// Copyright 2015 Citra Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.

#include <array>
#include <cstddef>
#include <cstring>
#include "common/assert.h"
#include "common/bit_field.h"
#include "common/logging/log.h"
#include "core/core.h"
#include "video_core/regs_framebuffer.h"
#include "video_core/regs_lighting.h"
#include "video_core/regs_rasterizer.h"
#include "video_core/regs_texturing.h"
#include "video_core/renderer_opengl/gl_rasterizer.h"
#include "video_core/renderer_opengl/gl_shader_gen.h"
#include "video_core/renderer_opengl/gl_shader_util.h"

using Pica::FramebufferRegs;
using Pica::LightingRegs;
using Pica::RasterizerRegs;
using Pica::TexturingRegs;
using TevStageConfig = TexturingRegs::TevStageConfig;

namespace GLShader {

PicaShaderConfig PicaShaderConfig::BuildFromRegs(const Pica::Regs& regs) {
    PicaShaderConfig res;

    auto& state = res.state;
    std::memset(&state, 0, sizeof(PicaShaderConfig::State));

    state.scissor_test_mode = regs.rasterizer.scissor_test.mode;

    state.depthmap_enable = regs.rasterizer.depthmap_enable;

    state.alpha_test_func = regs.framebuffer.output_merger.alpha_test.enable
                                ? regs.framebuffer.output_merger.alpha_test.func.Value()
                                : Pica::FramebufferRegs::CompareFunc::Always;

    state.texture0_type = regs.texturing.texture0.type;

    state.texture2_use_coord1 = regs.texturing.main_config.texture2_use_coord1 != 0;

    // Copy relevant tev stages fields.
    // We don't sync const_color here because of the high variance, it is a
    // shader uniform instead.
    const auto& tev_stages = regs.texturing.GetTevStages();
    DEBUG_ASSERT(state.tev_stages.size() == tev_stages.size());
    for (size_t i = 0; i < tev_stages.size(); i++) {
        const auto& tev_stage = tev_stages[i];
        state.tev_stages[i].sources_raw = tev_stage.sources_raw;
        state.tev_stages[i].modifiers_raw = tev_stage.modifiers_raw;
        state.tev_stages[i].ops_raw = tev_stage.ops_raw;
        state.tev_stages[i].scales_raw = tev_stage.scales_raw;
    }

    state.fog_mode = regs.texturing.fog_mode;
    state.fog_flip = regs.texturing.fog_flip != 0;

    state.combiner_buffer_input = regs.texturing.tev_combiner_buffer_input.update_mask_rgb.Value() |
                                  regs.texturing.tev_combiner_buffer_input.update_mask_a.Value()
                                      << 4;

    // Fragment lighting

    state.lighting.enable = !regs.lighting.disable;
    state.lighting.src_num = regs.lighting.max_light_index + 1;

    for (unsigned light_index = 0; light_index < state.lighting.src_num; ++light_index) {
        unsigned num = regs.lighting.light_enable.GetNum(light_index);
        const auto& light = regs.lighting.light[num];
        state.lighting.light[light_index].num = num;
        state.lighting.light[light_index].directional = light.config.directional != 0;
        state.lighting.light[light_index].two_sided_diffuse = light.config.two_sided_diffuse != 0;
        state.lighting.light[light_index].geometric_factor_0 = light.config.geometric_factor_0 != 0;
        state.lighting.light[light_index].geometric_factor_1 = light.config.geometric_factor_1 != 0;
        state.lighting.light[light_index].dist_atten_enable =
            !regs.lighting.IsDistAttenDisabled(num);
        state.lighting.light[light_index].spot_atten_enable =
            !regs.lighting.IsSpotAttenDisabled(num);
    }

    state.lighting.lut_d0.enable = regs.lighting.config1.disable_lut_d0 == 0;
    state.lighting.lut_d0.abs_input = regs.lighting.abs_lut_input.disable_d0 == 0;
    state.lighting.lut_d0.type = regs.lighting.lut_input.d0.Value();
    state.lighting.lut_d0.scale = regs.lighting.lut_scale.GetScale(regs.lighting.lut_scale.d0);

    state.lighting.lut_d1.enable = regs.lighting.config1.disable_lut_d1 == 0;
    state.lighting.lut_d1.abs_input = regs.lighting.abs_lut_input.disable_d1 == 0;
    state.lighting.lut_d1.type = regs.lighting.lut_input.d1.Value();
    state.lighting.lut_d1.scale = regs.lighting.lut_scale.GetScale(regs.lighting.lut_scale.d1);

    // this is a dummy field due to lack of the corresponding register
    state.lighting.lut_sp.enable = true;
    state.lighting.lut_sp.abs_input = regs.lighting.abs_lut_input.disable_sp == 0;
    state.lighting.lut_sp.type = regs.lighting.lut_input.sp.Value();
    state.lighting.lut_sp.scale = regs.lighting.lut_scale.GetScale(regs.lighting.lut_scale.sp);

    state.lighting.lut_fr.enable = regs.lighting.config1.disable_lut_fr == 0;
    state.lighting.lut_fr.abs_input = regs.lighting.abs_lut_input.disable_fr == 0;
    state.lighting.lut_fr.type = regs.lighting.lut_input.fr.Value();
    state.lighting.lut_fr.scale = regs.lighting.lut_scale.GetScale(regs.lighting.lut_scale.fr);

    state.lighting.lut_rr.enable = regs.lighting.config1.disable_lut_rr == 0;
    state.lighting.lut_rr.abs_input = regs.lighting.abs_lut_input.disable_rr == 0;
    state.lighting.lut_rr.type = regs.lighting.lut_input.rr.Value();
    state.lighting.lut_rr.scale = regs.lighting.lut_scale.GetScale(regs.lighting.lut_scale.rr);

    state.lighting.lut_rg.enable = regs.lighting.config1.disable_lut_rg == 0;
    state.lighting.lut_rg.abs_input = regs.lighting.abs_lut_input.disable_rg == 0;
    state.lighting.lut_rg.type = regs.lighting.lut_input.rg.Value();
    state.lighting.lut_rg.scale = regs.lighting.lut_scale.GetScale(regs.lighting.lut_scale.rg);

    state.lighting.lut_rb.enable = regs.lighting.config1.disable_lut_rb == 0;
    state.lighting.lut_rb.abs_input = regs.lighting.abs_lut_input.disable_rb == 0;
    state.lighting.lut_rb.type = regs.lighting.lut_input.rb.Value();
    state.lighting.lut_rb.scale = regs.lighting.lut_scale.GetScale(regs.lighting.lut_scale.rb);

