skia/include/SkUnPreMultiply.h


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#ifndef SkUnPreMultiply_DEFINED
#define SkUnPreMultiply_DEFINED

#include "SkColor.h"

class SkUnPreMultiply {
public:
    typedef uint32_t Scale;
    
    // index this table with alpha [0..255]
    static const Scale* GetScaleTable() {
        return gTable;
    }

    static Scale GetScale(U8CPU alpha) {
        SkASSERT(alpha <= 255);
        return gTable[alpha];
    }
    
    /** Usage:
     
        const Scale* table = SkUnPreMultiply::GetScaleTable();
     
        for (...) {
            unsigned a = ...
            SkUnPreMultiply::Scale scale = table[a];
     
            red = SkUnPreMultiply::ApplyScale(scale, red);
            ...
            // now red is unpremultiplied
        }
    */
    static U8CPU ApplyScale(Scale scale, U8CPU component) {
        SkASSERT(component <= 255);
        return (scale * component + (1 << 23)) >> 24;
    }
    
    static SkColor PMColorToColor(SkPMColor c);
    
private:
    static const uint32_t gTable[256];
};

#endif