Finally some physics

src/app.cpp

@@ -1,6 +1,7 @@
 #include "app.hpp"
 #include "cloth.hpp"
 #include "window.hpp"
+#include "vec.hpp"
 #include <SDL2/SDL_events.h>
 #include <SDL2/SDL_keycode.h>
 #include <SDL2/SDL_render.h>
@@ -16,10 +17,20 @@ App* app_init(App_config conf) {
     if (conf.window_dimensions.y <= 0) {
         conf.window_dimensions.y = 500;
     }
+    if (conf.efficiency_factor < 0 || conf.efficiency_factor > 1) {
+        conf.efficiency_factor = 0.6;
+    }
     app->conf = conf;
     
     app->window = new_window(conf.win_name, conf.window_dimensions);
-    app->cloth = new_cloth(conf.cloth_startpos, conf.cloth_dimensions, conf.cloth_spacing);
+    app->cloth = new_cloth(
+        conf.cloth_startpos,
+        conf.cloth_dimensions,
+        conf.cloth_spacing,
+        conf.efficiency_factor,
+        conf.friction_factor,
+        Vec2{0, 0}, Vec2{app->window->dimensions.x-5, app->window->dimensions.y-5}
+    );
 
     if (app->window == NULL || app->cloth == NULL) {
         return NULL;
@@ -73,8 +84,10 @@ void app_update(App* app) {
     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);
+    app->cloth->constraint_bottom_right.x = app->window->dimensions.x;
-    satisfy_cloth_constraints(app->cloth, Vec2{0, 0}, Vec2{app->window->dimensions.x-5, app->window->dimensions.y-5});
+    app->cloth->constraint_bottom_right.y = app->window->dimensions.y-5;
+    cloth_step(app->cloth, app->conf.gravity, 1);
+    satisfy_cloth_constraints(app->cloth);
 }
 
 void destroy_app(App* app) {

src/app.hpp

@@ -11,6 +11,8 @@ struct App_config {
     Vec2 cloth_dimensions;
     unsigned int cloth_spacing;
     Vec2f gravity;
+    float efficiency_factor;
+    float friction_factor;
     RGB background_color;
     RGB point_color;
     RGB point_selected_color;

src/cloth.cpp

@@ -4,27 +4,37 @@
 #include <cstdio>
 #include <vector>
 
-Cloth* new_cloth(Vec2 startpos, Vec2 dimensions, unsigned int spacing) {
+Cloth* new_cloth(
+    Vec2 startpos,
+    Vec2 dimensions,
+    unsigned int spacing,
+    float efficiency_factor,
+    float friction_factor,
+    Vec2 constraint_top_left, Vec2 constraint_bottom_right
+    ) {
+
     Cloth* new_cloth = new Cloth;
+    new_cloth->efficiency_factor = efficiency_factor;
+    new_cloth->friction_factor = friction_factor;
     new_cloth->startpos = startpos;
     new_cloth->dimensions = dimensions;
+    new_cloth->constraint_top_left = constraint_top_left;
+    new_cloth->constraint_bottom_right = constraint_bottom_right;
     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) {
+            // if (y == 0 && x == new_cloth->dimensions.x/2) {
+            //     frozen_point = true;
+            // } else {
+            //     frozen_point = 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,
@@ -68,37 +78,58 @@ void destroy_cloth(Cloth* cloth) {
     delete cloth;
 }
 
-void compute_cloth_forces(Cloth* cloth, Vec2f gravity_vec) {
+// calculate forces and actually MOVE points 
+void cloth_step(Cloth* cloth, Vec2f gravity_vec, float timedelta) {
     for (Point* p : cloth->points) {
         if (p->frozen) {
             continue;
         }
-        p->x += gravity_vec.x;
+        
-        p->y += gravity_vec.y;
+        // calculate velocity
+        if (p->y == cloth->constraint_bottom_right.y) {
+            // if this point's x velocity is too small -> just stop it
+            // else -> handle friction
+            if (p->velocity.x <= 0.5) {
+                p->velocity.x = 0;
+            } else {
+                p->velocity.x = p->velocity.x*cloth->friction_factor * timedelta;
             }
+        } else {
+            p->velocity.x = p->velocity.x+(gravity_vec.x/p->mass) * timedelta;
+            p->velocity.y = p->velocity.y+(gravity_vec.y/p->mass) * timedelta;
         }
 
