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Prevent zoomout in both dimensions using double-pass system #150

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Merged
itsjunetime merged 1 commit into from
May 17, 2026
Merged

Prevent zoomout in both dimensions using double-pass system #150

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52 changes: 29 additions & 23 deletions src/tui.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -262,7 +262,7 @@ impl Tui {
let img_page_w_ratio = img_section_w / initial_page_w;
let img_page_h_ratio = img_section_h / initial_page_h;

let shrink_move_page = |dim: &mut u16, pos: &mut u16, axis_zoom_factor: f32| {
fn shrink_move_page(dim: &mut u16, pos: &mut u16, axis_zoom_factor: f32) {
let old_dim = *dim;
// The axis zoom factor tells us what portion of the axis
// we need to show.
Expand All @@ -272,50 +272,56 @@ impl Tui {
.checked_sub(*dim)
.expect("zooming out should shrink the image")
/ 2;
};
}

if img_page_w_ratio < img_page_h_ratio {
fn shrink_move_two_pass(
zoom: &mut Zoom,
dim: &mut u16,
pos: &mut u16,
zoom_factor: f32,
axis_zoom_factor: f32
) {
// To detect if we're already at fit-screen, we perform a first
// pass on `img_area` that emulates the last call to
// `render_zoomed` by subtracting from the `zoom`'s level. This
// holds because the `img_area` that gets passed is always the
// same.
let mut first_pass_area = img_area;
let mut first_pass_dim = *dim;
let mut first_pass_pos = *pos;
let mut first_pass_zoom = *zoom;

if first_pass_zoom.level.is_negative() {
first_pass_zoom.step_in();
}
let first_pass_zoom_factor = first_pass_zoom.factor();
shrink_move_page(
&mut first_pass_area.width,
&mut first_pass_area.x,
first_pass_zoom_factor.max(1.0 / img_page_h_ratio)
&mut first_pass_dim,
&mut first_pass_pos,
first_pass_zoom_factor.max(1.0 / axis_zoom_factor)
);
log::debug!("first_pass_area: {first_pass_area:#?}");

log::debug!("first_pass_dim: {first_pass_dim}, first_pass_pos: {first_pass_pos}");
// vertical scroll / tall image. zooming out means decreasing
// the width of the page area
shrink_move_page(
&mut img_area.width,
&mut img_area.x,
// disallow zooming out past fit-screen
zoom_factor.max(1.0 / img_page_h_ratio)
);
log::debug!("img_area: {img_area:#?}");
// use `max` to disallow zooming out past fit-screen
shrink_move_page(dim, pos, zoom_factor.max(1.0 / axis_zoom_factor));

log::debug!("new dim: {dim}, new pos: {pos}");
// The moment the image area is left unmodified, we've hit
// fit-screen and the zoom level ought be normalized.
if first_pass_area == img_area {
if first_pass_dim == *dim && first_pass_pos == *pos {
zoom.step_in();
}
}

let (dim, pos, axis_zoom_factor) = if img_page_w_ratio < img_page_h_ratio {
(&mut img_area.width, &mut img_area.x, img_page_h_ratio)
} else {
// horizontal scroll / wide image. zooming out means decreasing
// the height of the page area
shrink_move_page(
&mut img_area.height,
&mut img_area.y,
// disallow zooming out past fit-screen
zoom_factor.max(1.0 / img_page_w_ratio)
);
}
(&mut img_area.height, &mut img_area.y, img_page_w_ratio)
};
shrink_move_two_pass(zoom, dim, pos, zoom_factor, axis_zoom_factor);
}
log::debug!("after adjustment, page area is {img_area:#?}");

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