QColor(3qt)QColor(3qt)NAMEQColor - 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)
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QColor(3qt)QColor(3qt)
QDataStream & operator<< (QDataStream & s, const QColor &
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
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represents color in a way more suited to traditional human
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 DOCUMENTATIONQColor::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
setNamedColor().
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QColor(3qt)QColor(3qt)
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().
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QColor(3qt)QColor(3qt)int QColor::currentAllocContext () [static]
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 )
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QColor::destroyAllocContext( 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:
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*h, hue.
*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.
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See also dark().
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().
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QColor(3qt)QColor(3qt)void QColor::rgb ( int * r, int * g, int * b ) const
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.
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QColor(3qt)QColor(3qt)void QColor::setRgb ( QRgb rgb )
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 DOCUMENTATIONint 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<;< (QDataStream & s, const QColor & c)
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
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QColor(3qt)QColor(3qt)int qAlpha (QRgb rgba)
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.
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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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