+        // move point
+        p->x += p->velocity.x;
+        p->y += p->velocity.y;
+    }
+}
 
-void satisfy_cloth_constraints(Cloth* cloth, Vec2 top_left, Vec2 bottom_right) {
+// handle constraints, bounces
+void satisfy_cloth_constraints(Cloth* cloth) {
     for (Point* p : cloth->points) {
         // bottom
-        if (p->y > bottom_right.y) {
+        if (p->y > cloth->constraint_bottom_right.y) {
-            p->y = bottom_right.y;
+            p->y = cloth->constraint_bottom_right.y;
+            p->velocity.y = -p->velocity.y*cloth->efficiency_factor;
         }
 
         // right
-        if (p->x > bottom_right.x) {
+        if (p->x > cloth->constraint_bottom_right.x) {
-            p->x = bottom_right.x;
+            p->x = cloth->constraint_bottom_right.x;
+            p->velocity.x = -p->velocity.x*cloth->efficiency_factor;
         }
 
         // left
-        if (p->x < top_left.x) {
+        if (p->x < cloth->constraint_top_left.x) {
-            p->x = top_left.x;
+            p->x = cloth->constraint_top_left.x;
+            p->velocity.x = -p->velocity.x*cloth->efficiency_factor;
         }
 
         // up
-        if (p->y < top_left.y) {
+        if (p->y < cloth->constraint_top_left.y) {
-            p->y = top_left.y;
+            p->y = cloth->constraint_top_left.y;
+            p->velocity.y = -p->velocity.y*cloth->efficiency_factor;
         }
     }
 }

src/cloth.hpp

@@ -6,13 +6,24 @@
 #include <vector>
 
 struct Cloth {
+    float efficiency_factor;
+    float friction_factor;
     Vec2 startpos;
     Vec2 dimensions;
+    Vec2 constraint_top_left;
+    Vec2 constraint_bottom_right;
     std::vector<Point*> points;
     std::vector<Connection*> connections;
 };
 
-Cloth* new_cloth(Vec2 startpos, Vec2 dimensions, unsigned int spacing);
+Cloth* new_cloth(
+    Vec2 startpos,
+    Vec2 dimensions,
+    unsigned int spacing,
+    float efficiency_factor,
+    float friction_factor,
+    Vec2 constraint_top_left, Vec2 constraint_bottom_right
+);
 void destroy_cloth(Cloth* cloth);
-void compute_cloth_forces(Cloth* cloth, Vec2f gravity_vec);
+void cloth_step(Cloth* cloth, Vec2f gravity_vec, float timedelta);
-void satisfy_cloth_constraints(Cloth* cloth, Vec2 top_left, Vec2 bottom_right);
+void satisfy_cloth_constraints(Cloth* cloth);

src/main.cpp

@@ -64,15 +64,16 @@ int main(const int argc, char** argv) {
 
     App_config config = {
         .win_name = window_name.c_str(),
-        .window_dimensions = Vec2{500, 500},
+        .window_dimensions = Vec2{800, 700},
         .cloth_startpos = Vec2{50, 50},
         .cloth_dimensions = Vec2{400, 400},
         .cloth_spacing = 20,
-        .gravity = Vec2f{0.0f, 1.5f},
+        .gravity = Vec2f{0.65f, 0.45f},
-        .background_color = RGB{80, 100, 255},
+        .efficiency_factor = 0.25f,
-        .point_color = RGB{10, 10, 10},
+        .background_color = RGB{205, 222, 242},
+        .point_color = RGB{2, 10, 1},
         .point_selected_color = RGB{200, 40, 12},
-        .connection_color = RGB{100, 100, 100},
+        .connection_color = RGB{48, 142, 31},
     };
     App* app = app_init(config);
 

src/point.hpp

@@ -1,20 +1,13 @@
 #pragma once
 
-// struct Point {
+
-//     unsigned int x;
+#include "vec.hpp"
-//     unsigned int y;
-//     unsigned int prev_x;
-//     unsigned int prev_y;
-//     unsigned int mass;
-//     bool selected;
-// };
 
 struct Point {
     float x;
     float y;
-    float prev_x;
-    float prev_y;
     float mass;
     bool frozen;
     bool selected;
+    Vec2f velocity;
 };