feat(renderer): smooth shadow sun direction transitions using quantized directions and slerp

include/Cubed/renderer.hpp

@@ -45,6 +45,7 @@ private:
     static constexpr float SUN_SIZE = 50.0f;
     static constexpr float MOON_SIZE = 50.0f;
     static constexpr float DEPTH_MAP_SIZE = 4096.0f;
+    static constexpr float ANGLE_STEP_DEG = 0.5f;
     float m_ambient_strength = 0.1f;
 
     const Camera& m_camera;
@@ -93,6 +94,12 @@ private:
     glm::mat4 m_ui_m_matrix;
     std::unordered_map<std::size_t, Shader> m_shaders;
 
+    glm::vec3 m_blend_from_sundir;
+    glm::vec3 m_blend_to_sundir;
+    float m_blend_t = 1.0f;
+    bool m_blend_initialized = false;
+    static constexpr float BLEND_DURATION = 0.15f;
+
     /*
     0 - quad vao
     1 - sky vao
@@ -114,6 +121,11 @@ private:
     void render_world();
     void render_underwater();
     void render_dev_panel();
+
+    glm::vec3 quantize_sun_direction(const glm::vec3& sundir,
+                                     float angle_step_deg) const;
+    glm::vec3 get_smoothed_shadow_sundir(const glm::vec3& raw_shadow_sundir,
+                                         float dt);
 };
 
 } // namespace Cubed

include/Cubed/tools/math_tools.hpp

@@ -12,6 +12,8 @@ float smootherstep(float edge0, float edge1, float x);
 bool is_aabb_in_frustum(const glm::vec3& center, const glm::vec3& half_extents,
                         const std::vector<glm::vec4>& planes);
 float deterministic_random(int x, int z, uint64_t seed);
+glm::vec3 slerp(const glm::vec3& from, const glm::vec3& to, float t);
+
 } // namespace Math
 
 } // namespace Cubed

src/gameplay/world.cpp

@@ -6,6 +6,7 @@
 #include "Cubed/tools/cubed_hash.hpp"
 
 #include <execution>
+#include <glm/gtc/constants.hpp>
 #include <numbers>
 using namespace std::chrono;
 
@@ -1047,7 +1048,7 @@ glm::vec3 World::sunlight_dir() const {
     glm::vec3 dir{cos(altitude) * cos(azimuth), sin(altitude),
                   cos(altitude) * sin(azimuth)};
 
-    return glm::normalize(dir);
+    return glm::normalize(-dir);
 }
 */
 

src/renderer.cpp

@@ -18,6 +18,7 @@
 #include <GLFW/glfw3.h>
 #include <format>
 #include <glm/gtc/type_ptr.hpp>
+
 namespace Cubed {
 
 Renderer::Renderer(const Camera& camera, World& world,
@@ -515,10 +516,14 @@ void Renderer::render_world() {
         glm::vec3 center = cam_pos + cam_fwd * (half_extent * 0.5f);
 
         glm::vec3 sundir = glm::normalize(m_world.sunlight_dir());
-        glm::vec3 up =
-            fabs(sundir.y) > 0.99f ? glm::vec3(0, 0, 1) : glm::vec3(0, 1, 0);
+        glm::vec3 raw_shadow_sundir =
+            quantize_sun_direction(sundir, ANGLE_STEP_DEG);
+        glm::vec3 shadow_sundir =
+            get_smoothed_shadow_sundir(raw_shadow_sundir, m_delta_time);
+        glm::vec3 up = fabs(shadow_sundir.y) > 0.99f ? glm::vec3(0, 0, 1)
+                                                     : glm::vec3(0, 1, 0);
 
-        glm::mat4 light_basis = glm::lookAt(glm::vec3(0.0f), sundir, up);
+        glm::mat4 light_basis = glm::lookAt(glm::vec3(0.0f), shadow_sundir, up);
         float texels_per_unit = DEPTH_MAP_SIZE / (half_extent * 2.0f);
         glm::vec3 ls_center = glm::vec3(light_basis * glm::vec4(center, 1.0f));
         ls_center.x =
@@ -531,7 +536,7 @@ void Renderer::render_world() {
         float distance = half_extent * 1.5f;
         float near_plane = 1.0f;
         float far_plane = distance + half_extent * 2.0f;
-        glm::vec3 light_pos = snapped_center - sundir * distance;
+        glm::vec3 light_pos = snapped_center - shadow_sundir * distance;
         glm::mat4 light_view = glm::lookAt(light_pos, snapped_center, up);
         glm::mat4 light_projection =
             glm::ortho(-half_extent, half_extent, -half_extent, half_extent,
@@ -757,6 +762,53 @@ void Renderer::render_dev_panel() {
     glEnable(GL_DEPTH_TEST);
 }
 
