/*
 * This source file is part of RmlUi, the HTML/CSS Interface Middleware
 *
 * For the latest information, see http://github.com/mikke89/RmlUi
 *
 * Copyright (c) 2008-2010 CodePoint Ltd, Shift Technology Ltd
 * Copyright (c) 2019-2023 The RmlUi Team, and contributors
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 */

#include "GeometryBoxShadow.h"
#include "../../Include/RmlUi/Core/Box.h"
#include "../../Include/RmlUi/Core/CompiledFilterShader.h"
#include "../../Include/RmlUi/Core/DecorationTypes.h"
#include "../../Include/RmlUi/Core/Element.h"
#include "../../Include/RmlUi/Core/Geometry.h"
#include "../../Include/RmlUi/Core/Math.h"
#include "../../Include/RmlUi/Core/MeshUtilities.h"
#include "../../Include/RmlUi/Core/RenderManager.h"

namespace Rml {

void GeometryBoxShadow::Generate(Geometry& out_shadow_geometry, CallbackTexture& out_shadow_texture, RenderManager& render_manager, Element* element,
	Geometry& background_border_geometry, BoxShadowList shadow_list, const Vector4f border_radius, const float opacity)
{
	// Find the box-shadow texture dimension and offset required to cover all box-shadows and element boxes combined.
	Vector2f element_offset_in_texture;
	Vector2i texture_dimensions;

	// Resolve all lengths to px units.
	for (BoxShadow& shadow : shadow_list)
	{
		shadow.blur_radius = NumericValue(element->ResolveLength(shadow.blur_radius), Unit::PX);
		shadow.spread_distance = NumericValue(element->ResolveLength(shadow.spread_distance), Unit::PX);
		shadow.offset_x = NumericValue(element->ResolveLength(shadow.offset_x), Unit::PX);
		shadow.offset_y = NumericValue(element->ResolveLength(shadow.offset_y), Unit::PX);
	}

	{
		Vector2f extend_min;
		Vector2f extend_max;

		// Extend the render-texture to encompass box-shadow blur and spread.
		for (const BoxShadow& shadow : shadow_list)
		{
			if (!shadow.inset)
			{
				const float extend = 1.5f * shadow.blur_radius.number + shadow.spread_distance.number;
				const Vector2f offset = {shadow.offset_x.number, shadow.offset_y.number};
				extend_min = Math::Min(extend_min, offset - Vector2f(extend));
				extend_max = Math::Max(extend_max, offset + Vector2f(extend));
			}
		}

		Rectanglef texture_region;

		// Extend the render-texture further to cover all the element's boxes.
		for (int i = 0; i < element->GetNumBoxes(); i++)
		{
			Vector2f offset;
			const Box& box = element->GetBox(i, offset);
			texture_region = texture_region.Join(Rectanglef::FromPositionSize(offset, box.GetSize(BoxArea::Border)));
		}

		texture_region = texture_region.Extend(-extend_min, extend_max);
		Math::ExpandToPixelGrid(texture_region);

		element_offset_in_texture = -texture_region.TopLeft();
		texture_dimensions = Vector2i(texture_region.Size());
	}

	// Callback for generating the box-shadow texture. Using a callback ensures that the texture can be regenerated at any time, for example if the
	// device loses its GPU context and the client calls Rml::ReleaseTextures().
	auto texture_callback = [&background_border_geometry, element, border_radius, texture_dimensions, element_offset_in_texture,
								shadow_list = std::move(shadow_list)](const CallbackTextureInterface& texture_interface) -> bool {
		RenderManager& render_manager = texture_interface.GetRenderManager();

		Mesh mesh_padding;        // Render geometry for inner box-shadow.
		Mesh mesh_padding_border; // Clipping mask for outer box-shadow.

		bool has_inner_shadow = false;
		bool has_outer_shadow = false;
		for (const BoxShadow& shadow : shadow_list)
		{
			if (shadow.inset)
				has_inner_shadow = true;
			else
				has_outer_shadow = true;
		}

