path: root/libs/litehtml/src/background.cpp

#include <cmath>

#include "html.h"
#include "background.h"
#include "render_item.h"

#ifndef M_PI
#       define M_PI    3.14159265358979323846
#endif

namespace litehtml
{

bool litehtml::background::get_layer(int idx, position pos, const element* el, const std::shared_ptr<render_item>& ri, background_layer& layer) const
{
	if(idx < 0 || idx >= get_layers_number())
	{
		return false;
	}

	position content_box = pos;
	position padding_box = pos;
	padding_box += ri->get_paddings();
	position border_box = padding_box;
	border_box += ri->get_borders();

	layer.border_radius	= el->css().get_borders().radius.calc_percents(border_box.width, border_box.height);
	layer.border_box = border_box;
	layer.is_root = el->is_root();

	int clip;
	css_size size;
	css_length position_x;
	css_length position_y;

	if(idx == (int) m_image.size())
	{
		if(m_image.empty())
		{
			clip = !m_clip.empty() ? m_clip.front() : background_box_border;
		} else
		{
			clip = m_clip.empty() ? background_box_border :
				   m_clip[(idx - 1) % m_clip.size()];
		}
	} else
	{
		layer.attachment = m_attachment.empty() ? background_attachment_scroll :
						   (background_attachment) m_attachment[idx % m_attachment.size()];
		layer.repeat = m_repeat.empty() ? background_repeat_repeat :
					   (background_repeat) m_repeat[idx % m_repeat.size()];
		clip = m_clip.empty() ? background_box_border :
				   m_clip[idx % m_clip.size()];
		int origin = m_origin.empty() ? background_box_padding :
					 m_origin[idx % m_origin.size()];
		const css_size auto_auto(css_length::predef_value(background_size_auto),
								 css_length::predef_value(background_size_auto));
		size = m_size.empty() ? auto_auto :
						m_size[idx % m_size.size()];
		position_x = m_position_x.empty() ? css_length(0, css_units_percentage) :
								m_position_x[idx % m_position_x.size()];
		position_y = m_position_y.empty() ? css_length(0, css_units_percentage) :
								m_position_y[idx % m_position_y.size()];

		switch(origin)
		{
			case background_box_border:
				layer.origin_box = border_box;
				break;
			case background_box_content:
				layer.origin_box = content_box;
				break;
			default:
				layer.origin_box = padding_box;
				break;
		}
	}

	switch(clip)
	{
		case background_box_padding:
			layer.clip_box = padding_box;
			break;
		case background_box_content:
			layer.clip_box = content_box;
			break;
		default:
			layer.clip_box = border_box;
			break;
	}

	litehtml::size bg_size(layer.origin_box.width, layer.origin_box.height);

	if(get_layer_type(idx) == type_image)
	{
		auto image_layer = get_image_layer(idx);
		if(image_layer)
		{
			litehtml::size img_size;
			el->get_document()->container()->get_image_size(image_layer->url.c_str(), image_layer->base_url.c_str(),
															img_size);
			if (img_size.width && img_size.height)
			{
				litehtml::size img_new_sz = img_size;
				double img_ar_width = (double) img_size.width / (double) img_size.height;
				double img_ar_height = (double) img_size.height / (double) img_size.width;

				if (size.width.is_predefined())
				{
					switch (size.width.predef())
					{
						case background_size_contain:
							if ((int) ((double) layer.origin_box.width * img_ar_height) <= layer.origin_box.height)
							{
								img_new_sz.width = layer.origin_box.width;
								img_new_sz.height = (int) ((double) layer.origin_box.width * img_ar_height);
							} else
							{
								img_new_sz.height = layer.origin_box.height;
								img_new_sz.width = (int) ((double) layer.origin_box.height * img_ar_width);
							}
							break;
						case background_size_cover:
							if ((int) ((double) layer.origin_box.width * img_ar_height) >= layer.origin_box.height)
							{
								img_new_sz.width = layer.origin_box.width;
								img_new_sz.height = (int) ((double) layer.origin_box.width * img_ar_height);
							} else
							{
								img_new_sz.height = layer.origin_box.height;
								img_new_sz.width = (int) ((double) layer.origin_box.height * img_ar_width);
							}
							break;
						case background_size_auto:
							if (!size.height.is_predefined())
							{
								img_new_sz.height = size.height.calc_percent(layer.origin_box.height);
								img_new_sz.width = (int) ((double) img_new_sz.height * img_ar_width);
							}
							break;
					}
				} else
				{
					img_new_sz.width = size.width.calc_percent(layer.origin_box.width);
					if (size.height.is_predefined())
					{
						img_new_sz.height = (int) ((double) img_new_sz.width * img_ar_height);
					} else
					{
						img_new_sz.height = size.height.calc_percent(layer.origin_box.height);
					}
				}
				bg_size = img_new_sz;
			}
		}
	} else
	{
		if(!size.width.is_predefined())
		{
			bg_size.width = size.width.calc_percent(layer.origin_box.width);
		}
		if(!size.height.is_predefined())
		{
			bg_size.height = size.height.calc_percent(layer.origin_box.height);
		}
	}

