From 9527d32521265f389d6c8c591127b56cc5d107ec Mon Sep 17 00:00:00 2001
From: Corwin Kuiper <corwin@kuiper.dev>
Date: Sun, 7 Mar 2021 00:47:39 +0000
Subject: [PATCH] allow only one vblank handler

---
 examples/bitmap3.rs |  7 ++----
 examples/bitmap4.rs | 11 ++++-----
 src/display/mod.rs  | 57 ++++++++++++++++++++++++++++++++++++++++-----
 3 files changed, 57 insertions(+), 18 deletions(-)

diff --git a/examples/bitmap3.rs b/examples/bitmap3.rs
index 584d8ccc..ebb13ac0 100644
--- a/examples/bitmap3.rs
+++ b/examples/bitmap3.rs
@@ -14,6 +14,7 @@ struct Vector2D {
 fn main(_argc: isize, _argv: *const *const u8) -> isize {
     let gba = gba::Gba::new();
     let bitmap = gba.display.bitmap3();
+    let vblank = gba.display.get_vblank();
 
     let mut input = gba::input::ButtonController::new();
     let mut pos = Vector2D {
@@ -21,12 +22,8 @@ fn main(_argc: isize, _argv: *const *const u8) -> isize {
         y: display::HEIGHT / 2,
     };
 
-    gba::interrupt::enable(gba::interrupt::Interrupt::VBlank);
-    gba::interrupt::enable_interrupts();
-    gba::display::enable_VBlank_interrupt();
-
     loop {
-        gba::display::wait_for_VBlank();
+        vblank.wait_for_VBlank();
 
         input.update();
         pos.x += input.x_tri() as i32;
diff --git a/examples/bitmap4.rs b/examples/bitmap4.rs
index 07996436..7cb2a1e8 100644
--- a/examples/bitmap4.rs
+++ b/examples/bitmap4.rs
@@ -9,6 +9,7 @@ use gba::display;
 fn main(_argc: isize, _argv: *const *const u8) -> isize {
     let gba = gba::Gba::new();
     let bitmap = gba.display.bitmap4();
+    let vblank = gba.display.get_vblank();
 
     bitmap.set_palette_entry(1, 0x001F);
     bitmap.set_palette_entry(2, 0x03E0);
@@ -17,23 +18,19 @@ fn main(_argc: isize, _argv: *const *const u8) -> isize {
         display::WIDTH / 2,
         display::HEIGHT / 2,
         1,
-        display::Page::Front,
+        display::bitmap4::Page::Front,
     );
     bitmap.draw_point_page(
         display::WIDTH / 2 + 5,
         display::HEIGHT / 2,
         2,
-        display::Page::Back,
+        display::bitmap4::Page::Back,
     );
 
-    gba::interrupt::enable(gba::interrupt::Interrupt::VBlank);
-    gba::interrupt::enable_interrupts();
-    gba::display::enable_VBlank_interrupt();
-
     let mut count = 0;
 
     loop {
-        gba::display::wait_for_VBlank();
+        vblank.wait_for_VBlank();
         count += 1;
         if count % 6 == 0 {
             bitmap.flip_page();
diff --git a/src/display/mod.rs b/src/display/mod.rs
index 2bbcb8db..3901074f 100644
--- a/src/display/mod.rs
+++ b/src/display/mod.rs
@@ -1,11 +1,14 @@
-use crate::{memory_mapped::MemoryMapped, single::Single};
+use crate::{
+    memory_mapped::MemoryMapped,
+    single::{Single, SingleToken},
+};
 use bitflags::bitflags;
 
 use bitmap3::Bitmap3;
 use bitmap4::Bitmap4;
 
-mod bitmap3;
-mod bitmap4;
+pub mod bitmap3;
+pub mod bitmap4;
 
 const DISPLAY_CONTROL: MemoryMapped<u16> = unsafe { MemoryMapped::new(0x0400_0000) };
 const DISPLAY_STATUS: MemoryMapped<u16> = unsafe { MemoryMapped::new(0x0400_0004) };
@@ -42,12 +45,14 @@ pub enum DisplayMode {
 
 pub struct Display {
     in_mode: Single,
+    vblank: Single,
 }
 
 impl Display {
     pub(crate) const unsafe fn new() -> Self {
         Display {
             in_mode: Single::new(),
+            vblank: Single::new(),
         }
     }
 
@@ -65,6 +70,15 @@ impl Display {
                 .expect("Cannot create new mode as mode already taken"),
         )
     }
+    pub fn get_vblank(&self) -> VBlank {
+        unsafe {
+            VBlank::new(
+                self.vblank
+                    .take()
+                    .expect("Cannot create another vblank handler"),
+            )
+        }
+    }
 }
 
 fn set_graphics_mode(mode: DisplayMode) {
@@ -85,18 +99,49 @@ pub fn set_graphics_settings(settings: GraphicsSettings) {
 }
 
 #[allow(non_snake_case)]
+/// Waits until vblank using a busy wait loop, this should almost never be used.
+/// I only say almost because whilst I don't believe there to be a reason to use
+/// this I can't rule it out.
 pub fn busy_wait_for_VBlank() {
     while VCOUNT.get() >= 160 {}
     while VCOUNT.get() < 160 {}
 }
 
+pub struct VBlank<'a> {
+    _got: SingleToken<'a>,
+}
+
+impl<'a> VBlank<'a> {
+    unsafe fn new(a: SingleToken<'a>) -> Self {
+        crate::interrupt::enable_interrupts();
+        crate::interrupt::enable(crate::interrupt::Interrupt::VBlank);
+        enable_VBlank_interrupt();
+        VBlank { _got: a }
+    }
+
+    #[allow(non_snake_case)]
+    pub fn wait_for_VBlank(&self) {
+        crate::syscall::wait_for_VBlank();
+    }
+}
+
+impl<'a> Drop for VBlank<'a> {
+    fn drop(&mut self) {
+        unsafe {
+            disable_VBlank_interrupt();
+            crate::interrupt::disable(crate::interrupt::Interrupt::VBlank);
+        }
+    }
+}
+
 #[allow(non_snake_case)]
-pub fn enable_VBlank_interrupt() {
+unsafe fn enable_VBlank_interrupt() {
     let status = DISPLAY_STATUS.get() | (1 << 3);
     DISPLAY_STATUS.set(status);
 }
 
 #[allow(non_snake_case)]
-pub fn wait_for_VBlank() {
-    crate::syscall::wait_for_VBlank();
+unsafe fn disable_VBlank_interrupt() {
+    let status = DISPLAY_STATUS.get() & !(1 << 3);
+    DISPLAY_STATUS.set(status);
 }