QColor - Colors based on RGB

       #include <qcolor.h>

   Public Members
       enum Spec { Rgb, Hsv }
       QColor ()
       QColor ( int r, int g, int b )
       QColor ( int x, int y, int z, Spec )
       QColor ( QRgb rgb, uint pixel=0xffffffff )
       QColor ( const QString & name )
       QColor ( const char * name )
       QColor ( const QColor & )
       QColor& operator= ( const QColor & )
       bool isValid () const
       bool isDirty () const
       QString name () const
       void setNamedColor ( const QString & name )
       void rgb ( int * r, int * g, int * b ) const
       QRgb rgb () const
       void setRgb ( int r, int g, int b )
       void setRgb ( QRgb rgb )
       int red () const
       int green () const
       int blue () const
       void hsv ( int * h, int * s, int * v ) const
       void getHsv ( int & h, int & s, int & v ) const (obsolete)
       void setHsv ( int h, int s, int v )
       QColor light ( int f = 150 ) const
       QColor dark ( int f = 200 ) const
       bool operator== ( const QColor & c ) const
       bool operator!= ( const QColor & c ) const
       uint alloc ()
       uint pixel () const

   Static Public Members
       bool lazyAlloc ()
       void setLazyAlloc ( bool )
       int maxColors ()
       int numBitPlanes ()
       int enterAllocContext ()
       void leaveAllocContext ()
       int currentAllocContext ()
       void destroyAllocContext ( int )
       void initialize ()
       void cleanup ()


RELATED FUNCTION DOCUMENTATION

       (Note that these are not member functions.)
       int qBlue (QRgb rgb)
       QRgb qRgb (int r, int g, int b)
       QRgb qRgba (int r, int g, int b, int a)

           c)
       QDataStream & operator>> (QDataStream & s, QColor & c)
       int qGreen (QRgb rgb)
       int qAlpha (QRgb rgba)
       int qGray (int r, int g, int b)
       int qRed (QRgb rgb)
       int qGray (qRgb rgb)


DESCRIPTION

       The QColor class provides colors based on RGB.

       A color is normally specified in terms of RGB (red,green
       and blue) components, but it is also possible to specify
       HSV (hue,saturation and value) or set a color name (the
       names are copied from from the X11 color database).

       In addition to the RGB value, a QColor also has a pixel
       value. This value is used by the underlying window system
       to refer to a color. It can be thought of as an index into
       the display hardware's color table.

       There are 19 predefined QColor objects: black, white,
       darkGray, gray, lightGray, red, green, blue, cyan,
       magenta, yellow, darkRed, darkGreen, darkBlue, darkCyan,
       darkMagenta, darkYellow, color0 and color1.

       The colors color0 (zero pixel value) and color1 (non-zero
       pixel value) are special colors for drawing in bitmaps.

       The QColor class has an efficient, dynamic color
       allocation strategy. A color is normally allocated the
       first time it is used (lazy allocation), that is, whenever
       the pixel() function is called:

       1      Is the pixel value valid? If it is, just return it,
              otherwise, allocate a pixel value.

       2      Check an internal hash table to see if we allocated
              an equal RGB value earlier. If we did, set the
              pixel value and return.

       3      Try to allocate the RGB value. If we succeed, we
              get a pixel value which we save in the internal
              table with the RGB value. Return the pixel value.

       4      The color could not be allocated. Find the closest
              matching color and save it in the internal table.

       Since many people don't know the HSV color model very
       well, we'll cover it briefly here.

       The RGB model is hardware-oriented. Its representation is
       close to what most monitors show. In contrast, HSV

       perception of color. For example, the relationships
       "stronger than", "darker than", "the opposite of" are
       easily expressed in HSV, but are much harder to express in
       RGB.

       HSV, like RGB, has three components. They are:

       H, for hue, is either 0-360 if the color is chromatic (not
              gray), or meaningless if it is gray. It represents
              degrees on the color wheel familiar to most people.
              Red is 0 (degrees), green is 120 and blue is 240.

       S, for saturation, is 0-255 and the bigger it is, the
              stronger the color is. Grayish colors have
              saturation near 0, very strong colors have
              saturation near 255.

       V, for value, is 0-255 and represents lightness or
              brightness of the color. 0 is black, 255 is far
              from black as possible.