	position new_origin_box;
	new_origin_box.width = bg_size.width;
	new_origin_box.height = bg_size.height;
	new_origin_box.x = layer.origin_box.x + (int) position_x.calc_percent(layer.origin_box.width - bg_size.width);
	new_origin_box.y = layer.origin_box.y + (int) position_y.calc_percent(layer.origin_box.height - bg_size.height);
	layer.origin_box = new_origin_box;

	return true;
}

std::unique_ptr<litehtml::background_layer::image> litehtml::background::get_image_layer(int idx) const
{
	if(idx >= 0 && idx < (int) m_image.size())
	{
		if(m_image[idx].type == image::type_url)
		{
			auto ret = std::make_unique<background_layer::image>();
			ret->url = m_image[idx].url;
			ret->base_url = m_baseurl;
			return ret;
		}
	}
	return {};
}

std::unique_ptr<litehtml::background_layer::color> litehtml::background::get_color_layer(int idx) const
{
	if(idx == (int) m_image.size())
	{
		auto ret = std::make_unique<background_layer::color>();
		ret->color = m_color;
		return ret;
	}
	return {};
}

// Compute the endpoints so that a gradient of the given angle covers a box of
// the given size.
// https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/css/css_gradient_value.cc;drc=7061f1585ab97cc3358d1e0fc9e950e5a107a7f9;l=1070
static void EndPointsFromAngle(float angle_deg,
							   const litehtml::size& size,
							   litehtml::pointF& first_point,
							   litehtml::pointF& second_point)
{
	angle_deg = fmodf(angle_deg, 360);
	if (angle_deg < 0)
		angle_deg += 360;

	if (angle_deg == 0)
	{
		first_point.set(0, (float) size.height);
		second_point.set(0, 0);
		return;
	}

	if (angle_deg == 90)
	{
		first_point.set(0, 0);
		second_point.set((float) size.width, 0);
		return;
	}

	if (angle_deg == 180)
	{
		first_point.set(0, 0);
		second_point.set(0, (float) size.height);
		return;
	}

	if (angle_deg == 270)
	{
		first_point.set((float) size.width, 0);
		second_point.set(0, 0);
		return;
	}

	// angleDeg is a "bearing angle" (0deg = N, 90deg = E),
	// but tan expects 0deg = E, 90deg = N.
	auto slope = (float) tan((90.0 - angle_deg) * M_PI / 180.0);

	// We find the endpoint by computing the intersection of the line formed by
	// the slope, and a line perpendicular to it that intersects the corner.
	float perpendicular_slope = -1 / slope;

	// Compute start corner relative to center, in Cartesian space (+y = up).
	float half_height = (float) size.height / 2.0f;
	float half_width = (float) size.width / 2.0f;
	litehtml::pointF end_corner;
	if (angle_deg < 90)
		end_corner.set(half_width, half_height);
	else if (angle_deg < 180)
		end_corner.set(half_width, -half_height);
	else if (angle_deg < 270)
		end_corner.set(-half_width, -half_height);
	else
		end_corner.set(-half_width, half_height);

	// Compute c (of y = mx + c) using the corner point.
	float c = end_corner.y - perpendicular_slope * end_corner.x;
	float end_x = c / (slope - perpendicular_slope);
	float end_y = perpendicular_slope * end_x + c;

