gtk2/gtk/theme/Adwaita/_drawing.scss

// Drawing mixins

// generic drawing of more complex things

@function _widget_edge($c:$borders_edge) {
// outer highlight "used" on most widgets
  @if $c == none { @return none; }
  @else { @return 0 1px $c; }
}

@mixin _shadows($list...) {
//
// Helper mixin to stack up to box-shadows;
//
  $shadows: null;

  @each $shadow in $list {
    @if $shadow!=none { $shadows: $shadows, $shadow; }
  }

  box-shadow: $shadows;
}

// entries
@function entry_focus_border($fc:$selected_bg_color) {
  @if $variant == 'light' { @return $fc; }
  @else { @return if($fc==$selected_bg_color, $selected_borders_color, darken($fc, 35%)); }
}

@function entry_focus_shadow($fc:$selected_bg_color) { @return inset 0 0 0 1px $fc; }

@mixin entry($t, $fc:$selected_bg_color, $edge: none) {
//
// Entries drawing function
//
// $t: entry type
// $fc: focus color
// $edge: set to none to not draw the bottom edge or specify a color to not
//        use the default one
//
// possible $t values:
// normal, focus, insensitive, backdrop, backdrop-insensitive, osd, osd-focus, osd-backdrop, block_cursor;
//

  $_blank_edge: if($edge == none, none, 0 1px transparentize($edge, 1));
  $_entry_edge: if($edge == none, none, _widget_edge($edge));

  @if $t==normal {
    color: $text_color;
    border-color: $borders_color;
    background-color: $base_color;
    @include _shadows(entry_focus_shadow(transparentize($fc, 1)), $_entry_edge);
    // for the transition to work the number of shadows in different states needs to match, hence the transparent shadow here.
  }
  @if $t==focus {
    @include _shadows(entry_focus_shadow($fc), $_entry_edge);
    border-color: entry_focus_border($fc);
    outline: none;
  }
  @if $t==insensitive {
    color: $insensitive_fg_color;
    border-color: $borders_color;
    background-color: $insensitive_bg_color;
    box-shadow: $_entry_edge;
  }
  @if $t==backdrop {
    color: $backdrop_text_color;
    border-color: $backdrop_borders_color;
    background-color: $backdrop_base_color;
    box-shadow: $_blank_edge;
  }
  @if $t==backdrop-insensitive {
    color: $backdrop_insensitive_color;
    border-color: $backdrop_borders_color;
    background-color: $insensitive_bg_color;
    box-shadow: $_blank_edge;
  }
  @if $t==osd {
    color: $osd_text_color;
    border-color: $osd_borders_color;
    background-color: transparentize(opacify($osd_borders_color, 1), 0.5);
    background-clip: padding-box;
    box-shadow: none;
    text-shadow: 0 1px black;
    -gtk-icon-shadow: 0 1px black;
  }
  @if $t==osd-focus {
    color: $osd_text_color;
    border-color: $selected_bg_color;
    background-color: transparentize(opacify($osd_borders_color, 1), 0.5);
    background-clip: padding-box;
    box-shadow: entry_focus_shadow($fc);
    text-shadow: 0 1px black;
    -gtk-icon-shadow: 0 1px black;
  }
  @if $t==osd-insensitive {
    color: $osd_insensitive_fg_color;
    border-color: $osd_borders_color;
    background-color: $osd_insensitive_bg_color;
    background-clip: padding-box;
    box-shadow: none;
    text-shadow: none;
    -gtk-icon-shadow: none;
  }
  @if $t==osd-backdrop {
    color: $osd_text_color;
    border-color: $osd_borders_color;
    background-color: transparentize(opacify($osd_borders_color, 1), 0.5);
    background-clip: padding-box;
    box-shadow: none;
    text-shadow: none;
    -gtk-icon-shadow: none;
  }
  @if $t==block_cursor {
    color: $base_color;
    background-color: $text_color;
  }
}

