Add scoring

Makefile

@@ -17,5 +17,5 @@ clean:
 distclean: clean
 
 test: $(BIN)
-	sipsi-8.py $<
+	sipsi-8.py $< 900
 	chip8 $<

mato8.asm

@@ -4,18 +4,26 @@
 ; Under Creative Commons Zero 1.0
 ; Assemble with c8asm (https://github.com/wernsey/chip8)
 
-define frames_wait 4
+define frames_wait 5
 
 define up_key 2
 define down_key 8
 define left_key 4
 define right_key 6
 
-define game_over_reg v8
-define fruit_x_reg v9
-define fruit_y_reg va
-define head_dx_reg vb
-define head_dy_reg vc
+define direction_up 0
+define direction_down 6
+define direction_left 12
+define direction_right 18
+
+define score_high_reg v5
+define score_low_reg v6
+define game_over_reg v7
+define fruit_x_reg v8
+define fruit_y_reg v9
+define tail_x_reg va
+define tail_y_reg vb
+define head_direction_reg vc
 define head_x_reg vd
 define head_y_reg ve
 
@@ -23,11 +31,16 @@ start:
 	cls
 	ld game_over_reg, 0
 
+	ld score_high_reg, 0
+	ld score_low_reg, 0
+
 	rnd head_x_reg, 63
 	rnd head_y_reg, 31
 
-	ld head_dx_reg, 1
-	ld head_dy_reg, 0
+	ld tail_x_reg, head_x_reg
+	ld tail_y_reg, head_y_reg
+
+	ld head_direction_reg, direction_right
 
 	ld i, single_pixel
 	drw head_x_reg, head_y_reg, 1
@@ -38,21 +51,23 @@ mainloop:
 	ld v0, frames_wait
 	ld dt, v0
 
+	ld v1, head_direction_reg
+
 	ld v0, up_key
 	sknp v0
-	call dir_up
+	call turn_up
 
 	ld v0, down_key
 	sknp v0
-	call dir_down
+	call turn_down
 
 	ld v0, left_key
 	sknp v0
-	call dir_left
+	call turn_left
 
 	ld v0, right_key
 	sknp v0
-	call dir_right
+	call turn_right
 
 	call move_snake
 
@@ -70,6 +85,8 @@ game_over:
 	ld st, v0
 	call wait
 
+	call display_score
+
 	ld v0, 30
 	call wait
 
@@ -86,6 +103,42 @@ game_over:
 
 	jp start
 
+display_score:
+	cls
+
+	ld i, score_high_bcd
+	ld b, score_high_reg
+	ld i, score_low_bcd
+	ld b, score_low_reg
+
+	ld i, score_low_bcd
+	ld v2, [i]
+	; v0 and v1 are zero, v2 is ones
+	ld v3, v2
+	ld i, score_high_bcd
+	ld v2, [i]
+	; v0 is thousands, v1 is hundreds, v2 is tens
+
+	; Score is a four-digit number stored in v0 to v3
+	ld v4, 0
+	ld v5, 0
+	ld f, v0
+	drw v4, v5, 5
+
+	add v4, 5
+	ld f, v1
+	drw v4, v5, 5
+
+	add v4, 5
+	ld f, v2
+	drw v4, v5, 5
+
+	add v4, 5
+	ld f, v3
+	drw v4, v5, 5
+
+	ret
+
 wait:
 	ld dt, v0
 	wait_loop:
@@ -106,54 +159,142 @@ spawn_fruit:
 
 	ret
 
-dir_up:
-	; Allow only 90° turns
-	se head_dy_reg, 0
-	ret
-	ld head_dx_reg, 0
-	ld head_dy_reg, #ff
+turn_up:
+	; Don't allow 180° turns (which would kill the snake instantly)
+	se v1, direction_down
+	ld head_direction_reg, direction_up
 	ret
 
-dir_down:
-	se head_dy_reg, 0
-	ret
-	ld head_dx_reg, 0
-	ld head_dy_reg, 1
+turn_down:
+	se v1, direction_up
+	ld head_direction_reg, direction_down
 	ret
 
-dir_left:
-	se head_dx_reg, 0
-	ret
-	ld head_dx_reg, #ff
-	ld head_dy_reg, 0
+turn_left:
+	se v1, direction_right
+	ld head_direction_reg, direction_left
 	ret
 
