Implement PBR

assets/shaders/pbr.frag

@@ -0,0 +1,160 @@
+#version 330 core
+
+in  vec3 v_normal;
+in  vec2 v_tex;
+in  vec3 v_position; // view-space position
+
+out vec4 frag_color;
+
+// Material inputs
+uniform sampler2D u_base_color_map;      // sRGB
+uniform int       u_has_base_color_map;
+uniform vec4      u_base_color_factor;
+
+uniform sampler2D u_metallic_roughness_map; // linear, (r=occlusion in glTF separate, g=roughness, b=metallic)
+uniform int       u_has_metallic_roughness_map;
+uniform float     u_metallic_factor;
+uniform float     u_roughness_factor;
+
+uniform sampler2D u_occlusion_map; // linear (r)
+uniform int       u_has_occlusion_map;
+
+uniform sampler2D u_emissive_map; // sRGB
+uniform int       u_has_emissive_map;
+uniform vec3      u_emissive_factor;
+
+// Directional light (in view space)
+uniform vec3  u_dir_light_dir;       // direction from light towards the scene (L)
+uniform vec3  u_dir_light_color;
+uniform float u_dir_light_intensity;
+
+// Point lights (in view space)
+#define MAX_POINT_LIGHTS 4
+uniform int   u_point_light_count;
+uniform vec3  u_point_light_pos[MAX_POINT_LIGHTS];
+uniform vec3  u_point_light_color[MAX_POINT_LIGHTS];
+uniform float u_point_light_intensity[MAX_POINT_LIGHTS];
+uniform float u_point_light_range[MAX_POINT_LIGHTS];
+
+const float PI = 3.14159265359;
+
+vec3 fresnel_schlick(float cosTheta, vec3 F0) {
+    return F0 + (1.0 - F0) * pow(1.0 - cosTheta, 5.0);
+}
+
+float distribution_ggx(float NdotH, float alpha) {
+    float a2 = alpha * alpha;
+    float denom = (NdotH * NdotH) * (a2 - 1.0) + 1.0;
+    return a2 / (PI * denom * denom + 1e-6);
+}
+
+float geometry_schlick_ggx(float NdotV, float k) {
+    return NdotV / (NdotV * (1.0 - k) + k + 1e-6);
+}
+
+float geometry_smith(float NdotV, float NdotL, float alpha) {
+    // Schlick-GGX with k from alpha for direct lighting
+    float k = (alpha + 1.0);
+    k = (k * k) / 8.0;
+    float ggx1 = geometry_schlick_ggx(NdotV, k);
+    float ggx2 = geometry_schlick_ggx(NdotL, k);
+    return ggx1 * ggx2;
+}
+
+struct PBRMaterial {
+    vec3 baseColor;
+    float metallic;
+    float roughness;
+    float ao;
+    vec3 emissive;
+};
+
+PBRMaterial getMaterial() {
+    // Base color (sampled as sRGB then assumed linear by GL; still gamma-correct final output)
+    vec3 baseTex = (u_has_base_color_map != 0) ? texture(u_base_color_map, v_tex).rgb : vec3(1.0);
+    vec3 baseColor = baseTex * u_base_color_factor.rgb;
+
+    float metallicTex = (u_has_metallic_roughness_map != 0) ? texture(u_metallic_roughness_map, v_tex).b : 1.0;
+    float roughnessTex = (u_has_metallic_roughness_map != 0) ? texture(u_metallic_roughness_map, v_tex).g : 1.0;
+
+    float metallic  = clamp(u_metallic_factor  * metallicTex,  0.0, 1.0);
+    float roughness = clamp(u_roughness_factor * roughnessTex, 0.04, 1.0);
+
+    float ao = (u_has_occlusion_map != 0) ? texture(u_occlusion_map, v_tex).r : 1.0;
+
+    vec3 emissiveTex = (u_has_emissive_map != 0) ? texture(u_emissive_map, v_tex).rgb : vec3(0.0);
+    vec3 emissive = emissiveTex * u_emissive_factor;
+
+    PBRMaterial m;
+    m.baseColor = baseColor;
+    m.metallic = metallic;
+    m.roughness = roughness;
+    m.ao = ao;
+    m.emissive = emissive;
+    return m;
+}
+
+vec3 evaluatePBR(vec3 N, vec3 V, vec3 L, vec3 lightColor, float lightIntensity, PBRMaterial m) {
+    vec3 H = normalize(V + L);
+    float NdotV = max(dot(N, V), 0.0);
+    float NdotL = max(dot(N, L), 0.0);
+    float NdotH = max(dot(N, H), 0.0);
+    float HdotV = max(dot(H, V), 0.0);
+
+    if (NdotL <= 0.0 || NdotV <= 0.0) return vec3(0.0);
+
+    float alpha = m.roughness * m.roughness;
+
+    vec3 F0 = mix(vec3(0.04), m.baseColor, m.metallic);
+    vec3  F = fresnel_schlick(HdotV, F0);
+    float D = distribution_ggx(NdotH, alpha);
+    float G = geometry_smith(NdotV, NdotL, alpha);
+
+    vec3  numerator   = F * D * G;
+    float denominator = max(4.0 * NdotV * NdotL, 1e-6);
+    vec3  specular    = numerator / denominator;
+
+    vec3 kS = F;
+    vec3 kD = (vec3(1.0) - kS) * (1.0 - m.metallic);
+
+    vec3 diffuse = (m.baseColor / PI) * kD;
+
+    vec3 radiance = lightColor * lightIntensity;
+
+    return (diffuse + specular) * radiance * NdotL;
+}
+
+void main() {
+    PBRMaterial mat = getMaterial();
+
+    vec3 N = normalize(v_normal);
+    vec3 V = normalize(-v_position); // camera at origin in view-space
+
+    vec3 color = vec3(0.0);
+
+    // Directional light contribution
+    vec3 Ld = normalize(u_dir_light_dir);
+    color += evaluatePBR(N, V, Ld, u_dir_light_color, u_dir_light_intensity, mat);
+
+    // Point lights
+    for (int i = 0; i < u_point_light_count && i < MAX_POINT_LIGHTS; ++i) {
+        vec3 toLight = u_point_light_pos[i] - v_position;
+        float dist   = length(toLight);
+        vec3  L      = toLight / max(dist, 1e-4);
+
+        float cutoff = 1.0 - smoothstep(0.9 * u_point_light_range[i], u_point_light_range[i], dist);
+        float attenuation = (1.0 / max(dist * dist, 1e-4)) * cutoff;
+
+        vec3 contrib = evaluatePBR(N, V, L, u_point_light_color[i], u_point_light_intensity[i] * attenuation, mat);
+        color += contrib;
+    }
+
+    // Simple ambient and AO
+    vec3 ambient = 0.03 * mat.baseColor * (1.0 - mat.metallic) * mat.ao;
+    color += ambient + mat.emissive;
+
+    // Gamma correction to sRGB
+    color = pow(color, vec3(1.0 / 2.2));
+
+    frag_color = vec4(color, u_base_color_factor.a);
+}