// buttons

@function _border_color($c, $darker: false) {
  @if $darker == true { @return darken($c, 20%); }
  @else { @return darken($c, 10%); }
}

@function _text_shadow_color ($tc: $fg_color, $bg: $bg_color) {
//
// calculate the color of text shadows
//
// $tc is the text color
// $bg is the background color
//
  $_lbg: lightness($bg)/100%;
  @if lightness($tc)<50% { @return transparentize(white, 1-$_lbg/($_lbg*1.3)); }
  @else { @return transparentize(black, $_lbg*0.8); }
}

@function _button_hilight_color($c) {
//
// calculate the right top hilight color for buttons
//
// $c: base color;
//
  @if lightness($c)>95% { @return white; }
  @else if lightness($c)>90% { @return transparentize(white, 0.2); }
  @else if lightness($c)>80% { @return transparentize(white, 0.5); }
  @else if lightness($c)>50% { @return transparentize(white, 0.8); }
  @else if lightness($c)>40% { @return transparentize(white, 0.9); }
  @else { @return transparentize(white, 0.98); }
}

@mixin _button_text_shadow ($tc:$fg_color, $bg:$bg_color) {
//
// helper function for the text emboss effect
//
// $tc is the optional text color, not the shadow color
//
// TODO: this functions needs a way to deal with special cases
//

  $_shadow: _text_shadow_color($tc, $bg);

  @if lightness($tc)<50% {
    text-shadow: 0 1px $_shadow;
    -gtk-icon-shadow: 0 1px $_shadow;
  }
  @else {
    text-shadow: 0 -1px $_shadow;
    -gtk-icon-shadow: 0 -1px $_shadow;
  }
}

@mixin button($t, $c:$bg_color, $tc:$fg_color, $edge: none) {
//
// Button drawing function
//
// $t:    button type,
// $c:    base button color for colored* types
// $tc:   optional text color for colored* types
// $edge: set to none to not draw the bottom edge or specify a color to not
//        use the default one
//
// possible $t values:
// normal, hover, active, insensitive, insensitive-active,
// backdrop, backdrop-active, backdrop-insensitive, backdrop-insensitive-active,
// osd, osd-hover, osd-active, osd-insensitive, osd-backdrop, undecorated
//
// This mixin sets the $button_fill global variable which containts the button background-image
//
  $_hilight_color: _button_hilight_color($c);
  $_button_edge: if($edge == none, none, _widget_edge($edge));
  $_blank_edge: if($edge == none, none, _widget_edge(transparentize($edge,1)));
  $_button_shadow: 0 1px 2px transparentize($shadow_color, 0.03);

  @if $t==normal {
  //
  // normal button
  //
    color: $tc;
    outline-color: transparentize($tc, 0.7);
    border-color: if($c != $bg_color, _border_color($c), $borders_color);
    border-bottom-color: if($c != $bg_color, _border_color($c, true), $alt_borders_color);
    $button_fill: if($variant == 'light', linear-gradient(to top, darken($c, 4%) 2px, $c),
                                          linear-gradient(to top, darken($c,1%) 2px, $c)) !global;
    background-image: $button_fill;
    @include _button_text_shadow($tc, $c);
    @include _shadows(inset 0 1px $_hilight_color, $_button_edge, $_button_shadow);
  }

  @else if $t==hover {
  //
  // hovered button
  //
    color: $tc;
    outline-color: transparentize($tc, 0.7);
    border-color: if($c != $bg_color, _border_color($c), $borders_color);
    border-bottom-color: if($c != $bg_color, _border_color($c, true), $alt_borders_color);
    @if $variant == 'light' {
      $button_fill: linear-gradient(to top, $c, lighten($c, 1%) 1px) !global;
      @include _button_text_shadow($tc, lighten($c, 6%));
      @include _shadows(inset 0 1px _button_hilight_color(lighten($c, 6%)), $_button_edge, $_button_shadow);
    }
    @else {
      $button_fill: linear-gradient(to top, darken($c,1%), lighten($c, 1%) 1px) !global;
      @include _button_text_shadow($tc,lighten($c, 6%));
      @include _shadows(inset 0 1px _button_hilight_color(darken($c, 2%)), $_button_edge, $_button_shadow);
    }
    background-image: $button_fill;
  }

