Fix arc 1 not drawing when centre of circle 1 is off screen

Signed-off-by: Warrick Lo <wlo@warricklo.net>

1 files changed, 12 insertions, 12 deletions

diff --git a/task4/reuleaux.sv b/task4/reuleaux.sv
index 68a3540..dbf57f8 100644
--- a/task4/reuleaux.sv
+++ b/task4/reuleaux.sv
@@ -16,15 +16,15 @@ module reuleaux(clk, rst_n, colour, centre_x, centre_y, diameter, start, done,
 
 	logic clear, ready, vga_plot_next;
 	logic [2:0] octant;
-	logic [7:0] offset_x, offset_y, offset_x_next, offset_y_next;
-	/* One bit larger since these are signed. */
-	logic signed [7:0] vga_y_next;
-	logic signed [8:0] vga_x_next, crit, crit_next;
+	/* Auxiliary value for calculations. 21-bit number since we multiply
+	 * 8-bit and 13-bit numbers together. */
+	logic [20:0] diameter_scaled;
 
-	logic [6:0] centre_y1, centre_y2, centre_y3;
-	logic [7:0] centre_x1, centre_x2, centre_x3, radius;
-	/* Auxiliary value for calculations. */
-	logic [19:0] y_offset;
+	/* One bit larger since these are signed. */
+	logic signed [7:0] vga_y_next, offset_y, offset_y_next,
+		centre_y1, centre_y2, centre_y3;
+	logic signed [8:0] vga_x_next, offset_x, offset_x_next,
+		centre_x1, centre_x2, centre_x3, crit, crit_next, radius;
 
 	assign vga_colour = clear ? 3'b000 : colour;
 	/* Circle radius is the same as the Reuleaux triangle diameter. */
@@ -32,13 +32,13 @@ module reuleaux(clk, rst_n, colour, centre_x, centre_y, diameter, start, done,
 
 	/* sqrt(3)/3 * 2^12 = 2364.826...
 	 * Add 2^(N-1) before shifting by N to round to the nearest integer. */
-	assign y_offset = diameter * 2365;
+	assign diameter_scaled = diameter * 2365;
 	assign centre_x1 = centre_x;
-	assign centre_y1 = centre_y - ((y_offset + (1 << 11)) >> 12);
+	assign centre_y1 = centre_y - ((diameter_scaled + (1 << 11)) >> 12);
 	assign centre_x2 = centre_x + (diameter >> 1);
-	assign centre_y2 = centre_y + ((y_offset + (1 << 12)) >> 13);
+	assign centre_y2 = centre_y + ((diameter_scaled + (1 << 12)) >> 13);
 	assign centre_x3 = centre_x - (diameter >> 1);
-	assign centre_y3 = centre_y + ((y_offset + (1 << 12)) >> 13);
+	assign centre_y3 = centre_y + ((diameter_scaled + (1 << 12)) >> 13);
 
 	/* Draw only the octants that are needed for each circle.
 	 * Extra pixels will be taken care further below. */