neco-editor-viewport

日本語

Viewport geometry calculations for editor rendering. Converts between byte offsets, logical/visual lines, and pixel coordinates without depending on any DOM or Canvas API.

How it works

All functions are stateless and take ViewportMetrics (line height, ASCII character width, CJK character width, tab width) as input. ViewportLayout adds gutter and content-area offsets.

visible_line_range returns the first and last visual line numbers visible in a scrolled container. caret_rect computes the pixel rectangle for the cursor at a given byte offset. selection_rects returns one rectangle per visual line covered by a selection. hit_test goes the other direction: given a click at pixel (x, y), it returns the byte offset in the text.

Logical-to-visual line translation relies on neco-wrap::WrapMap. Line/column resolution uses neco-textview::LineIndex. The viewport layer itself holds no state.

Usage

use neco_editor_viewport::{
    ViewportMetrics, ViewportLayout, visible_line_range,
    caret_rect, hit_test, gutter_width,
};
use neco_textview::LineIndex;
use neco_wrap::{WrapMap, WrapPolicy};

let text = "hello\nworld";
let li = LineIndex::new(text);
let lines: Vec<&str> = text.split('\n').collect();
let wm = WrapMap::new(lines.iter().copied(), 80, &WrapPolicy::code());
let metrics = ViewportMetrics {
    line_height: 20.0,
    char_width: 8.0,
    cjk_char_width: 14.0,
    tab_width: 4,
};

// Which visual lines are visible?
let (first, last) = visible_line_range(0.0, 100.0, &wm, &metrics);

// Where should the caret be drawn?
let gw = gutter_width(li.line_count(), &metrics);
let layout = ViewportLayout {
    gutter_width: gw,
    content_left: gw + 8.0,
};
let rect = caret_rect(text, 0, &li, &wm, &metrics, &layout).unwrap();

// Click to offset
let offset = hit_test(rect.x, rect.y, 0.0, text, &li, &wm, &metrics, &layout);
assert_eq!(offset, 0);

API

License

MIT