Fix extra pixels plotting on the Reuleaux triangle

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

1 files changed, 21 insertions, 11 deletions

diff --git a/task4/reuleaux.sv b/task4/reuleaux.sv
index 0b08225..b6c35a2 100644
--- a/task4/reuleaux.sv
+++ b/task4/reuleaux.sv
@@ -31,8 +31,7 @@ module reuleaux(clk, rst_n, colour, centre_x, centre_y, diameter, start, done,
 	assign radius = diameter;
 
 	/* sqrt(3)/3 * 2^12 = 2364.826...
-	 * Add 2^(N-1) before shifting by N to round
-	 * to the nearest integer. */
+	 * Add 2^(N-1) before shifting by N to round to the nearest integer. */
 	assign y_offset = diameter * 2365;
 	assign centre_x1 = centre_x;
 	assign centre_y1 = centre_y - ((y_offset + (1 << 11)) >> 12);
@@ -45,50 +44,60 @@ module reuleaux(clk, rst_n, colour, centre_x, centre_y, diameter, start, done,
 	 * - circle 1: octants 2 & 3;
 	 * - circle 2: octants 5 & 6;
 	 * - circle 3: octants 7 & 8.
-	 * Extra pixels will be taken care further below (not implemented). */
+	 * Extra pixels will be taken care further below. */
 	always_comb case (octant)
 		3'd0: begin
-			vga_plot_next = 1'b0;
 			vga_x_next = centre_x + offset_x;
 			vga_y_next = centre_y + offset_y;
 		end
 		3'd1: begin
-			vga_plot_next = 1'b1;
 			vga_x_next = centre_x1 + offset_y;
 			vga_y_next = centre_y1 + offset_x;
 		end
 		3'd2: begin
-			vga_plot_next = 1'b1;
 			vga_x_next = centre_x1 - offset_y;
 			vga_y_next = centre_y1 + offset_x;
 		end
 		3'd3: begin
-			vga_plot_next = 1'b0;
 			vga_x_next = centre_x - offset_x;
 			vga_y_next = centre_y + offset_y;
 		end
 		3'd4: begin
-			vga_plot_next = 1'b1;
 			vga_x_next = centre_x2 - offset_x;
 			vga_y_next = centre_y2 - offset_y;
 		end
 		3'd5: begin
-			vga_plot_next = 1'b1;
 			vga_x_next = centre_x2 - offset_y;
 			vga_y_next = centre_y2 - offset_x;
 		end
 		3'd6: begin
-			vga_plot_next = 1'b1;
 			vga_x_next = centre_x3 + offset_y;
 			vga_y_next = centre_y3 - offset_x;
 		end
 		3'd7: begin
-			vga_plot_next = 1'b1;
 			vga_x_next = centre_x3 + offset_x;
 			vga_y_next = centre_y3 - offset_y;
 		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 (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 (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 (vga_x_next >= centre_x)
+				vga_plot_next = 1'b1;
+	end
+
+	/* Main combinational logic for the Bresenham circle algorithm. */
 	always_comb begin
 		offset_x_next = offset_x;
 		offset_y_next = offset_y + 1;
@@ -172,4 +181,5 @@ module reuleaux(clk, rst_n, colour, centre_x, centre_y, diameter, start, done,
 		end else if (~start && done)
 			done <= 1'b0;
 	end
+
 endmodule: reuleaux