Constraints

.gitignore

@@ -1 +1 @@
-./cloth_sim
+cloth_sim

src/app.cpp

@@ -68,14 +68,13 @@ void app_update(App* app) {
         return;
     }
 
-    compute_cloth_forces(app->cloth, app->conf.gravity);
-
-    app->conf.gravity = Vec2f{app->conf.gravity.x-0.0005f, app->conf.gravity.y-0.001f};
-
     int updated_window_w;
     int updated_window_h;
     SDL_GetWindowSize(app->window->sdl_win, &updated_window_w, &updated_window_h);
     app->window->dimensions = Vec2{(unsigned int) updated_window_w, (unsigned int) updated_window_h};
+
+    compute_cloth_forces(app->cloth, app->conf.gravity);
+    satisfy_cloth_constraints(app->cloth, Vec2{0, 0}, Vec2{app->window->dimensions.x-5, app->window->dimensions.y-5});
 }
 
 void destroy_app(App* app) {

src/cloth.cpp

@@ -11,9 +11,24 @@ Cloth* new_cloth(Vec2 startpos, Vec2 dimensions, unsigned int spacing) {
     new_cloth->points = std::vector<Point*>();
     new_cloth->connections = std::vector<Connection*>();
 
+    bool frozen_point = false;
     for (unsigned int y = 0; y < dimensions.y; y += spacing) {
+        if (y == 0) {
+            frozen_point = true;
+        } else {
+            frozen_point = false;
+        }
+        
         for (unsigned int x = 0; x < dimensions.x; x += spacing) {
-            Point* new_point = new Point{static_cast<float>(startpos.x + x), static_cast<float>(startpos.y + y), startpos.x + x, startpos.y + y, false};
+            Point* new_point = new Point{
+                .x = static_cast<float>(startpos.x + x),
+                .y = static_cast<float>(startpos.y + y),
+                .prev_x = static_cast<float>(startpos.x + x),
+                .prev_y = static_cast<float>(startpos.y + y),
+                .mass = 10.0f,
+                .frozen = frozen_point,
+                .selected = false,
+            };
             new_cloth->points.push_back(new_point);
 
             if (x > 0) {
@@ -55,7 +70,35 @@ void destroy_cloth(Cloth* cloth) {
 
 void compute_cloth_forces(Cloth* cloth, Vec2f gravity_vec) {
     for (Point* p : cloth->points) {
+        if (p->frozen) {
+            continue;
+        }
         p->x += gravity_vec.x;
-        p->y += gravity_vec.y;    
+        p->y += gravity_vec.y;
+    }
+}
+
+
+void satisfy_cloth_constraints(Cloth* cloth, Vec2 top_left, Vec2 bottom_right) {
+    for (Point* p : cloth->points) {
+        // bottom
+        if (p->y > bottom_right.y) {
+            p->y = bottom_right.y;
+        }
+
+        // right
+        if (p->x > bottom_right.x) {
+            p->x = bottom_right.x;
+        }
+
+        // left
+        if (p->x < top_left.x) {
+            p->x = top_left.x;
+        }
+
+        // up
+        if (p->y < top_left.y) {
+            p->y = top_left.y;
+        }
     }
 }

src/cloth.hpp

@@ -14,4 +14,5 @@ struct Cloth {
 
 Cloth* new_cloth(Vec2 startpos, Vec2 dimensions, unsigned int spacing);
 void destroy_cloth(Cloth* cloth);
-void compute_cloth_forces(Cloth* cloth, Vec2f gravity_vec);
+void compute_cloth_forces(Cloth* cloth, Vec2f gravity_vec);
+void satisfy_cloth_constraints(Cloth* cloth, Vec2 top_left, Vec2 bottom_right);

src/main.cpp

@@ -68,7 +68,7 @@ int main(const int argc, char** argv) {
         .cloth_startpos = Vec2{50, 50},
         .cloth_dimensions = Vec2{400, 400},
         .cloth_spacing = 20,
-        .gravity = Vec2f{0.3f, 0.8f},
+        .gravity = Vec2f{0.0f, 1.5f},
         .background_color = RGB{80, 100, 255},
         .point_color = RGB{10, 10, 10},
         .point_selected_color = RGB{200, 40, 12},

src/point.hpp

@@ -12,8 +12,9 @@
 struct Point {
     float x;
     float y;
-    unsigned int prev_x;
-    unsigned int prev_y;
-    unsigned int mass;
+    float prev_x;
+    float prev_y;
+    float mass;
+    bool frozen;
     bool selected;
 };