    state.lighting.config = regs.lighting.config0.config;
    state.lighting.fresnel_selector = regs.lighting.config0.fresnel_selector;
    state.lighting.bump_mode = regs.lighting.config0.bump_mode;
    state.lighting.bump_selector = regs.lighting.config0.bump_selector;
    state.lighting.bump_renorm = regs.lighting.config0.disable_bump_renorm == 0;
    state.lighting.clamp_highlights = regs.lighting.config0.clamp_highlights != 0;

    state.proctex.enable = regs.texturing.main_config.texture3_enable;
    if (state.proctex.enable) {
        state.proctex.coord = regs.texturing.main_config.texture3_coordinates;
        state.proctex.u_clamp = regs.texturing.proctex.u_clamp;
        state.proctex.v_clamp = regs.texturing.proctex.v_clamp;
        state.proctex.color_combiner = regs.texturing.proctex.color_combiner;
        state.proctex.alpha_combiner = regs.texturing.proctex.alpha_combiner;
        state.proctex.separate_alpha = regs.texturing.proctex.separate_alpha;
        state.proctex.noise_enable = regs.texturing.proctex.noise_enable;
        state.proctex.u_shift = regs.texturing.proctex.u_shift;
        state.proctex.v_shift = regs.texturing.proctex.v_shift;
        state.proctex.lut_width = regs.texturing.proctex_lut.width;
        state.proctex.lut_offset = regs.texturing.proctex_lut_offset;
        state.proctex.lut_filter = regs.texturing.proctex_lut.filter;
    }

    return res;
}

/// Detects if a TEV stage is configured to be skipped (to avoid generating unnecessary code)
static bool IsPassThroughTevStage(const TevStageConfig& stage) {
    return (stage.color_op == TevStageConfig::Operation::Replace &&
            stage.alpha_op == TevStageConfig::Operation::Replace &&
            stage.color_source1 == TevStageConfig::Source::Previous &&
            stage.alpha_source1 == TevStageConfig::Source::Previous &&
            stage.color_modifier1 == TevStageConfig::ColorModifier::SourceColor &&
            stage.alpha_modifier1 == TevStageConfig::AlphaModifier::SourceAlpha &&
            stage.GetColorMultiplier() == 1 && stage.GetAlphaMultiplier() == 1);
}

static std::string SampleTexture(const PicaShaderConfig& config, unsigned texture_unit) {
    const auto& state = config.state;
    switch (texture_unit) {
    case 0:
        // Only unit 0 respects the texturing type
        switch (state.texture0_type) {
        case TexturingRegs::TextureConfig::Texture2D:
            return "texture(tex[0], texcoord[0])";
        case TexturingRegs::TextureConfig::Projection2D:
            return "textureProj(tex[0], vec3(texcoord[0], texcoord0_w))";
        default:
            LOG_CRITICAL(HW_GPU, "Unhandled texture type %x",
                         static_cast<int>(state.texture0_type));
            UNIMPLEMENTED();
            return "texture(tex[0], texcoord[0])";
        }
    case 1:
        return "texture(tex[1], texcoord[1])";
    case 2:
        if (state.texture2_use_coord1)
            return "texture(tex[2], texcoord[1])";
        else
            return "texture(tex[2], texcoord[2])";
    case 3:
        if (state.proctex.enable) {
            return "ProcTex()";
        } else {
            LOG_ERROR(Render_OpenGL, "Using Texture3 without enabling it");
            return "vec4(0.0)";
        }
    default:
        UNREACHABLE();
        return "";
    }
}

/// Writes the specified TEV stage source component(s)
static void AppendSource(std::string& out, const PicaShaderConfig& config,
                         TevStageConfig::Source source, const std::string& index_name) {
    const auto& state = config.state;
    using Source = TevStageConfig::Source;
    switch (source) {
    case Source::PrimaryColor:
        out += "primary_color";
        break;
    case Source::PrimaryFragmentColor:
        out += "primary_fragment_color";
        break;
    case Source::SecondaryFragmentColor:
        out += "secondary_fragment_color";
        break;
    case Source::Texture0:
        out += SampleTexture(config, 0);
        break;
    case Source::Texture1:
        out += SampleTexture(config, 1);
        break;
    case Source::Texture2:
        out += SampleTexture(config, 2);
        break;
    case Source::Texture3:
        out += SampleTexture(config, 3);
        break;
    case Source::PreviousBuffer:
        out += "combiner_buffer";
        break;
    case Source::Constant:
        ((out += "const_color[") += index_name) += ']';
        break;
    case Source::Previous:
        out += "last_tex_env_out";
        break;
    default:
        out += "vec4(0.0)";
        LOG_CRITICAL(Render_OpenGL, "Unknown source op %u", source);
        break;
    }
}

/// Writes the color components to use for the specified TEV stage color modifier
static void AppendColorModifier(std::string& out, const PicaShaderConfig& config,
                                TevStageConfig::ColorModifier modifier,
                                TevStageConfig::Source source, const std::string& index_name) {
    using ColorModifier = TevStageConfig::ColorModifier;
    switch (modifier) {
    case ColorModifier::SourceColor:
        AppendSource(out, config, source, index_name);
        out += ".rgb";
        break;
    case ColorModifier::OneMinusSourceColor:
        out += "vec3(1.0) - ";
        AppendSource(out, config, source, index_name);
        out += ".rgb";
        break;
    case ColorModifier::SourceAlpha:
        AppendSource(out, config, source, index_name);
        out += ".aaa";
        break;
    case ColorModifier::OneMinusSourceAlpha:
        out += "vec3(1.0) - ";
        AppendSource(out, config, source, index_name);
        out += ".aaa";
        break;
    case ColorModifier::SourceRed:
        AppendSource(out, config, source, index_name);
        out += ".rrr";
        break;
    case ColorModifier::OneMinusSourceRed:
        out += "vec3(1.0) - ";
        AppendSource(out, config, source, index_name);
        out += ".rrr";
        break;
    case ColorModifier::SourceGreen:
        AppendSource(out, config, source, index_name);
        out += ".ggg";
        break;
    case ColorModifier::OneMinusSourceGreen:
        out += "vec3(1.0) - ";
        AppendSource(out, config, source, index_name);
        out += ".ggg";
        break;
    case ColorModifier::SourceBlue:
        AppendSource(out, config, source, index_name);
        out += ".bbb";
        break;
    case ColorModifier::OneMinusSourceBlue:
        out += "vec3(1.0) - ";
        AppendSource(out, config, source, index_name);
        out += ".bbb";
        break;
    default:
        out += "vec3(0.0)";
        LOG_CRITICAL(Render_OpenGL, "Unknown color modifier op %u", modifier);
        break;
    }
}

