add 'angle_spread' property

src/graphics/render/Emitter.cpp

@@ -23,8 +23,9 @@ Emitter::Emitter(
       texture(texture),
       count(count),
       preset(std::move(preset)) {
+    random.setSeed(rand());
     this->prototype.emitter = this;
-    timer = preset.spawnInterval;
+    timer = preset.spawnInterval * random.randFloat();
 }
 
 const Texture* Emitter::getTexture() const {
@@ -83,6 +84,10 @@ void Emitter::update(
         Particle particle = prototype;
         particle.emitter = this;
         particle.random = random.rand32();
+        if (glm::abs(preset.angleSpread) >= 0.005f) {
+            particle.angle =
+                random.randFloat() * preset.angleSpread * glm::pi<float>() * 2;
+        }
 
         glm::vec3 spawnOffset = generate_coord(preset.spawnShape);
         spawnOffset *= preset.spawnSpread;

src/graphics/render/Emitter.hpp

@@ -27,6 +27,8 @@ struct Particle {
     float lifetime;
     /// @brief UV region
     UVRegion region;
+    /// @brief Current rotation angle
+    float angle;
 };
 
 class Texture;
@@ -39,7 +41,7 @@ class Emitter {
     EmitterOrigin origin;
     /// @brief Particle prototype
     Particle prototype;
-    /// @brief Particle
+    /// @brief Particle texture
     const Texture* texture;
     /// @brief Number of particles should be spawned before emitter deactivation.
     /// -1 is infinite.

src/graphics/render/ParticlesRenderer.cpp

@@ -91,10 +91,23 @@ void ParticlesRenderer::renderParticles(const Camera& camera, float delta) {
             }
             float scale = 1.0f + ((particle.random ^ 2628172) % 1000) *
                                      0.001f * preset.sizeSpread;
+
+            glm::vec3 localRight = right;
+            glm::vec3 localUp = preset.globalUpVector ? glm::vec3(0, 1, 0) : up;
+            float angle = particle.angle;
+            if (glm::abs(angle) >= 0.005f) {
+                glm::vec3 rotatedRight(glm::cos(angle), -glm::sin(angle), 0.0f);
+                glm::vec3 rotatedUp(glm::sin(angle), glm::cos(angle), 0.0f);
+
+                localRight = right * rotatedRight.x + localUp * rotatedRight.y +
+                            camera.front * rotatedRight.z;
+                localUp = right * rotatedUp.x + localUp * rotatedUp.y +
+                        camera.front * rotatedUp.z;
+            }
             batch->quad(
                 particle.position,
-                right,
-                preset.globalUpVector ? glm::vec3(0, 1, 0) : up,
+                localRight,
+                localUp,
                 preset.size * scale,
                 light,
                 glm::vec3(1.0f),