====== Colours in PDF ======

PDF distinguishes between filling (paint the interior of a closed path) and stroking (paint the outline of a path) when painting. Each mode has its own color and is used with the appropriate paint operators.

For example, a filled rectangle with border can be painted with one operator (**/re**) using both the filling and stroking color (which can be different).

In order to set a color, first the colorspace and then the actual color has to be set with the right parameters for that colorspace. For example setting the stroking color to red in RGB:
  /DeviceRGB CS   % set colorspace for stroking
  1 0 0 SC        % set stroking color

For the device colorspaces, there exist short cut operators doing both at once. For the above example one can write:
  1 0 0 RG        % set RGB colorspace and color for stroking

There are 11 distinct colorspaces available in PDF:

===== Device colorspaces =====

Device dependent, Not reproducable.

  * **DeviceGray** 1 components [0..1]; `0` is black, `1` is white.
  * **DeviceRGB** additive (for screens); 3 components [0..1]; `0 0 0` is black, `1 1 1` is white.
  * **DeviceCMYK** subtractive (for printing); 4 components [0..1]; `0 0 0 1` is black, `0 0 0 0` is white.

===== CIE-based colorspaces =====

Calibrated: device independent, reproducable.

  * **CalGray**
  * **CalRGB**
  * **Lab**
  * **ICCBased**

===== Special colorspaces =====

  * **Indexed**
  * **Pattern**
  * **Separation**
  * **DeviceN**

Most commonly used and easiest are the device colorspaces. Setting black is done like this in the different colorspaces:
  % DeviceGray
  0 G        % stroking
  0 g        % filling
  % DeviceRGB
  0 0 0 RG   % stroking
  0 0 0 rg   % filling
  % DeviceCMYK
  0 0 0 1 K  % stroking
  0 0 0 1 k  % filling

The renderer supports the device color spaces. If you need other color spaces, you need to work directly with the color operators.

<code smalltalk>
renderer strokeColor: <ColorValue or CMYKColor>.
renderer fillColor: <ColorValue or CMYKColor>.
</code>

The renderer will insert ''/DeviceRGB'' operators for ColorValues and ''/DeviceCMYK'' for CMYKColors. If the color is gray, ''/DevideGray'' is used.

Example:
<code smalltalk>
page := Page newInBounds: (0 @ 0 corner: 100 @ 100) colorspace: DeviceRGB new render: [:renderer |
  renderer fillColor: ColorValue red.
  renderer addRectangleLeft: 20 bottom: 20 width: 20 height: 40.
  renderer fill.
  renderer strokeColor: ColorValue blue.
  renderer linewidth: 5.
  renderer addRectangleLeft: 20 bottom: 20 width: 20 height: 40.
  renderer stroke].
</code>