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surface: calculate scroll amount directly from yoff/xoff for non-precision scrolls

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Calculate the scroll amount for non-precision scrolls as a direct
multiple of yoff. This fixes an issue where Ghostty sends scroll wheel
events (or arrow keys if in alternate scroll mode) that are variable,
dependent on the screen size. I checked multiple terminals, and each
responds to a single wheel click by sending only a single wheel / arrow
key - independent of screen size.

```sh
printf "\x1b[?1049h"
printf "\x1b[?1007h"

cat -v

```

Using the above procedure, with varying screen sizes:

```
 # 50% Screen height
| terminal   | arrows keys sent| wheels events sent|
|------------|-----------------|-------------------|
| alacritty  |        3        |          1        |
| foot       |        3        |          1        |
| xterm      |        5        |          1        |
| kitty      |        3        |          1        |
| ghostty    |        2        |          2        |

 # 100% Screen height
| terminal   | arrows keys sent| wheels events sent|
|------------|-----------------|-------------------|
| alacritty  |        3        |          1        |
| foot       |        3        |          1        |
| xterm      |        5        |          1        |
| kitty      |        5        |          1        |
| ghostty    |        3        |          3        |
```

Both ghostty and kitty scale the number of arrow keys sent in proportion
to the screen size. However, when mouse reporting is on, only ghostty
does this.

This commit makes Ghostty behave like foot, and more generally removes
the dependence on screen size.
This commit is contained in:
Tim Culverhouse
2025-03-02 07:14:29 -06:00
parent 8721f2ae51
commit 34388ab5df
1 changed files with 7 additions and 19 deletions
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26
src/Surface.zig
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@ -2348,22 +2348,12 @@ pub fn scrollCallback(
if (self.mouse.hidden) self.showMouse();
const y: ScrollAmount = if (yoff == 0) .{} else y: {
// Non-precision scrolling is easy to calculate. We don't use
// the given offset at all and instead just treat a positive
// as a scroll up and a negative as a scroll down and scroll in
// steps.
// Non-precision scrolls don't accumulate. We cast that raw yoff to an isize and interpret
// it as the number of lines to scroll.
if (!scroll_mods.precision) {
// Calculate our magnitude of scroll. This is constant (not
// dependent on yoff).
const grid_size = self.size.grid();
const grid_rows_f64: f64 = @floatFromInt(grid_size.rows);
const y_delta_f64: f64 = @round((grid_rows_f64 * self.config.mouse_scroll_multiplier) / 15.0);
const y_delta_usize: usize = @max(1, @as(usize, @intFromFloat(y_delta_f64)));
// Calculate our direction of scroll based on the sign of yoff.
const y_sign: isize = if (yoff >= 0) 1 else -1;
const y_delta_isize: isize = y_sign * @as(isize, @intCast(y_delta_usize));
// Calculate our magnitude of scroll. This is a direct multiple of yoff
const y_delta_f64: f64 = @round(yoff * self.config.mouse_scroll_multiplier);
const y_delta_isize: isize = @intFromFloat(y_delta_f64);
break :y .{ .delta = y_delta_isize };
}
@ -2404,10 +2394,8 @@ pub fn scrollCallback(
// For detailed comments see the y calculation above.
const x: ScrollAmount = if (xoff == 0) .{} else x: {
if (!scroll_mods.precision) {
const x_delta_f64: f64 = @round(1 * self.config.mouse_scroll_multiplier);
const x_delta_usize: usize = @max(1, @as(usize, @intFromFloat(x_delta_f64)));
const x_sign: isize = if (xoff >= 0) 1 else -1;
const x_delta_isize: isize = x_sign * @as(isize, @intCast(x_delta_usize));
const x_delta_f64: f64 = @round(xoff * self.config.mouse_scroll_multiplier);
const x_delta_isize: isize = @intFromFloat(x_delta_f64);
break :x .{ .delta = x_delta_isize };
}