Optimise screen output and group writer state into a struct

src/fbuffer.rs

@@ -1,22 +1,27 @@
+use crate::bootinfo::BOOTINFO;
+use alloc::{
+    borrow::Cow, string::{String, ToString}, vec::Vec, vec
+};
 use bootloader_api::info::FrameBufferInfo;
-use fontdue::{layout::{CoordinateSystem, Layout, LayoutSettings, TextStyle}, Font, FontSettings};
+use core::{fmt, slice};
+use fontdue::{
+    layout::{CoordinateSystem, GlyphRasterConfig, Layout, LayoutSettings, TextStyle},
+    Font, FontSettings
+};
+use hashbrown::HashMap;
 use spin::{Lazy, Mutex};
-use crate::{bootinfo::BOOTINFO, dbg};
-use alloc::{string::String, vec::Vec, vec};
-use core::slice;
-
 
 struct Framebuffer<'a> {
     info: FrameBufferInfo,
     buffer: &'a mut [u8],
     draw_buffer: Vec<u8>,
+    scroll_offset: usize,
 }
 
 impl<'a> Framebuffer<'a> {
-    pub fn new(info: FrameBufferInfo, buffer: &'a mut [u8]) -> Self {
-        dbg!(&info);
-        let draw_buffer = vec![0; buffer.len()];
-        Self { info, buffer, draw_buffer }
+    fn new(info: FrameBufferInfo, buffer: &'a mut [u8]) -> Self {
+        let draw_buffer = vec![0; 2 * buffer.len()];
+        Self { info, buffer, draw_buffer, scroll_offset: 0 }
     }
 
     fn get_row_buf(&mut self, row: usize) -> &mut [u8] {
@@ -30,26 +35,36 @@ impl<'a> Framebuffer<'a> {
         &mut self.get_row_buf(row)[pbuf_start..][..pbuf_len]
     }
 
-    pub fn set_pixel(&mut self, row: usize, col: usize, value: u8) {
+    fn set_pixel(&mut self, row: usize, col: usize, value: u8) {
         if row >= self.info.height || col >= self.info.width {
             return;
         }
-        self.get_pixel_buf(row, col).fill(value);
+        self.get_pixel_buf((row + self.scroll_offset) % (self.info.height * 2), col).fill(value);
     }
 
-    pub fn clear(&mut self) {
-        for row in 0..self.info.height {
+    fn clear(&mut self) {
+        for row in 0..self.info.height * 2 {
             self.get_row_buf(row).fill(0);
         }
     }
 
-    pub fn update_screen(&mut self) {
-        self.buffer.copy_from_slice(&self.draw_buffer);
+    fn update_screen(&mut self) {
+        let scroll_top_byte_offset = self.row_byte_offset(self.scroll_offset);
+        let scroll_bot_byte_offset = self.row_byte_offset(self.scroll_offset + self.info.height);
+        self.buffer
+            .copy_from_slice(&self.draw_buffer[scroll_top_byte_offset..scroll_bot_byte_offset]);
+    }
+
+    fn row_byte_offset(&self, row: usize) -> usize {
+        self.info.stride * self.info.bytes_per_pixel * row
+    }
+
+    fn scroll_by(&mut self, offset: usize) {
+        self.scroll_offset = (self.scroll_offset + offset) % (self.info.height * 2);
     }
 }
 
-static FBUFFER: Lazy<Mutex<Framebuffer<'static>>> = Lazy::new(|| {
-    // Testing the framebuffer
+pub static FRAMEBUFFER_WRITER: Lazy<Mutex<FramebufferWriter>> = Lazy::new(|| {
     let fbuf = BOOTINFO.framebuffer.as_ref().unwrap();
 
