Video version of the code

c/bounce.c

@@ -0,0 +1,148 @@
+#include <math.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <windows.h>
+
+#define MAX_WINDOWS 1024
+
+// == globals ==
+uint32_t res_y;
+void globals_update() {
+    res_y = GetSystemMetrics(SM_CYSCREEN);
+}
+
+// == bodies ==
+typedef struct body_t {
+    float offset_y;
+    float velocity;
+} body_t;
+
+void body_init(body_t* body) {
+    body->offset_y = 0.5;
+    body->velocity = 0.0;
+}
+
+void body_update(body_t* body, int32_t *y_ptr) {
+    int32_t y = *y_ptr;
+
+    float y_float = y + body->offset_y;
+
+    for (size_t step = 0; step < 100; step++) {
+        body->velocity += 0.0002;
+        y_float += body->velocity;
+
+        if (y_float > res_y && body->velocity > 0) {
+            body->velocity = -body->velocity * 0.75;
+            if (-body->velocity < 0.05) {
+                body->velocity = 0;
+            }
+        }
+    }
+
+    *y_ptr = min((int) y_float, res_y);
+
+    body->offset_y = y_float - *y_ptr;
+}
+
+// == mouse ==
+typedef struct mouse_body_t {
+    body_t body;
+} mouse_body_t;
+
+mouse_body_t mouse_body;
+
+void mouse_init() {
+    body_init(&mouse_body.body);
+}
+
+void mouse_update() {
+    POINT xy;
+    GetCursorPos(&xy);
+    int32_t x = xy.x, y = xy.y;
+    body_update(&mouse_body.body, &y);
+    SetCursorPos(x, y);
+}
+
+// == window ==
+typedef struct window_body_t {
+    HWND window;
+    body_t body;
+} window_body_t;
+
+size_t n_windows;
+window_body_t* windows;
+size_t _n_new_windows;
+window_body_t* _new_windows;
+
+void window_init() {
+    n_windows = 0;
+    windows = calloc(sizeof(window_body_t), MAX_WINDOWS);
+    _n_new_windows = 0;
+    _new_windows = calloc(sizeof(window_body_t), MAX_WINDOWS);
+}
+
+BOOL CALLBACK window_handle_enum(HWND window, LPARAM _) {
+    if (_n_new_windows >= MAX_WINDOWS) { return 0; }
+    if (!IsWindowVisible(window)) { return 1; }
+
+    window_body_t new;
+    new.window = window;
+    body_init(&new.body);
+    for (size_t i = 0; i < n_windows; i++) {
+        if (windows[i].window == new.window) {
+            new.body = windows[i].body;
+            break;
+        }
+    }
+    _new_windows[_n_new_windows++] = new;
+    return 1;
+}
+
+void window_enumerate() {
+    EnumWindows(window_handle_enum, 0);
+
+    window_body_t* tmp_windows = windows;
+
+    n_windows = _n_new_windows;
+    windows = _new_windows;
+
+    _n_new_windows = 0;
+    _new_windows = tmp_windows;
+}
+
+void window_update() {
+    window_enumerate();
+
+    for (size_t i = 0; i < n_windows; i++) {
+        RECT rect;
+        GetWindowRect(windows[i].window, &rect);
+        int32_t x = rect.left;
+        int32_t y = rect.bottom;
+
+        body_update(&windows[i].body, &y);
+
+        int32_t height = rect.bottom - rect.top;
+        SetWindowPos(
+            windows[i].window, 0, 
+            x, y - height,
+            -1, -1,
+            SWP_NOACTIVATE | SWP_NOSIZE |
+            SWP_NOZORDER | SWP_ASYNCWINDOWPOS
+        );
+    }
+}
+
+// == main ==
+int main() {
+    mouse_init();
+    window_init();
+
+    while (1) {
+        globals_update();
+
+        mouse_update();
+        window_update();
+
+        Sleep(1000/120);
+    }
+}

c/run.bat

@@ -0,0 +1,3 @@
+del bounce.exe
+zig cc bounce.c -o bounce.exe -Wall -Ofast
+bounce.exe