// Copyright 2014 Dolphin Emulator Project
// Licensed under GPLv2+
// Refer to the license.txt file included.

#include <cmath>
#include <cstring>

#include "Common/CommonTypes.h"
#include "VideoCommon/BPMemory.h"
#include "VideoCommon/GeometryShaderGen.h"
#include "VideoCommon/LightingShaderGen.h"
#include "VideoCommon/VideoConfig.h"

static const char* primitives_ogl[] = {"points", "lines", "triangles"};

static const char* primitives_d3d[] = {"point", "line", "triangle"};

template <class T>
static void EmitVertex(T& out, const char* vertex, API_TYPE ApiType, bool first_vertex = false);
template <class T>
static void EndPrimitive(T& out, API_TYPE ApiType);

GeometryShaderUid GetGeometryShaderUid(u32 primitive_type)
{
  ShaderUid<geometry_shader_uid_data> out;
  geometry_shader_uid_data* uid_data = out.GetUidData<geometry_shader_uid_data>();
  memset(uid_data, 0, sizeof(geometry_shader_uid_data));

  uid_data->primitive_type = primitive_type;
  uid_data->wireframe = g_ActiveConfig.bWireFrame;
  uid_data->msaa = g_ActiveConfig.iMultisamples > 1;
  uid_data->ssaa = g_ActiveConfig.iMultisamples > 1 && g_ActiveConfig.bSSAA;
  uid_data->stereo = g_ActiveConfig.iStereoMode > 0;
  uid_data->numTexGens = xfmem.numTexGen.numTexGens;
  uid_data->pixel_lighting = g_ActiveConfig.bEnablePixelLighting;

  return out;
}

static void EmitVertex(ShaderCode& out, const geometry_shader_uid_data* uid_data,
                       const char* vertex, API_TYPE ApiType, bool first_vertex = false);
static void EndPrimitive(ShaderCode& out, const geometry_shader_uid_data* uid_data,
                         API_TYPE ApiType);

ShaderCode GenerateGeometryShaderCode(API_TYPE ApiType, const geometry_shader_uid_data* uid_data)
{
  ShaderCode out;
  // Non-uid template parameters will write to the dummy data (=> gets optimized out)

  const unsigned int vertex_in = uid_data->primitive_type + 1;
  unsigned int vertex_out = uid_data->primitive_type == PRIMITIVE_TRIANGLES ? 3 : 4;

  if (uid_data->wireframe)
    vertex_out++;

  if (ApiType == API_OPENGL)
  {
    // Insert layout parameters
    if (g_ActiveConfig.backend_info.bSupportsGSInstancing)
    {
      out.Write("layout(%s, invocations = %d) in;\n", primitives_ogl[uid_data->primitive_type],
                uid_data->stereo ? 2 : 1);
      out.Write("layout(%s_strip, max_vertices = %d) out;\n",
                uid_data->wireframe ? "line" : "triangle", vertex_out);
    }
    else
    {
      out.Write("layout(%s) in;\n", primitives_ogl[uid_data->primitive_type]);
      out.Write("layout(%s_strip, max_vertices = %d) out;\n",
                uid_data->wireframe ? "line" : "triangle",
                uid_data->stereo ? vertex_out * 2 : vertex_out);
    }
  }

  out.Write("%s", s_lighting_struct);

  // uniforms
  if (ApiType == API_OPENGL)
    out.Write("layout(std140%s) uniform GSBlock {\n",
              g_ActiveConfig.backend_info.bSupportsBindingLayout ? ", binding = 3" : "");
  else
    out.Write("cbuffer GSBlock {\n");
  out.Write("\tfloat4 " I_STEREOPARAMS ";\n"
            "\tfloat4 " I_LINEPTPARAMS ";\n"
            "\tint4 " I_TEXOFFSET ";\n"
            "};\n");

  out.Write("struct VS_OUTPUT {\n");
  GenerateVSOutputMembers<ShaderCode>(out, ApiType, uid_data->numTexGens, uid_data->pixel_lighting,
                                      "");
  out.Write("};\n");

  if (ApiType == API_OPENGL)
  {
    if (g_ActiveConfig.backend_info.bSupportsGSInstancing)
      out.Write("#define InstanceID gl_InvocationID\n");

    out.Write("in VertexData {\n");
    GenerateVSOutputMembers<ShaderCode>(
        out, ApiType, uid_data->numTexGens, uid_data->pixel_lighting,
        GetInterpolationQualifier(uid_data->msaa, uid_data->ssaa, true, true));
    out.Write("} vs[%d];\n", vertex_in);

    out.Write("out VertexData {\n");
    GenerateVSOutputMembers<ShaderCode>(
        out, ApiType, uid_data->numTexGens, uid_data->pixel_lighting,
        GetInterpolationQualifier(uid_data->msaa, uid_data->ssaa, false, true));

    if (uid_data->stereo)
      out.Write("\tflat int layer;\n");

    out.Write("} ps;\n");

