feat(underwater): add volume scattering and shadow mapping for light shafts

- Increase DEPTH_FADE_DISTANCE from 8 to 10
- Remove conditional so depth fade always applies
- Darken deepColor from (0, 0.08, 0.15) to (0, 0.015, 0.045)

assets/shaders/under_water_f_shader.glsl

@@ -1,14 +1,75 @@
 #version 460
 
 in vec2 TexCoord;
+in vec3 rayDir;
 
 out vec4 FragColor;
 
-uniform sampler2D u_sceneTexture;
+layout (binding = 0) uniform sampler2D u_sceneTexture;
+layout (binding = 1) uniform sampler2D u_depthTexture;
+layout (binding = 2) uniform sampler2D u_shadowMap;
+uniform mat4 u_lightSpaceMatrix;
 uniform float u_time;
 uniform bool u_underwater;
 uniform vec3 u_waterColor;
 uniform float u_fogDensity;
+uniform mat4 InverseViewProjection; 
+uniform vec3 cameraPos;
+uniform vec3 sunDir;
+uniform vec3 sunColor;
+uniform float waterDensity;
+
+float hash(vec2 p) {
+    return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453);
+}
+
+float noise(vec2 p) {
+    vec2 i = floor(p);
+    vec2 f = fract(p);
+    f = f * f * (3.0 - 2.0 * f);   
+
+    return mix(
+        mix(hash(i), hash(i + vec2(1.0, 0.0)), f.x),
+        mix(hash(i + vec2(0.0, 1.0)), hash(i + vec2(1.0, 1.0)), f.x),
+        f.y
+    );
+}
+
+float fbm(vec2 p) {
+    float value = 0.0;
+    float amp = 0.5;
+    float freq = 1.0;
+    for (int i = 0; i < 4; ++i) {
+        value += amp * noise(p * freq);
+        freq *= 2.0;
+        amp *= 0.5;
+    }
+    return value;
+}
+
+float getCausticValue(float x, float y, float z) {
+    float w = 8.0;      
+    float strength = 4.0;  
+    vec2 coord = vec2(x, y) * w + z * 0.5; 
+ 
+    float n = fbm(coord);
+
+    float caustic = pow(n, 3.0) * strength;
+    return caustic;
+}
+
+float getShadow(vec3 worldPos) {
+    vec4 posLightSpace = u_lightSpaceMatrix * vec4(worldPos, 1.0);
+    vec3 projCoords = posLightSpace.xyz / posLightSpace.w;
+    projCoords = projCoords * 0.5 + 0.5;
+    
+    if (projCoords.z > 1.0) return 1.0; 
+    
+    float closestDepth = texture(u_shadowMap, projCoords.xy).r;
+    float currentDepth = projCoords.z;
+    
+    return currentDepth - 0.005 > closestDepth ? 0.0 : 1.0; 
+}
 
 void main() {
     vec4 original = texture(u_sceneTexture, TexCoord);
@@ -18,6 +79,12 @@ void main() {
         return;
     }
 
+    float rawDepth = texture(u_depthTexture, TexCoord).r;
+    vec3 ndc = vec3(TexCoord * 2.0 - 1.0, rawDepth * 2.0 - 1.0);
+    vec4 worldPosH = InverseViewProjection * vec4(ndc, 1.0);
+    vec3 worldPos = worldPosH.xyz / worldPosH.w;
+    float sceneDistance = distance(cameraPos, worldPos);
+    
     vec2 distoredUV = TexCoord;
     float strength = 0.003;
     distoredUV.x += sin(TexCoord.y * 15.0 + u_time * 5.0) * strength;
@@ -25,11 +92,46 @@ void main() {
     distoredUV = clamp(distoredUV, 0.001, 0.999);
     vec4 distorted = texture(u_sceneTexture, distoredUV);  
 
-    float caustic = 0.9 + 0.1 * sin(TexCoord.x * 20.0 + u_time) * cos(TexCoord.y * 20.0 + u_time * 1.2);
-    vec3 causticLight = vec3(caustic, caustic * 0.95, caustic * 0.9);
-    //vec3 causticLight = vec3(1.0);
+    float rawCaustic = getCausticValue(TexCoord.x, TexCoord.y, u_time * 0.3);
+    float caustic = 0.5 + rawCaustic * 0.5;    
+    vec3 causticLight = vec3(caustic * 0.9, caustic, caustic * 0.7);
+
     float fogFactor = clamp(1.0 - (TexCoord.y * u_fogDensity * 10.0), 0.0, 1.0);
     vec3 mixed = mix(u_waterColor, distorted.rgb * causticLight, fogFactor);
+    // Volume Scattering
+    vec3 rayOrigin = cameraPos;
+    vec3 rayDirection = normalize(rayDir);
 