/// Writes the alpha component to use for the specified TEV stage alpha modifier
static void AppendAlphaModifier(std::string& out, const PicaShaderConfig& config,
                                TevStageConfig::AlphaModifier modifier,
                                TevStageConfig::Source source, const std::string& index_name) {
    using AlphaModifier = TevStageConfig::AlphaModifier;
    switch (modifier) {
    case AlphaModifier::SourceAlpha:
        AppendSource(out, config, source, index_name);
        out += ".a";
        break;
    case AlphaModifier::OneMinusSourceAlpha:
        out += "1.0 - ";
        AppendSource(out, config, source, index_name);
        out += ".a";
        break;
    case AlphaModifier::SourceRed:
        AppendSource(out, config, source, index_name);
        out += ".r";
        break;
    case AlphaModifier::OneMinusSourceRed:
        out += "1.0 - ";
        AppendSource(out, config, source, index_name);
        out += ".r";
        break;
    case AlphaModifier::SourceGreen:
        AppendSource(out, config, source, index_name);
        out += ".g";
        break;
    case AlphaModifier::OneMinusSourceGreen:
        out += "1.0 - ";
        AppendSource(out, config, source, index_name);
        out += ".g";
        break;
    case AlphaModifier::SourceBlue:
        AppendSource(out, config, source, index_name);
        out += ".b";
        break;
    case AlphaModifier::OneMinusSourceBlue:
        out += "1.0 - ";
        AppendSource(out, config, source, index_name);
        out += ".b";
        break;
    default:
        out += "0.0";
        LOG_CRITICAL(Render_OpenGL, "Unknown alpha modifier op %u", modifier);
        break;
    }
}

/// Writes the combiner function for the color components for the specified TEV stage operation
static void AppendColorCombiner(std::string& out, TevStageConfig::Operation operation,
                                const std::string& variable_name) {
    out += "clamp(";
    using Operation = TevStageConfig::Operation;
    switch (operation) {
    case Operation::Replace:
        out += variable_name + "[0]";
        break;
    case Operation::Modulate:
        out += variable_name + "[0] * " + variable_name + "[1]";
        break;
    case Operation::Add:
        out += variable_name + "[0] + " + variable_name + "[1]";
        break;
    case Operation::AddSigned:
        out += variable_name + "[0] + " + variable_name + "[1] - vec3(0.5)";
        break;
    case Operation::Lerp:
        out += variable_name + "[0] * " + variable_name + "[2] + " + variable_name +
               "[1] * (vec3(1.0) - " + variable_name + "[2])";
        break;
    case Operation::Subtract:
        out += variable_name + "[0] - " + variable_name + "[1]";
        break;
    case Operation::MultiplyThenAdd:
        out += variable_name + "[0] * " + variable_name + "[1] + " + variable_name + "[2]";
        break;
    case Operation::AddThenMultiply:
        out += "min(" + variable_name + "[0] + " + variable_name + "[1], vec3(1.0)) * " +
               variable_name + "[2]";
        break;
    case Operation::Dot3_RGB:
    case Operation::Dot3_RGBA:
        out += "vec3(dot(" + variable_name + "[0] - vec3(0.5), " + variable_name +
               "[1] - vec3(0.5)) * 4.0)";
        break;
    default:
        out += "vec3(0.0)";
        LOG_CRITICAL(Render_OpenGL, "Unknown color combiner operation: %u", operation);
        break;
    }
    out += ", vec3(0.0), vec3(1.0))"; // Clamp result to 0.0, 1.0
}

/// Writes the combiner function for the alpha component for the specified TEV stage operation
static void AppendAlphaCombiner(std::string& out, TevStageConfig::Operation operation,
                                const std::string& variable_name) {
    out += "clamp(";
    using Operation = TevStageConfig::Operation;
    switch (operation) {
    case Operation::Replace:
        out += variable_name + "[0]";
        break;
    case Operation::Modulate:
        out += variable_name + "[0] * " + variable_name + "[1]";
        break;
    case Operation::Add:
        out += variable_name + "[0] + " + variable_name + "[1]";
        break;
    case Operation::AddSigned:
        out += variable_name + "[0] + " + variable_name + "[1] - 0.5";
        break;
    case Operation::Lerp:
        out += variable_name + "[0] * " + variable_name + "[2] + " + variable_name +
               "[1] * (1.0 - " + variable_name + "[2])";
        break;
    case Operation::Subtract:
        out += variable_name + "[0] - " + variable_name + "[1]";
        break;
    case Operation::MultiplyThenAdd:
        out += variable_name + "[0] * " + variable_name + "[1] + " + variable_name + "[2]";
        break;
    case Operation::AddThenMultiply:
        out += "min(" + variable_name + "[0] + " + variable_name + "[1], 1.0) * " + variable_name +
               "[2]";
        break;
    default:
        out += "0.0";
        LOG_CRITICAL(Render_OpenGL, "Unknown alpha combiner operation: %u", operation);
        break;
    }
    out += ", 0.0, 1.0)";
}

/// Writes the if-statement condition used to evaluate alpha testing
static void AppendAlphaTestCondition(std::string& out, FramebufferRegs::CompareFunc func) {
    using CompareFunc = FramebufferRegs::CompareFunc;
    switch (func) {
    case CompareFunc::Never:
        out += "true";
        break;
    case CompareFunc::Always:
        out += "false";
        break;
    case CompareFunc::Equal:
    case CompareFunc::NotEqual:
    case CompareFunc::LessThan:
    case CompareFunc::LessThanOrEqual:
    case CompareFunc::GreaterThan:
    case CompareFunc::GreaterThanOrEqual: {
        static const char* op[] = {"!=", "==", ">=", ">", "<=", "<"};
        unsigned index = (unsigned)func - (unsigned)CompareFunc::Equal;
        out += "int(last_tex_env_out.a * 255.0) " + std::string(op[index]) + " alphatest_ref";
        break;
    }

    default:
        out += "false";
        LOG_CRITICAL(Render_OpenGL, "Unknown alpha test condition %u", func);
        break;
    }
}

