asgrad(1)

NAME
asgrad - demonstrates rendering of multi point linear gradients libAfterImage/tutorials/ASGrad

NAMEASGrad

SYNOPSIS
libAfterImage application for drawing multipoint linear gradients.

DESCRIPTION
New steps described in this tutorial are :
ASGrad.1. Building gradient specs.
ASGrad.2. Actual rendering gradient.

SEE ALSO
Tutorial 1: ASView  - explanation of basic steps needed to use
                      libAfterImage and some other simple things.
Tutorial 2: ASScale - image scaling basics.
Tutorial 3: ASTile  - image tiling and tinting.
Tutorial 4: ASMerge - scaling and blending of arbitrary number of
                      images.

SOURCE
Source :
#include "../afterbase.h"
#include "../afterimage.h"
#include "common.h"
ARGB32 default_colors[] = {
    0xFF000000,
    0xFF700070,                                /* violet */
    0xFF0000FF,                                /* blue   */
    0xFF00FFFF,                                /* cyan   */
    0xFF00FF00,
    0XFFFFFF00,
    0XFF700000,
    0XFFFF0000,
    0xFF8080A0,
    0xFFE0E0FF,
    0xFFa0a0FF,
};
double default_offsets[] = { 0, 0.1, 0.15, 0.20, 0.35, 0.45, 0.55, 0.50,
                             0.65, 0.8, 1.0} ;
void usage()
{
    printf( "  Usage: asgrad -h | <geometry> <gradient_type> <color1> "
            "<offset2> <color2> [ <offset3> <color3> ...]);
    printf( "  Where: geometry - size of the resulting image and window;);
    printf( "         gradient_type - One of the fiollowing values :);
    printf( "            0 - linear   left-to-right gradient,);
    printf( "            1 - diagonal lefttop-to-rightbottom,);
    printf( "            2 - linear   top-to-bottom gradient,);
    printf( "            3 - diagonal righttop-to-leftbottom;);
    printf( "         offset   - floating point value from 0.0 to 1.0);
}
int main(int argc, char* argv[])
{
    Display *dpy = NULL;
    ASVisual *asv ;
    int screen = 0, depth = 0;
    int dummy, geom_flags = 0;
    unsigned int to_width, to_height ;
    ASGradient grad ;
    ASGradient default_grad = { 1, 11, &(default_colors[0]),
                                       &(default_offsets[0])} ;
    ASImage *grad_im = NULL;
    /* see ASView.1 : */
    set_application_name( argv[0] );
#if (HAVE_AFTERBASE_FLAG==1)
    set_output_threshold(OUTPUT_LEVEL_DEBUG);
#endif
    if( argc > 1 )
    {
        if( strcmp( argv[1], "-h") == 0 )
        {
            usage();
            return 0;
        }
        /* see ASScale.1 : */
        geom_flags = XParseGeometry( argv[1], &dummy, &dummy,
                                     &to_width, &to_height );
    }else
        usage();
    memset( &grad, 0x00, sizeof(ASGradient));
#ifndef X_DISPLAY_MISSING
    dpy = XOpenDisplay(NULL);
    _XA_WM_DELETE_WINDOW = XInternAtom( dpy, "WM_DELETE_WINDOW", False);
    screen = DefaultScreen(dpy);
    depth = DefaultDepth( dpy, screen );
#endif
    if( argc >= 5 )
    {
        int i = 2;
        /* see ASGrad.1 : */
        grad.type = atoi( argv[2] );
        grad.npoints = 0 ;
        grad.color = safemalloc( ((argc-2)/2)*sizeof(ARGB32));
        grad.offset = safemalloc( ((argc-2)/2)*sizeof(double));
        while( ++i < argc )
        {
            if( grad.npoints > 0 )
            {
                if( i == argc-1 )
                    grad.offset[grad.npoints] = 1.0;
                else
                    grad.offset[grad.npoints] = atof( argv[i] );
                ++i ;
            }
            /* see ASTile.1 : */
            if( parse_argb_color( argv[i], &(grad.color[grad.npoints]))
                != argv[i] )
                if( grad.offset[grad.npoints] >= 0. &&
                    grad.offset[grad.npoints]<= 1.0 )
                    grad.npoints++ ;
        }
    }else
    {
        grad = default_grad ;
        if( argc >= 3 )
            grad.type = atoi( argv[2] );
    }
    if( grad.npoints <= 0 )
    {
        show_error( " not enough gradient points specified.");
        return 1;
    }
    /* Making sure tiling geometry is sane : */
#ifndef X_DISPLAY_MISSING
    if( !get_flags(geom_flags, WidthValue ) )
        to_width  = DisplayWidth(dpy, screen)*2/3 ;
    if( !get_flags(geom_flags, HeightValue ) )
        to_height = DisplayHeight(dpy, screen)*2/3 ;
#else
    if( !get_flags(geom_flags, WidthValue ) )
        to_width  = 500 ;
    if( !get_flags(geom_flags, HeightValue ) )
        to_height = 500 ;
#endif
    printf( "%s: rendering gradient of type %d to %dx%d,
            get_application_name(), grad.type&GRADIENT_TYPE_MASK,
            to_width, to_height );
    /* see ASView.3 : */
    asv = create_asvisual( dpy, screen, depth, NULL );
    /* see ASGrad.2 : */
    grad_im = make_gradient( asv, &grad, to_width, to_height,
                             SCL_DO_ALL,
#ifndef X_DISPLAY_MISSING
                             ASA_XImage,
#else
                             ASA_ASImage,
#endif
                             0, ASIMAGE_QUALITY_DEFAULT );
    if( grad_im )
    {
#ifndef X_DISPLAY_MISSING
        /* see ASView.4 : */
        Window w = create_top_level_window( asv,
                                            DefaultRootWindow(dpy), 32, 32,
                                            to_width, to_height, 1, 0, NULL,
                                            "ASGradient", NULL );
        if( w != None )
        {
            Pixmap p ;
            XMapRaised   (dpy, w);
            /* see ASView.5 : */
            p = asimage2pixmap( asv, DefaultRootWindow(dpy), grad_im,
                                NULL, True );
            destroy_asimage( &grad_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);
        dpy = NULL;
#else
        ASImage2file( grad_im, NULL, "asgrad.jpg", ASIT_Jpeg, NULL );
        destroy_asimage( &grad_im );
#endif
    }
    return 0 ;
}