		// Generate the geometry for all the element's boxes and extend the render-texture further to cover all of them.
		for (int i = 0; i < element->GetNumBoxes(); i++)
		{
			Vector2f offset;
			const Box& box = element->GetBox(i, offset);
			ColourbPremultiplied white(255);

			if (has_inner_shadow)
				MeshUtilities::GenerateBackground(mesh_padding, box, offset, border_radius, white, BoxArea::Padding);
			if (has_outer_shadow)
				MeshUtilities::GenerateBackground(mesh_padding_border, box, offset, border_radius, white, BoxArea::Border);
		}

		const RenderState initial_render_state = render_manager.GetState();
		render_manager.ResetState();
		render_manager.SetScissorRegion(Rectanglei::FromSize(texture_dimensions));

		render_manager.PushLayer();

		background_border_geometry.Render(element_offset_in_texture);

		for (int shadow_index = (int)shadow_list.size() - 1; shadow_index >= 0; shadow_index--)
		{
			const BoxShadow& shadow = shadow_list[shadow_index];
			const Vector2f shadow_offset = {shadow.offset_x.number, shadow.offset_y.number};
			const bool inset = shadow.inset;
			const float spread_distance = shadow.spread_distance.number;
			const float blur_radius = shadow.blur_radius.number;

			Vector4f spread_radii = border_radius;
			for (int i = 0; i < 4; i++)
			{
				float& radius = spread_radii[i];
				float spread_factor = (inset ? -1.f : 1.f);
				if (radius < spread_distance)
				{
					const float ratio_minus_one = (radius / spread_distance) - 1.f;
					spread_factor *= 1.f + ratio_minus_one * ratio_minus_one * ratio_minus_one;
				}
				radius = Math::Max(radius + spread_factor * spread_distance, 0.f);
			}

			Mesh mesh_shadow;

			// Generate the shadow geometry. For outer box-shadows it is rendered normally, while for inner box-shadows it is used as a clipping mask.
			for (int i = 0; i < element->GetNumBoxes(); i++)
			{
				Vector2f offset;
				Box box = element->GetBox(i, offset);
				const float signed_spread_distance = (inset ? -spread_distance : spread_distance);
				offset -= Vector2f(signed_spread_distance);

				for (int j = 0; j < Box::num_edges; j++)
				{
					BoxEdge edge = (BoxEdge)j;
					const float new_size = box.GetEdge(BoxArea::Padding, edge) + signed_spread_distance;
					box.SetEdge(BoxArea::Padding, edge, new_size);
				}

				MeshUtilities::GenerateBackground(mesh_shadow, box, offset, spread_radii, shadow.color, inset ? BoxArea::Padding : BoxArea::Border);
			}

			CompiledFilter blur;
			if (blur_radius >= 0.5f)
			{
				blur = render_manager.CompileFilter("blur", Dictionary{{"sigma", Variant(0.5f * blur_radius)}});
				if (blur)
					render_manager.PushLayer();
			}

			Geometry geometry_shadow = render_manager.MakeGeometry(std::move(mesh_shadow));

			if (inset)
			{
				render_manager.SetClipMask(ClipMaskOperation::SetInverse, &geometry_shadow, shadow_offset + element_offset_in_texture);

				for (Rml::Vertex& vertex : mesh_padding.vertices)
					vertex.colour = shadow.color;

				// @performance: Don't need to copy the mesh if this is the last use of it.
				Geometry geometry_padding = render_manager.MakeGeometry(Mesh(mesh_padding));
				geometry_padding.Render(element_offset_in_texture);

				render_manager.SetClipMask(ClipMaskOperation::Set, &geometry_padding, element_offset_in_texture);
			}
			else
			{
				Mesh mesh = mesh_padding_border;
				Geometry geometry_padding_border = render_manager.MakeGeometry(std::move(mesh));
				render_manager.SetClipMask(ClipMaskOperation::SetInverse, &geometry_padding_border, element_offset_in_texture);
				geometry_shadow.Render(shadow_offset + element_offset_in_texture);
			}

			if (blur)
			{
				FilterHandleList filters;
				blur.AddHandleTo(filters);
				render_manager.CompositeLayers(render_manager.GetTopLayer(), render_manager.GetNextLayer(), BlendMode::Blend, filters);
				render_manager.PopLayer();
				blur.Release();
			}
		}

		RMLUI_ASSERT(render_manager.GetScissorRegion() == Rectanglei::FromSize(texture_dimensions))
		texture_interface.SaveLayerAsTexture();

		render_manager.PopLayer();
		render_manager.SetState(initial_render_state);

		return true;
	};

	Mesh mesh = out_shadow_geometry.Release(Geometry::ReleaseMode::ClearMesh);
	const byte alpha = byte(opacity * 255.f);
	MeshUtilities::GenerateQuad(mesh, -element_offset_in_texture, Vector2f(texture_dimensions), ColourbPremultiplied(alpha, alpha));

	out_shadow_texture = render_manager.MakeCallbackTexture(std::move(texture_callback));
	out_shadow_geometry = render_manager.MakeGeometry(std::move(mesh));
}

} // namespace Rml