gradient_interpolation.hpp

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#pragma once
 
// The colour space a gradient blends its stops in — CSS Color 4's
// `<color-interpolation-method>` (`linear-gradient(in oklab, ...)`).
//
// Kept apart from canvas.hpp so the enum can travel through the view and
// importer layers without pulling the whole Canvas surface along, and so the
// reference interpolation below has one home that backends and tests share.
 
#include <cstdint>
#include <vector>
 
namespace pulp::canvas {
 
struct Color;

enum class GradientColorSpace : std::uint8_t {
    srgb,        
    srgb_linear, 
    display_p3,
    a98_rgb,
    prophoto_rgb,
    rec2020,
    lab,   
    oklab, 
    hsl,
    hwb,
    lch, 
    oklch,
};

enum class GradientHueMethod : std::uint8_t { shorter, longer, increasing, decreasing };
 
struct GradientInterpolation {
    GradientColorSpace space = GradientColorSpace::srgb;
    GradientHueMethod hue = GradientHueMethod::shorter;
 
    bool operator==(const GradientInterpolation&) const = default;
};

constexpr bool is_polar(GradientColorSpace space) {
    return space == GradientColorSpace::hsl || space == GradientColorSpace::hwb ||
           space == GradientColorSpace::lch || space == GradientColorSpace::oklch;
}

Color interpolate_gradient_color(const Color& a, const Color& b, float t,
                                 GradientInterpolation method);

void resample_gradient_stops(const Color* colors, const float* positions, int count,
                             GradientInterpolation method, int samples_per_segment,
                             std::vector<Color>& out_colors, std::vector<float>& out_positions);
 
} // namespace pulp::canvas