/*
 * Copyright 2022 Rive
 */

#pragma once

#include "rive/math/aabb.hpp"
#include "rive/math/mat2d.hpp"
#include "rive/math/path_types.hpp"
#include "rive/math/simd.hpp"
#include "rive/math/vec2d.hpp"
#include "rive/shapes/paint/color.hpp"
#include "rive/shapes/paint/stroke_join.hpp"

// This header defines constants and data structures for Rive's pixel local storage path rendering
// algorithm.
//
// Main algorithm:
// https://docs.google.com/document/d/19Uk9eyFxav6dNSYsI2ZyiX9zHU1YOaJsMB2sdDFVz6s/edit
//
// Batching multiple unique paths:
// https://docs.google.com/document/d/1DLrQimS5pbNaJJ2sAW5oSOsH6_glwDPo73-mtG5_zns/edit
//
// Batching strokes as well:
// https://docs.google.com/document/d/1CRKihkFjbd1bwT08ErMCP4fwSR7D4gnHvgdw_esY9GM/edit
namespace rive::pls
{
// Tessellate in parametric space until each segment is within 1/4 pixel of the true curve.
constexpr static int kParametricPrecision = 4;

// Tessellate in polar space until the outset edge is within 1/8 pixel of the true stroke.
constexpr static int kPolarPrecision = 8;

// Maximum supported numbers of tessellated segments in a single curve.
constexpr static uint32_t kMaxParametricSegments = 1023;
constexpr static uint32_t kMaxPolarSegments = 1023;

// We allocate all our GPU buffers in rings. This ensures the CPU can prepare frames in parallel
// while the GPU renders them.
constexpr static int kBufferRingSize = 3;

// Every coverage value in pixel local storage has an associated 16-bit path ID. This ID enables us
// to batch multiple paths together without having to clear the coverage buffer in between. This ID
// is implemented as an fp16, so the maximum path ID therefore cannot be NaN (or conservatively, all
// 5 exponent bits cannot be 1's). We also skip denormalized values (exp == 0) because they have
// been empirically unreliable on Android as ID values.
constexpr static int kLargestFP16BeforeExponentAll1s = (0x1f << 10) - 1;
constexpr static int kLargestDenormalizedFP16 = 1023;
constexpr static int MaxPathID(int granularity)
{
    // Floating point equality gets funky when the exponent bits are all 1's, so the largest pathID
    // we can support is kLargestFP16BeforeExponentAll1s.
    //
    // The shader converts an integer path ID to fp16 as:
    //
    //     (id + kLargestDenormalizedFP16) * granularity
    //
    // So the largest path ID we can support is as follows.
    return kLargestFP16BeforeExponentAll1s / granularity - kLargestDenormalizedFP16;
}

// In order to support WebGL2, we implement the path data buffer as a texture.
constexpr static size_t kPathTextureWidthInItems = 128;
constexpr static size_t kPathTexelsPerItem = 3;

// Each contour has its own unique ID, which it uses to index a data record containing per-contour
// information. This value is currently 16 bit.
constexpr static size_t kMaxContourID = 65535;
constexpr static uint32_t kContourIDMask = 0xffff;
static_assert((kMaxContourID & kContourIDMask) == kMaxContourID);

// In order to support WebGL2, we implement the contour data buffer as a texture.
constexpr static size_t kContourTextureWidthInItems = 256;
constexpr static size_t kContourTexelsPerItem = 1;

// Tessellation is performed by rendering vertices into a data texture. These values define the
// dimensions of the tessellation data texture.
constexpr static size_t kTessTextureWidth = 2048; // GL_MAX_TEXTURE_SIZE spec minimum on ES3/WebGL2.
constexpr static size_t kTessTextureWidthLog2 = 11;
static_assert(1 << kTessTextureWidthLog2 == kTessTextureWidth);

// Gradients are implemented by sampling a horizontal ramp of pixels allocated in a global gradient
// texture.
constexpr size_t kGradTextureWidth = 512;
constexpr size_t kGradTextureWidthInSimpleRamps = kGradTextureWidth / 2;