/// Writes the code to emulate the specified TEV stage
static void WriteTevStage(std::string& out, const PicaShaderConfig& config, unsigned index) {
    const auto stage =
        static_cast<const TexturingRegs::TevStageConfig>(config.state.tev_stages[index]);
    if (!IsPassThroughTevStage(stage)) {
        std::string index_name = std::to_string(index);

        out += "vec3 color_results_" + index_name + "[3] = vec3[3](";
        AppendColorModifier(out, config, stage.color_modifier1, stage.color_source1, index_name);
        out += ", ";
        AppendColorModifier(out, config, stage.color_modifier2, stage.color_source2, index_name);
        out += ", ";
        AppendColorModifier(out, config, stage.color_modifier3, stage.color_source3, index_name);
        out += ");\n";

        out += "vec3 color_output_" + index_name + " = ";
        AppendColorCombiner(out, stage.color_op, "color_results_" + index_name);
        out += ";\n";

        if (stage.color_op == TevStageConfig::Operation::Dot3_RGBA) {
            // result of Dot3_RGBA operation is also placed to the alpha component
            out += "float alpha_output_" + index_name + " = color_output_" + index_name + "[0];\n";
        } else {
            out += "float alpha_results_" + index_name + "[3] = float[3](";
            AppendAlphaModifier(out, config, stage.alpha_modifier1, stage.alpha_source1,
                                index_name);
            out += ", ";
            AppendAlphaModifier(out, config, stage.alpha_modifier2, stage.alpha_source2,
                                index_name);
            out += ", ";
            AppendAlphaModifier(out, config, stage.alpha_modifier3, stage.alpha_source3,
                                index_name);
            out += ");\n";

            out += "float alpha_output_" + index_name + " = ";
            AppendAlphaCombiner(out, stage.alpha_op, "alpha_results_" + index_name);
            out += ";\n";
        }

        out += "last_tex_env_out = vec4("
               "clamp(color_output_" +
               index_name + " * " + std::to_string(stage.GetColorMultiplier()) +
               ".0, vec3(0.0), vec3(1.0)),"
               "clamp(alpha_output_" +
               index_name + " * " + std::to_string(stage.GetAlphaMultiplier()) +
               ".0, 0.0, 1.0));\n";
    }

    out += "combiner_buffer = next_combiner_buffer;\n";

    if (config.TevStageUpdatesCombinerBufferColor(index))
        out += "next_combiner_buffer.rgb = last_tex_env_out.rgb;\n";

    if (config.TevStageUpdatesCombinerBufferAlpha(index))
        out += "next_combiner_buffer.a = last_tex_env_out.a;\n";
}

/// Writes the code to emulate fragment lighting
static void WriteLighting(std::string& out, const PicaShaderConfig& config) {
    const auto& lighting = config.state.lighting;

    // Define lighting globals
    out += "vec4 diffuse_sum = vec4(0.0, 0.0, 0.0, 1.0);\n"
           "vec4 specular_sum = vec4(0.0, 0.0, 0.0, 1.0);\n"
           "vec3 light_vector = vec3(0.0);\n"
           "vec3 refl_value = vec3(0.0);\n"
           "vec3 spot_dir = vec3(0.0);\n"
           "vec3 half_vector = vec3(0.0);\n"
           "float geo_factor = 1.0;\n";

    // Compute fragment normals and tangents
    auto Perturbation = [&]() {
        return "2.0 * (" + SampleTexture(config, lighting.bump_selector) + ").rgb - 1.0";
    };
    if (lighting.bump_mode == LightingRegs::LightingBumpMode::NormalMap) {
        // Bump mapping is enabled using a normal map
        out += "vec3 surface_normal = " + Perturbation() + ";\n";

        // Recompute Z-component of perturbation if 'renorm' is enabled, this provides a higher
        // precision result
        if (lighting.bump_renorm) {
            std::string val =
                "(1.0 - (surface_normal.x*surface_normal.x + surface_normal.y*surface_normal.y))";
            out += "surface_normal.z = sqrt(max(" + val + ", 0.0));\n";
        }

        // The tangent vector is not perturbed by the normal map and is just a unit vector.
        out += "vec3 surface_tangent = vec3(1.0, 0.0, 0.0);\n";
    } else if (lighting.bump_mode == LightingRegs::LightingBumpMode::TangentMap) {
        // Bump mapping is enabled using a tangent map
        out += "vec3 surface_tangent = " + Perturbation() + ";\n";
        // Mathematically, recomputing Z-component of the tangent vector won't affect the relevant
        // computation below, which is also confirmed on 3DS. So we don't bother recomputing here
        // even if 'renorm' is enabled.

        // The normal vector is not perturbed by the tangent map and is just a unit vector.
        out += "vec3 surface_normal = vec3(0.0, 0.0, 1.0);\n";
    } else {
        // No bump mapping - surface local normal and tangent are just unit vectors
        out += "vec3 surface_normal = vec3(0.0, 0.0, 1.0);\n";
        out += "vec3 surface_tangent = vec3(1.0, 0.0, 0.0);\n";
    }

    // Rotate the surface-local normal by the interpolated normal quaternion to convert it to
    // eyespace.
    out += "vec4 normalized_normquat = normalize(normquat);\n";
    out += "vec3 normal = quaternion_rotate(normalized_normquat, surface_normal);\n";
    out += "vec3 tangent = quaternion_rotate(normalized_normquat, surface_tangent);\n";

    // Samples the specified lookup table for specular lighting
    auto GetLutValue = [&lighting](LightingRegs::LightingSampler sampler, unsigned light_num,
                                   LightingRegs::LightingLutInput input, bool abs) {
        std::string index;
        switch (input) {
        case LightingRegs::LightingLutInput::NH:
            index = "dot(normal, normalize(half_vector))";
            break;

        case LightingRegs::LightingLutInput::VH:
            index = std::string("dot(normalize(view), normalize(half_vector))");
            break;

        case LightingRegs::LightingLutInput::NV:
            index = std::string("dot(normal, normalize(view))");
            break;

        case LightingRegs::LightingLutInput::LN:
            index = std::string("dot(light_vector, normal)");
            break;

        case LightingRegs::LightingLutInput::SP:
            index = std::string("dot(light_vector, spot_dir)");
            break;

        case LightingRegs::LightingLutInput::CP:
            // CP input is only available with configuration 7
            if (lighting.config == LightingRegs::LightingConfig::Config7) {
                // Note: even if the normal vector is modified by normal map, which is not the
                // normal of the tangent plane anymore, the half angle vector is still projected
                // using the modified normal vector.
                std::string half_angle_proj =
                    "normalize(half_vector) - normal * dot(normal, normalize(half_vector))";
                // Note: the half angle vector projection is confirmed not normalized before the dot
                // product. The result is in fact not cos(phi) as the name suggested.
                index = "dot(" + half_angle_proj + ", tangent)";
            } else {
                index = "0.0";
            }
            break;

        default:
            LOG_CRITICAL(HW_GPU, "Unknown lighting LUT input %d\n", (int)input);
            UNIMPLEMENTED();
            index = "0.0";
            break;
        }

        std::string sampler_string = std::to_string(static_cast<unsigned>(sampler));

        if (abs) {
            // LUT index is in the range of (0.0, 1.0)
            index = lighting.light[light_num].two_sided_diffuse ? "abs(" + index + ")"
                                                                : "max(" + index + ", 0.0)";
            return "LookupLightingLUTUnsigned(" + sampler_string + ", " + index + ")";
        } else {
            // LUT index is in the range of (-1.0, 1.0)
            return "LookupLightingLUTSigned(" + sampler_string + ", " + index + ")";
        }

