flowchart TD
A((START)) --> B[/Display initial\nstack block/]
subgraph Display initial stack block
B -.-> Ba(Draw one row) --> Bc(Pause for GAME_DELAY ms) --> Bd{Drawn\nINITIAL_BLOCK_HEIGHT\nrows yet?}
Bd -- NO --> Ba
end
Bd -- YES --> C
subgraph Draw Title Screen
C[/Draw the title screen/] -.-> D
D(Draw each letter in 'MIPS'\n in blue color) --> E(Draw the word 'STACKER'\n in white color) --> F(Underline 'STACKER'\nin blue color) --> G(Flash the color of 'STACKER'\n between yellow and white)
end
subgraph Choose Difficulty
G --> choosediff{{Popup input dialog to choose the difficulty}}
choosediff -- Input == 1 --> easy[Set GAME_DELAY to 75 ms]
choosediff -- Input == 2 --> med[Set GAME_DELAY to 50 ms]
choosediff -- Input == 3 --> hard[Set GAME_DELAY to 25 ms]
choosediff -- Input == 4 --> impos[Set GAME_DELAY to 10 ms]
end
removed{Has the title screen\n been removed yet?}
easy --> removed
med --> removed
hard --> removed
impos --> removed
removed -- NO --> I
removed -- YES --> drawleft
subgraph Remove Title Screen
I[/Remove Title Screen/]
I -.-> J(Draw over each letter of \n'MIPS' in black color) --> K(Draw over 'STACKER' in black color) --> L(Remove the underline)
end
L --> drawleft(Draw new block from the left side of the screen) 
drawleft -- Set current direction to right: +1 --> N(Move the block in current direction)
subgraph Animate Block
N --> O{Reached the end\n of the screen?}
O -- NO --> Q[/Check for input/]
O -- YES --> R(Negate the current direction)
R --> Q
Q --> S{Spacebar key\nentered?}
S -- NO --> T(Pause for GAME_DELAY ms)
T --> N
end
subgraph Place Block on Stack
S -- YES --> U[/Place down block on the stack/] 
U -.-> V{Right edge of block < Left edge of stack\nOR\nLeft edge of block > Right edge of stack?}
V -- NO --> remove(Remove parts of block\n hanging off the stack) --> sound(Play woodblock sound) --> score(Increment score by 1) --> height(Increase current Y position\nby BLOCK_HEIGHT) --> checkheight{Y position past half\n the screen height?}
checkheight -- NO --> checkdir{Just drew block from left?}
checkheight -- YES --> moveup(Move entire stack \ndown by BLOCK_HEIGHT)
end
checkdir -- YES --> drawright(Draw new block from right side of screen)
checkdir -- NO --> drawleft
drawright -- Set current direction to left: -1 --> N
moveup --> checkdir
subgraph Game Over
V -- YES --> gameover[/Game is over/] -.-> Va(Play sad trombone sound) --> Vb(Popup 'game over' dialog\nand score count) -- dialog closed --> Vc(Popup 'play again?' dialog) --> playagain{User wishes to\nplay again?}
playagain -- YES --> restscore(Set score to 0) --> clear(Clear the screen) 
clear --> choosediff
playagain -- NO --> goodbye(Popup 'goodbye' dialog)
end
goodbye --> done((END))