    out.Write("void main()\n{\n");
  }
  else  // D3D
  {
    out.Write("struct VertexData {\n");
    out.Write("\tVS_OUTPUT o;\n");

    if (uid_data->stereo)
      out.Write("\tuint layer : SV_RenderTargetArrayIndex;\n");

    out.Write("};\n");

    if (g_ActiveConfig.backend_info.bSupportsGSInstancing)
    {
      out.Write("[maxvertexcount(%d)]\n[instance(%d)]\n", vertex_out, uid_data->stereo ? 2 : 1);
      out.Write("void main(%s VS_OUTPUT o[%d], inout %sStream<VertexData> output, in uint "
                "InstanceID : SV_GSInstanceID)\n{\n",
                primitives_d3d[uid_data->primitive_type], vertex_in,
                uid_data->wireframe ? "Line" : "Triangle");
    }
    else
    {
      out.Write("[maxvertexcount(%d)]\n", uid_data->stereo ? vertex_out * 2 : vertex_out);
      out.Write("void main(%s VS_OUTPUT o[%d], inout %sStream<VertexData> output)\n{\n",
                primitives_d3d[uid_data->primitive_type], vertex_in,
                uid_data->wireframe ? "Line" : "Triangle");
    }

    out.Write("\tVertexData ps;\n");
  }

  if (uid_data->primitive_type == PRIMITIVE_LINES)
  {
    if (ApiType == API_OPENGL)
    {
      out.Write("\tVS_OUTPUT start, end;\n");
      AssignVSOutputMembers(out, "start", "vs[0]", uid_data->numTexGens, uid_data->pixel_lighting);
      AssignVSOutputMembers(out, "end", "vs[1]", uid_data->numTexGens, uid_data->pixel_lighting);
    }
    else
    {
      out.Write("\tVS_OUTPUT start = o[0];\n");
      out.Write("\tVS_OUTPUT end = o[1];\n");
    }

    // GameCube/Wii's line drawing algorithm is a little quirky. It does not
    // use the correct line caps. Instead, the line caps are vertical or
    // horizontal depending the slope of the line.
    out.Write("\tfloat2 offset;\n"
              "\tfloat2 to = abs(end.pos.xy / end.pos.w - start.pos.xy / start.pos.w);\n"
              // FIXME: What does real hardware do when line is at a 45-degree angle?
              // FIXME: Lines aren't drawn at the correct width. See Twilight Princess map.
              "\tif (" I_LINEPTPARAMS ".y * to.y > " I_LINEPTPARAMS ".x * to.x) {\n"
              // Line is more tall. Extend geometry left and right.
              // Lerp LineWidth/2 from [0..VpWidth] to [-1..1]
              "\t\toffset = float2(" I_LINEPTPARAMS ".z / " I_LINEPTPARAMS ".x, 0);\n"
              "\t} else {\n"
              // Line is more wide. Extend geometry up and down.
              // Lerp LineWidth/2 from [0..VpHeight] to [1..-1]
              "\t\toffset = float2(0, -" I_LINEPTPARAMS ".z / " I_LINEPTPARAMS ".y);\n"
              "\t}\n");
  }
  else if (uid_data->primitive_type == PRIMITIVE_POINTS)
  {
    if (ApiType == API_OPENGL)
    {
      out.Write("\tVS_OUTPUT center;\n");
      AssignVSOutputMembers(out, "center", "vs[0]", uid_data->numTexGens, uid_data->pixel_lighting);
    }
    else
    {
      out.Write("\tVS_OUTPUT center = o[0];\n");
    }

    // Offset from center to upper right vertex
    // Lerp PointSize/2 from [0,0..VpWidth,VpHeight] to [-1,1..1,-1]
    out.Write("\tfloat2 offset = float2(" I_LINEPTPARAMS ".w / " I_LINEPTPARAMS
              ".x, -" I_LINEPTPARAMS ".w / " I_LINEPTPARAMS ".y) * center.pos.w;\n");
  }

  if (uid_data->stereo)
  {
    // If the GPU supports invocation we don't need a for loop and can simply use the
    // invocation identifier to determine which layer we're rendering.
    if (g_ActiveConfig.backend_info.bSupportsGSInstancing)
      out.Write("\tint eye = InstanceID;\n");
    else
      out.Write("\tfor (int eye = 0; eye < 2; ++eye) {\n");
  }

  if (uid_data->wireframe)
    out.Write("\tVS_OUTPUT first;\n");

  out.Write("\tfor (int i = 0; i < %d; ++i) {\n", vertex_in);

  if (ApiType == API_OPENGL)
  {
    out.Write("\tVS_OUTPUT f;\n");
    AssignVSOutputMembers(out, "f", "vs[i]", uid_data->numTexGens, uid_data->pixel_lighting);
  }
  else
  {
    out.Write("\tVS_OUTPUT f = o[i];\n");
  }

  if (uid_data->stereo)
  {
    // Select the output layer
    out.Write("\tps.layer = eye;\n");
    if (ApiType == API_OPENGL)
      out.Write("\tgl_Layer = eye;\n");

