colourmat.h

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// $Id: colourmat.h 751 2006-03-31 15:43:49Z alex $
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 */

#ifndef INC_COLOURMAT
#define INC_COLOURMAT

class ColourMatrix;


class ColourVector : public SimpleCCObject
{
public:
    double elements[5];

    enum ColourVectorElement
    {
        Red     = 0,
        Green   = 1,
        Blue    = 2,
        Alpha   = 3,
        Spare   = 4
    };

    ColourVector(double r=0.0, double g=0.0, double b=0.0, double a=1.0, double s=1.0)
    {   
        elements[Red]=r;
        elements[Green]=g;
        elements[Blue]=b;
        elements[Alpha]=a;
        elements[Spare]=s;
    }

    void SetRGBA(UINT32 r, UINT32 g, UINT32 b, UINT32 a=255)
    {
        elements[Red]   = ((double)r)/255.0;
        elements[Green] = ((double)g)/255.0;
        elements[Blue]  = ((double)b)/255.0;
        elements[Alpha] = ((double)a)/255.0;
    }

    static UINT32 Get(double v)
    {
        if (v<0) return 0;
        UINT32 x = (UINT32)(v*255.0+0.5);
        return (x>255)?255:x;
    }

    UINT32 GetR() {return Get(elements[Red]);}
    UINT32 GetG() {return Get(elements[Green]);}
    UINT32 GetB() {return Get(elements[Blue]);}
    UINT32 GetA (){return Get(elements[Alpha]);}

    ColourVector Apply(ColourMatrix &cm);

    ColourVector ComposeOnTop(ColourVector &v)
    {
        // Check if either is transparent
        if (elements[Alpha]==0.0) return v;
        if (v.elements[Alpha]==0.0) return *this;

        // Generate the new alpha value
        double newalpha = v.elements[Alpha] + elements[Alpha] - v.elements[Alpha]*elements[Alpha];
        if (newalpha == 0.0) return ColourVector(elements[Red], elements[Green], elements[Blue], 0.0);

        /* Here's how this works:
            on a normal composition, of (x1,a1), x= x0 * (1-a1) + x1 * a1
            So where (x2,a2) are imposed on top, x = ( x1 * a1 + x0 * (1-a1) ) * (1-a2) + x2 * a2;
            Which can be rewritten as
                x = x0 ( 1- (a1+a2-a1a2) ) + ( a1+a2-a1a2 )/(a1+a2-a1a2)*((1-a2)(x1a1)+x2a2)
            Substituting A = (a1+a2-a2a2), X=((1-a2)(x1a1)+x2a2)/A we get
                x = x0 (1-A) + X A
            Which is the formula for transparency with alpha A, colour X
        */

        return ColourVector(
                ((1-v.elements[Alpha])*(elements[Alpha]*elements[Red]  ) + (v.elements[Red]   * v.elements[Alpha])) / newalpha,
                ((1-v.elements[Alpha])*(elements[Alpha]*elements[Green]) + (v.elements[Green] * v.elements[Alpha])) / newalpha,
                ((1-v.elements[Alpha])*(elements[Alpha]*elements[Blue] ) + (v.elements[Blue]  * v.elements[Alpha])) / newalpha,
                newalpha);
    }
};

class ColourMatrix : public SimpleCCObject
{
public:
    typedef struct {double el[5*5];} elements_t;

    elements_t elements;

    ColourMatrix()
    {
        INT32 i,j;
        for (i = 0; i<5; i++) for (j=0 ; j<5; j++) elements.el[i+j*5]=(i==j)?1.0:0.0;
    }

    static ColourMatrix Boost(double d=1.2);
    static ColourMatrix Whiten();
    static ColourMatrix Grey();
};



#endif

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