  @if $t==normal-alt {
  //
  // normal button alternative look
  //
    color: $tc;
    outline-color: transparentize($tc, 0.7);
    border-color: if($c != $bg_color, _border_color($c, true), $alt_borders_color);
    @include _button_text_shadow($tc, $c);
    @if $variant == 'light' {
      background-image: linear-gradient(to bottom, lighten($c, 5%) 20%, $c 90%);
      @include _shadows(inset 0 1px _button_hilight_color(lighten($c, 6%)),
                        $_button_edge, $_button_shadow);
    }
    @else {
      background-image: linear-gradient(to bottom, darken($c, 3%) 20%, darken($c, 6%) 90%);
      @include _shadows(inset 0 1px $_hilight_color,
                        $_button_edge, $_button_shadow);
    }
  }

  @else if $t==hover-alt {
  //
  // hovered button alternative look
  //
    color: $tc;
    outline-color: transparentize($tc, 0.7);
    border-color: if($c != $bg_color, _border_color($c, true), $alt_borders_color);
    @if $variant == 'light' {
      $button_fill: linear-gradient(to bottom, lighten($c, 9%) 10%, lighten($c, 4%) 90%) !global;
      @include _shadows(inset 0 1px _button_hilight_color(lighten($c, 6%)),
                        $_button_edge, $_button_shadow);
    }
    @else {
      $button_fill: linear-gradient(to bottom, $c 20%, darken($c, 4%) 90%) !global;
      @include _shadows(inset 0 1px $_hilight_color,
                        $_button_edge, $_button_shadow);
    }
    background-image: $button_fill;
  }

  @else if $t==active {
  //
  // pushed button
  //
    color: $tc;
    outline-color: transparentize($tc, 0.7);
    border-color: if($c != $bg_color, _border_color($c), $borders_color);
    $button_fill: if($variant == 'light', image(darken($c, 14%)), image(darken($c, 9%))) !global;
    background-image: $button_fill;
    @include _shadows(inset 0 1px transparentize($_hilight_color, 1), $_button_edge);

    text-shadow: none;
    -gtk-icon-shadow: none;
  }

  @else if $t==insensitive {
  //
  // insensitive button
  //
    $_bg: if($c != $bg_color, mix($c, $base_color, 85%), $insensitive_bg_color);

    label, & { color: if($tc != $fg_color, mix($tc, $_bg, 50%), $insensitive_fg_color); }

    border-color: if($c != $bg_color, _border_color($c), $insensitive_borders_color);
    $button_fill: image($_bg) !global;
    background-image: $button_fill;
    text-shadow: none;
    -gtk-icon-shadow: none;
    // white with 0 alpha to avoid an ugly transition, since no color means
    // black with 0 alpha
    @include _shadows(inset 0 1px transparentize(white, 1), $_button_edge);
  }

  @else if $t==insensitive-active {
  //
  // insensitive pushed button
  //
    $_bg: if($variant == 'light', darken(mix($c, $base_color, 85%), 8%), darken(mix($c, $base_color, 85%), 6%));
    $_bc: if($c != $bg_color, _border_color($c), $insensitive_borders_color);

    label, & { color: if($c != $bg_color, mix($tc, $_bg, 60%), $insensitive_fg_color); }

    border-color: $_bc;
    $button_fill: image($_bg) !global;
    background-image: $button_fill;
    // white with 0 alpha to avoid an ugly transition, since no color means
    // black with 0 alpha
    @include _shadows(inset 0 1px transparentize(white, 1), $_button_edge);
  }