       Here are some examples: Pure red is H=0, S=255, V=255. A
       dark red, moving slightly towards the magenta, could be
       H=350 (equivalent to -10), S=255, V=180. A grayish light
       red could have H about 0 (say 350-359 or 0-10), S about
       50-100, and S=255.

       See also QPalette, QColorGroup,
       QApplication::setColorSpec() and Color FAQ.

       Examples: grapher/grapher.cpp drawlines/connect.cpp
       i18n/main.cpp drawdemo/drawdemo.cpp progress/progress.cpp
       desktop/desktop.cpp picture/picture.cpp


MEMBER FUNCTION DOCUMENTATION


QColor::QColor ()

       Constructs an invalid color with the RGB value (0,0,0). An
       invalid color is a color that is not properly set up for
       the underlying window system.

       See also isValid().


QColor::QColor ( QRgb rgb, uint pixel=0xffffffff )

       Constructs a color with a RGB value and a custom pixel
       value.

       If the pixel = 0xffffffff, then the color uses the RGB
       value in a standard way. If pixel is something else, then
       the pixel value will be set directly to pixel (skips the
       normal allocation procedure).


QColor::QColor ( const QString & name )

       Constructs a named color in the same way as


       See also setNamedColor().


QColor::QColor ( const QColor & c )

       Constructs a color that is a copy of c.


QColor::QColor ( const char * name )

       Constructs a named color in the same way as
       setNamedColor().

       See also setNamedColor().


QColor::QColor ( int r, int g, int b )

       Constructs a color with the RGB value (r,g,b). r, g and b
       must be in the range 0..255.

       See also setRgb().


QColor::QColor ( int x, int y, int z, Spec colorSpec )

       Constructs a color with the RGB or HSV value (x,y,z).

       The (x,y,z) triplet defines an RGB value if colorSpec ==
       QColor::Rgb. x (red), y (green) and z (blue) must be in
       the range 0..255.

       The (x,y,z) triplet defines a HSV value if colorSpec ==
       QColor::Hsv. x (hue) must be in the range -1..360 (-1
       means achromatic), and y (saturation) and z (value) must
       be in the range 0..255.

       See also setRgb() and setHsv().


uint QColor::alloc ()

       Allocates the RGB color and returns the pixel value.

       Allocating a color means to obtain a pixel value from the
       RGB specification. The pixel value is an index into the
       global color table, but should be considered an arbitrary
       platform-dependent value.

       The pixel() function calls alloc() if necessary, so in
       general you don't need to call this function.

       See also setLazyAlloc() and enterAllocContext().


int QColor::blue () const

       Returns the B (blue) component of the RGB value.


void QColor::cleanup () [static]

       Internal clean up required for QColor. This function is
       called from the QApplication destructor.

       See also initialize().

       Returns the current color allocation context.

       The default context is 0.

       See also enterAllocContext() and leaveAllocContext().


QColor QColor::dark ( int factor = 200 ) const

       Returns a darker (or lighter) color.

       Returns a darker color if factor is greater than 100.
       Setting factor to 300 returns a color that has one third
       the brightness.

       Returns a lighter color if factor is less than 100, equal
       to light(10000 / factor).

       This function converts the current RGB color to HSV,
       divides V by factor and converts back to RGB.

       See also light().

       Examples: desktop/desktop.cpp


void QColor::destroyAllocContext ( int context ) [static]

       Destroys a color allocation context, context.

       This function deallocates all colors that were allocated
       in the specified context. If context == -1, it frees up
       all colors that the application has allocated. If context
       == -2, it frees up all colors that the application has
       allocated, except those in the default context.

       The function does nothing for true color displays.

       See also enterAllocContext() and alloc().


int QColor::enterAllocContext () [static]

       Enters a color allocation context and returns a nonzero
       unique identifier.

       Color allocation contexts are useful for programs that
       need to allocate many colors and throw them away later,
       like image viewers. The allocation context functions work
       for true color displays as well as colormap display,
       except that QColor::destroyAllocContext() does nothing for
       true color.

