Scroll by less than a full cell

[pfgithub]

Few terminals do this but I like it when they do. When scrolling on a trackpad, it would be nice to be able to stop partway through a cell rather than having the minimum scroll amount being a full cell (except when scrolling is handled by an application, like vim).

my proposal: (xfce4-terminal and some others do this)

EXAMPLE.SMOOTH.mp4

current scrolling:

EXAMPLE.DISCRETE.mp4

I looked at this a little bit and it doesn't seem like it should be too hard to implement, there's already a property for pending_scroll_y - it changing needs to trigger a rerender, have the value passed through to rendering, ask the shader to vertically offset the result by that amount, and also maybe render an extra line above/below and clip so that there's never blank space that turns into a line when you get past a certain scroll point.

[tonku321]

also would really like to see this feature 😄

[rightaditya]

This would make for a really smooth experience, both on laptops with touchpads (or discrete touchpad) but also for devices that have high-resolution scrolling capabilities. These aren't too common, but some open-source trackballs (and keyboards with trackballs) use high-resolution sensors and have started adding this functionality. Whether or not something will handle the high-resolution scrolling events is hit-or-miss—Chromium (etc.) and Nautilus do, but Firefox and GNOME terminal don't.

FTR, GNOME terminal does scroll smoothly with touchpads, just not with high-resolution scroll wheels (or devices presenting as such). I don't think any of the high-performance GPU-rendered terminals do this at all... I even seem to remember one of them flat out refusing.

In case it's of interest, GNOME terminal lets you scroll smoothly (again, on a touchpad) through the shell history, but I think that's the extent of it. It doesn't affect any applications; e.g., in (n)vim, scrolling is discretized to number of lines, since (AIUI) the application either only receives or only understands regular scroll detents and can't scroll in fractions of lines.

[pfgithub]

Firefox supports smooth scrolling if you set the environment variable MOZ_USE_INPUT2=1 (or use wayland)

[rhodes-b]

smooth scrolling is a separate discussion
#2355

[pfgithub]

I looked at that one, I don't think so? They talk about a configurable scrolling curve and doing animations interpolating cells in vim. I think it's more about smoothly animating between full cell positions, not allowing scrolls that are partway through a cell. I'm not entirely sure what they're asking for so it could be a duplicate.

[00-kat]

@pfgithub is indeed right, this is not a duplicate of that, for the exact reason they mentioned.

[pfgithub]

I made a hacky version of this using shaders and a ghostty patch

Screen.Recording.2025-08-25.at.8.40.35.PM.mov

diff --git a/src/Surface.zig b/src/Surface.zig
index 96aaf84d8..85e8abcaa 100644
--- a/src/Surface.zig
+++ b/src/Surface.zig
@@ -3252,13 +3252,12 @@ pub fn scrollCallback(
             break :y .{};
         }
 
-        // We scroll by the number of rows in the offset and save the remainder
-        const amount = poff / cell_size;
+        // We scroll by the number of rows in the offset, rounded towards zero and save the remainder
+        const amount: f64 = @trunc(poff / cell_size);
         assert(@abs(amount) >= 1);
         self.mouse.pending_scroll_y = poff - (amount * cell_size);
 
-        // Round towards zero.
-        const delta: isize = @intFromFloat(@trunc(amount));
+        const delta: isize = @intFromFloat(amount);
         assert(@abs(delta) >= 1);
 
         break :y .{ .delta = delta };
@@ -3278,10 +3277,10 @@ pub fn scrollCallback(
             break :x .{};
         }
 
-        const amount = poff / cell_size;
+        const amount: f64 = @trunc(poff / cell_size);
         assert(@abs(amount) >= 1);
         self.mouse.pending_scroll_x = poff - (amount * cell_size);
-        const delta: isize = @intFromFloat(@trunc(amount));
+        const delta: isize = @intFromFloat(amount);
         assert(@abs(delta) >= 1);
         break :x .{ .delta = delta };
     };
diff --git a/src/renderer/generic.zig b/src/renderer/generic.zig
index 39eec7b43..ce144b1fa 100644
--- a/src/renderer/generic.zig
+++ b/src/renderer/generic.zig
@@ -746,6 +746,7 @@ pub fn Renderer(comptime GraphicsAPI: type) type {
                     .current_cursor_color = @splat(0),
                     .previous_cursor_color = @splat(0),
                     .cursor_change_time = 0,
+                    .pending_scroll = @splat(0),
                 },
                 .bg_image_buffer = undefined,
 
@@ -2287,6 +2288,22 @@ pub fn Renderer(comptime GraphicsAPI: type) type {
                 0,
             };
 
