Tessellation

#version 410 core

layout (location = 0) in vec3 Position_VS_in;
layout (location = 1) in vec2 TexCoord_VS_in;
layout (location = 2) in vec3 Normal_VS_in;

uniform mat4 gWorld;

out vec3 WorldPos_CS_in;
out vec2 TexCoord_CS_in;
out vec3 Normal_CS_in;

void main()
{
    WorldPos_CS_in = (gWorld * vec4(Position_VS_in, 1.0)).xyz;
    TexCoord_CS_in = TexCoord_VS_in;
    Normal_CS_in = (gWorld * vec4(Normal_VS_in, 0.0)).xyz;
}

#version 410 core

// define the number of CPs in the output patch
layout (vertices = 3) out;

uniform vec3 gEyeWorldPos;

// attributes of the input CPs
in vec3 WorldPos_CS_in[];
in vec2 TexCoord_CS_in[];
in vec3 Normal_CS_in[];

// attributes of the output CPs
out vec3 WorldPos_ES_in[];
out vec2 TexCoord_ES_in[];
out vec3 Normal_ES_in[];

void main()
{
    // Set the control points of the output patch
    TexCoord_ES_in[gl_InvocationID] = TexCoord_CS_in[gl_InvocationID];
    Normal_ES_in[gl_InvocationID] = Normal_CS_in[gl_InvocationID];
    WorldPos_ES_in[gl_InvocationID] = WorldPos_CS_in[gl_InvocationID];
    // Calculate the distance from the camera to the three control points
    float EyeToVertexDistance0 = distance(gEyeWorldPos, WorldPos_ES_in[0]);
    float EyeToVertexDistance1 = distance(gEyeWorldPos, WorldPos_ES_in[1]);
    float EyeToVertexDistance2 = distance(gEyeWorldPos, WorldPos_ES_in[2]);

    // Calculate the tessellation levels
    gl_TessLevelOuter[0] = GetTessLevel(EyeToVertexDistance1, EyeToVertexDistance2);
    gl_TessLevelOuter[1] = GetTessLevel(EyeToVertexDistance2, EyeToVertexDistance0);
    gl_TessLevelOuter[2] = GetTessLevel(EyeToVertexDistance0, EyeToVertexDistance1);
    gl_TessLevelInner[0] = gl_TessLevelOuter[2];
}

float GetTessLevel(float Distance0, float Distance1)
{
    float AvgDistance = (Distance0 + Distance1) / 2.0;

    if (AvgDistance <= 2.0) {
        return 10.0;
    }
    else if (AvgDistance <= 5.0) {
        return 7.0;
    }
    else {
        return 3.0;
    }
}

#version 410 core

layout(triangles, equal_spacing, ccw) in;
uniform mat4 gVP;
uniform sampler2D gDisplacementMap;
uniform float gDispFactor;

in vec3 WorldPos_ES_in[];
in vec2 TexCoord_ES_in[];
in vec3 Normal_ES_in[];

out vec3 WorldPos_FS_in;
out vec2 TexCoord_FS_in;
out vec3 Normal_FS_in;

void main()
{
    // Interpolate the attributes of the output vertex using the barycentric coordinates
    TexCoord_FS_in = interpolate2D(TexCoord_ES_in[0], TexCoord_ES_in[1], TexCoord_ES_in[2]);
    Normal_FS_in = interpolate3D(Normal_ES_in[0], Normal_ES_in[1], Normal_ES_in[2]);
    Normal_FS_in = normalize(Normal_FS_in);
    WorldPos_FS_in = interpolate3D(WorldPos_ES_in[0], WorldPos_ES_in[1], WorldPos_ES_in[2]);
    // Displace the vertex along the normal
    float Displacement = texture(gDisplacementMap, TexCoord_FS_in.xy).x;
    WorldPos_FS_in += Normal_FS_in * Displacement * gDispFactor;
    gl_Position = gVP * vec4(WorldPos_FS_in, 1.0);
}

vec2 interpolate2D(vec2 v0, vec2 v1, vec2 v2)
{
    return vec2(gl_TessCoord.x) * v0 + vec2(gl_TessCoord.y) * v1 + vec2(gl_TessCoord.z) * v2;
}

vec3 interpolate3D(vec3 v0, vec3 v1, vec3 v2)
{
    return vec3(gl_TessCoord.x) * v0 + vec3(gl_TessCoord.y) * v1 + vec3(gl_TessCoord.z) * v2;
}