       Example:

           QPixmap loadPixmap( QString fileName )
           {
               static int alloc_context = 0;
               if ( alloc_context )

               alloc_context = QColor::enterAllocContext();
               QPixmap pm( fileName );
               QColor::leaveAllocContext();
               return pm;
           }

       The example code loads a pixmap from file. It frees up all
       colors that were allocated the last time loadPixmap() was
       called.

       The initial/default context is 0. Qt keeps a list of
       colors associated with their allocation contexts. You can
       call destroyAllocContext() to get rid of all colors that
       were allocated in a specific context.

       Calling enterAllocContext() enters an allocation context.
       The allocation context lasts until you call
       leaveAllocContext(). QColor has an internal stack of
       allocation contexts. Each call to enterAllocContex() must
       have a corresponding leaveAllocContext().

             // context 0 active
           int c1 = QColor::enterAllocContext();       // enter context c1
             // context c1 active
           int c2 = QColor::enterAllocContext();       // enter context c2
             // context c2 active
           QColor::leaveAllocContext();                // leave context c2
             // context c1 active
           QColor::leaveAllocContext();                // leave context c1
             // context 0 active
             // Now, free all colors that were allocated in context c2
           QColor::destroyAllocContext( c2 );

       You may also want to set the application's color
       specification. See QApplication::setColorSpec() for more
       information.

       See also leaveAllocContext(), currentAllocContext(),
       destroyAllocContext() and QApplication::setColorSpec().


void QColor::getHsv ( int & h, int & s, int & v ) const

       This function is obsolete. It is provided to keep old
       source working, and will probably be removed in a future
       version of Qt. We strongly advise against using it in new
       code.


int QColor::green () const

       Returns the G (green) component of the RGB value.


void QColor::hsv ( int * h, int * s, int * v ) const

       Returns the current RGB value as HSV.

       Arguments:


       *s, saturation.

       *v, value. The hue defines the color. Its range is 0..359
              if the color is chromatic and -1 if the color is
              achromatic. The saturation and value both vary
              between 0 and 255 inclusive.

       See also setHsv() and rgb().


void QColor::initialize () [static]

       Internal initialization required for QColor. This function
       is called from the QApplication constructor.

       See also cleanup().


bool QColor::isDirty () const

       Returns TRUE if the color is dirty, i.e. lazy allocation
       is enabled and an RGB/HSV value has been set but not
       allocated.

       See also setLazyAlloc(), alloc() and pixel().


bool QColor::isValid () const

       Returns FALSE if the color is invalid, i.e. it was
       constructed using the default constructor.


bool QColor::lazyAlloc () [static]

       Returns TRUE if lazy color allocation is enabled (on-
       demand allocation), or FALSE if it is disabled (immediate
       allocation).

       See also setLazyAlloc().


void QColor::leaveAllocContext () [static]

       Leaves a color allocation context.

       See enterAllocContext() for a detailed explanation.

       See also enterAllocContext() and currentAllocContext().


QColor QColor::light ( int factor = 150 ) const

       Returns a lighter (or darker) color.

       Returns a lighter color if factor is greater than 100.
       Setting factor to 150 returns a color that is 50%
       brighter.

       Returns a darker color if factor is less than 100, equal
       to dark(10000 / factor).

       This function converts the current RGB color to HSV,
       multiplies V with factor and converts back to RGB.


       Examples: desktop/desktop.cpp


int QColor::maxColors () [static]

       Returns the maximum number of colors supported by the
       underlying window system.


QString QColor::name () const

       Returns the name of the color in the format #RRGGBB.

       See also setNamedColor().


int QColor::numBitPlanes () [static]

       Returns the number of color bit planes for the underlying
       window system.

       The returned values is equal to the default pixmap depth;

       See also QPixmap::defaultDepth().


bool QColor::operator!= ( const QColor & c ) const

       Returns TRUE if this color has different RGB value from c,
       or FALSE if they have equal RGB values.


QColor & QColor::operator= ( const QColor & c )

       Assigns a copy of the color and returns a reference to
       this color.


bool QColor::operator== ( const QColor & c ) const

       Returns TRUE if this color has the same RGB value as c, or
       FALSE if they have different RGB values.


uint QColor::pixel () const

       Returns the pixel value.

       This value is used by the underlying window system to
       refer to a color. It can be thought of as an index into
       the display hardware's color table, but the value is an
       arbitrary 32-bit value.