     // No good way to get mutable buffer, so do this. No, its probably not safe. Too lazy to do it
@@ -61,69 +76,106 @@ static FBUFFER: Lazy<Mutex<Framebuffer<'static>>> = Lazy::new(|| {
     let mut fbuf = Framebuffer::new(fbuf_info, fbuf_buf);
     fbuf.clear();
     fbuf.update_screen();
-    Mutex::new(fbuf)
+    let font = Font::from_bytes(
+        include_bytes!("../FiraCode-Regular.ttf").as_slice(),
+        FontSettings::default(),
+    )
+    .unwrap();
+    Mutex::new(FramebufferWriter::new(fbuf, font))
 });
 
-pub static OUT_STRING: Lazy<Mutex<String>> = Lazy::new(|| {
-    Mutex::new(String::new())
-});
-
-pub static FIRA_CODE: Lazy<Font> = Lazy::new(|| {
-    Font::from_bytes(include_bytes!("../FiraCode-Regular.ttf").as_slice(), FontSettings::default()).unwrap()
-});
-
-pub fn write_str(s: &str) {
-    OUT_STRING.lock().push_str(s);
+pub struct FramebufferWriter {
+    fbuf: Framebuffer<'static>,
+    out_string: String,
+    font: Font,
+    layout: Layout,
+    next_line_y: usize,
+    glyph_cache: HashMap<GlyphRasterConfig, Vec<u8>>,
 }
 
-pub fn write_char(c: char) {
-    OUT_STRING.lock().push(c);
-}
-
-pub fn update_screen() {
-    let out_string = OUT_STRING.lock();
-    let mut fbuf = FBUFFER.lock();
-    fbuf.clear();
+impl FramebufferWriter {
+    fn new(fbuf: Framebuffer<'static>, font: Font) -> Self {
         let mut layout = Layout::new(CoordinateSystem::PositiveYDown);
-
         layout.reset(&LayoutSettings {
             max_width: Some(fbuf.info.width as f32),
             max_height: Some(fbuf.info.height as f32),
             ..Default::default()
         });
+        Self {
+            fbuf,
+            out_string: String::new(),
+            font,
+            layout,
+            next_line_y: 0,
+            glyph_cache: HashMap::new(),
+        }
+    }
 
-    layout.append(&[&*FIRA_CODE], &TextStyle::new(&out_string, 12.0, 0));
+    fn update_screen(&mut self) {
+        self.layout.clear();
+        self.layout.append(&[&self.font], &TextStyle::new(&self.out_string, 12.0, 0));
 
-    let height = layout.height();
-    let top_row = if height as usize > fbuf.info.height {
-        height as usize - fbuf.info.height
-    } else {
-        0
-    };
+        if (self.next_line_y + self.layout.height() as usize) > self.fbuf.info.height {
+            let excess_y =
+                self.layout.height() as usize - (self.fbuf.info.height - self.next_line_y);
+            self.fbuf.scroll_by(excess_y);
+            self.next_line_y = self.fbuf.info.height - self.layout.height() as usize;
+        }
 
-    let glyphs = layout.glyphs();
+        let glyphs = self.layout.glyphs();
 
         let mut first_line_top_offset = None;
 
