#include <psemek/pcg/perlin.hpp>

#include <psemek/geom/interval.hpp>

#include <psemek/util/assert.hpp>

namespace psemek::pcg
{

	perlin::perlin(util::basic_pixmap<geom::vector<float, 2>> grad_map)
		: grad_map_(std::move(grad_map))
	{}

	static float step(float x0, float x1, float t)
	{
		return x0 * (1.f - t) + x1 * t;
	}

	static float smoothstep(float x0, float x1, float t)
	{
		float const s = t * t * (3.f - 2.f * t);
		return step(x0, x1, s);
	}

	float perlin::operator() (float x, float y) const
	{
		assert(x >= 0.f);
		assert(y >= 0.f);

		assert(x <= 1.f);
		assert(y <= 1.f);

		x *= width();
		y *= height();

		int const ix = geom::clamp<int>(std::floor(x), {0, static_cast<int>(width()) - 1});
		int const iy = geom::clamp<int>(std::floor(y), {0, static_cast<int>(height()) - 1});

		float const tx = x - ix;
		float const ty = y - iy;

		float const d00 = tx * grad_map_(ix, iy)[0] + ty * grad_map_(ix, iy)[1];
		float const d10 = (tx-1.f) * grad_map_(ix+1, iy)[0] + ty * grad_map_(ix+1, iy)[1];
		float const d01 = tx * grad_map_(ix, iy+1)[0] + (ty-1.f) * grad_map_(ix, iy+1)[1];
		float const d11 = (tx-1.f) * grad_map_(ix+1, iy+1)[0] + (ty-1.f) * grad_map_(ix+1, iy+1)[1];

		return smoothstep(smoothstep(d00, d10, tx), smoothstep(d01, d11, tx), ty);
	}

}