Rough draft line drawing

Cargo.toml

@@ -23,3 +23,7 @@ bitflags = "1.2.1"
 conquer-once = { version = "0.2.0", default-features = false }
 spinning_top = { version = "0.1.0", features = ["nightly"] }
 x86_64 = "0.9.6"
+
+[dependencies.num-traits]
+version = "0.2.11"
+default-features = false

src/drawing/bresenham.rs

@@ -0,0 +1,57 @@
+use super::{Octant, Point, SignedNum};
+
+pub(crate) struct Bresenham<T> {
+    point: Point<T>,
+    end_x: T,
+    delta_x: T,
+    delta_y: T,
+    error: T,
+    octant: Octant,
+}
+
+impl<T: SignedNum> Bresenham<T> {
+    #[inline]
+    pub fn new(start: Point<T>, end: Point<T>) -> Self {
+        let octant = Octant::new(start, end);
+        let start = octant.to(start);
+        let end = octant.to(end);
+
+        let delta_x = end.0 - start.0;
+        let delta_y = end.1 - start.1;
+
+        Self {
+            delta_x,
+            delta_y,
+            octant,
+            point: start,
+            end_x: end.0,
+            error: delta_y - delta_x,
+        }
+    }
+}
+
+impl<T> Iterator for Bresenham<T>
+where
+    T: SignedNum,
+{
+    type Item = Point<T>;
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.point.0 <= self.end_x {
+            let point = self.octant.from(self.point);
+
+            if self.error >= T::zero() {
+                self.point.1 += T::one();
+                self.error -= self.delta_x;
+            }
+
+            self.point.0 += T::one();
+            self.error += self.delta_y;
+
+            Some(point)
+        } else {
+            None
+        }
+    }
+}

src/drawing/mod.rs

@@ -0,0 +1,20 @@
+//! Common functionality for drawing in vga graphics mode.
+//! Original implementation here https://github.com/expenses/line_drawing.
+use num_traits::{NumAssignOps, NumCast, Signed};
+
+mod bresenham;
+mod octant;
+
+pub(crate) use bresenham::Bresenham;
+use octant::Octant;
+
+/// A point in 2D space.
+pub type Point<T> = (T, T);
+
+pub(crate) trait SignedNum: Signed + Ord + Copy + NumCast + NumAssignOps {
+    fn cast<T: NumCast>(value: T) -> Self {
+        NumCast::from(value).unwrap()
+    }
+}
+
+impl<T: Signed + Ord + Copy + NumCast + NumAssignOps> SignedNum for T {}

src/drawing/octant.rs

@@ -0,0 +1,75 @@
+use super::Point;
+use core::ops::{Neg, Sub};
+use num_traits::Zero;
+
+/// A simple octant struct for transforming line points.
+pub struct Octant {
+    value: u8,
+}
+
+impl Octant {
+    #[inline]
+    /// Get the relevant octant from a start and end point.
+    pub fn new<T>(start: Point<T>, end: Point<T>) -> Self
+    where
+        T: Sub<Output = T> + Neg<Output = T> + PartialOrd + Zero,
+    {
+        let mut value = 0;
+        let mut dx = end.0 - start.0;
+        let mut dy = end.1 - start.1;
+
+        if dy < T::zero() {
+            dx = -dx;
+            dy = -dy;
+            value += 4;
+        }
+
+        if dx < T::zero() {
+            let tmp = dx;
+            dx = dy;
+            dy = -tmp;
+            value += 2;
+        }
+
+        if dx < dy {
+            value += 1;
+        }
+
+        Self { value }
+    }
+
+    /// Convert a point to its position in the octant.
+    #[inline]
+    pub fn to<T>(&self, point: Point<T>) -> Point<T>
+    where
+        T: Neg<Output = T>,
+    {
+        match self.value {
+            0 => (point.0, point.1),
+            1 => (point.1, point.0),
+            2 => (point.1, -point.0),
+            3 => (-point.0, point.1),
+            4 => (-point.0, -point.1),
+            5 => (-point.1, -point.0),
+            6 => (-point.1, point.0),
+            7 => (point.0, -point.1),
+            _ => unreachable!(),
+        }
+    }
+
+    /// Convert a point from its position in the octant.
+    #[inline]
+    pub fn from<T: Neg<Output = T>>(&self, point: Point<T>) -> Point<T> {
+        match self.value {
+            0 => (point.0, point.1),
+            1 => (point.1, point.0),
+            2 => (-point.1, point.0),
+            3 => (-point.0, point.1),
+            4 => (-point.0, -point.1),
+            5 => (-point.1, -point.0),
+            6 => (point.1, -point.0),
+            7 => (point.0, -point.1),
+            _ => unreachable!(),
+        }
+    }
+}

src/lib.rs

@@ -9,6 +9,7 @@
 
 pub mod colors;
 pub mod configurations;
+pub mod drawing;
 pub mod fonts;
 pub mod registers;
 pub mod vga;

src/registers/graphics_controller.rs

@@ -1,4 +1,4 @@
-use super::{Color16Bit, PlaneMask, GRX_DATA_ADDRESS, GRX_INDEX_ADDRESS};
+use super::{Color16Bit, GRX_DATA_ADDRESS, GRX_INDEX_ADDRESS};
 use core::convert::TryFrom;
 use x86_64::instructions::port::Port;
 
