From 68366c733176d131c9a64d51886f8428664148a1 Mon Sep 17 00:00:00 2001
From: Isaac Freund <mail@isaacfreund.com>
Date: Tue, 14 Nov 2023 15:36:25 +0100
Subject: [PATCH] Cursor: fix high polling rate resize regression

The previous commit ended up clamping the accumulated f64 offset to an
integer every frame, losing any sub-pixel cursor motions. This has been
known to cause problems with high polling rate mice in the past.

Return to the same approve the move cursor mode uses to solve this and
accumulate a separate sub-pixel delta.
---
 river/Cursor.zig | 38 ++++++++++++++++++++++++--------------
 1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/river/Cursor.zig b/river/Cursor.zig
index 03868a9..e4ab7b3 100644
--- a/river/Cursor.zig
+++ b/river/Cursor.zig
@@ -76,10 +76,15 @@ const Mode = union(enum) {
     resize: struct {
         view: *View,
 
-        /// Total x/y movement of the pointer device since the start of the resize.
-        /// This is not directly tied to cursor position.
-        x: f64 = 0,
-        y: f64 = 0,
+        delta_x: f64 = 0,
+        delta_y: f64 = 0,
+
+        /// Total x/y movement of the pointer device since the start of the resize,
+        /// clamped to the bounds of the resize as defined by the view min/max
+        /// dimensions and output dimensions.
+        /// This is not directly tied to the rendered cursor position.
+        x: i32 = 0,
+        y: i32 = 0,
 
         /// Resize edges, maximum of 2 are set and they may not be opposing edges.
         edges: wlr.Edges,
@@ -874,8 +879,13 @@ fn processMotion(self: *Self, device: *wlr.InputDevice, time: u32, delta_x: f64,
             server.root.applyPending();
         },
         .resize => |*data| {
-            data.x += dx;
-            data.y += dy;
+            dx += data.delta_x;
+            dy += data.delta_y;
+            data.delta_x = dx - @trunc(dx);
+            data.delta_y = dy - @trunc(dy);
+
+            data.x += @intFromFloat(dx);
+            data.y += @intFromFloat(dy);
 
             // Modify width/height of the pending box, taking constraints into account
             // The x/y coordinates of the view will be adjusted as needed in View.resizeCommit()
@@ -891,32 +901,32 @@ fn processMotion(self: *Self, device: *wlr.InputDevice, time: u32, delta_x: f64,
 
             if (data.edges.left) {
                 const x2 = box.x + box.width;
-                box.width = data.initial_width - @as(i32, @intFromFloat(data.x));
+                box.width = data.initial_width - data.x;
                 box.width = @max(box.width, constraints.min_width);
                 box.width = @min(box.width, constraints.max_width);
                 box.width = @min(box.width, x2 - border_width);
-                data.x = @floatFromInt(data.initial_width - box.width);
+                data.x = data.initial_width - box.width;
             } else if (data.edges.right) {
-                box.width = data.initial_width + @as(i32, @intFromFloat(data.x));
+                box.width = data.initial_width + data.x;
                 box.width = @max(box.width, constraints.min_width);
                 box.width = @min(box.width, constraints.max_width);
                 box.width = @min(box.width, output_width - border_width - box.x);
-                data.x = @floatFromInt(box.width - data.initial_width);
+                data.x = box.width - data.initial_width;
             }
 
             if (data.edges.top) {
                 const y2 = box.y + box.height;
-                box.height = data.initial_height - @as(i32, @intFromFloat(data.y));
+                box.height = data.initial_height - data.y;
                 box.height = @max(box.height, constraints.min_height);
                 box.height = @min(box.height, constraints.max_height);
                 box.height = @min(box.height, y2 - border_width);
-                data.y = @floatFromInt(data.initial_height - box.height);
+                data.y = data.initial_height - box.height;
             } else if (data.edges.bottom) {
-                box.height = data.initial_height + @as(i32, @intFromFloat(data.y));
+                box.height = data.initial_height + data.y;
                 box.height = @max(box.height, constraints.min_height);
                 box.height = @min(box.height, constraints.max_height);
                 box.height = @min(box.height, output_height - border_width - box.y);
-                data.y = @floatFromInt(box.height - data.initial_height);
+                data.y = box.height - data.initial_height;
             }
 
             server.root.applyPending();