    // For stereoscopy add a small horizontal offset in Normalized Device Coordinates proportional
    // to the depth of the vertex. We retrieve the depth value from the w-component of the projected
    // vertex which contains the negated z-component of the original vertex.
    // For negative parallax (out-of-screen effects) we subtract a convergence value from
    // the depth value. This results in objects at a distance smaller than the convergence
    // distance to seemingly appear in front of the screen.
    // This formula is based on page 13 of the "Nvidia 3D Vision Automatic, Best Practices Guide"
    out.Write("\tf.pos.x += " I_STEREOPARAMS "[eye] * (f.pos.w - " I_STEREOPARAMS "[2]);\n");
  }

  if (uid_data->primitive_type == PRIMITIVE_LINES)
  {
    out.Write("\tVS_OUTPUT l = f;\n"
              "\tVS_OUTPUT r = f;\n");

    out.Write("\tl.pos.xy -= offset * l.pos.w;\n"
              "\tr.pos.xy += offset * r.pos.w;\n");

    out.Write("\tif (" I_TEXOFFSET "[2] != 0) {\n");
    out.Write("\tfloat texOffset = 1.0 / float(" I_TEXOFFSET "[2]);\n");

    for (unsigned int i = 0; i < uid_data->numTexGens; ++i)
    {
      out.Write("\tif (((" I_TEXOFFSET "[0] >> %d) & 0x1) != 0)\n", i);
      out.Write("\t\tr.tex%d.x += texOffset;\n", i);
    }
    out.Write("\t}\n");

    EmitVertex(out, uid_data, "l", ApiType, true);
    EmitVertex(out, uid_data, "r", ApiType);
  }
  else if (uid_data->primitive_type == PRIMITIVE_POINTS)
  {
    out.Write("\tVS_OUTPUT ll = f;\n"
              "\tVS_OUTPUT lr = f;\n"
              "\tVS_OUTPUT ul = f;\n"
              "\tVS_OUTPUT ur = f;\n");

    out.Write("\tll.pos.xy += float2(-1,-1) * offset;\n"
              "\tlr.pos.xy += float2(1,-1) * offset;\n"
              "\tul.pos.xy += float2(-1,1) * offset;\n"
              "\tur.pos.xy += offset;\n");

    out.Write("\tif (" I_TEXOFFSET "[3] != 0) {\n");
    out.Write("\tfloat2 texOffset = float2(1.0 / float(" I_TEXOFFSET
              "[3]), 1.0 / float(" I_TEXOFFSET "[3]));\n");

    for (unsigned int i = 0; i < uid_data->numTexGens; ++i)
    {
      out.Write("\tif (((" I_TEXOFFSET "[1] >> %d) & 0x1) != 0) {\n", i);
      out.Write("\t\tll.tex%d.xy += float2(0,1) * texOffset;\n", i);
      out.Write("\t\tlr.tex%d.xy += texOffset;\n", i);
      out.Write("\t\tur.tex%d.xy += float2(1,0) * texOffset;\n", i);
      out.Write("\t}\n");
    }
    out.Write("\t}\n");

    EmitVertex(out, uid_data, "ll", ApiType, true);
    EmitVertex(out, uid_data, "lr", ApiType);
    EmitVertex(out, uid_data, "ul", ApiType);
    EmitVertex(out, uid_data, "ur", ApiType);
  }
  else
  {
    EmitVertex(out, uid_data, "f", ApiType, true);
  }

  out.Write("\t}\n");

  EndPrimitive(out, uid_data, ApiType);

  if (uid_data->stereo && !g_ActiveConfig.backend_info.bSupportsGSInstancing)
    out.Write("\t}\n");

  out.Write("}\n");

  return out;
}

static void EmitVertex(ShaderCode& out, const geometry_shader_uid_data* uid_data,
                       const char* vertex, API_TYPE ApiType, bool first_vertex)
{
  if (uid_data->wireframe && first_vertex)
    out.Write("\tif (i == 0) first = %s;\n", vertex);

  if (ApiType == API_OPENGL)
  {
    out.Write("\tgl_Position = %s.pos;\n", vertex);
    AssignVSOutputMembers(out, "ps", vertex, uid_data->numTexGens, uid_data->pixel_lighting);
  }
  else
  {
    out.Write("\tps.o = %s;\n", vertex);
  }

  if (ApiType == API_OPENGL)
    out.Write("\tEmitVertex();\n");
  else
    out.Write("\toutput.Append(ps);\n");
}

static void EndPrimitive(ShaderCode& out, const geometry_shader_uid_data* uid_data,
                         API_TYPE ApiType)
{
  if (uid_data->wireframe)
    EmitVertex(out, uid_data, "first", ApiType);

  if (ApiType == API_OPENGL)
    out.Write("\tEndPrimitive();\n");
  else
    out.Write("\toutput.RestartStrip();\n");
}
