Every placement in the stack game is judged by one comparison, the offset between the moving block and the top block. When that offset is 4 pixels or less, the engine calls it perfect. Everything about tower width follows from that single threshold in dropBlock.
The perfect window in the stack game
The moving block spawns with the exact width of the top block. A placement is perfect when the absolute difference between the left edges is at most 4 pixels. A perfect drop snaps the block into exact alignment and keeps the full current width. Nothing is cut.
That tolerance is a window in time, and it shrinks as the run goes on.
1. The block moves at 2.5 pixels per frame at 60 frames per second, which is 150 pixels per second. The 8 pixel window from -4 to +4 then lasts about 53 milliseconds.
2. Speed compounds by 3 percent per placed block, capped at 2.5 times the base. The cap of 375 pixels per second is reached at block 31, because 1.03 raised to the 31st power is 2.5.
3. At the cap the same 8 pixel window lasts about 21 milliseconds.
Your timing target does not change. Your error budget does, and it is roughly cut in half by the time you pass 31 blocks.
What a miss costs in width
A non-perfect drop places only the overlap. The overhang is cut off and falls away. A 20 pixel offset on a 200 pixel base leaves you a 180 pixel tower, and the loss is permanent until you earn it back through perfect streaks.
The recovery rule reads as follows. Once three perfect placements line up in a row, every further perfect adds 5 pixels of width, capped at the original 200. Before that third consecutive perfect, a perfect only preserves width.
Run the arithmetic on a bad stretch. Drop to 160 pixels through accumulated misses, and you need 3 warmup perfects plus 8 growing perfects, so 11 consecutive perfect placements, just to return to 200. Losses are instant and recovery is a chain. Protecting a streak matters more than rescuing a thin tower, because a tower below about 30 pixels wide leaves an 8 pixel window that is a fifth of the whole block.
The run ends two ways. A complete miss, meaning zero overlap, ends immediately with the whole block falling. An overlap below MIN_WIDTH of 5 pixels also ends the run, after the sliver is placed. Aim never to release when the moving block is more than one block width away from the tower, because the engine will not save a near miss at the edge.
Where to aim in the stack game
The moving block alternates sides after every placement. It spawns 30 pixels offscreen and bounces between -50 and the canvas width minus block width plus 50. Two aim rules follow from the equal-width spawn.
1. Align the leading edge of the moving block with the leading edge of the top block. Equal widths mean aligned edges are a perfect drop, so judge one edge instead of the whole silhouette.
2. Drop in the middle of the screen half of the sweep when possible. The block spends the most visible time near center, and your eye tracks the edge alignment best there.
Judge the moment by the edge crossing, then release about one visual frame early on fast blocks. Human reaction time sits near 200 milliseconds, which exceeds the 21 millisecond window at cap speed. You must predict the crossing point, not react to it.
Scoring follows the streak counter
A normal placement adds 1 point. A perfect placement adds the current streak count on top of the base point, so the fifth consecutive perfect pays 6 total. The labels scale the same way, PERFECT x3 appears at streak 3, INCREDIBLE at 5, GODLIKE at 10. Chasing streaks for score is the same behavior that keeps the tower wide, so the incentives never conflict.
Stack game pre-drop checklist
- [ ] Watching one leading edge, not the block center.
- [ ] Tower width known, and streak count known.
- [ ] Below 3 streak, treat every drop as width preservation.
- [ ] At 3 or more streak, refuse risky drops because 5 pixels per perfect is the only growth.
- [ ] Past block 31, releasing on prediction rather than reaction.
- [ ] Never releasing while any part of the block is offscreen.
The honest downside. Perfect streaks demand a 53 to 21 millisecond window that shrinks through no action of yours, so long runs end on a speed ramp and not on strategy. Recovery of more than about 40 pixels of width within a fast section is unlikely, and restarting a collapsed streak is usually the better plan. Open the [stack game](/en/stack-game) and count your own pixel offsets against the 4 pixel threshold. If your recorded perfect rate at block 30 differs sharply from your rate at block 10, that curve is data worth sending, since it measures the speed cap against real reflexes.
