Re: [ZooLib-dev] Confused by color

[Andrew G. <ag...@em...>]

On 25 Sep 2001 16:55:34 -0700, Mark Wrenn wrote:
> I'm confused by Zoolib color support.  I would expect the following to fill
> the rectangle with the color red:
> 
> ZDCInk *ink = new ZDCInk( ZRGBColor( 255, 0, 0 ) );
> inDC.SetInk( *ink );
> inDC.Fill( theRect );
> 
> Instead I get a black rectangle.  I don't get it.  Tracing through the code
> hasn't helped.  Maybe this is a Mac issue?

ZRGBColor's components are 16 bit unsigned ints, although most pixmaps,
screens etc have at most a resolution of 8 bits per component -- 255
thus gets truncated to 0 (0x00FF --> 0x00), ie to black. On the other
hand, ZRGBColorSmall (better name anyone?) has 8 bit unsigned
components, and when it's converted to a ZRGBColor the 8 bits are
'smeared' across the full 16 bit range, so 0xFF --> 0xFFFF and 0x88 -->
0x8888.

Note that ZDCInk is geared towards use as a value-based type -- it's not
necessary nor generally desirable to allocate it from the heap. Under
the hood there is a reference counted representation, which will hold
either a single ZRGBColor, or a pair of colors and a bi-color pattern,
or a pixmap. It also has conversion constructors from ZRGBColorPOD (the
POD base for ZRGBColor) So to draw a red rectangle the following
suffices:

  inDC.SetInk(ZRGBColor(0xFFFF, 0, 0));
  inDC.Fill(theRect);

Or you could use the convenience static ZRGBColor::sRed thus:
  inDC.SetInk(ZRGBColor::sRed);

ZRGBColor (and ZRGBColorSmall) also support basic arithmetic -- adding
two ZRGBColors does a clamped add of each colors' components.

A+