// Flags for on-GPU rendering data.
namespace flags
{
// Tells the GPU that a given vertex is the *first* tessellated vertex in its contour.
//
// When emitting patches, this flag is how the GPU detects when it has crossed past the end of the
// current contour. When this happens, the GPU knows to no not connect those two vertices, and
// instead, either wraps back around to the beginning of the contour to close it, or else handles
// the endcap if it's an open stroke.
constexpr static uint32_t kFirstVertexOfContour = 1u << 31;

// Tells shaders that a cubic should actually be drawn as the single, non-AA triangle: [p0, p1, p3].
// This is used to squeeze in more rare triangles, like "grout" triangles from self intersections on
// interior triangulation, where it wouldn't be worth it to put them in their own dedicated draw
// call.
constexpr static uint32_t kRetrofittedTriangle = 1u << 30;

// Tells the tessellation shader to re-run Wang's formula on the given curve, figure out how many
// segments it actually needs, and make any excess segments degenerate by co-locating their vertices
// at T=0. (Used on the "outerCurve" patches that are drawn with interior triangulations.)
constexpr static uint32_t kCullExcessTessellationSegments = 1u << 29;

// Flags for specifying the join type.
constexpr static uint32_t kJoinTypeMask = 3u << 27;
constexpr static uint32_t kMiterClipJoin = 3u << 27;   // Miter that clips when too sharp.
constexpr static uint32_t kMiterRevertJoin = 2u << 27; // Standard miter that pops when too sharp.
constexpr static uint32_t kBevelJoin = 1u << 27;

// When a join is being used to emulate a stroke cap, the shader emits additional vertices at T=0
// and T=1 for round joins, and changes the miter limit to 1 for miter-clip joins.
constexpr static uint32_t kEmulatedStrokeCap = 1u << 26;

RIVE_ALWAYS_INLINE static uint32_t JoinTypeFlags(StrokeJoin join)
{
    switch (join)
    {
        case StrokeJoin::miter:
            return flags::kMiterRevertJoin;
        case StrokeJoin::round:
            return 0;
        case StrokeJoin::bevel:
            return flags::kBevelJoin;
    }
    RIVE_UNREACHABLE();
}

// Tells the GPU that a given path has an even-odd fill rule.
constexpr static uint32_t kEvenOdd = 1u << 31;

// Tells the GPU that a given paint is a gradient.
constexpr static uint32_t kGradient = 1u << 30;

// Tells the GPU that a given gradient is a radial gradient.
constexpr static uint32_t kRadialGradient = 1u << 29;

// Says which part of the patch a vertex belongs to.
constexpr static int32_t kStrokeVertex = 0;
constexpr static int32_t kFanVertex = 1;
constexpr static int32_t kFanMidpointVertex = 2;
} // namespace flags

// Index of each pixel local storage plane.
constexpr static int kFramebufferPlaneIdx = 0;
constexpr static int kCoveragePlaneIdx = 1;
constexpr static int kOriginalDstColorPlaneIdx = 2;
constexpr static int kClipPlaneIdx = 3;

// Index at which we access each texture.
constexpr static int kTessVertexTextureIdx = 0;
constexpr static int kPathTextureIdx = 1;
constexpr static int kContourTextureIdx = 2;
constexpr static int kGradTextureIdx = 3;

// Backend-specific capabilities/workarounds and fine tuning.
struct PlatformFeatures
{
    uint8_t pathIDGranularity = 1; // Workaround for precision issues. Determines how far apart we
                                   // space unique path IDs.
    bool avoidFlatVaryings = false;
    bool invertOffscreenY = false; // Invert Y when drawing to offscreen render targets? (Gradient
                                   // and tessellation textures.)
};