	// We computed the end point, so set the second point, taking into account the
	// moved origin and the fact that we're in drawing space (+y = down).
	second_point.set(half_width + end_x, half_height - end_y);
	// Reflect around the center for the start point.
	first_point.set(half_width - end_x, half_height + end_y);
}

static float distance(const litehtml::pointF& p1, const litehtml::pointF& p2)
{
	double dx = p2.x - p1.x;
	double dy = p2.y - p1.y;
	return (float) sqrt(dx * dx + dy * dy);
}

std::unique_ptr<litehtml::background_layer::linear_gradient> litehtml::background::get_linear_gradient_layer(int idx, const background_layer& layer) const
{
	if(idx < 0 || idx >= (int) m_image.size()) return {};
	if(m_image[idx].type != image::type_gradient) return {};
	if(m_image[idx].m_gradient.m_type != _linear_gradient_ &&
		m_image[idx].m_gradient.m_type != _repeating_linear_gradient_) return {};

	auto ret = std::make_unique<background_layer::linear_gradient>();
	float angle;
	if(m_image[idx].m_gradient.m_side == 0)
	{
		angle = m_image[idx].m_gradient.angle;
	} else
	{
		auto rise = (float) layer.origin_box.width;
		auto run = (float) layer.origin_box.height;
		if(m_image[idx].m_gradient.m_side & gradient_side_left)
		{
			run *= -1;
		}
		if(m_image[idx].m_gradient.m_side & gradient_side_bottom)
		{
			rise *= -1;
		}
		angle = (float) (90 - atan2(rise, run) * 180 / M_PI);
	}
	EndPointsFromAngle(angle, {layer.origin_box.width, layer.origin_box.height}, ret->start,
					   ret->end);
	ret->start.x += (float) layer.origin_box.x;
	ret->start.y += (float) layer.origin_box.y;
	ret->end.x += (float) layer.origin_box.x;
	ret->end.y += (float) layer.origin_box.y;

	auto line_len = distance(ret->start, ret->end);

	if(!ret->prepare_color_points(line_len, m_image[idx].m_gradient.m_type, m_image[idx].m_gradient.m_colors))
	{
		return {};
	}

	return ret;
}

static inline litehtml::pointF calc_ellipse_radius(const litehtml::pointF& offset, float aspect_ratio)
{
	// If the aspectRatio is 0 or infinite, the ellipse is completely flat.
	// (If it is NaN, the ellipse is 0x0, and should be handled as zero width.)
	if (!std::isfinite(aspect_ratio) || aspect_ratio == 0)
	{
		return {0, 0};
	}

	// x^2/a^2 + y^2/b^2 = 1
	// a/b = aspectRatio, b = a/aspectRatio
	// a = sqrt(x^2 + y^2/(1/aspect_ratio^2))
	float a = sqrtf(offset.x * offset.x +
					offset.y * offset.y *
					aspect_ratio * aspect_ratio);
	return {a, a / aspect_ratio};
}

static inline litehtml::pointF find_corner(const litehtml::pointF& center, const litehtml::position& box, bool farthest)
{
	struct descr
	{
		float distance;
		float x;
		float y;

		descr(float _distance, float _x, float _y) : distance(_distance), x(_x), y(_y) {}
	};

	litehtml::pointF ret;

	// Default is left-top corner
	ret.x = (float) box.left();
	ret.y = (float) box.top();
	auto dist = distance(center, {(float) box.left(), (float) box.top()});

	// Check right-top corner
	auto next_dist = distance(center, {(float) box.right(), (float) box.top()});
	if((farthest && next_dist > dist) || (!farthest && next_dist < dist))
	{
		ret.x = (float) box.right();
		ret.y = (float) box.top();
		dist = next_dist;
	}

	// Check right-bottom corner
	next_dist = distance(center, {(float) box.right(), (float) box.bottom()});
	if((farthest && next_dist > dist) || (!farthest && next_dist < dist))
	{
		ret.x = (float) box.right();
		ret.y = (float) box.bottom();
		dist = next_dist;
	}

