Function draw_fps_overlay

rustcv-camera/examples/camera_demo.rs:84–124

Draw FPS value as white pixels in the top-left corner. 在左上角用白色像素绘制 FPS 数值。 Uses a minimal 5x7 bitmap font — no external font dependencies. 使用最小的 5x7 位图字体 —— 无外部字体依赖。

(buf: &mut [u32], stride: usize, fps: f64)

/// Uses a minimal 5x7 bitmap font — no external font dependencies.
/// 使用最小的 5x7 位图字体 —— 无外部字体依赖。
fn draw_fps_overlay(buf: &mut [u32], stride: usize, fps: f64) {
    let text = format!("FPS: {:.1}", fps);
    let scale = 2; // 2x scale for visibility / 2 倍放大以便可见
    let x0 = 8;
    let y0 = 8;

    // Draw black background rectangle.
    // 绘制黑色背景矩形。
    let text_w = text.len() * 6 * scale;
    let text_h = 7 * scale;
    for dy in 0..text_h + 4 {
        for dx in 0..text_w + 8 {
            let px = x0 + dx - 2;
            let py = y0 + dy - 2;
            if py < buf.len() / stride && px < stride {
                buf[py * stride + px] = 0x00000000;
            }
        }
    }

    // Draw each character.
    // 绘制每个字符。
    for (ci, ch) in text.chars().enumerate() {
        let glyph = char_glyph(ch);
        for (row, &glyph_row) in glyph.iter().enumerate() {
            for col in 0..5 {
                if glyph_row & (1 << (4 - col)) != 0 {
                    for sy in 0..scale {
                        for sx in 0..scale {
                            let px = x0 + ci * 6 * scale + col * scale + sx;
                            let py = y0 + row * scale + sy;
                            if py < buf.len() / stride && px < stride {
                                buf[py * stride + px] = 0x00FFFFFF; // white
                            }
                        }
                    }
                }
            }
        }
    }
}

/// Minimal 5x7 bitmap font glyph for a character.
/// 字符的最小 5x7 位图字体字形。