// Per-flush shared uniforms used by all shaders.
struct FlushUniforms
{
    FlushUniforms(size_t complexGradientsHeight,
                  size_t tessDataHeight,
                  size_t renderTargetWidth,
                  size_t renderTargetHeight,
                  size_t gradTextureHeight,
                  const PlatformFeatures& platformFeatures) :
        inverseViewports(
            (platformFeatures.invertOffscreenY ? float4{-2.f, -2.f, 2.f, 2.f} : float4(2.f)) /
            float4{static_cast<float>(complexGradientsHeight),
                   static_cast<float>(tessDataHeight),
                   static_cast<float>(renderTargetWidth),
                   static_cast<float>(renderTargetHeight)}),
        gradTextureInverseHeight(1.f / static_cast<float>(gradTextureHeight)),
        pathIDGranularity(platformFeatures.pathIDGranularity)
    {}
    float4 inverseViewports; // [complexGradientsY, tessDataY, renderTargetX, renderTargetY]
    float gradTextureInverseHeight;
    uint32_t pathIDGranularity; // Spacing between adjacent path IDs (1 if IEEE compliant).
    float vertexDiscardValue = std::numeric_limits<float>::quiet_NaN();
    uint32_t pad = 0;
};
static_assert(sizeof(FlushUniforms) == 8 * sizeof(uint32_t));

// Gradient color stops are implemented as a horizontal span of pixels in a global gradient texture.
// They are rendered by "GradientSpan" instances.
struct GradientSpan
{
    // x0Fixed and x1Fixed are normalized texel x coordinates, in the fixed-point range 0..65535.
    RIVE_ALWAYS_INLINE void set(uint32_t x0Fixed,
                                uint32_t x1Fixed,
                                float y_,
                                ColorInt color0_,
                                ColorInt color1_)
    {
        assert(x0Fixed < 65536);
        assert(x1Fixed < 65536);
        horizontalSpan = (x1Fixed << 16) | x0Fixed;
        y = y_;
        color0 = color0_;
        color1 = color1_;
    }
    uint32_t horizontalSpan;
    uint32_t y;
    uint32_t color0;
    uint32_t color1;
};

enum class PaintType : uint32_t
{
    solidColor,
    linearGradient,
    radialGradient,
    clipReplace // Replace the clip buffer with path coverage instead of painting color.
};

// Mirrors rive::BlendMode, but 0-based and contiguous for tighter packing.
enum class PLSBlendMode : uint32_t
{
    // Tier 1.
    srcOver,

    // Tier 2.
    screen,
    overlay,
    darken,
    lighten,
    colorDodge,
    colorBurn,
    hardLight,
    softLight,
    difference,
    exclusion,
    multiply,

    // Tier 3.
    hue,
    saturation,
    color,
    luminosity,
};

// Packs the data for a gradient or solid color into 4 floats.
struct PaintData
{
    void setColor(ColorInt color) { UnpackColorToRGBA32F(color, data); }
    void setGradient(uint32_t row, uint32_t left, uint32_t right, const float coeffs[3])
    {
        static_assert(kGradTextureWidth <= (1 << 10));
        assert(row < (1 << 12));
        // Subtract 1 from right so we can support a 1024-wide gradient texture (so the rightmost
        // pixel would be 0x3ff and still fit in 10 bits).
        uint32_t span = (row << 20) | ((right - 1) << 10) | left;
        RIVE_INLINE_MEMCPY(data, &span, sizeof(float));
        RIVE_INLINE_MEMCPY(data + 1, coeffs, 3 * sizeof(float));
    }
    float data[4]; // Packed, type-specific paint data.
};

