From 700d657e25ea7d1ef7fa3a9af89368ff97904abf Mon Sep 17 00:00:00 2001
From: Ryan Kennedy <rkennedy9064@gmail.com>
Date: Sat, 21 Mar 2020 22:26:59 -0500
Subject: [PATCH] Faster clear screen

---
 src/vga.rs                         | 10 ++++++----
 src/writers/graphics_640x480x16.rs | 18 +++++++++---------
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/src/vga.rs b/src/vga.rs
index 44e6420..6e47adc 100644
--- a/src/vga.rs
+++ b/src/vga.rs
@@ -90,13 +90,15 @@ bitflags! {
     /// Represents the plane masks of the `SequencerIndex::PlaneMask` register.
     pub struct PlaneMask: u8 {
         /// Represents `Plane0` of vga memory.
-        const PLANE0 = 0b00000001;
+        const PLANE0 = 0b0000_0001;
         /// Represents `Plane1` of vga memory.
-        const PLANE1 = 0b00000010;
+        const PLANE1 = 0b0000_0010;
         /// Represents `Plane2` of vga memory.
-        const PLANE2 = 0b00000100;
+        const PLANE2 = 0b0000_0100;
         /// Represents `Plane3` of vga memory.
-        const PLANE3 = 0b00001000;
+        const PLANE3 = 0b0000_1000;
+        /// Represents a combination of all the plane masks.
+        const ALL_PLANES = Self::PLANE0.bits() | Self::PLANE1.bits() | Self::PLANE2.bits() | Self::PLANE3.bits();
     }
 }
 
diff --git a/src/writers/graphics_640x480x16.rs b/src/writers/graphics_640x480x16.rs
index 8914011..59c9a1c 100644
--- a/src/writers/graphics_640x480x16.rs
+++ b/src/writers/graphics_640x480x16.rs
@@ -1,12 +1,13 @@
 use crate::{
     colors::{Color16Bit, DEFAULT_PALETTE},
-    vga::{Vga, VideoMode, VGA},
+    vga::{PlaneMask, Vga, VideoMode, VGA},
 };
 use core::convert::TryInto;
 use spinning_top::SpinlockGuard;
 
 const WIDTH: usize = 640;
 const HEIGHT: usize = 480;
+const ALL_PLANES_SCREEN_SIZE: usize = (WIDTH * HEIGHT) / 4;
 
 /// A basic interface for interacting with vga graphics mode 640x480x16
 ///
@@ -33,20 +34,19 @@ impl Graphics640x480x16 {
 
     /// Clears the screen by setting all pixels to `Color16Bit::Black`.
     pub fn clear_screen(&self) {
-        // TODO: Clear the screen by using 4-plane mode instead of slow `set_pixel`.
-        for x in 0..WIDTH {
-            for y in 0..HEIGHT {
-                self.set_pixel(x, y, Color16Bit::Black);
+        let (mut vga, frame_buffer) = self.get_frame_buffer();
+        vga.set_plane_mask(PlaneMask::ALL_PLANES);
+        for offset in 0..ALL_PLANES_SCREEN_SIZE {
+            unsafe {
+                frame_buffer
+                    .add(offset)
+                    .write_volatile(Color16Bit::Black as u8);
             }
         }
     }
 
     /// Sets the given pixel at `(x, y)` to the given `color`.
-    ///
-    /// Panics if `x >= 640` or `y >= 480`.
     pub fn set_pixel(&self, x: usize, y: usize, color: Color16Bit) {
-        assert!(x < WIDTH, "x >= {}", WIDTH);
-        assert!(y < HEIGHT, "y >= {}", HEIGHT);
         let (mut vga, frame_buffer) = self.get_frame_buffer();
         let offset = x / 8 + (WIDTH / 8) * y;