draw_pterosaur.sv

module draw_pterosaur(  input frame_Clk, Reset,
							input Dead,
							//input Speed_up,
							input [1:0] Game_State,
							input [9:0] WriteX, WriteY,	
							input int Cactus_PosX, Cactus_PosY,
							input int Cactus_SizeX, Cactus_SizeY,
							output logic pterosaur_on_wr,
							output int Ptero_PosX, Ptero_PosY,
							output logic [17:0] address,
							output logic pt_off);

	//$readmemh("sprite/pterosaur_wingdown_92x80.txt", mem, 171995, 179354);
	//$readmemh("sprite/pterosaur_wingup_92x80.txt", mem, 179355, 186714);
	parameter [17:0] pterosaur1 = 18'd171995;
	parameter [17:0] pterosaur2 = 18'd179355;
	int pterosaur_X = 92;
	int pterosaur_Y = 80;
	int PosX, PosY;
	int X_Motion = -4;
//	int Y_Motion = 0;
	//int reference = 0;
	int frame_count1, frame_count2;
	logic draw_pt1;
	logic change_height;
	logic [17:0] start, offset;
	int SizeX, SizeY, DistX, DistY;
	
	initial
	begin
		PosX = 1000;
		PosY = 120;
		frame_count1 = 1;
		frame_count2 = 1;
		draw_pt1 = 1'b1;
		change_height = 1'b0;
	end
	
	enum logic [3:0] {Height1, Height2, Height3, None} draw_type, Next_draw_type;
	
	always_ff @ (posedge change_height or posedge Reset)
	begin
		if (Reset) 
			draw_type <= None;
		else 
			draw_type <= Next_draw_type;
	end
	
	always_comb
	begin
		unique case (draw_type)
			Height1 : 
				begin
					PosY = 210;
					pt_off = 1'b0;
					//reference = 120;
				end
			Height2 :
				begin
					PosY = 270;
					pt_off = 1'b0;
					//reference = 210;
				end
			Height3:
				begin
					PosY = 300;
					pt_off = 1'b0;
					//reference = 300
				end
			None :
				begin
					PosY = 480;
					pt_off = 1'b1;
					// reference = 500;
				end
		endcase
	end
	
	always_comb
	begin
		SizeX = pterosaur_X;
		SizeY = pterosaur_Y;
		DistX = WriteX - PosX;
		DistY = WriteY - PosY;
	end
	
	always_comb 
	begin
		if ((Game_State == 2'b00) || (Game_State == 2'b10) || Dead)
		begin
//			Y_Motion = 0;
			X_Motion = 0;
		end
//		else if (Speed_up)
//			X_Motion = X_Motion*2;
		else
			X_Motion = -4;
	end
	always_ff @ (posedge frame_Clk or posedge Reset)
	begin
		if (Reset)
		begin
			PosX <= 980;
			frame_count1 <= 1;
			frame_count2 <= 1;
			draw_pt1 <= 1'b1;
			change_height <= 1'b0;
		end
		else
		begin
			if (frame_count1 == 10)
			begin
				draw_pt1 <= ~(draw_pt1);
				frame_count1 <= 1;
			end
			else
				frame_count1 <= frame_count1 + 1;
			if (frame_count2 == 1)
			begin
				if (PosX <= 640 && PosX > 0)
					change_height <= 0;
				if (PosX <= -pterosaur_X)
				begin
					change_height <= 1;
					PosX <= 980;
				end
				else
				begin
	//				Y_Motion <= $cos(PosY-reference);
	//				PosY <= PosY + Y_Motion;
					PosX <= PosX + X_Motion;
	//				PosX <= PosX - 4;
				end
				frame_count2 <= 1;
			end
			else
				frame_count2 <= frame_count2 + 1;
		end
	end
	//Random number
	logic Load_Seed, Done;
	logic [5:0] Seed;
	logic [5:0] rand_num;
	int pulse_counter;
	assign Seed = 6'b101010;
	
	initial
	begin
		Load_Seed = 1;
		pulse_counter = 0;
	end
	always_ff @ (posedge frame_Clk)
	begin
		if (pulse_counter >= 2)
		begin
			Load_Seed <= 0;
			pulse_counter <= 2;
		end
		else
			pulse_counter <= pulse_counter + 1;
	end
	LFSR #(6) gen_rand (.*, .Clk(~frame_Clk), .Enable(1'b1), .Out(rand_num));
	
	//Change height according to the random number
	always_comb
	begin:Choose_height
		Next_draw_type = draw_type;
		if (Cactus_PosX + Cactus_SizeX > 320 || Cactus_PosX < 0)
			Next_draw_type = None;
		else
		begin
			if (rand_num >= 6'd0 && rand_num < 6'd16)			//Possibility = 1/4
				Next_draw_type = Height1;
			else if (rand_num >= 6'd16 && rand_num < 6'd48) //Possibility = 1/2
				Next_draw_type = Height2;
			else															//Possibility = 1/4
				Next_draw_type = Height3;
		end
	end
	
	always_comb
	begin
		if (draw_pt1)
			start = pterosaur1;
		else
			start = pterosaur2;
		offset = DistY*SizeX + DistX;
	end
	assign address = start + offset;
	
	always_comb
   begin:Pterosaur_on_wr_proc
	 if ((WriteX >= PosX || PosX < 0) &&
       (WriteX < PosX + pterosaur_X) &&
       (WriteY >= PosY) &&
       (WriteY < PosY + pterosaur_Y) &&
		 (~pt_off))
      pterosaur_on_wr = 1'b1;
    else 
		pterosaur_on_wr = 1'b0;
   end
	
	assign Ptero_PosX = PosX;
	assign Ptero_PosY = PosY;
endmodule