	// Check left-bottom corner
	next_dist = distance(center, {(float) box.left(), (float) box.bottom()});
	if((farthest && next_dist > dist) || (!farthest && next_dist < dist))
	{
		ret.x = (float) box.left();
		ret.y = (float) box.bottom();
		dist = next_dist;
	}

	ret.x -= center.x;
	ret.y -= center.y;

	return ret;
}

std::unique_ptr<litehtml::background_layer::radial_gradient> litehtml::background::get_radial_gradient_layer(int idx, const background_layer& layer) const
{
	if(idx < 0 || idx >= (int) m_image.size()) return {};
	if(m_image[idx].type != image::type_gradient) return {};
	if(m_image[idx].m_gradient.m_type != _radial_gradient_ &&
		m_image[idx].m_gradient.m_type != _repeating_radial_gradient_) return {};

	auto ret = std::make_unique<background_layer::radial_gradient>();

	ret->position.x = (float) layer.origin_box.x + (float) layer.origin_box.width / 2.0f;
	ret->position.y = (float) layer.origin_box.y + (float) layer.origin_box.height / 2.0f;

	if(m_image[idx].m_gradient.m_side & gradient_side_left)
	{
		ret->position.x = (float) layer.origin_box.left();
	} else if(m_image[idx].m_gradient.m_side & gradient_side_right)
	{
		ret->position.x = (float) layer.origin_box.right();
	} else if(m_image[idx].m_gradient.m_side & gradient_side_x_center)
	{
		ret->position.x = (float) layer.origin_box.left() + (float) layer.origin_box.width / 2.0f;
	} else if(m_image[idx].m_gradient.m_side & gradient_side_x_length)
	{
		ret->position.x = (float) layer.origin_box.left() + (float) m_image[idx].m_gradient.position_x.calc_percent(layer.origin_box.width);
	}

	if(m_image[idx].m_gradient.m_side & gradient_side_top)
	{
		ret->position.y = (float) layer.origin_box.top();
	} else if(m_image[idx].m_gradient.m_side & gradient_side_bottom)
	{
		ret->position.y = (float) layer.origin_box.bottom();
	} else if(m_image[idx].m_gradient.m_side & gradient_side_y_center)
	{
		ret->position.y = (float) layer.origin_box.top() + (float) layer.origin_box.height / 2.0f;
	} else if(m_image[idx].m_gradient.m_side & gradient_side_y_length)
	{
		ret->position.y = (float) layer.origin_box.top() + (float) m_image[idx].m_gradient.position_y.calc_percent(layer.origin_box.height);
	}

	if(m_image[idx].m_gradient.radial_extent)
	{
		switch (m_image[idx].m_gradient.radial_extent)
		{

			case radial_extent_closest_corner:
				{
					if (m_image[idx].m_gradient.radial_shape == radial_shape_circle)
					{
						float corner1 = distance(ret->position, {(float) layer.origin_box.left(), (float) layer.origin_box.top()});
						float corner2 = distance(ret->position, {(float) layer.origin_box.right(), (float) layer.origin_box.top()});
						float corner3 = distance(ret->position, {(float) layer.origin_box.left(), (float) layer.origin_box.bottom()});
						float corner4 = distance(ret->position, {(float) layer.origin_box.right(), (float) layer.origin_box.bottom()});
						ret->radius.x = ret->radius.y = std::min({corner1, corner2, corner3, corner4});
					} else
					{
						// Aspect ratio is the same as for radial_extent_closest_side
						float aspect_ration = std::min(
								std::abs(ret->position.x - (float) layer.origin_box.left()),
								std::abs(ret->position.x - (float) layer.origin_box.right())
						) / std::min(
								std::abs(ret->position.y - (float) layer.origin_box.top()),
								std::abs(ret->position.y - (float) layer.origin_box.bottom())
						);

						auto corner = find_corner(ret->position, layer.origin_box, false);
						auto radius = calc_ellipse_radius(corner, aspect_ration);
						ret->radius.x = radius.x;
						ret->radius.y = radius.y;
					}
				}
				break;
			case radial_extent_closest_side:
				if (m_image[idx].m_gradient.radial_shape == radial_shape_circle)
				{
					ret->radius.x = ret->radius.y = std::min(
							{
								std::abs(ret->position.x - (float) layer.origin_box.left()),
								std::abs(ret->position.x - (float) layer.origin_box.right()),
								std::abs(ret->position.y - (float) layer.origin_box.top()),
								std::abs(ret->position.y - (float) layer.origin_box.bottom()),
							});
				} else
				{
					ret->radius.x = std::min(
									std::abs(ret->position.x - (float) layer.origin_box.left()),
									std::abs(ret->position.x - (float) layer.origin_box.right())
									);
					ret->radius.y = std::min(
									std::abs(ret->position.y - (float) layer.origin_box.top()),
									std::abs(ret->position.y - (float) layer.origin_box.bottom())
									);
				}
				break;
			case radial_extent_farthest_corner:
				{
					if (m_image[idx].m_gradient.radial_shape == radial_shape_circle)
					{
						float corner1 = distance(ret->position, {(float) layer.origin_box.left(), (float) layer.origin_box.top()});
						float corner2 = distance(ret->position, {(float) layer.origin_box.right(), (float) layer.origin_box.top()});
						float corner3 = distance(ret->position, {(float) layer.origin_box.left(), (float) layer.origin_box.bottom()});
						float corner4 = distance(ret->position, {(float) layer.origin_box.right(), (float) layer.origin_box.bottom()});
						ret->radius.x = ret->radius.y = std::max({corner1, corner2, corner3, corner4});
					} else
					{
						// Aspect ratio is the same as for radial_extent_farthest_side
						float aspect_ration = std::max(
								std::abs(ret->position.x - (float) layer.origin_box.left()),
								std::abs(ret->position.x - (float) layer.origin_box.right())
						) / std::max(
								std::abs(ret->position.y - (float) layer.origin_box.top()),
								std::abs(ret->position.y - (float) layer.origin_box.bottom())
						);

