argc > 1 )
            {
                if( strncmp( argv[1], "-h", 2 ) == 0 )
                {
                    usage();
                    return 0;
                }
                image_file = argv[1] ;
                if( argc > 2 )   /* see ASScale.1 : */
                    geom_flags = XParseGeometry( argv[2], &dummy, &dummy,
                                                 &to_width, &to_height );
            }else
            {
                show_warning( "no image file or scale geometry - defaults used: \"%s\" ",
                              image_file );
                usage();
            }
            /* see ASView.2 : */
            im = file2ASImage( image_file, 0xFFFFFFFF, SCREEN_GAMMA, 0, NULL );

            if( im != NULL )
            {
                ASVisual *asv ;
                ASImage *scaled_im ;
                /* Making sure tiling geometry is sane : */
                if( !get_flags(geom_flags, WidthValue ) )
                    to_width = im->width*2 ;
                if( !get_flags(geom_flags, HeightValue ) )
                    to_height = im->height*2;
                printf( "%s: scaling image \"%s\" to %dx%d by factor of %fx%f\n",
                        get_application_name(), image_file, to_width, to_height,
                        (double)to_width/(double)(im->width),
                        (double)to_height/(double)(im->height) );

        #ifndef X_DISPLAY_MISSING
                {
                    Window w ;
                    int screen, depth ;

                    dpy = XOpenDisplay(NULL);
                    _XA_WM_DELETE_WINDOW = XInternAtom( dpy, "WM_DELETE_WINDOW", False);
                    screen = DefaultScreen(dpy);
                    depth = DefaultDepth( dpy, screen );
                    /* see ASView.3 : */
                    asv = create_asvisual( dpy, screen, depth, NULL );
                    /* see ASView.4 : */
                    w = create_top_level_window( asv, DefaultRootWindow(dpy), 32, 32,
                                                 to_width, to_height, 1, 0, NULL,
                                                 "ASScale" );
                    if( w != None )
                    {
                        Pixmap p ;

                        XMapRaised   (dpy, w);
                        /* see ASScale.2 : */
                        scaled_im = scale_asimage( asv, im, to_width, to_height,
                                                   ASA_XImage, 0, ASIMAGE_QUALITY_DEFAULT );
                        destroy_asimage( &im );
                        /* see ASView.5 : */
                        p = asimage2pixmap( asv, DefaultRootWindow(dpy), scaled_im,
                                            NULL, True );
                        destroy_asimage( &scaled_im );
                        /* see common.c: set_window_background_and_free() : */
                        p = set_window_background_and_free( w, p );
                    }
                    /* see common.c: wait_closedown() : */
                    wait_closedown(w);
                }
        #else
                asv = create_asvisual( NULL, 0, 0, NULL );
                scaled_im = scale_asimage( asv, im, to_width, to_height,
                                           ASA_ASImage, 0, ASIMAGE_QUALITY_DEFAULT );
                /* writing result into the file */
                ASImage2file( scaled_im, NULL, "asscale.jpg", ASIT_Jpeg, NULL );
                destroy_asimage( &scaled_im );
                destroy_asimage( &im );
        #endif
            }
            return 0 ;
        }

## libAfterImage/tutorials/ASScale.1

SYNOPSIS

     Step 1. Parsing the geometry.

DESCRIPTION

     Geometry can be specified in WIDTHxHEIGHT+X+Y format. Accordingly we
     use standard X function to parse it: XParseGeometry. Returned flags
     tell us what values has been specified. Since we only need size -
     we check if it is specified and if not - simply default it to twice
     as big as original image. Accordingly we use dummy variable to pass
     to XParseGeometry.

EXAMPLE

         geom_flags = XParseGeometry( argv[3], &dummy, &dummy,
                                      &to_width, &to_height );

## libAfterImage/tutorials/ASScale.2

SYNOPSIS

     Step 2. Actual scaling the image.

DESCRIPTION

     scale_asimage() scales image both up and down, and is very easy to
     use - just pass it new size. In this example we use default quality.
     Default is equivalent to GOOD which should be sufficient in
     most cases. Compression is set to 0 since we do not intend to store
     image for long time. Even better - we don't need to store it at all -
     all we need is XImage, so we can transfer it to the server easily.
     That is why to_xim argument is set to ASA_XImage. As the result obtained
     ASImage will not have any data in its buffers, but it will have
     ximage member set to point to valid XImage. Subsequently we enjoy
     that convenience, by setting use_cached to True in call to
     asimage2pixmap. That ought to save us alot of processing.

     Scaling algorithm is rather sophisticated and is implementing 4 point
     interpolation. Which basically means that we try to approximate each
     missing point as an extension of the trend of 4 neighboring points -
     two on each side. Closest neighbor's have more weight then outside
     ones. 2D scaling is performed by scaling each scanline first, and
     then interpolating missing scanlines.
     Scaling down is somewhat skimpier, as it amounts to simple averaging
     of the multiple pixels. All calculations are done in integer math on
     per channel basis, and with precision 24.8 bits per channel per pixel.

EXAMPLE

         scaled_im = scale_asimage( asv, im, to_width, to_height,
                                      ASA_XImage, 0, ASIMAGE_QUALITY_DEFAULT );
         destroy_asimage( &im );

NOTES

     Scaling image up to very large height is much slower then to same
     width due to algorithm specifics. Yet even on inferior hardware it
     yields decent speeds.
     When we successfully scaled image - we no longer need the original -
     getting rid of it so it does not clog memory.

SEE ALSO

     scale_asimage().