//
// Created by sfd on 25-7-28.
//

#include "DemoShader.h"

#include <cmath>

void DemoVertexShader(BlinnVaryings& varyings, const BlinnVertex& vertex, const BlinnUniform& uniform)
{
    varyings.ClipPos = uniform.MVP * vertex.ModelPosition;
    varyings.TexCoord = vertex.TexCoord;
    varyings.WorldPos = uniform.Model * vertex.ModelPosition;
    varyings.WorldNormal = uniform.ModelNormalToWorld * Math::Vec4{ vertex.ModelNormal, 0.0f};
}

Math::Vec4 DemoFragmentShader(bool& discard, const BlinnVaryings& varyings, const BlinnUniform& uniform)
{
    discard = false;

    const Math::Vec3 cameraPos = uniform.Camera;
    const Math::Vec3 lightPos = uniform.LightPos;
    const Math::Vec3 worldPos = varyings.WorldPos;

    Math::Vec3 worldNormal = Math::Normalize(varyings.WorldNormal);
    const Math::Vec3 viewDir = Math::Normalize(cameraPos - worldPos);
    const Math::Vec3 lightDir = Math::Normalize(lightPos - worldPos);

    Math::Vec3 halfDir = Math::Normalize(viewDir + lightDir);

    Math::Vec3 ambient = uniform.LightAmbient;
    Math::Vec3 specularStrength {1.0f, 1.0f, 1.0f};
    Math::Vec3 diffColor {1.0f , 1.0f , 1.0f};
    if (uniform.Diffuse)
    {
        const Math::Vec2& texCoord = varyings.TexCoord;
        diffColor = uniform.Diffuse->Sample(texCoord);
        ambient = ambient * diffColor;
        if (uniform.Specular)
            specularStrength = uniform.Specular->Sample(texCoord);
    }


    Math::Vec3 diffuse = std::max(0.0f, Math::Dot(worldNormal, lightDir)) * uniform.LightDiffuse * diffColor;
    Math::Vec3 specular = (float)pow(std::max(0.0f, Math::Dot(halfDir, worldNormal)), uniform.Shininess) * uniform.LightSPecular * specularStrength;

    Math::Vec3 result = (ambient + diffuse + specular);

    return {result, 1.0f};
}