From dad6f6cf87a94f5a1e804b2f68afa4ef680540e0 Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Fri, 13 Mar 2026 20:19:47 -0700
Subject: Support trackpad scrolling

---
 src/xplorer.c | 38 +++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)

(limited to 'src')

diff --git a/src/xplorer.c b/src/xplorer.c
index 6dd1bbf..da66f0d 100644
--- a/src/xplorer.c
+++ b/src/xplorer.c
@@ -270,11 +270,13 @@ int main(
   State state = {0};
 
   if (!SDL_Init(SDL_INIT_VIDEO | SDL_INIT_EVENTS)) {
-    return false;
+    success = false;
+    goto cleanup;
   }
 
   if (!uiInit()) {
-    return false;
+    success = false;
+    goto cleanup;
   }
 
   if (!Initialize(&state)) {
@@ -297,6 +299,12 @@ int main(
   // Initially true to perform an initial draw before the window is displayed.
   bool redraw = true;
 
+  // Scrolling on a trackpad often results in scroll values in [0,1], but the UI
+  // library handles integer scroll deltas only.
+  // Accumulate floating-point deltas and issue them to the UI library when
+  // the integer part becomes non-zero.
+  float scroll = 0.f;
+
   while (running) {
     EVENT_LOOP_PRINT("loop\n");
 
@@ -366,21 +374,21 @@ int main(
       };
       redraw = uiSendEvent(state.frame, &ev);
     } else if (event.type == SDL_EVENT_MOUSE_WHEEL) {
-      int x, y;
-      MouseCoordsToUiCoords(
-          state.window, event.wheel.mouse_x, event.wheel.mouse_y, &x, &y);
-      // TODO: Scrolling on a trackpad results in 0<event.wheel.y<1 values,
-      //  which become 0 with integer truncation. Have the UI library handle
-      //  float values for smooth scrolling. Though that means a lot of the UI
-      //  input will have to be float-based. Should we handle it here in the
-      //  client instead? That seems inconvenient.
-      const uiInputEvent ev = {
+      scroll += event.wheel.y;
+      const int scroll_int = (int)scroll;
+      scroll = scroll - (float)scroll_int;
+      if (scroll_int != 0) {
+        int x, y;
+        MouseCoordsToUiCoords(
+            state.window, event.wheel.mouse_x, event.wheel.mouse_y, &x, &y);
+        const uiInputEvent ev = {
           .type = uiEventMouseScroll,
           .mouse_scroll =
-              (uiMouseScrollEvent){.scroll_offset  = (int)event.wheel.y,
+              (uiMouseScrollEvent){.scroll_offset  = scroll_int,
                                    .mouse_position = (uiPoint){x, y}}
-      };
-      redraw = uiSendEvent(state.frame, &ev);
+        };
+        redraw = uiSendEvent(state.frame, &ev);
+      }
     } else if (event.type == SDL_EVENT_MOUSE_MOTION) {
       int x, y;
       MouseCoordsToUiCoords(
@@ -415,7 +423,7 @@ cleanup:
   }
   if (state.window) {
     SDL_DestroyWindow(state.window);
-    state.window = 0;
+    state.window = nullptr;
   }
 
   uiShutdown();
-- 
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