-    for line in layout.lines().unwrap() {
-        if ((line.baseline_y - line.max_ascent) as usize) < top_row {
-            continue;
-        }
+        for line in self.layout.lines().unwrap() {
             if first_line_top_offset.is_none() {
-            first_line_top_offset = Some(((line.baseline_y - line.max_ascent) as usize) - top_row);
+                first_line_top_offset = Some((line.baseline_y - line.max_ascent) as usize);
             }
             let first_line_top_offset = first_line_top_offset.unwrap();
             for glyph_pos in &glyphs[line.glyph_start..=line.glyph_end] {
                 if glyph_pos.width == 0 || glyph_pos.height == 0 {
                     continue;
                 }
-            let (_, bitmap) = FIRA_CODE.rasterize_config(glyph_pos.key);
+                let bitmap: Cow<[u8]> = if let Some(bitmap) = self.glyph_cache.get(&glyph_pos.key) {
+                    bitmap.into()
+                } else {
+                    let bitmap = self.font.rasterize_config(glyph_pos.key).1;
+                    self.glyph_cache.insert(glyph_pos.key, bitmap.clone());
+                    bitmap.into()
+                };
                 for (i, &pixel) in bitmap.iter().enumerate() {
                     let row = i / glyph_pos.width;
                     let col = i % glyph_pos.width;
-                fbuf.set_pixel(row + glyph_pos.y as usize - top_row - first_line_top_offset, col + glyph_pos.x as usize, pixel);
+                    self.fbuf.set_pixel(
+                        row + glyph_pos.y as usize - first_line_top_offset + self.next_line_y,
+                        col + glyph_pos.x as usize,
+                        pixel,
+                    );
                 }
             }
         }
-    fbuf.update_screen();
+        self.fbuf.update_screen();
+        if self.out_string.ends_with('\n') {
+            self.out_string.clear();
+            self.next_line_y += self.layout.height() as usize;
+        } else {
+            self.out_string = self.out_string.split('\n').last().unwrap().to_string();
+        }
+    }
+}
+
+impl fmt::Write for FramebufferWriter {
+    fn write_char(&mut self, c: char) -> fmt::Result {
+        self.out_string.push(c);
+        if c == '\n' {
+            self.update_screen();
+        }
+        Ok(())
+    }
+    fn write_str(&mut self, s: &str) -> core::fmt::Result {
+        self.out_string.push_str(s);
+        if s.contains('\n') {
+            self.update_screen();
+        }
+        Ok(())
+    }
 }

src/interrupts.rs

@@ -1,5 +1,6 @@
 use crate::{
     bootinfo::BOOTINFO,
+    fbuffer::FRAMEBUFFER_WRITER,
     print, println,
     serial::SECOND_PORT,
     tasking::SleepReason,
@@ -9,7 +10,7 @@ use crate::{
 use alloc::{boxed::Box, string::ToString, vec::Vec};
 use az::WrappingCast;
 use cast::{u64, usize};
-use core::{arch::asm, ffi::CStr, ptr, slice};
+use core::{arch::asm, ffi::CStr, fmt::Write, ptr, slice};
 use hashbrown::HashMap;
 use pic8259::ChainedPics;
 use saturating_cast::SaturatingCast;
@@ -251,9 +252,8 @@ extern "C" fn syscall_handler() {
     match regs.rax {
         0 => {
             let rval = if let Some(chr) = char::from_u32(regs.rcx.wrapping_cast()) {
-                crate::fbuffer::write_char(chr);
+                let _ = FRAMEBUFFER_WRITER.lock().write_char(chr); // writer never gives an error
                 if chr == '\n' {
-                    crate::fbuffer::update_screen();
                     print!("\r\n");
                 } else {
                     print!("{}", chr);

src/main.rs

@@ -73,6 +73,7 @@
 extern crate alloc;
 
 mod bootinfo;
+mod fbuffer;
 mod gdt;
 mod interrupts;
 mod kernel_heap;
@@ -84,7 +85,6 @@ mod serial;
 mod start;
 mod tasking;
 mod virtual_memory;
-mod fbuffer;
 
 use core::{ptr, slice};
 
@@ -99,6 +99,7 @@ use elf::{
     endian::AnyEndian,
     ElfBytes,
 };
+use fbuffer::FRAMEBUFFER_WRITER;
 use physical_memory::PHYSICAL_MEMORY;
 use serial::SECOND_PORT;
 use spin::lazy::Lazy;
@@ -129,6 +130,7 @@ pub fn main() {
     Lazy::force(&PHYSICAL_MEMORY);
     Lazy::force(&KERNEL_SPACE);
     Lazy::force(&ACTIVE_SPACE);
+    Lazy::force(&FRAMEBUFFER_WRITER);
     interrupts::init();
     pit::init(100);
     let initrd = unsafe {