// Each path has a unique data record on the GPU that is accessed from the vertex shader.
struct PathData
{
    RIVE_ALWAYS_INLINE void set(const Mat2D& m,
                                float strokeRadius_, // 0 if the path is filled.
                                FillRule fillRule,
                                PaintType paintType,
                                uint32_t clipID,
                                PLSBlendMode blendMode,
                                const PaintData& paintData_)
    {
        matrix = m;
        strokeRadius = strokeRadius_;
        uint32_t localParams = static_cast<uint32_t>(blendMode);
        localParams |= clipID << 4;
        localParams |= static_cast<uint32_t>(paintType) << 20;
        if (fillRule == FillRule::evenOdd && strokeRadius_ == 0)
        {
            localParams |= flags::kEvenOdd;
        }
        params = localParams;
        paintData = paintData_;
    }
    Mat2D matrix;
    float strokeRadius; // "0" indicates that the path is filled, not stroked.
    uint32_t params;    // [fillRule, paintType, clipID, blendMode]
    PaintData paintData;
};

// Each contour of every path has a unique data record on the GPU that is accessed from the vertex
// shader.
struct ContourData
{
    Vec2D midpoint;        // Midpoint of the curve endpoints in just this contour.
    uint32_t pathID;       // ID of the path this contour belongs to.
    uint32_t vertexIndex0; // Index of the first tessellation vertex of the contour.
};

// Each curve gets tessellated into vertices. This is performed by rendering a horizontal span of
// positions and normals into the tessellation data texture, GP-GPU style. TessVertexSpan defines
// one instance of a horizontal tessellation span for rendering.
struct TessVertexSpan
{
    RIVE_ALWAYS_INLINE void set(const Vec2D pts_[4],
                                Vec2D joinTangent_,
                                int32_t x0,
                                int32_t x1,
                                uint32_t y_,
                                uint32_t parametricSegmentCount,
                                uint32_t polarSegmentCount,
                                uint32_t joinSegmentCount,
                                uint32_t contourIDWithFlags_)
    {
        RIVE_INLINE_MEMCPY(pts, pts_, sizeof(pts));
        joinTangent = joinTangent_;
        x0x1 = (x1 << 16) | (x0 & 0xffff);
        y = y_;
        segmentCounts =
            (joinSegmentCount << 20) | (polarSegmentCount << 10) | parametricSegmentCount;
        contourIDWithFlags = contourIDWithFlags_;

        // Ensure we didn't lose any data from packing.
        assert(x0 == (x0x1 << 16) >> 16);
        assert(x1 == x0x1 >> 16);
        assert((segmentCounts & 0x3ff) == parametricSegmentCount);
        assert(((segmentCounts >> 10) & 0x3ff) == polarSegmentCount);
        assert(segmentCounts >> 20 == joinSegmentCount);
    }
    Vec2D pts[4];      // Cubic bezier curve.
    Vec2D joinTangent; // Ending tangent of the join that follows the cubic.
    Vec2D pad;         // Align our attributes on 128-bit boundaries.
    int32_t x0x1;
    uint32_t y;
    uint32_t segmentCounts;      // [joinSegmentCount, polarSegmentCount, parametricSegmentCount]
    uint32_t contourIDWithFlags; // flags | contourID
};
static_assert(sizeof(TessVertexSpan) == sizeof(float) * 16);

// Per-vertex data for shaders that draw triangles.
struct TriangleVertex
{
    TriangleVertex() = default;
    TriangleVertex(Vec2D point_, int16_t weight, uint16_t pathID) :
        point(point_), weight_pathID((static_cast<int32_t>(weight) << 16) | pathID)
    {}
    Vec2D point;
    int32_t weight_pathID; // [(weight << 16]
};
static_assert(sizeof(TriangleVertex) == sizeof(float) * 3);

// Once all curves in a contour have been tessellated, we render the tessellated vertices in
// "patches" (aka specific instanced geometry).
//
// See:
// https://docs.google.com/document/d/19Uk9eyFxav6dNSYsI2ZyiX9zHU1YOaJsMB2sdDFVz6s/edit#heading=h.fa4kubk3vimk
//
// With strokes:
// https://docs.google.com/document/d/1CRKihkFjbd1bwT08ErMCP4fwSR7D4gnHvgdw_esY9GM/edit#heading=h.dcd0c58pxfs5
//
// A single patch spans N tessellation segments, connecting N + 1 tessellation vertices. It is
// composed of a an AA border and fan triangles. The specifics of the fan triangles depend on the
// PatchType.
enum class PatchType
{
    // Patches fan around the contour midpoint. Outer edges are inset by ~1px, followed by a ~1px AA
    // ramp.
    midpointFan,