  @else if $t==backdrop {
  //
  // backdrop button
  //
    $_bg: if($c != $bg_color, $c, $backdrop_bg_color);
    $_bc: if($variant == 'light', $c, _border_color($c));

    label, & { color: if($tc != $fg_color, mix($tc, $_bg, 80%), $backdrop_fg_color); }

    border-color: if($c != $bg_color, $_bc, $backdrop_borders_color);
    $button_fill: image($_bg) !global;
    background-image: $button_fill;
    text-shadow: none;
    -gtk-icon-shadow: none;
    @include _shadows(inset 0 1px transparentize(white, 1), $_blank_edge);
  }

  @else if $t==backdrop-active {
  //
  // backdrop pushed button
  //
    $_bg: if($variant == 'light', darken(mix($c, $base_color, 85%), 8%), darken(mix($c, $base_color, 85%), 4%));
    $_bc: if($variant == 'light', $_bg ,_border_color($c));

    label, & { color: if($tc != $fg_color, mix($tc, $_bg, 80%), $backdrop_fg_color); }

    border-color: if($c != $bg_color, $_bc, $backdrop_borders_color);
    $button_fill: image($_bg) !global;
    background-image: $button_fill;
    @include _shadows(inset 0 1px transparentize(white, 1), $_blank_edge);
  }

  @else if $t==backdrop-insensitive {
  //
  // backdrop insensitive button
  //

    $_bg: if($c != $bg_color, mix($c, $base_color, 85%), $insensitive_bg_color);
    $_bc: if($variant == 'light', $_bg,_border_color($c));

    label, & { color: if($c != $bg_color, mix($tc, $_bg, 35%), $backdrop_insensitive_color); }

    border-color: if($c != $bg_color, $_bc, $backdrop_borders_color);
    $button_fill: image($_bg) !global;
    background-image: $button_fill;
    text-shadow: none;
    -gtk-icon-shadow: none;
    // white with 0 alpha to avoid an ugly transition, since no color means
    // black with 0 alpha
    @include _shadows(inset 0 1px transparentize(white, 1), $_blank_edge);
  }

  @else if $t==backdrop-insensitive-active {
  //
  // backdrop insensitive pushed button
  //

    $_bg: if($variant == 'light', darken(mix($c, $base_color, 85%), 8%), darken(mix($c, $base_color, 85%), 4%));
    $_bc: if($variant == 'light', $_bg, _border_color($c));

    label { color: if($c != $bg_color, mix($tc, $_bg, 35%), $backdrop_insensitive_color); }

    border-color: if($c != $bg_color, $_bc, $backdrop_borders_color);
    $button_fill: image($_bg) !global;
    background-image: $button_fill;
    @include _shadows(inset 0 1px transparentize(white, 1), $_blank_edge);
  }

  @else if $t==osd {
  //
  // normal osd button
  //
    $_bg: if($c != $bg_color, transparentize($c, 0.5), $osd_bg_color);

    color: $osd_fg_color;
    border-color: $osd_borders_color;
    background-color: transparent;
    $button_fill: image($_bg) !global;
    background-image: $button_fill;
    background-clip: padding-box;
    box-shadow: inset 0 1px transparentize(white, 0.9);
    text-shadow: none;
    -gtk-icon-shadow: none;
    outline-color: transparentize($osd_fg_color, 0.7);
  }

  @else if $t==osd-hover {
  //
  // active osd button
  //
    $_bg: if($c != $bg_color, transparentize($c, 0.3), lighten($osd_bg_color, 12%));

    color: white;
    border-color: $osd_borders_color;
    background-color: transparent;
    $button_fill: image($_bg) !global;
    background-image: $button_fill;
    background-clip: padding-box;
    box-shadow: inset 0 1px transparentize(white, 0.9);
    text-shadow: none;
    -gtk-icon-shadow: none;
    outline-color: transparentize($osd_fg_color, 0.7);
  }

