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# AFTERImage example 5: Gradient rendering

demonstrates rendering of multi point linear gradients

libAfterImage/tutorials/ASGrad

- NAME

  ASGrad

- 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

      #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> ...]\n");
          printf( "  Where: geometry - size of the resulting image and window;\n");
          printf( "         gradient_type - One of the fiollowing values :\n");
          printf( "            0 - linear   left-to-right gradient,\n");
          printf( "            1 - diagonal lefttop-to-rightbottom,\n");
          printf( "            2 - linear   top-to-bottom gradient,\n");
          printf( "            3 - diagonal righttop-to-leftbottom;\n");
          printf( "         offset   - floating point value from 0.0 to 1.0\n");
      }

      int main(int argc, char* argv[])
      {
          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\n",
                  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);
              }
              if( dpy )
                  XCloseDisplay (dpy);
      #else
              ASImage2file( grad_im, NULL, "asgrad.jpg", ASIT_Jpeg, NULL );
              destroy_asimage( &grad_im );
      #endif
          }
          return 0 ;
      }

libAfterImage/tutorials/ASGrad.1 [5.1]

- 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

libAfterImage/tutorials/ASGrad.2 [5.2]

- 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.

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libAfterImage version 1.18