Support absolute font sizing in the vertical rhythm module

doc-src/content/CHANGELOG.markdown

@@ -14,6 +14,11 @@ The Documentation for the [latest stable release](http://compass-style.org/docs/
 
 The Documentation for the [latest preview release](http://beta.compass-style.org/)
 
+0.11.4 (UNRELEASED)
+-------------------
+
+* Vertical rhythm now supports absolute units like pixels. Set `$relative-font-sizing` to `false` to enable.
+
 0.11.3 (06/11/2011)
 -------------------
 

frameworks/compass/stylesheets/compass/typography/_vertical_rhythm.scss

@@ -10,22 +10,43 @@ $default-rhythm-border-style: solid !default;
 // The IE font ratio is a fact of life. Deal with it.
 $ie-font-ratio: 16px / 100%;
 
+// Set to false if you want to use absolute pixes in sizing your typography.
+$relative-font-sizing: true !default;
+
+// $base-font-size but in your output unit of choice.
+// Defaults to 1em when `$relative-font-sizing`
+$font-unit: if($relative-font-sizing, 1em, $base-font-size) !default;
+
 // The basic unit of font rhythm
-$base-rhythm-unit: $base-line-height / $base-font-size * 1em;
+$base-rhythm-unit: $base-line-height / $base-font-size * $font-unit;
 
 // The leader is the amount of whitespace in a line.
 // It might be useful in your calculations
-$base-leader: ($base-line-height - $base-font-size) * 1em / $base-font-size;
+$base-leader: ($base-line-height - $base-font-size) * $font-unit / $base-font-size;
 
 // The half-leader is the amount of whitespace above and below a line.
 // It might be useful in your calculations
 $base-half-leader: $base-leader / 2;
 
+// True if a number has a relative unit
+@function relative-unit($number) {
+  @return unit($number) == "%" or unit($number) == "em" or unit($number) == "rem"
+}
+
+// True if a number has an absolute unit
+@function absolute-unit($number) {
+  @return not (relative-unit($number) or unitless($number));
+}
+
+@if $relative-font-sizing and not relative-unit($font-unit) {
+  @warn "$relative-font-sizing is true but $font-unit is set to #{$font-unit} which is not a relative unit.";
+}
+
 // Establishes a font baseline for the given font-size in pixels
 @mixin establish-baseline($font-size: $base-font-size) {
   body {
     font-size: $font-size / $ie-font-ratio;
-    @include adjust-leading-to(1, $font-size);
+    @include adjust-leading-to(1, if($relative-font-sizing, $font-size, $base-font-size));
   }
   html>body {
     font-size: $font-size;
@@ -43,20 +64,29 @@ $base-half-leader: $base-leader / 2;
 // to the smallest integer that is large enough to fit the font.
 // Use $from_size to adjust from a non-base font-size.
 @mixin adjust-font-size-to($to-size, $lines: ceil($to-size / $base-line-height), $from-size: $base-font-size) {
-  font-size: 1em * $to-size / $from-size;
-  @include adjust-leading-to($lines, $to-size);
+  @if $relative-font-sizing and $from-size != $base-font-size {
+    @warn "$relative-font-sizing is false but a relative font size was passed to adjust-font-size-to";
+  }
+  font-size: $font-unit * $to-size / $from-size;
+  @include adjust-leading-to($lines, if($relative-font-sizing, $to-size, $base-font-size));
 }
 
 @mixin adjust-leading-to($lines, $font-size: $base-font-size) {
-  line-height: 1em * $lines * $base-line-height / $font-size;
+  @if $relative-font-sizing and $font-size != $base-font-size {
+    @warn "$relative-font-sizing is false but a relative font size was passed to adjust-leading-to";
+  }
+  line-height: $font-unit * $lines * $base-line-height / $font-size;
 }
 
 // Calculate rhythm units
 @function rhythm(
   $lines: 1,
   $font-size: $base-font-size
 ) {
-  $rhythm: 1em * $lines * $base-line-height / $font-size;
+  @if $relative-font-sizing and $font-size != $base-font-size {
+    @warn "$relative-font-sizing is false but a relative font size was passed to the rhythm function";
+  }
+  $rhythm: $font-unit * $lines * $base-line-height / $font-size;
   @return $rhythm;
 }
 
@@ -97,19 +127,25 @@ $base-half-leader: $base-leader / 2;
 
 // Apply a border width to any side without destroying the vertical rhythm
 @mixin apply-side-rhythm-border($side, $width: 1px, $lines: 1, $font-size: $base-font-size, $border-style: $default-rhythm-border-style) {
+  @if $relative-font-sizing and $font-size != $base-font-size {
+    @warn "$relative-font-sizing is false but a relative font size was passed to apply-side-rhythm-border";
+  }
   border-#{$side}: {
     style: $border-style;
-    width: 1em * $width / $font-size;
+    width: $font-unit * $width / $font-size;
   };
-  padding-#{$side}: 1em / $font-size * ($lines * $base-line-height - $width);
+  padding-#{$side}: $font-unit / $font-size * ($lines * $base-line-height - $width);
 }
 
 // Aplly rhythm borders equally to all sides
 @mixin rhythm-borders($width: 1px, $lines: 1, $font-size: $base-font-size, $border-style: $default-rhythm-border-style) {
+  @if $relative-font-sizing and $font-size != $base-font-size {
+    @warn "$relative-font-sizing is false but a relative font size was passed to rhythm-borders";
+  }
   border: {
     style: $border-style;
-    width: 1em * $width / $font-size; };
-  padding: 1em / $font-size * ($lines * $base-line-height - $width);
+    width: $font-unit * $width / $font-size; };
+  padding: $font-unit / $font-size * ($lines * $base-line-height - $width);
 }
 
 // Apply a leading rhythm border