Write a console that does not flush gfx buffers

ctru-rs/src/console.rs

@@ -5,6 +5,8 @@ use ctru_sys::{consoleClear, consoleInit, consoleSelect, consoleSetWindow, Print
 
 use crate::gfx::Screen;
 
+mod non_flushing;
+
 static mut EMPTY_CONSOLE: PrintConsole = unsafe { const_zero::const_zero!(PrintConsole) };
 
 pub struct Console<'screen> {
@@ -27,6 +29,18 @@ impl<'screen> Console<'screen> {
         }
     }
 
+    /// Initialize a console that prints to the screen *without* flushing after every newline
+    /// or carriage return. This can prevent deadlocks when trying to print from multiple
+    /// threads simultaneously, but [`Gfx::flush_buffers`]
+    /// must be called for the printed output to be visible
+    ///
+    /// [`Gfx::flush_buffers`]: crate::gfx::Gfx::flush_buffers
+    pub fn non_flushing(screen: RefMut<'screen, dyn Screen>) -> Self {
+        let mut console = Self::init(screen);
+        console.context.PrintChar = Some(non_flushing::print_char);
+        console
+    }
+
     /// Returns true if a valid Console to print on is selected
     pub fn exists() -> bool {
         unsafe {

ctru-rs/src/console/non_flushing.rs

@@ -0,0 +1,90 @@
+//! This is a bit of a hack, but allows us to reuse most of the libctru console
+//! implementation without writing one from scratch. This lets the user control
+//! when the console characters are flushed to the screen, which can help prevent
+//! deadlocks while using the console and graphics simultaneously.
+
+use ctru_sys::PrintConsole;
+
+/// Print a character to the console, without flushing the graphics buffers.
+/// Falls back to the default implementation for any characters other than
+/// `\n` or `\r`, which are the only ones that normally result in a flush.
+pub extern "C" fn print_char(console: *mut libc::c_void, c: i32) -> bool {
+    let console = unsafe { &mut *(console.cast::<PrintConsole>()) };
+
+    let ret = match c {
+        // '\r'
+        10 => {
+            new_row(console);
+            console.cursorX = 0;
+            true
+        }
+        // '\n'
+        13 => {
+            console.cursorX = 0;
+            true
+        }
+        _ => false, // use default console printer
+    };
+
+    if console.cursorX >= console.windowWidth {
+        console.cursorX = 0;
+        new_row(console);
+        true
+    } else {
+        ret
+    }
+}
+
+/// Direct port of
+/// <https://github.com/devkitPro/libctru/blob/master/libctru/source/console.c#L724>
+fn new_row(console: &mut PrintConsole) {
+    console.cursorY += 1;
+
+    if console.cursorY >= console.windowHeight {
+        console.cursorY -= 1;
+        let idx = (console.windowX * 8 * 240) + (239 - (console.windowY * 8));
+
+        unsafe {
+            let mut dst: *mut u16 = console.frameBuffer.offset(idx as _);
+            let mut src: *mut u16 = dst.offset(-8);
+
+            for _ in 0..console.windowWidth * 8 {
+                let mut from: *mut u32 = (src as i32 & !3) as _;
+                let mut to: *mut u32 = (dst as i32 & !3) as _;
+                for _ in 0..(((console.windowHeight - 1) * 8) / 2) {
+                    *to = *from;
+                    to = to.offset(-1);
+                    from = from.offset(-1);
+                }
+
+                dst = dst.offset(240);
+                src = src.offset(240);
+            }
+        }
+
+        clear_line(console);
+    }
+}
+
+// HACK: this is technically an implementation detail of libctru's console,
+//  but it has a that we can link to. We use this so we don't need to re-implement
+// the entire call stack down from clear_line just to print some spaces characters.
+extern "C" {
+    fn consolePrintChar(c: i32);
+}
+
+/// Direct port of `consoleClearLine('2')`, minus the flush at the end.
+/// <https://github.com/devkitPro/libctru/blob/master/libctru/source/console.c#L231>
+fn clear_line(console: &mut PrintConsole) {
+    let col_tmp = console.cursorX;
+
+    console.cursorX = 0;
+
+    for _ in 0..console.windowWidth {
+        unsafe {
+            consolePrintChar(b' ' as i32);
+        }
+    }
+
+    console.cursorX = col_tmp;
+}