+            const surface: *Surface = @fieldParentPtr("renderer", self);
+            var pending_y = surface.mouse.pending_scroll_y;
+            if (pending_y != 0) {
+                if (surface.io.terminal.flags.mouse_event != .none) {
+                    pending_y = 0;
+                } else {
+                    const top_left = surface.io.terminal.screens.active.pages.getTopLeft(.viewport);
+                    if (pending_y > 0 and top_left.up(1) == null) pending_y = 0;
+                    if (pending_y < 0 and surface.io.terminal.screens.active.pages.pinIsActive(top_left)) pending_y = 0;
+                }
+            }
+            self.custom_shader_uniforms.pending_scroll = .{
+                0,
+                @floatCast(pending_y),
+            };
+
             // Update custom cursor uniforms, if we have a cursor.
             if (self.cells.getCursorGlyph()) |cursor| {
                 const cursor_width: f32 = @floatFromInt(cursor.glyph_size[0]);
diff --git a/src/renderer/shaders/shadertoy_prefix.glsl b/src/renderer/shaders/shadertoy_prefix.glsl
index 6d9cf0f68..689edad0c 100644
--- a/src/renderer/shaders/shadertoy_prefix.glsl
+++ b/src/renderer/shaders/shadertoy_prefix.glsl
@@ -16,6 +16,7 @@ layout(binding = 1, std140) uniform Globals {
     uniform vec4  iCurrentCursorColor;
     uniform vec4  iPreviousCursorColor;
     uniform float iTimeCursorChange;
+    uniform vec2  iPendingScroll;
 };
 
 layout(binding = 0) uniform sampler2D iChannel0;
diff --git a/src/renderer/shadertoy.zig b/src/renderer/shadertoy.zig
index 0d096c0fc..d6cd8f4f6 100644
--- a/src/renderer/shadertoy.zig
+++ b/src/renderer/shadertoy.zig
@@ -25,6 +25,7 @@ pub const Uniforms = extern struct {
     current_cursor_color: [4]f32 align(16),
     previous_cursor_color: [4]f32 align(16),
     cursor_change_time: f32 align(4),
+    pending_scroll: [2]f32 align(8),
 };
 
 /// The target to load shaders for.
diff --git a/src/terminal/PageList.zig b/src/terminal/PageList.zig
index 9e14e2a75..90880feb5 100644
--- a/src/terminal/PageList.zig
+++ b/src/terminal/PageList.zig
@@ -3223,7 +3223,7 @@ pub fn pinIsValid(self: *const PageList, p: Pin) bool {
 
 /// Returns the viewport for the given pin, preferring to pin to
 /// "active" if the pin is within the active area.
-fn pinIsActive(self: *const PageList, p: Pin) bool {
+pub fn pinIsActive(self: *const PageList, p: Pin) bool {
     // If the pin is in the active page, then we can quickly determine
     // if we're beyond the end.
     const active = self.getTopLeft(.active);

// smoothscroll.glsl
void mainImage(out vec4 fragColor, in vec2 fragCoord) {
    fragCoord -= iPendingScroll;
    fragColor = texture(iChannel0, fragCoord / iResolution.xy);
}

custom-shader=./smoothscroll.glsl
custom-shader-animation = true

What it would need:

• It needs to be disabled while an application is getting scroll events (like in nvim)
• It needs to show an extra line at the top/bottom while scrolling
• Scrolling past the bottom shouldn't cause it to behave like that.
• The scroll speed seems to be limited to one line per frame? That needs to be fixed
• It shouldn't use fieldParentPtr in generic.zig
• Typing text should reset the pending y scroll
• It shouldn't need a shader
• It shouldn't need custom-shader-animation = true
• Selecting text should be accurate when partially scrolled
• Ideally it could use the default macOS elastic scrolling

[pfgithub]

@toto1384 you have to build ghostty yourself. paste the patch into a file patch.patch and add a newline at the end. git apply patch.patch. zig build -Doptimize=ReleaseFast && sh -c "cd macos && xcodebuild" && ./macos/build/ReleaseLocal/Ghostty.app/Contents/MacOS/ghostty. and have to add the shader in the config.

[alicealysia]

Hmm, not really building for me.

Would this be better in a draft pr? That way we can review and tweak it and there's at least some hope of it eventually being added.

[dwt]

This looks like it should go into a draft PR. I would be happy to help test this!

[pfgithub]

I updated the diff and shader, it's working again on the ghostty main branch

[dwt]

I updated the diff and shader, it's working again on the ghostty main branch

Can you point me to a pr?