    };

    // Write the code to emulate each enabled light
    for (unsigned light_index = 0; light_index < lighting.src_num; ++light_index) {
        const auto& light_config = lighting.light[light_index];
        std::string light_src = "light_src[" + std::to_string(light_config.num) + "]";

        // Compute light vector (directional or positional)
        if (light_config.directional)
            out += "light_vector = normalize(" + light_src + ".position);\n";
        else
            out += "light_vector = normalize(" + light_src + ".position + view);\n";

        out += "spot_dir = " + light_src + ".spot_direction;\n";
        out += "half_vector = normalize(view) + light_vector;\n";

        // Compute dot product of light_vector and normal, adjust if lighting is one-sided or
        // two-sided
        std::string dot_product = light_config.two_sided_diffuse
                                      ? "abs(dot(light_vector, normal))"
                                      : "max(dot(light_vector, normal), 0.0)";

        // If enabled, compute spot light attenuation value
        std::string spot_atten = "1.0";
        if (light_config.spot_atten_enable &&
            LightingRegs::IsLightingSamplerSupported(
                lighting.config, LightingRegs::LightingSampler::SpotlightAttenuation)) {
            std::string value =
                GetLutValue(LightingRegs::SpotlightAttenuationSampler(light_config.num),
                            light_config.num, lighting.lut_sp.type, lighting.lut_sp.abs_input);
            spot_atten = "(" + std::to_string(lighting.lut_sp.scale) + " * " + value + ")";
        }

        // If enabled, compute distance attenuation value
        std::string dist_atten = "1.0";
        if (light_config.dist_atten_enable) {
            std::string index = "clamp(" + light_src + ".dist_atten_scale * length(-view - " +
                                light_src + ".position) + " + light_src +
                                ".dist_atten_bias, 0.0, 1.0)";
            auto sampler = LightingRegs::DistanceAttenuationSampler(light_config.num);
            dist_atten = "LookupLightingLUTUnsigned(" +
                         std::to_string(static_cast<unsigned>(sampler)) + "," + index + ")";
        }

        // If enabled, clamp specular component if lighting result is negative
        std::string clamp_highlights =
            lighting.clamp_highlights ? "(dot(light_vector, normal) <= 0.0 ? 0.0 : 1.0)" : "1.0";

        if (light_config.geometric_factor_0 || light_config.geometric_factor_1) {
            out += "geo_factor = dot(half_vector, half_vector);\n"
                   "geo_factor = geo_factor == 0.0 ? 0.0 : min(" +
                   dot_product + " / geo_factor, 1.0);\n";
        }

        // Specular 0 component
        std::string d0_lut_value = "1.0";
        if (lighting.lut_d0.enable &&
            LightingRegs::IsLightingSamplerSupported(
                lighting.config, LightingRegs::LightingSampler::Distribution0)) {
            // Lookup specular "distribution 0" LUT value
            std::string value =
                GetLutValue(LightingRegs::LightingSampler::Distribution0, light_config.num,
                            lighting.lut_d0.type, lighting.lut_d0.abs_input);
            d0_lut_value = "(" + std::to_string(lighting.lut_d0.scale) + " * " + value + ")";
        }
        std::string specular_0 = "(" + d0_lut_value + " * " + light_src + ".specular_0)";
        if (light_config.geometric_factor_0) {
            specular_0 = "(" + specular_0 + " * geo_factor)";
        }

        // If enabled, lookup ReflectRed value, otherwise, 1.0 is used
        if (lighting.lut_rr.enable &&
            LightingRegs::IsLightingSamplerSupported(lighting.config,
                                                     LightingRegs::LightingSampler::ReflectRed)) {
            std::string value =
                GetLutValue(LightingRegs::LightingSampler::ReflectRed, light_config.num,
                            lighting.lut_rr.type, lighting.lut_rr.abs_input);
            value = "(" + std::to_string(lighting.lut_rr.scale) + " * " + value + ")";
            out += "refl_value.r = " + value + ";\n";
        } else {
            out += "refl_value.r = 1.0;\n";
        }

        // If enabled, lookup ReflectGreen value, otherwise, ReflectRed value is used
        if (lighting.lut_rg.enable &&
            LightingRegs::IsLightingSamplerSupported(lighting.config,
                                                     LightingRegs::LightingSampler::ReflectGreen)) {
            std::string value =
                GetLutValue(LightingRegs::LightingSampler::ReflectGreen, light_config.num,
                            lighting.lut_rg.type, lighting.lut_rg.abs_input);
            value = "(" + std::to_string(lighting.lut_rg.scale) + " * " + value + ")";
            out += "refl_value.g = " + value + ";\n";
        } else {
            out += "refl_value.g = refl_value.r;\n";
        }

        // If enabled, lookup ReflectBlue value, otherwise, ReflectRed value is used
        if (lighting.lut_rb.enable &&
            LightingRegs::IsLightingSamplerSupported(lighting.config,
                                                     LightingRegs::LightingSampler::ReflectBlue)) {
            std::string value =
                GetLutValue(LightingRegs::LightingSampler::ReflectBlue, light_config.num,
                            lighting.lut_rb.type, lighting.lut_rb.abs_input);
            value = "(" + std::to_string(lighting.lut_rb.scale) + " * " + value + ")";
            out += "refl_value.b = " + value + ";\n";
        } else {
            out += "refl_value.b = refl_value.r;\n";
        }

        // Specular 1 component
        std::string d1_lut_value = "1.0";
        if (lighting.lut_d1.enable &&
            LightingRegs::IsLightingSamplerSupported(
                lighting.config, LightingRegs::LightingSampler::Distribution1)) {
            // Lookup specular "distribution 1" LUT value
            std::string value =
                GetLutValue(LightingRegs::LightingSampler::Distribution1, light_config.num,
                            lighting.lut_d1.type, lighting.lut_d1.abs_input);
            d1_lut_value = "(" + std::to_string(lighting.lut_d1.scale) + " * " + value + ")";
        }
        std::string specular_1 =
            "(" + d1_lut_value + " * refl_value * " + light_src + ".specular_1)";
        if (light_config.geometric_factor_1) {
            specular_1 = "(" + specular_1 + " * geo_factor)";
        }

