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render: cut per-frame cost with a fast clear and row fills

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Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I96cdacecbe2a55c42825006e84fede076a6a6964
This commit is contained in:
raf 2026-06-24 13:14:55 +03:00
commit 7254cbf381
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GPG key ID: 29D95B64378DB4BF
2 changed files with 33 additions and 14 deletions
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42
src/render.rs
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@ -12,7 +12,7 @@ use crate::grid::{Cell, Color, CursorShape, Flags, Grid, Underline};
const DEFAULT_FG: Rgb = Rgb(0xc5, 0xc8, 0xc6);
const DEFAULT_BG: Rgb = Rgb(0x18, 0x18, 0x18);
#[derive(Clone, Copy)]
#[derive(Clone, Copy, PartialEq, Eq)]
struct Rgb(u8, u8, u8);
/// A mutable view over a BGRA pixel buffer.
@ -30,15 +30,29 @@ impl Canvas<'_> {
Some((y as usize * self.width + x as usize) * 4)
}
/// Fill the whole buffer with one colour (fast path, no per-pixel bounds
/// checks).
fn clear(&mut self, c: Rgb) {
let bytes = [c.2, c.1, c.0, 0xff];
for px in self.pixels.chunks_exact_mut(4) {
px.copy_from_slice(&bytes);
}
}
fn fill_rect(&mut self, x0: i32, y0: i32, w: u32, h: u32, c: Rgb) {
for dy in 0..h as i32 {
for dx in 0..w as i32 {
if let Some(i) = self.index(x0 + dx, y0 + dy) {
self.pixels[i] = c.2;
self.pixels[i + 1] = c.1;
self.pixels[i + 2] = c.0;
self.pixels[i + 3] = 0xff;
}
let x_start = x0.max(0) as usize;
let x_end = ((x0 + w as i32).max(0) as usize).min(self.width);
let y_start = y0.max(0) as usize;
let y_end = ((y0 + h as i32).max(0) as usize).min(self.height);
if x_start >= x_end {
return;
}
let bytes = [c.2, c.1, c.0, 0xff];
for y in y_start..y_end {
let row =
&mut self.pixels[(y * self.width + x_start) * 4..(y * self.width + x_end) * 4];
for px in row.chunks_exact_mut(4) {
px.copy_from_slice(&bytes);
}
}
}
@ -109,15 +123,19 @@ impl Renderer {
width,
height,
};
canvas.fill_rect(0, 0, width as u32, height as u32, DEFAULT_BG);
canvas.clear(DEFAULT_BG);
let m = self.fonts.metrics();
// Cell backgrounds: only paint cells that differ from the cleared
// default - most of a screen is default background.
for y in 0..grid.rows() {
for x in 0..grid.cols() {
let (_, bg) = cell_colors(grid.cell(x, y));
let (px, py) = (x as i32 * m.width as i32, y as i32 * m.height as i32);
canvas.fill_rect(px, py, m.width, m.height, bg);
if bg != DEFAULT_BG {
let (px, py) = (x as i32 * m.width as i32, y as i32 * m.height as i32);
canvas.fill_rect(px, py, m.width, m.height, bg);
}
}
}