						auto corner = find_corner(ret->position, layer.origin_box, true);
						auto radius = calc_ellipse_radius(corner, aspect_ration);
						ret->radius.x = radius.x;
						ret->radius.y = radius.y;
					}
				}
				break;
			case radial_extent_farthest_side:
				if (m_image[idx].m_gradient.radial_shape == radial_shape_circle)
				{
					ret->radius.x = ret->radius.y = std::max(
							{
									std::abs(ret->position.x - (float) layer.origin_box.left()),
									std::abs(ret->position.x - (float) layer.origin_box.right()),
									std::abs(ret->position.y - (float) layer.origin_box.top()),
									std::abs(ret->position.y - (float) layer.origin_box.bottom()),
							});
				} else
				{
					ret->radius.x = std::max(
							std::abs(ret->position.x - (float) layer.origin_box.left()),
							std::abs(ret->position.x - (float) layer.origin_box.right())
					);
					ret->radius.y = std::max(
							std::abs(ret->position.y - (float) layer.origin_box.top()),
							std::abs(ret->position.y - (float) layer.origin_box.bottom())
					);
				}
				break;
			default:
				break;
		}
	}
	if(!m_image[idx].m_gradient.radial_radius_x.is_predefined())
	{
		ret->radius.x = (float) m_image[idx].m_gradient.radial_radius_x.calc_percent(layer.origin_box.width);
	}
	if(!m_image[idx].m_gradient.radial_radius_y.is_predefined())
	{
		ret->radius.y = (float) m_image[idx].m_gradient.radial_radius_y.calc_percent(layer.origin_box.height);
	}

	if(ret->prepare_color_points(ret->radius.x, m_image[idx].m_gradient.m_type, m_image[idx].m_gradient.m_colors))
	{
		return ret;
	}

	return {};
}

std::unique_ptr<litehtml::background_layer::conic_gradient> litehtml::background::get_conic_gradient_layer(int idx, const background_layer& layer) const
{
	if(idx < 0 || idx >= (int) m_image.size()) return {};
	if(m_image[idx].type != image::type_gradient) return {};
	if (m_image[idx].m_gradient.m_type != _conic_gradient_ &&
		m_image[idx].m_gradient.m_type != _repeating_conic_gradient_) return {};

	auto ret = std::make_unique<background_layer::conic_gradient>();

	ret->position.x = (float) layer.origin_box.x + (float) layer.origin_box.width / 2.0f;
	ret->position.y = (float) layer.origin_box.y + (float) layer.origin_box.height / 2.0f;

	if(m_image[idx].m_gradient.m_side & gradient_side_left)
	{
		ret->position.x = (float) layer.origin_box.left();
	} else if(m_image[idx].m_gradient.m_side & gradient_side_right)
	{
		ret->position.x = (float) layer.origin_box.right();
	} else if(m_image[idx].m_gradient.m_side & gradient_side_x_center)
	{
		ret->position.x = (float) layer.origin_box.left() + (float) layer.origin_box.width / 2.0f;
	} else if(m_image[idx].m_gradient.m_side & gradient_side_x_length)
	{
		ret->position.x = (float) layer.origin_box.left() + (float) m_image[idx].m_gradient.position_x.calc_percent(layer.origin_box.width);
	}