#version 410 core

const int MAX_POINT_LIGHTS = 2;
const int MAX_SPOT_LIGHTS = 2;

in vec2 TexCoord_FS_in;
in vec3 Normal_FS_in;
in vec3 WorldPos_FS_in;

out vec4 FragColor;

struct BaseLight
{
    vec3 Color;
    float AmbientIntensity;
    float DiffuseIntensity;
};

struct DirectionalLight
{
    BaseLight Base;
    vec3 Direction;
};

struct Attenuation
{
    float Constant;
    float Linear;
    float Exp;
};

struct PointLight
{
    BaseLight Base;
    vec3 Position;
    Attenuation Atten;
};

struct SpotLight
{
    PointLight Base;
    vec3 Direction;
    float Cutoff;
};

uniform int gNumPointLights;
uniform int gNumSpotLights;
uniform DirectionalLight gDirectionalLight;
uniform PointLight gPointLights[MAX_POINT_LIGHTS];
uniform SpotLight gSpotLights[MAX_SPOT_LIGHTS];
uniform sampler2D gColorMap;
uniform vec3 gEyeWorldPos;
uniform float gMatSpecularIntensity;
uniform float gSpecularPower;

vec4 CalcLightInternal(BaseLight Light, vec3 LightDirection, vec3 Normal)
{
    vec4 AmbientColor = vec4(Light.Color * Light.AmbientIntensity, 1.0f);
    float DiffuseFactor = dot(Normal, -LightDirection);

    vec4 DiffuseColor  = vec4(0, 0, 0, 0);
    vec4 SpecularColor = vec4(0, 0, 0, 0);

    if (DiffuseFactor > 0) {
        DiffuseColor = vec4(Light.Color * Light.DiffuseIntensity * DiffuseFactor, 1.0f);

        vec3 VertexToEye = normalize(gEyeWorldPos - WorldPos_FS_in);
        vec3 LightReflect = normalize(reflect(LightDirection, Normal));
        float SpecularFactor = dot(VertexToEye, LightReflect);
        if (SpecularFactor > 0) {
            SpecularFactor = pow(SpecularFactor, gSpecularPower);
            SpecularColor = vec4(Light.Color * gMatSpecularIntensity * SpecularFactor, 1.0f);
        }
    }

    return (AmbientColor + DiffuseColor + SpecularColor);
}

vec4 CalcDirectionalLight(vec3 Normal)
{
    return CalcLightInternal(gDirectionalLight.Base, gDirectionalLight.Direction, Normal);
}

vec4 CalcPointLight(PointLight l, vec3 Normal)
{
    vec3 LightDirection = WorldPos_FS_in - l.Position;
    float Distance = length(LightDirection);
    LightDirection = normalize(LightDirection);

    vec4 Color = CalcLightInternal(l.Base, LightDirection, Normal);
    float AttenuationFactor =  l.Atten.Constant +
                         l.Atten.Linear * Distance +
                         l.Atten.Exp * Distance * Distance;

    return Color / AttenuationFactor;
}

vec4 CalcSpotLight(SpotLight l, vec3 Normal)
{
    vec3 LightToPixel = normalize(WorldPos_FS_in - l.Base.Position);
    float SpotFactor = dot(LightToPixel, l.Direction);

    if (SpotFactor > l.Cutoff) {
        vec4 Color = CalcPointLight(l.Base, Normal);
        return Color * (1.0 - (1.0 - SpotFactor) * 1.0/(1.0 - l.Cutoff));
    }
    else {
        return vec4(0,0,0,0);
    }
}

void main()
{
    vec3 Normal = normalize(Normal_FS_in);
    vec4 TotalLight = CalcDirectionalLight(Normal);

    for (int i = 0 ; i < gNumPointLights ; i++) {
        TotalLight += CalcPointLight(gPointLights[i], Normal);
    }

    for (int i = 0 ; i < gNumSpotLights ; i++) {
        TotalLight += CalcSpotLight(gSpotLights[i], Normal);
    }

    FragColor = texture(gColorMap, TexCoord_FS_in.xy) * TotalLight;
}