       See also setLazyAlloc() and alloc().


int QColor::red () const

       Returns the R (red) component of the RGB value.


QRgb QColor::rgb () const

       Returns the RGB value.

       The return type QRgb is equivalent to unsigned int.

       See also setRgb(), hsv(), qRed(), qBlue() and qGreen().

       Returns the red, green and blue components of the RGB
       value in *r, *g and *b. The value range for a component is
       0..255.

       See also setRgb() and hsv().


void QColor::setHsv ( int h, int s, int v )

       Sets a HSV color value.

       Arguments:

       h, hue (-1,0..360). -1 means achromatic.

       s, saturation (0..255).

       v, value (0..255).

       See also hsv() and setRgb().

       Examples: grapher/grapher.cpp drawdemo/drawdemo.cpp
       progress/progress.cpp


void QColor::setLazyAlloc ( bool enable ) [static]

       Enables or disables lazy color allocation.

       If lazy allocation is enabled, colors are allocated the
       first time they are used (upon calling the pixel()
       function). If lazy allocation is disabled, colors are
       allocated when they are constructed or when either
       setRgb() or setHsv() is called.

       Lazy color allocation is enabled by default.

       See also lazyAlloc(), pixel() and alloc().


void QColor::setNamedColor ( const QString & name )

       Sets the RGB value to that of the named color.

       The color name may be in one of five formats:

       #RGB (each of R, G and B is a single hex digit)

       #RRGGBB

       #RRRGGGBBB

       #RRRRGGGGBBBB

       A named from the X color database (rgb.txt), e.g."
              steelblue" or "gainsboro". These color names also
              work under Qt for Windows.

       Sets the RGB value to rgb.

       The type QRgb is equivalent to unsigned int.

       See also rgb() and setHsv().


void QColor::setRgb ( int r, int g, int b )

       Sets the RGB value to (r,g,b). r, g and b must be in the
       range 0..255.

       See also rgb() and setHsv().


RELATED FUNCTION DOCUMENTATION


int qBlue (QRgb rgb)

       Returns the blue component of the RGB triplet rgb.

       See also qRgb() and QColor::blue().

       Examples: qmag/qmag.cpp


QRgb qRgb (int r, int g, int b)

       Returns the RGB triplet (r,g,b).

       The return type QRgb is equivalent to unsigned int.

       See also qRgba(), qRed(), qGreen() and qBlue().

       Examples: desktop/desktop.cpp


QRgb qRgba (int r, int g, int b, int a)

       Returns the RGBA quadruplet (r,g,b,a).

       The return type QRgb is equivalent to unsigned int.

       See also qRgb(), qRed(), qGreen() and qBlue().


QDataStream & operator
       Writes a color object to the stream.

       See also Format of the QDataStream operators


QDataStream & operator>> (QDataStream & s, QColor & c)

       Reads a color object from the stream.

       See also Format of the QDataStream operators


int qGreen (QRgb rgb)

       Returns the green component of the RGB triplet rgb.

       See also qRgb() and QColor::green().

       Examples: qmag/qmag.cpp

       Returns the alpha component of the RGBA quadruplet rgb.


int qGray (int r, int g, int b)

       Returns a gray value 0..255 from the (r,g,b) triplet.

       The gray value is calculated using the formula: (r*11 +
       g*16 + b*5)/32


int qRed (QRgb rgb)

       Returns the red component of the RGB triplet rgb.

       See also qRgb() and QColor::red().

       Examples: qmag/qmag.cpp


int qGray (qRgb rgb)

       This is an overloaded member function, provided for
       convenience.  It differs from the above function only in
       what argument(s) it accepts.


SEE ALSO

       http://doc.trolltech.com/qcolor.html
       http://www.trolltech.com/faq/tech.html


COPYRIGHT

       Copyright 1992-2001 Trolltech AS,
       http://www.trolltech.com.  See the license file included
       in the distribution for a complete license statement.


AUTHOR

       Generated automatically from the source code.


BUGS

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       http://doc.trolltech.com/bughowto.html.  Good bug reports
       make our job much simpler. Thank you.

       In case of content or formattting problems with this
       manual page, please report them to qt-bugs@trolltech.com.
       Please include the name of the manual page (qcolor.3qt)
       and the Qt version (2.3.1).


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