From 42068ebcb63969b7339736b2806d949c3071a351 Mon Sep 17 00:00:00 2001
From: Simon Forman <sforman@hushmail.com>
Date: Sun, 26 Feb 2023 20:02:14 -0800
Subject: [PATCH] Is this fun?  Kinda.

I should break out the graph papaer and Abrash's Black Book and figure
out WTF I'm doing rather than just noodling around, eh?
---
 implementations/uvm-ncc/graphics.h | 25 ++++++++++++++++++++-----
 implementations/uvm-ncc/xerblin.c  |  5 ++++-
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/implementations/uvm-ncc/graphics.h b/implementations/uvm-ncc/graphics.h
index a74cad8..1c27b46 100644
--- a/implementations/uvm-ncc/graphics.h
+++ b/implementations/uvm-ncc/graphics.h
@@ -96,23 +96,38 @@ plot_pixel(u32* dest, size_t dest_stride, u64 x, u64 y, u32 color, u8 alpha)
 
 
 void
-carefree_wu_line(u32* dest, size_t dest_stride, u64 x, u64 y, int w, int h, u32 color)
+carefree_wu_line(u32* dest, size_t dest_stride, u64 x, u64 y, u64 w, u64 h, u32 color)
 {
 	// Yeah...  crunchy fun for the whole family.
 	// https://dl.acm.org/doi/pdf/10.1145/127719.122734
 	
 	// > Without loss of generality only lines in the first octant are considered.
-	assert(w > 0 && h > 0 && h >= w);
+	assert(w > 0 && h > 0 && w >= h);
 
 	// > We translate the point (x0, y0) to the origin,
 	// so y = kx where k = h/w with k <= 1
+	u16 k = 0xFFFF * h / w;
+	//print_i64(w); print_str(" x ");	print_i64(h); print_endl();
+	print_i64(k>>8); print_endl();
 	u64 x1 = x + w;
 	u64 y1 = y + h;
-	int d = 0;
+	u16 d = 0;
 	while (x1 > x) {
-		plot_pixel(dest, dest_stride, x, y, color, 0xFF);
-		plot_pixel(dest, dest_stride, x1, y1, color, 0xFF);
+		//print_i64(d); print_endl();
+		if (d) {
+			plot_pixel(dest, dest_stride,  x,  y, color, d >> 8);
+			plot_pixel(dest, dest_stride, x1, y1, color, d >> 8);
+		}
+		plot_pixel(dest, dest_stride,  x,  y - 1, color, 0xFF - (d >> 8));
+		plot_pixel(dest, dest_stride, x1, y1 - 1, color, 0xFF - (d >> 8));
 		++x;
 		--x1;
+		d = d + k;
+		if (d > 0xFFFF) {
+			d = 0;
+			// opposite (de-)increment because computer y is negative cartesian y
+			++y;
+			--y1;
+		}
 	}
 }
diff --git a/implementations/uvm-ncc/xerblin.c b/implementations/uvm-ncc/xerblin.c
index 820ca9f..19a6529 100644
--- a/implementations/uvm-ncc/xerblin.c
+++ b/implementations/uvm-ncc/xerblin.c
@@ -104,7 +104,10 @@ main()
 	u64 w = 3 + 26 * font_Inconsolata_22_width;
 	u64 h = 4 + 4 * font_Inconsolata_22_height;
 	carefree_draw_box(frame_buffer, FRAME_WIDTH, 126, 126, w, h, WHITE);
-	carefree_wu_line(frame_buffer, FRAME_WIDTH, 10, 256, 100, 200, WHITE);
+	w = 200;
+	for (w = 101; w < (FRAME_WIDTH - 10); w = w + 3) {
+		carefree_wu_line(frame_buffer, FRAME_WIDTH, 10, 256, w, 100, WHITE);
+	}
 	window_draw_frame(wid, frame_buffer);
 	window_on_keydown(wid, keydown);
 	window_on_mousedown(wid, mousedown);