manual/color.tex

   1 \chapter{Module color}
   2 \label{color}
   3 \section{Color models}
   4 PostScript provides different color models. They are available to
   5 \PyX{} by different color classes, which just pass the colors down to
   6 the PostScript level. This implies, that there are no conversion
   7 routines between different color models available. However, some color
   8 model conversion routines are included in Python's standard library in
   9 the module \texttt{colorsym}. Furthermore also the comparison of
  10 colors within a color model is not supported, but might be added in
  11 future versions at least for checking color identity and for ordering
  12 gray colors.
  13
  14 There is a class for each of the supported color models, namely
  15 \verb|gray|, \verb|rgb|, \verb|cmyk|, and \verb|hsb|. The constructors
  16 take variables appropriate for the color model. Additionally, a list of
  17 named colors is given in appendix~\ref{colorname}.
  18
  19 \section{Example}
  20 \begin{quote}
  21 \begin{verbatim}
  22 from pyx import *
  23
  24 c = canvas.canvas()
  25
  26 c.fill(path.rect(0, 0, 7, 3), [color.gray(0.8)])
  27 c.fill(path.rect(1, 1, 1, 1), [color.rgb.red])
  28 c.fill(path.rect(3, 1, 1, 1), [color.rgb.green])
  29 c.fill(path.rect(5, 1, 1, 1), [color.rgb.blue])
  30
  31 c.writeEPSfile("color")
  32 \end{verbatim}
  33 \end{quote}
  34
  35 The file \verb|color.eps| is created and looks like:
  36 \begin{quote}
  37 \includegraphics{color}
  38 \end{quote}
  39
  40 \section{Color palettes}
  41
  42 The color module provides a class \verb|palette| for transitions between
  43 colors. A list of named palettes is available in appendix~\ref{palettename}.
  44
  45 \begin{classdesc}{palette}{min=0, max=1}
  46   This class provides the methods for the \verb|palette|. Different
  47   initializations can be found in \verb|linearpalette| and \verb|functionpalette|.
  48
  49   \var{min} and \var{max} provide the valid range of the arguments for
  50   \verb|getcolor|.
  51
  52   \begin{funcdesc}{getcolor}{parameter}
  53     Returns the color that corresponds to \var{parameter} (must be between
  54     \var{min} and \var{max}).
  55   \end{funcdesc}
  56
  57   \begin{funcdesc}{select}{index, n\_indices}
  58     When a total number of \var{n\_indices} different colors is needed from the
  59     palette, this method returns the \var{index}-th color.
  60   \end{funcdesc}
  61
  62 \end{classdesc}
  63
  64
  65 \begin{classdesc}{linearpalette}{startcolor, endcolor, min=0, max=1}
  66   This class provides a linear transition between two given colors. The linear
  67   interpolation is performed on the color components of the specific color
  68   model.
  69
  70   \var{startcolor} and \var{endcolor} must be colors of the same color model.
  71 \end{classdesc}
  72
  73 \begin{classdesc}{functionpalette}{functions, type, min=0, max=1}
  74   This class provides an arbitray transition between colors of the same
  75   color model.
  76
  77   \var{type} is a string indicating the color model (one of \code{"cmyk"},
  78   \code{"rgb"}, \code{"hsb"}, \code{"grey"})
  79
  80   \var{functions} is a dictionary that maps the color components onto given
  81   functions. E.g. for \code{type="rgb"} this dictionary must have the keys
  82   \code{"r"}, \code{"g"}, and \code{"b"}.
  83
  84 \end{classdesc}
  85
  86