        // Fresnel
        // Note: only the last entry in the light slots applies the Fresnel factor
        if (light_index == lighting.src_num - 1 && lighting.lut_fr.enable &&
            LightingRegs::IsLightingSamplerSupported(lighting.config,
                                                     LightingRegs::LightingSampler::Fresnel)) {
            // Lookup fresnel LUT value
            std::string value =
                GetLutValue(LightingRegs::LightingSampler::Fresnel, light_config.num,
                            lighting.lut_fr.type, lighting.lut_fr.abs_input);
            value = "(" + std::to_string(lighting.lut_fr.scale) + " * " + value + ")";

            // Enabled for diffuse lighting alpha component
            if (lighting.fresnel_selector == LightingRegs::LightingFresnelSelector::PrimaryAlpha ||
                lighting.fresnel_selector == LightingRegs::LightingFresnelSelector::Both) {
                out += "diffuse_sum.a = " + value + ";\n";
            }

            // Enabled for the specular lighting alpha component
            if (lighting.fresnel_selector ==
                    LightingRegs::LightingFresnelSelector::SecondaryAlpha ||
                lighting.fresnel_selector == LightingRegs::LightingFresnelSelector::Both) {
                out += "specular_sum.a = " + value + ";\n";
            }
        }

        // Compute primary fragment color (diffuse lighting) function
        out += "diffuse_sum.rgb += ((" + light_src + ".diffuse * " + dot_product + ") + " +
               light_src + ".ambient) * " + dist_atten + " * " + spot_atten + ";\n";

        // Compute secondary fragment color (specular lighting) function
        out += "specular_sum.rgb += (" + specular_0 + " + " + specular_1 + ") * " +
               clamp_highlights + " * " + dist_atten + " * " + spot_atten + ";\n";
    }

    // Sum final lighting result
    out += "diffuse_sum.rgb += lighting_global_ambient;\n";
    out += "primary_fragment_color = clamp(diffuse_sum, vec4(0.0), vec4(1.0));\n";
    out += "secondary_fragment_color = clamp(specular_sum, vec4(0.0), vec4(1.0));\n";
}

using ProcTexClamp = TexturingRegs::ProcTexClamp;
using ProcTexShift = TexturingRegs::ProcTexShift;
using ProcTexCombiner = TexturingRegs::ProcTexCombiner;
using ProcTexFilter = TexturingRegs::ProcTexFilter;

void AppendProcTexShiftOffset(std::string& out, const std::string& v, ProcTexShift mode,
                              ProcTexClamp clamp_mode) {
    std::string offset = (clamp_mode == ProcTexClamp::MirroredRepeat) ? "1.0" : "0.5";
    switch (mode) {
    case ProcTexShift::None:
        out += "0";
        break;
    case ProcTexShift::Odd:
        out += offset + " * ((int(" + v + ") / 2) % 2)";
        break;
    case ProcTexShift::Even:
        out += offset + " * (((int(" + v + ") + 1) / 2) % 2)";
        break;
    default:
        LOG_CRITICAL(HW_GPU, "Unknown shift mode %u", static_cast<u32>(mode));
        out += "0";
        break;
    }
}

void AppendProcTexClamp(std::string& out, const std::string& var, ProcTexClamp mode) {
    switch (mode) {
    case ProcTexClamp::ToZero:
        out += var + " = " + var + " > 1.0 ? 0 : " + var + ";\n";
        break;
    case ProcTexClamp::ToEdge:
        out += var + " = " + "min(" + var + ", 1.0);\n";
        break;
    case ProcTexClamp::SymmetricalRepeat:
        out += var + " = " + "fract(" + var + ");\n";
        break;
    case ProcTexClamp::MirroredRepeat: {
        out +=
            var + " = int(" + var + ") % 2 == 0 ? fract(" + var + ") : 1.0 - fract(" + var + ");\n";
        break;
    }
    case ProcTexClamp::Pulse:
        out += var + " = " + var + " > 0.5 ? 1.0 : 0.0;\n";
        break;
    default:
        LOG_CRITICAL(HW_GPU, "Unknown clamp mode %u", static_cast<u32>(mode));
        out += var + " = " + "min(" + var + ", 1.0);\n";
        break;
    }
}

void AppendProcTexCombineAndMap(std::string& out, ProcTexCombiner combiner,
                                const std::string& map_lut) {
    std::string combined;
    switch (combiner) {
    case ProcTexCombiner::U:
        combined = "u";
        break;
    case ProcTexCombiner::U2:
        combined = "(u * u)";
        break;
    case TexturingRegs::ProcTexCombiner::V:
        combined = "v";
        break;
    case TexturingRegs::ProcTexCombiner::V2:
        combined = "(v * v)";
        break;
    case TexturingRegs::ProcTexCombiner::Add:
        combined = "((u + v) * 0.5)";
        break;
    case TexturingRegs::ProcTexCombiner::Add2:
        combined = "((u * u + v * v) * 0.5)";
        break;
    case TexturingRegs::ProcTexCombiner::SqrtAdd2:
        combined = "min(sqrt(u * u + v * v), 1.0)";
        break;
    case TexturingRegs::ProcTexCombiner::Min:
        combined = "min(u, v)";
        break;
    case TexturingRegs::ProcTexCombiner::Max:
        combined = "max(u, v)";
        break;
    case TexturingRegs::ProcTexCombiner::RMax:
        combined = "min(((u + v) * 0.5 + sqrt(u * u + v * v)) * 0.5, 1.0)";
        break;
    default:
        LOG_CRITICAL(HW_GPU, "Unknown combiner %u", static_cast<u32>(combiner));
        combined = "0.0";
        break;
    }
    out += "ProcTexLookupLUT(" + map_lut + ", " + combined + ")";
}

void AppendProcTexSampler(std::string& out, const PicaShaderConfig& config) {
    // LUT sampling uitlity
    // For NoiseLUT/ColorMap/AlphaMap, coord=0.0 is lut[0], coord=127.0/128.0 is lut[127] and
    // coord=1.0 is lut[127]+lut_diff[127]. For other indices, the result is interpolated using
    // value entries and difference entries.
    out += R"(
float ProcTexLookupLUT(samplerBuffer lut, float coord) {
    coord *= 128;
    float index_i = clamp(floor(coord), 0.0, 127.0);
    float index_f = coord - index_i; // fract() cannot be used here because 128.0 needs to be
                                     // extracted as index_i = 127.0 and index_f = 1.0
    vec2 entry = texelFetch(lut, int(index_i)).rg;
    return clamp(entry.r + entry.g * index_f, 0.0, 1.0);
}
    )";

