feat(water): add noise-based caustics and configurable fog density

assets/shaders/under_water_f_shader.glsl

@@ -10,6 +10,45 @@ uniform bool u_underwater;
 uniform vec3 u_waterColor;
 uniform float u_fogDensity;
 
+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;
+}
+
 void main() {
     vec4 original = texture(u_sceneTexture, TexCoord);
 
@@ -23,11 +62,12 @@ void main() {
     distoredUV.x += sin(TexCoord.y * 15.0 + u_time * 5.0) * strength;
     distoredUV.y += cos(TexCoord.x * 15.0 + u_time * 4.3) * strength;
     distoredUV = clamp(distoredUV, 0.001, 0.999);
-    vec4 distorted = texture(u_sceneTexture, distoredUV);
+    vec4 distorted = texture(u_sceneTexture, distoredUV);  
+
+    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 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 fogFactor = clamp(1.0 - (TexCoord.y * u_fogDensity * 10.0), 0.0, 1.0);
     vec3 mixed = mix(u_waterColor, distorted.rgb * causticLight, fogFactor);
 

include/Cubed/renderer.hpp

@@ -45,6 +45,7 @@ public:
     float& cloud_threshold_low();
     float& cloud_threshold_high();
     float& refract_strength();
+    float& underwater_fog_density();
 
 private:
     struct ParallelLight {
@@ -152,6 +153,8 @@ private:
 
     float m_refract_strength = 0.03f;
 
+    float m_underwater_fog_density = 0.08f;
+
     ParallelLight m_parallel_light;
     SkyUniform m_sky_uniform;
     /*

src/dev_panel.cpp

@@ -662,6 +662,9 @@ 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::EndTabItem();
     }
 }

src/renderer.cpp

@@ -443,7 +443,7 @@ 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);
 
     glActiveTexture(GL_TEXTURE0);
     glBindTexture(GL_TEXTURE_2D, m_screen_texture);
@@ -980,4 +980,5 @@ 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; }
 } // namespace Cubed