	if(m_image[idx].m_gradient.m_side & gradient_side_top)
	{
		ret->position.y = (float) layer.origin_box.top();
	} else if(m_image[idx].m_gradient.m_side & gradient_side_bottom)
	{
		ret->position.y = (float) layer.origin_box.bottom();
	} else if(m_image[idx].m_gradient.m_side & gradient_side_y_center)
	{
		ret->position.y = (float) layer.origin_box.top() + (float) layer.origin_box.height / 2.0f;
	} else if(m_image[idx].m_gradient.m_side & gradient_side_y_length)
	{
		ret->position.y = (float) layer.origin_box.top() + (float) m_image[idx].m_gradient.position_y.calc_percent(layer.origin_box.height);
	}

	ret->angle = m_image[idx].m_gradient.conic_from_angle;
	ret->color_space = m_image[idx].m_gradient.color_space;
	ret->hue_interpolation = m_image[idx].m_gradient.hue_interpolation;

	if(ret->prepare_color_points(0, m_image[idx].m_gradient.m_type, m_image[idx].m_gradient.m_colors))
	{
		return ret;
	}

	return {};
}

litehtml::background::layer_type litehtml::background::get_layer_type(int idx) const
{
	if(idx >= 0 && idx < (int) m_image.size())
	{
		switch (m_image[idx].type)
		{

			case image::type_url:
				return type_image;
			case image::type_gradient:
				switch (m_image[idx].m_gradient.m_type)
				{
					case _linear_gradient_:
					case _repeating_linear_gradient_:
						return type_linear_gradient;
					case _radial_gradient_:
					case _repeating_radial_gradient_:
						return type_radial_gradient;
					case _conic_gradient_:
					case _repeating_conic_gradient_:
						return type_conic_gradient;
					default:
						break;
				}
				break;
			default:
				break;
		}
	} else if(idx == (int) m_image.size())
	{
		return type_color;
	}
	return type_none;
}

void litehtml::background::draw_layer(uint_ptr hdc, int idx, const background_layer& layer, document_container* container) const
{
	switch (get_layer_type(idx))
	{
		case background::type_color:
			{
				auto color_layer = get_color_layer(idx);
				if(color_layer)
				{
					container->draw_solid_fill(hdc, layer, color_layer->color);
				}
			}
			break;
		case background::type_image:
			if(layer.origin_box.width != 0 && layer.origin_box.height != 0)
			{
				auto image_layer = get_image_layer(idx);
				if(image_layer)
				{
					container->draw_image(hdc, layer, image_layer->url, image_layer->base_url);
				}
			}
			break;
		case background::type_linear_gradient:
			if(layer.origin_box.width != 0 && layer.origin_box.height != 0)
			{
				auto gradient_layer = get_linear_gradient_layer(idx, layer);
				if(gradient_layer)
				{
					container->draw_linear_gradient(hdc, layer, *gradient_layer);
				}
			}
			break;
		case background::type_radial_gradient:
			if(layer.origin_box.width != 0 && layer.origin_box.height != 0)
			{
				auto gradient_layer = get_radial_gradient_layer(idx, layer);
				if(gradient_layer)
				{
					container->draw_radial_gradient(hdc, layer, *gradient_layer);
				}
			}
			break;
		case background::type_conic_gradient:
			if(layer.origin_box.width != 0 && layer.origin_box.height != 0)
			{
				auto gradient_layer = get_conic_gradient_layer(idx, layer);
				if(gradient_layer)
				{
					container->draw_conic_gradient(hdc, layer, *gradient_layer);
				}
			}
			break;
		default:
			break;
	}
}

static void repeat_color_points(std::vector<litehtml::background_layer::color_point>& color_points)
{
	auto old_points = color_points;
	if(color_points.back().offset < 1)
	{
		float gd_size = color_points.back().offset - old_points.front().offset;
		auto iter = old_points.begin();
		while (color_points.back().offset < 1)
		{
			color_points.emplace_back(iter->offset + gd_size, iter->color);
			std::advance(iter, 1);
			if (iter == old_points.end())
			{
				iter = old_points.begin();
				gd_size = color_points.back().offset - old_points.front().offset;
			}
		}
	}
	if(color_points.front().offset > 0)
	{
		float gd_size = color_points.front().offset;
		auto iter = old_points.rbegin();
		while (color_points.front().offset > 0)
		{
			color_points.emplace(color_points.begin(), gd_size - (old_points.back().offset - iter->offset), iter->color);
			std::advance(iter, 1);
			if (iter == old_points.rend())
			{
				iter = old_points.rbegin();
				gd_size = color_points.front().offset;
			}
		}
	}
}