-    FragColor = vec4(mixed, 1.0);
+    float maxDist = 10.0;        // Maximum visible distance
+    float stepSize = 0.4;     
+    float phasePower = 8.0;      // Beam Sharpness
+
+    vec3 scattering = vec3(0.0);
+    float transmittance = 1.0;
+    
+    float cosTheta = dot(rayDirection, sunDir);
+    float phase = pow(max(cosTheta, 0.0), phasePower);
+
+    for (float t = 0.0; t < maxDist; t += stepSize) {
+
+        if (t > sceneDistance) break;
+        vec3 pos = rayOrigin + rayDirection * t;
+
+        float shadow = getShadow(pos);
+
+        float density = waterDensity; 
+
+
+        vec3 absorption = vec3(0.3, 0.08, 0.02); // Absorption coefficient per meter
+        vec3 sunLightAtPos = sunColor * exp(-absorption * t);
+
+        scattering += density * phase * sunLightAtPos * transmittance * stepSize * shadow;
+
+        float extinction = waterDensity * 1.5; // Extinction coefficient, tunable
+        transmittance *= exp(-extinction * stepSize);
+        if (transmittance < 0.01) break;
+    }
+
+    FragColor.rgb = mixed + scattering;
+    FragColor.a = 1.0;
 }

assets/shaders/under_water_v_shader.glsl

@@ -3,9 +3,18 @@
 layout (location = 0) in vec2 pos;
 layout (location = 1) in vec2 texCoord;
 
-out vec2 TexCoord;
+uniform mat4 InverseViewProjection; 
+uniform vec3 cameraPos;
 
+out vec2 TexCoord;
+out vec3 rayDir;
 void main() {
-    gl_Position = vec4(pos.x, pos.y, 0.0, 1.0);
     TexCoord = texCoord;
+    vec4 clipPos = vec4(pos, 1.0, 1.0);
+    vec4 worldPosH = InverseViewProjection * clipPos;
+    vec3 worldPos = worldPosH.xyz / worldPosH.w;
+    vec3 RayDir = worldPos - cameraPos;
+    rayDir = normalize(RayDir);
+    gl_Position = clipPos;
+    
 }

assets/shaders/water_f_shader.glsl

@@ -237,9 +237,9 @@ void main() {
     vec3 sceneViewPos = reconstructViewPos(screenUV, sceneDepthRaw);
     float waterDepth = vert_pos.z - sceneViewPos.z;  
     waterDepth = max(waterDepth, 0.0);  
-    // fully deep water
-    const float DEPTH_FADE_DISTANCE = 8.0;  
-    float depthFactor = underwater ? 0.0 : clamp(waterDepth / DEPTH_FADE_DISTANCE, 0.0, 1.0);
+
+    const float DEPTH_FADE_DISTANCE = 10; 
+    float depthFactor = clamp(waterDepth / DEPTH_FADE_DISTANCE, 0.0, 1.0);
 
     if (underwater) {
         reflectColor = vec3(0.0);
@@ -287,7 +287,7 @@ void main() {
 
     if (enableDepthFade) {
         vec3 shallowColor = vec3(0.4, 0.75, 0.7);   
-        vec3 deepColor = vec3(0.0, 0.08, 0.15);
+        vec3 deepColor = vec3(0.0, 0.015, 0.045); 
 
         vec3 waterTint = mix(shallowColor, deepColor, depthFactor);
 

include/Cubed/primitive_data.hpp

@@ -212,7 +212,7 @@ constexpr float CROSS_NORMALS[2][6][3] = {
      {0.0f, 1.0f, 0.0f}}};
 
 #pragma endregion
-
+// [-1, 1]
 constexpr float QUAD_VERTICES[] = {
     // postion        // texcoorlds
     -1.0f, 1.0f, 0.0f, 1.0f, -1.0f, -1.0f, 0.0f, 0.0f, 1.0f, -1.0f, 1.0f, 0.0f,

include/Cubed/renderer.hpp

@@ -45,10 +45,12 @@ public:
     float& cloud_threshold_low();
     float& cloud_threshold_high();
     float& refract_strength();
+    float& underwater_fog_density();
+    float& water_density();
 
 private:
     struct ParallelLight {
-        glm::vec3 sundir;
+        glm::vec3 sundir; // direction from sun to vertex
         glm::vec3 lightdir;
         float sun_height = 0.0f;
         float day_light = 0.0f;
@@ -56,6 +58,7 @@ private:
         glm::vec3 sun_color;
         glm::vec3 directional_light_color;
         glm::vec3 finnal_ambient_color;
+        glm::mat4 light_space_matrix;
     };
 
     struct SkyUniform {
@@ -115,7 +118,7 @@ private:
 
     GLuint m_fbo = 0;
     GLuint m_screen_texture = 0;
-    GLuint m_depth_texture = 0;
+    GLuint m_screen_depth_texture = 0;
 
     GLuint m_oit_fbo = 0;
     GLuint m_accum_texture = 0;
@@ -152,6 +155,10 @@ private:
 
     float m_refract_strength = 0.03f;
 
