gecko/gfx/public/nsColor.h

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#ifndef nsColor_h___
#define nsColor_h___

#include "gfxCore.h"
#include "nscore.h"

class nsAString;
class nsString;
class nsCString;

// A color is a 32 bit unsigned integer with four components: R, G, B
// and A.
typedef PRUint32 nscolor;

// Make a color out of r,g,b values. This assumes that the r,g,b values are
// properly constrained to 0-255. This also assumes that a is 255.
#define NS_RGB(_r,_g,_b) \
  ((nscolor) ((255 << 24) | ((_b)<<16) | ((_g)<<8) | (_r)))

// Make a color out of r,g,b,a values. This assumes that the r,g,b,a
// values are properly constrained to 0-255.
#define NS_RGBA(_r,_g,_b,_a) \
  ((nscolor) (((_a) << 24) | ((_b)<<16) | ((_g)<<8) | (_r)))

// Extract color components from nscolor
#define NS_GET_R(_rgba) ((PRUint8) ((_rgba) & 0xff))
#define NS_GET_G(_rgba) ((PRUint8) (((_rgba) >> 8) & 0xff))
#define NS_GET_B(_rgba) ((PRUint8) (((_rgba) >> 16) & 0xff))
#define NS_GET_A(_rgba) ((PRUint8) (((_rgba) >> 24) & 0xff))

// Fast approximate division by 255. It has the property that
// for all 0 <= n <= 255*255, FAST_DIVIDE_BY_255(n) == n/255.
// But it only uses two adds and two shifts instead of an 
// integer division (which is expensive on many processors).
//
// equivalent to target=v/255
#define FAST_DIVIDE_BY_255(target,v)               \
  PR_BEGIN_MACRO                                   \
    unsigned tmp_ = v;                             \
    target = ((tmp_ << 8) + tmp_ + 255) >> 16;     \
  PR_END_MACRO

// Blending macro
//
// equivalent to target=(bg*(255-alpha)+fg*alpha)/255
#define MOZ_BLEND(target, bg, fg, alpha) \
        FAST_DIVIDE_BY_255(target, (bg)*(255-(alpha)) + (fg)*(alpha))

// Translate a hex string to a color. Return true if it parses ok,
// otherwise return false.
// This accepts only 3 or 6 digits
NS_GFX_(PRBool) NS_HexToRGB(const nsString& aBuf, nscolor* aResult);

// Compose one NS_RGB color onto another. The result is what you get
// if you draw aBG onto RGBA(0,0,0,0) and then aFG on top of that,
// with operator OVER.
NS_GFX_(nscolor) NS_ComposeColors(nscolor aBG, nscolor aFG);

// Translate a hex string to a color. Return true if it parses ok,
// otherwise return false.
// This version accepts 1 to 9 digits (missing digits are 0)
NS_GFX_(PRBool) NS_LooseHexToRGB(const nsString& aBuf, nscolor* aResult);

// Translate a color to a hex string and prepend a '#'.
// The returned string is always 7 characters including a '#' character.
NS_GFX_(void) NS_RGBToHex(nscolor aColor, nsAString& aResult);

// Translate a color name to a color. Return true if it parses ok,
// otherwise return false.
NS_GFX_(PRBool) NS_ColorNameToRGB(const nsAString& aBuf, nscolor* aResult);

// function to convert from HSL color space to RGB color space
// the float parameters are all expected to be in the range 0-1
NS_GFX_(nscolor) NS_HSL2RGB(float h, float s, float l);

#endif /* nsColor_h___ */