perf: avoid useless copy of particle positions in renderpass

include/wobblywindow.h

@@ -17,7 +17,9 @@ class CWobblyWindow {
     static inline float s_dampingStrength = 12.f;
     static inline float s_drag = 0.4f;
 
-    std::vector<SParticle> m_particles;
+    std::vector<float> m_particlePositions;
+    std::vector<Vector2D> m_particleVelocities;
+
     std::vector<Vector2D> m_targetPositions;
     std::optional<Vector2D> m_grabPosition {std::nullopt};
     Vector2D m_windowMovement;
@@ -25,5 +27,7 @@ class CWobblyWindow {
     CWobblyWindow();
 
     bool step(Time::steady_tp time);
+
+    void applyMovement(const Vector2D& movement);
 };
 #endif

src/main.cpp

@@ -73,10 +73,7 @@ void hkRenderWindow(
                 wobble.m_grabPosition = std::nullopt;
             }
 
-            wobble.m_windowMovement = (pos - g_windowPositions[pWindow]) / windowSize;
-            for (auto&& particle : wobble.m_particles) {
-                particle.position -= wobble.m_windowMovement;
-            }
+            wobble.applyMovement((pos - g_windowPositions[pWindow]) / windowSize);
 
             // update last pos
             g_windowPositions[pWindow] = pos;

src/renderpasses.cpp

@@ -165,16 +165,13 @@ void CRenderWobblyWindowPassElement::draw(const CRegion& damage) {
         // TODO: these should never be nan
         // if (not std::isnan(wobble.m_particles[0].position.x)) {
 
-        // TODO: we need the particle positions in their own vec, to avoid this copy
-        std::vector<float> verts;
-        verts.reserve(vertsPerRow * vertsPerRow * 2);
-        for (auto&& particle : wobble.m_particles) {
-            verts.push_back(particle.position.x);
-            verts.push_back(particle.position.y);
-        }
-
         GLCALL(glBindBuffer(GL_ARRAY_BUFFER, s_VBO));
-        GLCALL(glBufferSubData(GL_ARRAY_BUFFER, 0, verts.size() * sizeof(float), verts.data()));
+        GLCALL(glBufferSubData(
+            GL_ARRAY_BUFFER,
+            0,
+            wobble.m_particlePositions.size() * sizeof(float),
+            wobble.m_particlePositions.data()
+        ));
         // }
     } else {
         // restore default verts

src/wobblywindow.cpp

@@ -5,11 +5,15 @@
 
 CWobblyWindow::CWobblyWindow() {
     auto&& verts = CRenderWobblyWindowPassElement::s_baseVerts;
-    m_particles.reserve(verts.size() / 2);
-    m_targetPositions.reserve(verts.size() / 2);
 
+    // copy directly
+    m_particlePositions = verts;
+
+    // init empty
+    m_particleVelocities.resize(verts.size() / 2);
+
+    m_targetPositions.reserve(verts.size() / 2);
     for (unsigned int i {}; i < verts.size(); i += 2) {
-        m_particles.push_back(SParticle {Vector2D {verts[i], verts[i + 1]}, {}});
         m_targetPositions.push_back(Vector2D {verts[i], verts[i + 1]});
     }
 }
@@ -22,42 +26,44 @@ bool CWobblyWindow::step(Time::steady_tp time) {
 
     Vector2D totalVel {};
 
-    for (unsigned int i {}; i < m_particles.size(); i++) {
-        auto&& particle = m_particles[i];
-        auto&& particlePositon = particle.position;
+    for (unsigned int i {}; i < m_particlePositions.size() / 2; i++) {
+        // TODO: avoid float -> double promotion
+        const auto& pos = Vector2D {m_particlePositions[i * 2], m_particlePositions[i * 2 + 1]};
+        auto&& vel = m_particleVelocities[i];
         auto&& targetPosition = m_targetPositions[i];
 
-        const Vector2D directionToTarget = targetPosition - particlePositon;
+        const Vector2D directionToTarget = targetPosition - pos;
 
         if (m_grabPosition.has_value()) {
-            const float distanceToDragPosition = m_grabPosition.value().distance(particlePositon);
+            const float distanceToDragPosition = m_grabPosition.value().distance(pos);
             const float dragStrength = std::clamp(distanceToDragPosition, 0.f, 1.f);
 
-            particle.position += m_windowMovement * dragStrength;
+            m_particlePositions[i * 2] += m_windowMovement.x * dragStrength;
+            m_particlePositions[i * 2 + 1] += m_windowMovement.y * dragStrength;
         }
 
-        const Vector2D springForce =
-            directionToTarget * s_springStrength - particle.velocity * s_dampingStrength;
-        particle.velocity += springForce * dt;
+        const Vector2D springForce = directionToTarget * s_springStrength - vel * s_dampingStrength;
+        vel += springForce * dt;
 
         // Apply drag
-        const Vector2D dragForceVector = (particle.velocity * particle.velocity) * -s_drag;
+        const Vector2D dragForceVector = (vel * vel) * -s_drag;
 
         // * Area
-        auto dir = particle.velocity;
+        auto dir = vel;
         float magnitude = dir.normalize();
 
         if (magnitude != 0)
-            particle.velocity += (dragForceVector * dir) * dt;
+            vel += (dragForceVector * dir) * dt;
 
         // Apply velocity
-        particle.position += particle.velocity * dt;
+        m_particlePositions[i * 2] += vel.x * dt;
+        m_particlePositions[i * 2 + 1] += vel.y * dt;
 
-        totalVel += particle.velocity;
+        totalVel += vel;
     }
 
-    const bool shouldEnd =
-        m_windowMovement.size() == 0 and totalVel.size() / m_particles.size() < .001f;
+    const bool shouldEnd = m_windowMovement.size() == 0
+        and totalVel.size() / (m_particlePositions.size() / 2.f) < .001f;
 
     // std::println(
     //     "Top left: {}, totalVel: {}",
@@ -68,3 +74,12 @@ bool CWobblyWindow::step(Time::steady_tp time) {
 
     return shouldEnd;
 }
+
+void CWobblyWindow::applyMovement(const Vector2D& movement) {
+    m_windowMovement = movement;
+
+    for (unsigned int i = 0; i < m_particlePositions.size() / 2; i++) {
+        m_particlePositions[i * 2] -= movement.x;
+        m_particlePositions[i * 2 + 1] -= movement.y;
+    }
+}