From 933e5ec714e97dad0951d560b90c301d233dc1b6 Mon Sep 17 00:00:00 2001
From: Warrick Lo <wlo@warricklo.net>
Date: Mon, 2 Mar 2026 16:46:07 -0800
Subject: Remove plotting unused octants

Signed-off-by: Warrick Lo <wlo@warricklo.net>
---
 task4/reuleaux.sv | 44 ++++++++++++++++++++------------------------
 1 file changed, 20 insertions(+), 24 deletions(-)

(limited to 'task4/reuleaux.sv')

diff --git a/task4/reuleaux.sv b/task4/reuleaux.sv
index b6c35a2..68a3540 100644
--- a/task4/reuleaux.sv
+++ b/task4/reuleaux.sv
@@ -40,59 +40,55 @@ module reuleaux(clk, rst_n, colour, centre_x, centre_y, diameter, start, done,
 	assign centre_x3 = centre_x - (diameter >> 1);
 	assign centre_y3 = centre_y + ((y_offset + (1 << 12)) >> 13);
 
-	/* Draw only the octants that are needed for each circle:
-	 * - circle 1: octants 2 & 3;
-	 * - circle 2: octants 5 & 6;
-	 * - circle 3: octants 7 & 8.
+	/* Draw only the octants that are needed for each circle.
 	 * Extra pixels will be taken care further below. */
 	always_comb case (octant)
+		/* Circle 1: octants 2 and 3. */
 		3'd0: begin
-			vga_x_next = centre_x + offset_x;
-			vga_y_next = centre_y + offset_y;
-		end
-		3'd1: begin
 			vga_x_next = centre_x1 + offset_y;
 			vga_y_next = centre_y1 + offset_x;
 		end
-		3'd2: begin
+		3'd1: begin
 			vga_x_next = centre_x1 - offset_y;
 			vga_y_next = centre_y1 + offset_x;
 		end
-		3'd3: begin
-			vga_x_next = centre_x - offset_x;
-			vga_y_next = centre_y + offset_y;
-		end
-		3'd4: begin
+		/* Circle 2: octants 5 and 6. */
+		3'd2: begin
 			vga_x_next = centre_x2 - offset_x;
 			vga_y_next = centre_y2 - offset_y;
 		end
-		3'd5: begin
+		3'd3: begin
 			vga_x_next = centre_x2 - offset_y;
 			vga_y_next = centre_y2 - offset_x;
 		end
-		3'd6: begin
+		/* Circle 3: octants 7 and 8. */
+		3'd4: begin
 			vga_x_next = centre_x3 + offset_y;
 			vga_y_next = centre_y3 - offset_x;
 		end
-		3'd7: begin
+		3'd5: begin
 			vga_x_next = centre_x3 + offset_x;
 			vga_y_next = centre_y3 - offset_y;
 		end
+		default: begin
+			vga_x_next = 9'bx;
+			vga_y_next = 8'bx;
+		end
 	endcase
 
 	/* Only plot the pixels of the triangle. */
 	always_comb begin
 		vga_plot_next = 1'b0;
 		/* Pixels of circle 1 that are below the centre of 2 or 3. */
-		if ((octant == 3'd1) || (octant == 3'd2))
+		if ((octant == 3'd0) || (octant == 3'd1))
 			if (vga_y_next > centre_y2)
 				vga_plot_next = 1'b1;
 		/* Pixels of circle 2 that are to the left of the centre. */
-		if ((octant == 3'd4) || (octant == 3'd5))
+		if ((octant == 3'd2) || (octant == 3'd3))
 			if (vga_x_next <= centre_x)
 				vga_plot_next = 1'b1;
 		/* Pixels of circle 3 that are to the right of the centre. */
-		if ((octant == 3'd6) || (octant == 3'd7))
+		if ((octant == 3'd4) || (octant == 3'd5))
 			if (vga_x_next >= centre_x)
 				vga_plot_next = 1'b1;
 	end
@@ -163,14 +159,14 @@ module reuleaux(clk, rst_n, colour, centre_x, centre_y, diameter, start, done,
 					&& (vga_y_next >= 0)
 					&& (vga_y_next <= `VGA_H));
 
-				octant <= octant + 1;
-
 				/* The last octant. */
-				if (octant == 7) begin
+				if (octant == 5) begin
 					offset_x <= offset_x_next;
 					offset_y <= offset_y_next;
 					crit <= crit_next;
-				end
+					octant <= 3'b0;
+				end else
+					octant <= octant + 1;
 			/* Finished. */
 			end else begin
 				done <= 1'b1;
-- 
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