SYNOPSIS
Step 1. Building gradient specs.

DESCRIPTION
Multipoint gradient is defined as set of color values with offsets
of each point from the beginning of the gradient on 1.0 scale.
Offsets of the first and last point in gradient should always be
0. and 1.0 respectively, and other points should go in between.
For example 2 point gradient will have always offsets 0. and 1.0,
3 points gradient will have 0. for first color, 1.0 for last color
and anything in between for middle color.
If offset is incorrect - point will be skipped at the time of
rendering.
There are 4 types of gradients supported : horizontal, top-left to
bottom-right diagonal, vertical and top-right to bottom-left diagonal.
Any cilindrical gradient could be drawn as a 3 point gradient with
border colors being the same.
Each gradient point has ARGB color, which means that it is possible
to draw gradients in alpha channel as well as RGB. That makes for
semitransparent gradients, fading gradients, etc.

EXAMPLE
    grad.type = atoi( argv[2] );
        grad.npoints = 0 ;
        grad.color = safemalloc( ((argc-2)/2)*sizeof(ARGB32));
        grad.offset = safemalloc( ((argc-2)/2)*sizeof(double));
        while( ++i < argc )
        {
            if( grad.npoints > 0 )
            {
                if( i == argc-1 )
                    grad.offset[grad.npoints] = 1.0;
                else
                    grad.offset[grad.npoints] = atof( argv[i] );
                ++i ;
            }
        if( parse_argb_color( argv[i], &(grad.color[grad.npoints]))
             != argv[i] )
                if(grad.offset[grad.npoints] >= 0. &&
                grad.offset[grad.npoints]<= 1.0 )
                    grad.npoints++ ;
        }

SEE ALSO
ARGB32, parse_argb_color(), ASGradient

SYNOPSIS
Step 2. Actually rendering gradient.

DESCRIPTION
All that is needed to draw gradient is to call make_gradient(),
passing pointer to ASGradient structure, that describes gradient.
Naturally size of the gradient is needed too. Another parameter is
filter - that is a bit mask that allows to draw gradient using only a
subset of the channels, represented by set bits. SCL_DO_ALL means
that all 4 channels must be rendered.
make_gradient() creates ASImage of requested size and fills it with
gradient. Special techinque based on error diffusion is utilized to
avoid sharp steps between grades of colors when limited range of
colors is used for gradient.

EXAMPLE
        grad_im = make_gradient( asv, &grad, to_width, to_height,
                                 SCL_DO_ALL,
                             ASA_XImage, 0, ASIMAGE_QUALITY_DEFAULT );

NOTES
make_gradient(), ASScanline, ASImage.