+glm::vec3 Renderer::quantize_sun_direction(const glm::vec3& sundir,
+                                           float angle_step_deg) const {
+    float elevation = std::asin(glm::clamp(sundir.y, -1.0f, 1.0f));
+    float azimuth = std::atan2(sundir.z, sundir.x);
+
+    float step = glm::radians(angle_step_deg);
+
+    float quantized_elevation = std::round(elevation / step) * step;
+    float quantized_azimuth = std::round(azimuth / step) * step;
+
+    glm::vec3 quantized_dir;
+    quantized_dir.x =
+        std::cos(quantized_elevation) * std::cos(quantized_azimuth);
+    quantized_dir.z =
+        std::cos(quantized_elevation) * std::sin(quantized_azimuth);
+    quantized_dir.y = std::sin(quantized_elevation);
+
+    return glm::normalize(quantized_dir);
+}
+
+glm::vec3
+Renderer::get_smoothed_shadow_sundir(const glm::vec3& raw_shadow_sundir,
+                                     float dt) {
+    if (!m_blend_initialized) {
+
+        m_blend_from_sundir = raw_shadow_sundir;
+        m_blend_to_sundir = raw_shadow_sundir;
+        m_blend_t = 1.0f;
+        m_blend_initialized = true;
+        return raw_shadow_sundir;
+    }
+
+    if (raw_shadow_sundir != m_blend_to_sundir) {
+        glm::vec3 current_displayed = glm::normalize(
+            Math::slerp(m_blend_from_sundir, m_blend_to_sundir, m_blend_t));
+
+        m_blend_from_sundir = current_displayed;
+        m_blend_to_sundir = raw_shadow_sundir;
+        m_blend_t = 0.0f;
+    }
+
+    m_blend_t = glm::min(m_blend_t + dt / BLEND_DURATION, 1.0f);
+
+    return glm::normalize(
+        Math::slerp(m_blend_from_sundir, m_blend_to_sundir, m_blend_t));
+}
+
 float& Renderer::ambient_strength() { return m_ambient_strength; }
 bool& Renderer::discard_transparent() { return m_discard_tranparent; }
 bool& Renderer::shader_on() { return m_shader_on; }

src/tools/math_tools.cpp

@@ -1,7 +1,9 @@
 #include "Cubed/tools/math_tools.hpp"
 
 #include <algorithm>
+#include <glm/glm.hpp>
 #include <glm/gtc/type_ptr.hpp>
+
 namespace Cubed {
 
 namespace Math {
@@ -65,6 +67,39 @@ float deterministic_random(int x, int z, uint64_t seed) {
     h = h * 6364136223846793005ULL + (uint64_t)z;
     return (float)(h >> 40) / (float)(1 << 24);
 }
+
+glm::vec3 slerp(const glm::vec3& from, const glm::vec3& to, float t) {
+
+    float cos_theta = glm::clamp(glm::dot(from, to), -1.0f, 1.0f);
+
+    if (cos_theta > 0.9995f) {
+        return glm::normalize(glm::mix(from, to, t));
+    }
+
+    if (cos_theta < -0.9995f) {
+
+        glm::vec3 axis = (std::fabs(from.x) < 0.9f)
+                             ? glm::vec3(1.0f, 0.0f, 0.0f)
+                             : glm::vec3(0.0f, 1.0f, 0.0f);
+        glm::vec3 ortho = glm::normalize(glm::cross(from, axis));
+
+        float angle = glm::pi<float>() * t;
+
+        glm::vec3 rotated =
+            from * std::cos(angle) + glm::cross(ortho, from) * std::sin(angle);
+
+        return glm::normalize(rotated);
+    }
+
+    float theta = std::acos(cos_theta);
+    float sin_theta = std::sin(theta);
+
+    float a = std::sin((1.0f - t) * theta) / sin_theta;
+    float b = std::sin(t * theta) / sin_theta;
+
+    return glm::normalize(a * from + b * to);
+}
+
 } // namespace Math
 
 } // namespace Cubed