    // Patches only cover the AA ramps and interiors of bezier curves. The interior path triangles
    // that connect the outer curves are triangulated on the CPU to eliminate overlap, and are drawn
    // in a separate call. AA ramps are split down the middle (on the same lines as the interior
    // triangulation), and drawn with a ~1/2px outset AA ramp and a ~1/2px inset AA ramp that
    // overlaps the inner tessellation and has negative coverage. A lone bowtie join is emitted at
    // the end of the patch to tie the outer curves together.
    outerCurves,
};

struct PatchVertex
{
    float localVertexID; // 0 or 1 -- which tessellated vertex of the two that we are connecting?
    float outset;        // Outset from the tessellated position, in the direction of the normal.
    float fillCoverage;  // 0..1 for the stroke. 1 all around for the triangles.
                         // (Coverage will be negated later for counterclockwise triangles.)
    int32_t params;      // "(patchSize << 2) | [flags::kStrokeVertex,
                         //                      flags::kFanVertex,
                         //                      flags::kFanMidpointVertex]"
};

// # of tessellation segments spanned by the midpoint fan patch.
constexpr static uint32_t kMidpointFanPatchSegmentSpan = 8;

// # of tessellation segments spanned by the outer curve patch. (In this particular instance, the
// final segment is a bowtie join with zero length and no fan triangle.)
constexpr static uint32_t kOuterCurvePatchSegmentSpan = 17;

// Define vertex and index buffers that contain all the triangles in every PatchType.
constexpr static uint32_t kMidpointFanPatchVertexCount =
    (kMidpointFanPatchSegmentSpan + 1) * 2 /*AA outer ramp*/ +
    (kMidpointFanPatchSegmentSpan + 1) /*Curve fan*/ + 1 /*Triangle from path midpoint*/;
constexpr static uint32_t kMidpointFanPatchIndexCount =
    kMidpointFanPatchSegmentSpan * 6 /*AA outer ramp*/ +
    (kMidpointFanPatchSegmentSpan - 1) * 3 /*Curve fan*/ + 3 /*Triangle from path midpoint*/;
constexpr static uint32_t kMidpointFanPatchBaseIndex = 0;
static_assert((kMidpointFanPatchBaseIndex * sizeof(uint16_t)) % 4 == 0);
constexpr static uint32_t kOuterCurvePatchVertexCount =
    (kOuterCurvePatchSegmentSpan + 1) * 3 /*AA center ramp with bowtie*/ +
    kOuterCurvePatchSegmentSpan /*Curve fan*/;
constexpr static uint32_t kOuterCurvePatchIndexCount =
    kOuterCurvePatchSegmentSpan * 12 /*AA center ramp with bowtie*/ +
    (kOuterCurvePatchSegmentSpan - 2) * 3 /*Curve fan*/;
constexpr static uint32_t kOuterCurvePatchBaseIndex = kMidpointFanPatchIndexCount;
static_assert((kOuterCurvePatchBaseIndex * sizeof(uint16_t)) % 4 == 0);
constexpr static uint32_t kPatchVertexBufferCount =
    kMidpointFanPatchVertexCount + kOuterCurvePatchVertexCount;
constexpr static uint32_t kPatchIndexBufferCount =
    kMidpointFanPatchIndexCount + kOuterCurvePatchIndexCount;
void GeneratePatchBufferData(PatchVertex[kPatchVertexBufferCount],
                             uint16_t indices[kPatchIndexBufferCount]);

// Returns the area of the (potentially non-rectangular) quadrilateral that results from
// transforming the given bounds by the given matrix.
float FindTransformedArea(const AABB& bounds, const Mat2D&);
} // namespace rive::pls