+    float m_underwater_fog_density = 0.08f;
+
+    float m_water_density = 0.12f;
+
     ParallelLight m_parallel_light;
     SkyUniform m_sky_uniform;
     /*

src/dev_panel.cpp

@@ -662,6 +662,11 @@ void DevPanel::show_shader_tab_item() {
         ImGui::Checkbox("Water Perturb", &m_app.renderer().water_perturb());
         ImGui::SameLine();
         ImGui::Checkbox("WaterDepthFade", &m_app.renderer().water_depth_fade());
+        ImGui::SliderFloat("Underwater Fog Density",
+                           &m_app.renderer().underwater_fog_density(), 0.0f,
+                           1.0f);
+        ImGui::SliderFloat("Water Density", &m_app.renderer().water_density(),
+                           0.0f, 1.0f);
         ImGui::EndTabItem();
     }
 }

src/renderer.cpp

@@ -37,7 +37,7 @@ Renderer::~Renderer() {
     glDeleteVertexArrays(NUM_VAO, m_vao.data());
     glDeleteFramebuffers(1, &m_fbo);
     glDeleteTextures(1, &m_screen_texture);
-    glDeleteTextures(1, &m_depth_texture);
+    glDeleteTextures(1, &m_screen_depth_texture);
 
     glDeleteFramebuffers(1, &m_oit_fbo);
     glDeleteTextures(1, &m_accum_texture);
@@ -443,11 +443,19 @@ void Renderer::render_underwater() {
     shader.set_loc("u_time", static_cast<float>(glfwGetTime()));
     shader.set_loc("u_underwater", m_camera.is_under_water());
     shader.set_loc("u_waterColor", glm::vec3(0.1f, 0.25f, 0.35f));
-    shader.set_loc("u_fogDensity", 0.08f);
-
+    shader.set_loc("u_fogDensity", m_underwater_fog_density);
+    shader.set_loc("cameraPos", m_camera.get_camera_pos());
+    shader.set_loc("sunDir", -m_parallel_light.sundir);
+    shader.set_loc("waterDensity", m_water_density);
+    shader.set_loc("InverseViewProjection", glm::inverse(m_p_mat * m_v_mat));
+    shader.set_loc("sunColor", m_parallel_light.sun_color);
+    shader.set_loc("u_lightSpaceMatrix", m_parallel_light.light_space_matrix);
     glActiveTexture(GL_TEXTURE0);
     glBindTexture(GL_TEXTURE_2D, m_screen_texture);
-
+    glActiveTexture(GL_TEXTURE1);
+    glBindTexture(GL_TEXTURE_2D, m_screen_depth_texture);
+    glActiveTexture(GL_TEXTURE2);
+    glBindTexture(GL_TEXTURE_2D, m_depth_map_texture);
     glDrawArrays(GL_TRIANGLES, 0, 6);
     glBindVertexArray(0);
 }
@@ -483,7 +491,7 @@ void Renderer::updata_framebuffer(int width, int height) {
     glBindFramebuffer(GL_FRAMEBUFFER, m_fbo);
 
     glDeleteTextures(1, &m_screen_texture);
-    glDeleteTextures(1, &m_depth_texture);
+    glDeleteTextures(1, &m_screen_depth_texture);
 
     glGenTextures(1, &m_screen_texture);
     glBindTexture(GL_TEXTURE_2D, m_screen_texture);
@@ -495,14 +503,14 @@ void Renderer::updata_framebuffer(int width, int height) {
     glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
                            m_screen_texture, 0);
 
-    glGenTextures(1, &m_depth_texture);
-    glBindTexture(GL_TEXTURE_2D, m_depth_texture);
+    glGenTextures(1, &m_screen_depth_texture);
+    glBindTexture(GL_TEXTURE_2D, m_screen_depth_texture);
     glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT32F, width, height, 0,
                  GL_DEPTH_COMPONENT, GL_FLOAT, NULL);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
     glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D,
-                           m_depth_texture, 0);
+                           m_screen_depth_texture, 0);
 
     if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
         Logger::error("FBO incomplete after resize!");
@@ -587,7 +595,7 @@ void Renderer::updata_framebuffer(int width, int height) {
 #pragma region render_world
 void Renderer::render_world() {
     // shader map
-    glm::mat4 light_space_matrix;
+    glm::mat4& light_space_matrix = m_parallel_light.light_space_matrix;
     auto& m_render_snapshots = m_world.render_snapshots();
     auto& camera_pos = m_camera.get_camera_pos();
     float texels_per_unit = 0.0f;
@@ -868,7 +876,7 @@ void Renderer::render_world() {
     glActiveTexture(GL_TEXTURE1);
     glBindTexture(GL_TEXTURE_2D, m_screen_texture);
     glActiveTexture(GL_TEXTURE2);
-    glBindTexture(GL_TEXTURE_2D, m_depth_texture);
+    glBindTexture(GL_TEXTURE_2D, m_screen_depth_texture);
 
     glActiveTexture(GL_TEXTURE0);
     for (const auto& snapshot : m_render_snapshots) {
@@ -980,4 +988,6 @@ float& Renderer::cloud_speed() { return m_cloud_speed; }
 float& Renderer::cloud_threshold_low() { return m_cloud_threshold_low; }
 float& Renderer::cloud_threshold_high() { return m_cloud_threshold_high; }
 float& Renderer::refract_strength() { return m_refract_strength; }
+float& Renderer::underwater_fog_density() { return m_underwater_fog_density; }
+float& Renderer::water_density() { return m_water_density; }
 } // namespace Cubed