@@ -177,13 +177,13 @@ impl GraphicsControllerRegisters {
         );
     }
 
-    /// Sets which planes are effected by `GraphicsControllerIndex::SetReset`,
-    /// as specified by `plane_mask`.
-    pub fn write_enable_set_reset(&mut self, plane_mask: PlaneMask) {
+    /// Sets which bits are effected by `GraphicsControllerIndex::SetReset`,
+    /// as specified by `bit_mask`.
+    pub fn write_enable_set_reset(&mut self, bit_mask: u8) {
         let original_value = self.read(GraphicsControllerIndex::EnableSetReset) & 0xF0;
         self.write(
             GraphicsControllerIndex::EnableSetReset,
-            original_value | u8::from(plane_mask),
+            original_value | bit_mask,
         );
     }
 

src/writers/graphics_640x480x16.rs

@@ -1,5 +1,6 @@
 use crate::{
     colors::{Color16Bit, DEFAULT_PALETTE},
+    drawing::{Bresenham, Point},
     registers::{PlaneMask, WriteMode},
     vga::{Vga, VideoMode, VGA},
 };
@@ -17,12 +18,13 @@ const WIDTH_IN_BYTES: usize = WIDTH / 8;
 /// Basic usage:
 ///
 /// ```no_run
+/// use vga::colors::Color16Bit;
 /// use vga::writers::Graphics640x480x16;
 ///
 /// let graphics_mode = Graphics640x480x16::new();
 ///
 /// graphics_mode.set_mode();
-/// graphics_mode.clear_screen();
+/// graphics_mode.clear_screen(Color16Bit::Black);
 /// ```
 #[derive(Default)]
 pub struct Graphics640x480x16;
@@ -36,14 +38,11 @@ impl Graphics640x480x16 {
     /// Clears the screen by setting all pixels to the specified `color`.
     pub fn clear_screen(&self, color: Color16Bit) {
         let (mut vga, frame_buffer) = self.get_frame_buffer();
-        // Set write mode 2 so data is modified by the bitmask
         vga.graphics_controller_registers
             .set_write_mode(WriteMode::Mode2);
-        // Write to all 4 planes at once
+        vga.graphics_controller_registers.set_bit_mask(0xFF);
         vga.sequencer_registers
             .set_plane_mask(PlaneMask::ALL_PLANES);
-        // Every bit should be set to the same color
-        vga.graphics_controller_registers.set_bit_mask(0xFF);
         for offset in 0..ALL_PLANES_SCREEN_SIZE {
             unsafe {
                 frame_buffer.add(offset).write_volatile(u8::from(color));
@@ -51,21 +50,32 @@ impl Graphics640x480x16 {
         }
     }
 
+    /// Draws a line from `start` to `end` with the specified `color`.
+    pub fn draw_line(&self, start: Point<isize>, end: Point<isize>, color: Color16Bit) {
+        {
+            let (mut vga, _frame_buffer) = self.get_frame_buffer();
+            vga.graphics_controller_registers.write_set_reset(color);
+            vga.graphics_controller_registers
+                .write_enable_set_reset(0xF);
+            vga.graphics_controller_registers
+                .set_write_mode(WriteMode::Mode0);
+        }
+
+        for (x, y) in Bresenham::new(start, end) {
+            self.set_pixel_with_set_reset(x as usize, y as usize);
+        }
+    }
+
     /// Sets the given pixel at `(x, y)` to the given `color`.
     pub fn set_pixel(&self, x: usize, y: usize, color: Color16Bit) {
         let (mut vga, frame_buffer) = self.get_frame_buffer();
         let offset = x / 8 + y * WIDTH_IN_BYTES;
         // Which pixel to modify this write
-        let pixel_offset = x & 7;
-        // Set write mode 2 so screen data is only modified by the bitmask
+        let pixel_mask = 0x80 >> (x & 0x07);
         vga.graphics_controller_registers
             .set_write_mode(WriteMode::Mode2);
-        // Write to all 4 planes at once
-        vga.sequencer_registers
-            .set_plane_mask(PlaneMask::ALL_PLANES);
         // Only modify 1 pixel, based on the offset
-        vga.graphics_controller_registers
-            .set_bit_mask(1 << pixel_offset);
+        vga.graphics_controller_registers.set_bit_mask(pixel_mask);
         unsafe {
             // Reads the current offset into the memory latches
             frame_buffer.add(offset).read_volatile();
@@ -75,6 +85,22 @@ impl Graphics640x480x16 {
         }
     }
 
+    fn set_pixel_with_set_reset(&self, x: usize, y: usize) {
+        let (mut vga, frame_buffer) = self.get_frame_buffer();
+        let offset = x / 8 + y * WIDTH_IN_BYTES;
+        // Which pixel to modify this write
+        let pixel_mask = 0x80 >> (x & 0x07);
+        // Only modify 1 pixel, based on the offset
+        vga.graphics_controller_registers.set_bit_mask(pixel_mask);
+        unsafe {
+            // Reads the current offset into the memory latches
+            frame_buffer.add(offset).read_volatile();
+            // Sets the pixel specified by the offset to the color. The
+            // pixels not inlcuded in the bit mask remain untouched.
+            frame_buffer.add(offset).write_volatile(0x00);
+        }
+    }
+
     /// Sets the graphics device to `VideoMode::Mode640x480x16`.
     pub fn set_mode(&self) {
         let mut vga = VGA.lock();