void litehtml::background_layer::gradient_base::color_points_transparent_fix()
{
	for(int i = 0; i < (int) color_points.size(); i++)
	{
		if(color_points[i].color.alpha == 0)
		{
			if(i == 0)
			{
				if(i + 1 < (int) color_points.size())
				{
					color_points[i].color = color_points[i + 1].color;
					color_points[i].color.alpha = 0;
				}
			} else if(i + 1 == (int) color_points.size())
			{
				if(i - 1 >= 0)
				{
					color_points[i].color = color_points[i - 1].color;
					color_points[i].color.alpha = 0;
				}
			} else
			{
				color_points[i].color = color_points[i + 1].color;
				color_points[i].color.alpha = 0;
				background_layer::color_point cpt;
				cpt.color = color_points[i - 1].color;
				cpt.color.alpha = 0;
				cpt.offset = color_points[i].offset;
				color_points.emplace(std::next(color_points.begin(), i), cpt);
				i++;
			}
		}
	}
}

// normalize length into value between 0 and 1
float normalize_length(css_length length, float line_len)
{
	if (length.units() == css_units_percentage)
	{
		return length.val() / 100.0f;
	}
	else if (line_len != 0)
	{
		return length.val() / line_len;
	}
	return length.val();
}

bool litehtml::background_layer::gradient_base::prepare_color_points(float line_len, string_id g_type, const std::vector<gradient::color_stop> &colors)
{
	bool repeating;
	if(g_type == _linear_gradient_ || g_type == _radial_gradient_ || g_type == _conic_gradient_)
	{
		repeating = false;
	} else if(g_type == _repeating_linear_gradient_ || g_type == _repeating_radial_gradient_ || g_type == _repeating_conic_gradient_)
	{
		repeating = true;
	} else
	{
		return false;
	}
	int none_units = 0;
	bool has_transparent = false;
	for(const auto& item : colors)
	{
		if (item.is_color_hint)
		{
			if (!color_points.empty())
			{
				color_points.back().hint = item.length ? 
					normalize_length(*item.length, line_len) :
					*item.angle / 360;
			}
			continue;
		}
		if (item.color.alpha == 0)
		{
			has_transparent = true;
		}
		if (item.length)
		{
			color_points.emplace_back(normalize_length(*item.length, line_len), item.color);
		}
		else if (item.angle)
		{
			color_points.emplace_back(*item.angle / 360, item.color);
		}
		else
		{
			if (!color_points.empty())
			{
				none_units++;
			}
			color_points.emplace_back(0.0f, item.color);
		}
	}
	if(color_points.empty())
	{
		return false;
	}

	if(!repeating)
	{
		// Add color point with offset 0 if not exists
		if(color_points[0].offset != 0)
		{
			color_points.emplace(color_points.begin(), 0.0f, color_points[0].color);
		}
		// Add color point with offset 1.0 if not exists
		if (color_points.back().offset < 1)
		{
			if (color_points.back().offset == 0)
			{
				color_points.back().offset = 1;
				none_units--;
			} else
			{
				color_points.emplace_back(1.0f, color_points.back().color);
			}
		}
	} else
	{
		// Add color point with offset 1.0 if not exists
		if (color_points.back().offset == 0)
		{
			color_points.back().offset = 1;
			none_units--;
		}
	}

	if(none_units > 0)
	{
		size_t i = 1;
		while(i < color_points.size())
		{
			if(color_points[i].offset != 0)
			{
				i++;
				continue;
			}
			// Find next defined offset
			size_t j = i + 1;
			while (color_points[j].offset == 0) j++;
			size_t num = j - i;
			float sum = color_points[i - 1].offset + color_points[j].offset;
			float offset = sum / (float) (num + 1);
			while(i < j)
			{
				color_points[i].offset = color_points[i - 1].offset + offset;
				i++;
			}
		}
	}

	// process transparent
	if(has_transparent)
	{
		color_points_transparent_fix();
	}

	if(repeating)
	{
		repeat_color_points(color_points);
	}

	return true;
}

} // namespace litehtml