  @else if $t==osd-active {
  //
  // active osd button
  //
    $_bg: if($c != $bg_color, $c, $osd_borders_color);

    color: white;
    border-color: $osd_borders_color;
    background-color: transparent;
    $button_fill: image($_bg) !global;
    background-image: $button_fill;
    background-clip: padding-box;
    box-shadow: none;
    text-shadow: none;
    -gtk-icon-shadow: none;
    outline-color: transparentize($osd_fg_color, 0.7);
  }

  @else if $t==osd-insensitive {
  //
  // insensitive osd button
  //
    color: $osd_insensitive_fg_color;
    border-color: $osd_borders_color;
    background-color: transparent;
    $button_fill: image($osd_insensitive_bg_color) !global;
    background-image: $button_fill;
    background-clip: padding-box;
    box-shadow: none;
    text-shadow: none;
    -gtk-icon-shadow: none;
  }

  @else if $t==osd-backdrop {
  //
  // backdrop osd button
  //
    $_bg: if($c != $bg_color, transparentize($c, 0.5), $osd_bg_color);

    color: $osd_fg_color;
    border-color: $osd_borders_color;
    background-color: transparent;
    $button_fill: image($_bg) !global;
    background-image: $button_fill;
    background-clip: padding-box;
    box-shadow: none;
    text-shadow: none;
    -gtk-icon-shadow: none;
  }

  @else if $t==undecorated {
  //
  // reset
  //
    border-color: transparent;
    background-color: transparent;
    $button_fill: none !global;
    background-image: $button_fill;

    @include _shadows(inset 0 1px transparentize(white, 1), $_blank_edge);

    text-shadow: none;
    -gtk-icon-shadow: none;
  }
}

@mixin headerbar_fill($c:$headerbar_color, $hc:$top_hilight, $ov: none) {
//
// headerbar fill
//
// $c:  base color
// $hc: top highlight color
// $ov: a background layer for background shorthand (hence no commas!)
//
  $gradient: linear-gradient(to top, darken($c, 2%), lighten($c, 1%));

  @if $variant == 'dark' { $gradient: linear-gradient(to top, lighten($c, 4%), lighten($c, 6%)); }

  @if $ov != none { background: $c $ov, $gradient; }
  @else { background: $c $gradient; }

  box-shadow: inset 0 1px $hc; // top highlight
}

@mixin overshoot($p, $t:normal, $c:$fg_color) {
//
// overshoot
//
// $p: position
// $t: type
// $c: base color
//
// possible $p values:
// top, bottom, right, left
//
// possible $t values:
// normal, backdrop
//

  $_small_gradient_length: 3%;
  $_big_gradient_length: 50%;

  $_small_gradient_size: 100% $_small_gradient_length;
  $_big_gradient_size: 100% $_big_gradient_length;

  @if $p==right or $p==left {
    $_small_gradient_size: $_small_gradient_length 100%;
    $_big_gradient_size: $_big_gradient_length 100%;
  }

  $_small_gradient_color: $c;
  $_big_gradient_color: transparentize($c, 0.93);

  @if $c==$fg_color {
    $_small_gradient_color: darken($borders_color, 10%);
    $_big_gradient_color: transparentize($fg_color, 0.93);

    @if $t==backdrop { $_small_gradient_color: $backdrop_borders_color; }
  }

  $_small_gradient: radial-gradient(farthest-side at $p,
                                    $_small_gradient_color 85%,
                                    transparentize($_small_gradient_color, 1));

  $_big_gradient: radial-gradient(farthest-side at $p,
                                  $_big_gradient_color,
                                  transparentize($_big_gradient_color, 1));

  @if $t==normal {
    background-image: $_small_gradient, $_big_gradient;
    background-size: $_small_gradient_size, $_big_gradient_size;
  }

  @else if $t==backdrop {
    background-image: $_small_gradient;
    background-size: $_small_gradient_size;
  }

  background-repeat: no-repeat;
  background-position: $p;

  background-color: transparent; // reset some properties to be sure to not inherit them somehow
  border: none;                  //
  box-shadow: none;              //
}