From 1da5ca0a7f582fd3a714d5020d7daa8821b0f0d0 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Sat, 6 Aug 2022 16:05:32 -0700
Subject: [PATCH] mouse xpos/ypos can be negative or larger than window size

When calculating the viewport point, we need to consider this. We clamp
the possible values to [0, width/height - 1]. Fixes #1.
---
 src/Window.zig | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/src/Window.zig b/src/Window.zig
index 8348bab35..09b10d838 100644
--- a/src/Window.zig
+++ b/src/Window.zig
@@ -777,12 +777,25 @@ fn cursorPosCallback(
 }
 
 fn posToViewport(self: Window, xpos: f64, ypos: f64) terminal.point.Viewport {
-    // Convert the mouse position to the viewport x/y
-    const cell_width = @floatCast(f64, self.grid.cell_size.width);
-    const cell_height = @floatCast(f64, self.grid.cell_size.height);
+    // xpos and ypos can be negative if while dragging, the user moves the
+    // mouse off the window. Likewise, they can be larger than our window
+    // width if the user drags out of the window positively.
     return .{
-        .x = @floatToInt(usize, xpos / cell_width),
-        .y = @floatToInt(usize, ypos / cell_height),
+        .x = if (xpos < 0) 0 else x: {
+            // Our cell is the mouse divided by cell width
+            const cell_width = @floatCast(f64, self.grid.cell_size.width);
+            const x = @floatToInt(usize, xpos / cell_width);
+
+            // Can be off the screen if the user drags it out, so max
+            // it out on our available columns
+            break :x @minimum(x, self.terminal.cols - 1);
+        },
+
+        .y = if (ypos < 0) 0 else y: {
+            const cell_height = @floatCast(f64, self.grid.cell_size.height);
+            const y = @floatToInt(usize, ypos / cell_height);
+            break :y @minimum(y, self.terminal.rows - 1);
+        },
     };
 }