    // Noise utility
    if (config.state.proctex.noise_enable) {
        // See swrasterizer/proctex.cpp for more information about these functions
        out += R"(
int ProcTexNoiseRand1D(int v) {
    const int table[] = int[](0,4,10,8,4,9,7,12,5,15,13,14,11,15,2,11);
    return ((v % 9 + 2) * 3 & 0xF) ^ table[(v / 9) & 0xF];
}

float ProcTexNoiseRand2D(vec2 point) {
    const int table[] = int[](10,2,15,8,0,7,4,5,5,13,2,6,13,9,3,14);
    int u2 = ProcTexNoiseRand1D(int(point.x));
    int v2 = ProcTexNoiseRand1D(int(point.y));
    v2 += ((u2 & 3) == 1) ? 4 : 0;
    v2 ^= (u2 & 1) * 6;
    v2 += 10 + u2;
    v2 &= 0xF;
    v2 ^= table[u2];
    return -1.0 + float(v2) * 2.0/ 15.0;
}

float ProcTexNoiseCoef(vec2 x) {
    vec2 grid  = 9.0 * proctex_noise_f * abs(x + proctex_noise_p);
    vec2 point = floor(grid);
    vec2 frac  = grid - point;

    float g0 = ProcTexNoiseRand2D(point) * (frac.x + frac.y);
    float g1 = ProcTexNoiseRand2D(point + vec2(1.0, 0.0)) * (frac.x + frac.y - 1.0);
    float g2 = ProcTexNoiseRand2D(point + vec2(0.0, 1.0)) * (frac.x + frac.y - 1.0);
    float g3 = ProcTexNoiseRand2D(point + vec2(1.0, 1.0)) * (frac.x + frac.y - 2.0);

    float x_noise = ProcTexLookupLUT(proctex_noise_lut, frac.x);
    float y_noise = ProcTexLookupLUT(proctex_noise_lut, frac.y);
    float x0 = mix(g0, g1, x_noise);
    float x1 = mix(g2, g3, x_noise);
    return mix(x0, x1, y_noise);
}
        )";
    }

    out += "vec4 ProcTex() {\n";
    out += "vec2 uv = abs(texcoord[" + std::to_string(config.state.proctex.coord) + "]);\n";

    // Get shift offset before noise generation
    out += "float u_shift = ";
    AppendProcTexShiftOffset(out, "uv.y", config.state.proctex.u_shift,
                             config.state.proctex.u_clamp);
    out += ";\n";
    out += "float v_shift = ";
    AppendProcTexShiftOffset(out, "uv.x", config.state.proctex.v_shift,
                             config.state.proctex.v_clamp);
    out += ";\n";

    // Generate noise
    if (config.state.proctex.noise_enable) {
        out += "uv += proctex_noise_a * ProcTexNoiseCoef(uv);\n";
        out += "uv = abs(uv);\n";
    }

    // Shift
    out += "float u = uv.x + u_shift;\n";
    out += "float v = uv.y + v_shift;\n";

    // Clamp
    AppendProcTexClamp(out, "u", config.state.proctex.u_clamp);
    AppendProcTexClamp(out, "v", config.state.proctex.v_clamp);

    // Combine and map
    out += "float lut_coord = ";
    AppendProcTexCombineAndMap(out, config.state.proctex.color_combiner, "proctex_color_map");
    out += ";\n";

    // Look up color
    // For the color lut, coord=0.0 is lut[offset] and coord=1.0 is lut[offset+width-1]
    out += "lut_coord *= " + std::to_string(config.state.proctex.lut_width - 1) + ";\n";
    // TODO(wwylele): implement mipmap
    switch (config.state.proctex.lut_filter) {
    case ProcTexFilter::Linear:
    case ProcTexFilter::LinearMipmapLinear:
    case ProcTexFilter::LinearMipmapNearest:
        out += "int lut_index_i = int(lut_coord) + " +
               std::to_string(config.state.proctex.lut_offset) + ";\n";
        out += "float lut_index_f = fract(lut_coord);\n";
        out += "vec4 final_color = texelFetch(proctex_lut, lut_index_i) + lut_index_f * "
               "texelFetch(proctex_diff_lut, lut_index_i);\n";
        break;
    case ProcTexFilter::Nearest:
    case ProcTexFilter::NearestMipmapLinear:
    case ProcTexFilter::NearestMipmapNearest:
        out += "lut_coord += " + std::to_string(config.state.proctex.lut_offset) + ";\n";
        out += "vec4 final_color = texelFetch(proctex_lut, int(round(lut_coord)));\n";
        break;
    }

    if (config.state.proctex.separate_alpha) {
        // Note: in separate alpha mode, the alpha channel skips the color LUT look up stage. It
        // uses the output of CombineAndMap directly instead.
        out += "float final_alpha = ";
        AppendProcTexCombineAndMap(out, config.state.proctex.alpha_combiner, "proctex_alpha_map");
        out += ";\n";
        out += "return vec4(final_color.xyz, final_alpha);\n}\n";
    } else {
        out += "return final_color;\n}\n";
    }
}

std::string GenerateFragmentShader(const PicaShaderConfig& config) {
    const auto& state = config.state;

    std::string out = R"(
#version 330 core
#define NUM_TEV_STAGES 6
#define NUM_LIGHTS 8

in vec4 primary_color;
in vec2 texcoord[3];
in float texcoord0_w;
in vec4 normquat;
in vec3 view;

in vec4 gl_FragCoord;

out vec4 color;

struct LightSrc {
    vec3 specular_0;
    vec3 specular_1;
    vec3 diffuse;
    vec3 ambient;
    vec3 position;
    vec3 spot_direction;
    float dist_atten_bias;
    float dist_atten_scale;
};

layout (std140) uniform shader_data {
    vec2 framebuffer_scale;
    int alphatest_ref;
    float depth_scale;
    float depth_offset;
    int scissor_x1;
    int scissor_y1;
    int scissor_x2;
    int scissor_y2;
    vec3 fog_color;
    vec2 proctex_noise_f;
    vec2 proctex_noise_a;
    vec2 proctex_noise_p;
    vec3 lighting_global_ambient;
    LightSrc light_src[NUM_LIGHTS];
    vec4 const_color[NUM_TEV_STAGES];
    vec4 tev_combiner_buffer_color;
};

uniform sampler2D tex[3];
uniform samplerBuffer lighting_lut;
uniform samplerBuffer fog_lut;
uniform samplerBuffer proctex_noise_lut;
uniform samplerBuffer proctex_color_map;
uniform samplerBuffer proctex_alpha_map;
uniform samplerBuffer proctex_lut;
uniform samplerBuffer proctex_diff_lut;

