Units.cpp
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#include <cmath>
#include <hueplusplus/Units.h>
namespace hueplusplus
{
namespace
{
float sign(const XY& p0, const XY& p1, const XY& p2)
{
return (p0.x - p2.x) * (p1.y - p2.y) - (p1.x - p2.x) * (p0.y - p2.y);
}
bool isRightOf(const XY& xy, const XY& p1, const XY& p2)
{
return sign(xy, p1, p2) < 0;
}
XY projectOntoLine(const XY& xy, const XY& p1, const XY& p2)
{
// Using dot product to project onto line
// Vector AB = B - A
// Vector AX = X - A
// Projected length l = (AX dot AB) / len(AB)
// Result: E = A + l*AB/len(AB) = A + AB * (AX dot AB) / (len(AB))^2
const float abX = p2.x - p1.x;
const float abY = p2.y - p1.y;
const float lenABSquared = abX * abX + abY * abY;
const float dot = (xy.x - p1.x) * abX + (xy.y - p1.y) * abY;
const float eX = p1.x + abX * dot / lenABSquared;
const float eY = p1.y + abY * dot / lenABSquared;
return XY {eX, eY};
}
} // namespace
bool ColorGamut::contains(const XY& xy) const
{
return !isRightOf(xy, redCorner, greenCorner) && !isRightOf(xy, greenCorner, blueCorner)
&& !isRightOf(xy, blueCorner, redCorner);
}
XY ColorGamut::corrected(const XY& xy) const
{
// red, green and blue are in counterclockwise orientation
if (isRightOf(xy, redCorner, greenCorner))
{
// Outside of triangle, check whether to use nearest corner or point on line
if (isRightOf(xy, greenCorner, blueCorner))
{
// Point is outside of red-green line, closest to green corner
return greenCorner;
}
else if (isRightOf(xy, blueCorner, redCorner))
{
// Point is outside of red-green line, closest to red corner
return redCorner;
}
else
{
// Point is closest to line, project onto it
return projectOntoLine(xy, redCorner, greenCorner);
}
}
else if (isRightOf(xy, greenCorner, blueCorner))
{
// Green corner already checked above
if (isRightOf(xy, blueCorner, redCorner))
{
// Point is outside of green-blue line, closest to blue corner
return blueCorner;
}
else
{
return projectOntoLine(xy, greenCorner, blueCorner);
}
}
else if (isRightOf(xy, blueCorner, redCorner))
{
// All corners already checked
return projectOntoLine(xy, blueCorner, redCorner);
}
return xy;
}
XYBrightness RGB::toXY() const
{
const float red = r / 255.f;
const float green = g / 255.f;
const float blue = b / 255.f;
const float redCorrected = (red > 0.04045f) ? pow((red + 0.055f) / (1.0f + 0.055f), 2.4f) : (red / 12.92f);
const float greenCorrected = (green > 0.04045f) ? pow((green + 0.055f) / (1.0f + 0.055f), 2.4f) : (green / 12.92f);
const float blueCorrected = (blue > 0.04045f) ? pow((blue + 0.055f) / (1.0f + 0.055f), 2.4f) : (blue / 12.92f);
const float X = redCorrected * 0.664511f + greenCorrected * 0.154324f + blueCorrected * 0.162028f;
const float Y = redCorrected * 0.283881f + greenCorrected * 0.668433f + blueCorrected * 0.047685f;
const float Z = redCorrected * 0.000088f + greenCorrected * 0.072310f + blueCorrected * 0.986039f;
const float x = X / (X + Y + Z);
const float y = Y / (X + Y + Z);
return XYBrightness {XY {x, y}, Y};
}
XYBrightness RGB::toXY(const ColorGamut& gamut) const
{
XYBrightness xy = toXY();
if (!gamut.contains(xy.xy))
{
xy.xy = gamut.corrected(xy.xy);
}
return xy;
}
RGB RGB::fromXY(const XYBrightness& xy)
{
const float z = 1.f - xy.xy.x - xy.xy.y;
const float Y = xy.brightness;
const float X = (Y / xy.xy.y) * xy.xy.x;
const float Z = (Y / xy.xy.y) * z;
const float r = X * 1.656492f - Y * 0.354851f - Z * 0.255038f;
const float g = -X * 0.707196f + Y * 1.655397f + Z * 0.036152f;
const float b = X * 0.051713f - Y * 0.121364f + Z * 1.011530f;
// Reverse gamma correction
const float gammaR = r <= 0.0031308f ? 12.92f * r : (1.0f + 0.055f) * pow(r, (1.0f / 2.4f)) - 0.055f;
const float gammaG = g <= 0.0031308f ? 12.92f * g : (1.0f + 0.055f) * pow(g, (1.0f / 2.4f)) - 0.055f;
const float gammaB = b <= 0.0031308f ? 12.92f * b : (1.0f + 0.055f) * pow(b, (1.0f / 2.4f)) - 0.055f;
return RGB {static_cast<int>(std::round(gammaR * 255.f)), static_cast<int>(std::round(gammaG * 255.f)),
static_cast<int>(std::round(gammaB * 255.f))};
}
RGB RGB::fromXY(const XYBrightness& xy, const ColorGamut& gamut)
{
if (gamut.contains(xy.xy))
{
return fromXY(xy);
}
else
{
return fromXY(XYBrightness {gamut.corrected(xy.xy), xy.brightness});
}
}
} // namespace hueplusplus