-dir_right:
-	se head_dx_reg, 0
-	ret
-	ld head_dx_reg, 1
-	ld head_dy_reg, 0
+turn_right:
+	se v1, direction_left
+	ld head_direction_reg, direction_right
 	ret
 
 move_snake:
+	; Save the direction the snake is moving at head's location
 	ld v0, head_x_reg
-	add head_x_reg, head_dx_reg
-	ld v2, 63
-	and head_x_reg, v2
-
 	ld v1, head_y_reg
-	add head_y_reg, head_dy_reg
-	ld v2, 31
-	and head_y_reg, v2
+	call direction_table_index
+	ld v0, head_direction_reg
+	ld [i], v0
 
+	; Move the snake's head
+	call unpack_direction
+	add head_x_reg, v0
+	ld v0, 63
+	and head_x_reg, v0
+	add head_y_reg, v1
+	ld v0, 31
+	and head_y_reg, v0
+
+	; Draw head location and erase tail location
 	ld i, single_pixel
 	drw head_x_reg, head_y_reg, 1
 	se vf, 0
-	call collision
-	drw v0, v1, 1
+	jp collision
+	drw tail_x_reg, tail_y_reg, 1
+
+	; Load the direction the snake was moving at tail's location
+	ld v0, tail_x_reg
+	ld v1, tail_y_reg
+	call direction_table_index
+	ld v0, [i]
+
+	; Move the snake's tail
+	call unpack_direction
+	add tail_x_reg, v0
+	ld v0, 63
+	and tail_x_reg, v0
+	add tail_y_reg, v1
+	ld v0, 31
+	and tail_y_reg, v0
 
 	ret
 
+direction_table_index:
+	; v0 is the X coördinate, from 0 to 63, 00xxxxxx
+	; v1 is the Y coördinate, from 0 to 31, 000yyyyy
+	shl v0, v0
+	shl v0, v0
+	; v0 is the X coördinate shifted left by two, xxxxxx00
+	ld v2, %11100000
+	and v2, v0
+	or v1, v2
+	; v1 is combination of high 3 bits of X coördinate and the Y coördinate, xxxyyyyy
+	ld v2, %00011100
+	and v0, v2
+	; v0 is the low 3 bits of the X coördinate shifted left by two, 000xxx00
+
+	jp v0, direction_table_index_table
+	direction_table_index_table:
+		; 0
+		ld i, #400
+		jp direction_table_index_end
+
+		; 1
+		ld i, #500
+		jp direction_table_index_end
+
+		; 2
+		ld i, #600
+		jp direction_table_index_end
+
+		; 3
+		ld i, #700
+		jp direction_table_index_end
+
+		; 4
+		ld i, #800
+		jp direction_table_index_end
+
+		; 5
+		ld i, #900
+		jp direction_table_index_end
+
+		; 6
+		ld i, #a00
+		jp direction_table_index_end
+
+		; 7
+		ld i, #b00
+
+direction_table_index_end:
+	add i, v1
+	ret
+
+unpack_direction:
+	jp v0, unpack_direction_table
+	unpack_direction_table:
+		; Up
+		ld v0, 0
+		ld v1, #ff
+		ret
+
+		; Down
+		ld v0, 0
+		ld v1, 1
+		ret
+
+		; Left
+		ld v0, #ff
+		ld v1, 0
+		ret
+
+		; Right
+		ld v0, 1
+		ld v1, 0
+		ret
+
 collision:
 	se head_x_reg, fruit_x_reg
 	jp tail_collision
@@ -161,13 +302,30 @@ collision:
 	jp tail_collision
 
 eat_fruit:
-	; TODO: Lenghten snake
+	; Jumping to collision skips tail moving code, so we get the snake
+	; lengthening for free
+	call increment_score
+
+	ld v0, 1
+	ld st, v0
+
 	ld i, single_pixel
 	drw fruit_x_reg, fruit_y_reg, 1
 	jp spawn_fruit
 
+increment_score:
+	; Low register stores 0…9
+	add score_low_reg, 1
+	se score_low_reg, 10
+	ret
+	ld score_low_reg, 0
+	add score_high_reg, 1
+	ret
+
 tail_collision:
 	ld game_over_reg, 1
 	ret
 
 single_pixel: db #80
+score_high_bcd: db 0, 0, 0
+score_low_bcd: db 0, 0, 0