// Rotate the vector v by the quaternion q
vec3 quaternion_rotate(vec4 q, vec3 v) {
    return v + 2.0 * cross(q.xyz, cross(q.xyz, v) + q.w * v);
}

float LookupLightingLUT(int lut_index, int index, float delta) {
    vec2 entry = texelFetch(lighting_lut, lut_index * 256 + index).rg;
    return entry.r + entry.g * delta;
}

float LookupLightingLUTUnsigned(int lut_index, float pos) {
    int index = clamp(int(pos * 256.0), 0, 255);
    float delta = pos * 256.0 - index;
    return LookupLightingLUT(lut_index, index, delta);
}

float LookupLightingLUTSigned(int lut_index, float pos) {
    int index = clamp(int(pos * 128.0), -128, 127);
    float delta = pos * 128.0 - index;
    if (index < 0) index += 256;
    return LookupLightingLUT(lut_index, index, delta);
}

)";

    if (config.state.proctex.enable)
        AppendProcTexSampler(out, config);

    out += R"(
void main() {
vec4 primary_fragment_color = vec4(0.0);
vec4 secondary_fragment_color = vec4(0.0);
)";

    // Do not do any sort of processing if it's obvious we're not going to pass the alpha test
    if (state.alpha_test_func == FramebufferRegs::CompareFunc::Never) {
        out += "discard; }";
        return out;
    }

    // Append the scissor test
    if (state.scissor_test_mode != RasterizerRegs::ScissorMode::Disabled) {
        out += "if (";
        // Negate the condition if we have to keep only the pixels outside the scissor box
        if (state.scissor_test_mode == RasterizerRegs::ScissorMode::Include)
            out += "!";
        out += "(gl_FragCoord.x >= scissor_x1 && "
               "gl_FragCoord.y >= scissor_y1 && "
               "gl_FragCoord.x < scissor_x2 && "
               "gl_FragCoord.y < scissor_y2)) discard;\n";
    }

    // After perspective divide, OpenGL transform z_over_w from [-1, 1] to [near, far]. Here we use
    // default near = 0 and far = 1, and undo the transformation to get the original z_over_w, then
    // do our own transformation according to PICA specification.
    out += "float z_over_w = 2.0 * gl_FragCoord.z - 1.0;\n";
    out += "float depth = z_over_w * depth_scale + depth_offset;\n";
    if (state.depthmap_enable == RasterizerRegs::DepthBuffering::WBuffering) {
        out += "depth /= gl_FragCoord.w;\n";
    }

    if (state.lighting.enable)
        WriteLighting(out, config);

    out += "vec4 combiner_buffer = vec4(0.0);\n";
    out += "vec4 next_combiner_buffer = tev_combiner_buffer_color;\n";
    out += "vec4 last_tex_env_out = vec4(0.0);\n";

    for (size_t index = 0; index < state.tev_stages.size(); ++index)
        WriteTevStage(out, config, (unsigned)index);

    if (state.alpha_test_func != FramebufferRegs::CompareFunc::Always) {
        out += "if (";
        AppendAlphaTestCondition(out, state.alpha_test_func);
        out += ") discard;\n";
    }

    // Append fog combiner
    if (state.fog_mode == TexturingRegs::FogMode::Fog) {
        // Get index into fog LUT
        if (state.fog_flip) {
            out += "float fog_index = (1.0 - depth) * 128.0;\n";
        } else {
            out += "float fog_index = depth * 128.0;\n";
        }

        // Generate clamped fog factor from LUT for given fog index
        out += "float fog_i = clamp(floor(fog_index), 0.0, 127.0);\n";
        out += "float fog_f = fog_index - fog_i;\n";
        out += "vec2 fog_lut_entry = texelFetch(fog_lut, int(fog_i)).rg;\n";
        out += "float fog_factor = fog_lut_entry.r + fog_lut_entry.g * fog_f;\n";
        out += "fog_factor = clamp(fog_factor, 0.0, 1.0);\n";

        // Blend the fog
        out += "last_tex_env_out.rgb = mix(fog_color.rgb, last_tex_env_out.rgb, fog_factor);\n";
    } else if (state.fog_mode == TexturingRegs::FogMode::Gas) {
        Core::Telemetry().AddField(Telemetry::FieldType::Session, "VideoCore_Pica_UseGasMode",
                                   true);
        LOG_CRITICAL(Render_OpenGL, "Unimplemented gas mode");
        UNIMPLEMENTED();
    }

    out += "gl_FragDepth = depth;\n";
    out += "color = last_tex_env_out;\n";

    out += "}";

    return out;
}

std::string GenerateVertexShader() {
    std::string out = "#version 330 core\n";

    out += "layout(location = " + std::to_string((int)ATTRIBUTE_POSITION) +
           ") in vec4 vert_position;\n";
    out += "layout(location = " + std::to_string((int)ATTRIBUTE_COLOR) + ") in vec4 vert_color;\n";
    out += "layout(location = " + std::to_string((int)ATTRIBUTE_TEXCOORD0) +
           ") in vec2 vert_texcoord0;\n";
    out += "layout(location = " + std::to_string((int)ATTRIBUTE_TEXCOORD1) +
           ") in vec2 vert_texcoord1;\n";
    out += "layout(location = " + std::to_string((int)ATTRIBUTE_TEXCOORD2) +
           ") in vec2 vert_texcoord2;\n";
    out += "layout(location = " + std::to_string((int)ATTRIBUTE_TEXCOORD0_W) +
           ") in float vert_texcoord0_w;\n";
    out += "layout(location = " + std::to_string((int)ATTRIBUTE_NORMQUAT) +
           ") in vec4 vert_normquat;\n";
    out += "layout(location = " + std::to_string((int)ATTRIBUTE_VIEW) + ") in vec3 vert_view;\n";

    out += R"(
out vec4 primary_color;
out vec2 texcoord[3];
out float texcoord0_w;
out vec4 normquat;
out vec3 view;

void main() {
    primary_color = vert_color;
    texcoord[0] = vert_texcoord0;
    texcoord[1] = vert_texcoord1;
    texcoord[2] = vert_texcoord2;
    texcoord0_w = vert_texcoord0_w;
    normquat = vert_normquat;
    view = vert_view;
    gl_Position = vert_position;
    gl_ClipDistance[0] = -vert_position.z; // fixed PICA clipping plane z <= 0
    // TODO (wwylele): calculate gl_ClipDistance[1] from user-defined clipping plane
}
)";

    return out;
}

} // namespace GLShader
