It captured the HUD strip into sprite 1 and the whole play field into sprite 2,
and its own header called them "the screen". That was never a choice: a drawing
lasted one frame, so a sprite was the only thing the interpreter would redraw for
nothing. Both slots are free now, and five things went with them.
**`WINDOW 0, 35, 49, 36` is the first executable line.** The text layer repaints
every row it owns and by default owns the whole window; moved to two rows at the
bottom, it leaves the other thirty-five to the drawing verbs, and what the
program draws stays.
**`PACE` is gone.** It spun on `TI#` until a batch boundary so an `SSHAPE`
capture would not be cut in half by a present. Nothing is captured, so a drawing
spanning two batches simply arrives over two frames and the layer keeps both
halves. The 256-line drawing deadline that shaped every draw routine in this
listing does not apply to it any more.
**The flattened live list is gone** -- `BUILDLIVE`, `BUILDROW`, `STAMPROW` and
the four arrays behind them. They existed so a full-field redraw could be one
stamp and an advance per brick, and a full-field redraw existed because removing
one brick meant rebuilding all sixty. A broken brick is now erased in place with
a blank stamp, so the field is drawn once per level and not again.
**`BALLBRICKS` and `TESTCELL` are gone** -- about sixty lines that turned the
ball's box into a range of candidate cells, walked them with a nested `DO`, and
computed an overlap rectangle to pick an axis. `SOLID` registers each brick as
the level is laid out, `COLLISION 2` fires, and `RCOLLISION` says which brick,
which way out, how far, and which axis to reverse.
**The `SSHAPE` pool accounting is gone.** `SHN#` counted slots because every
frame's capture spent another and `GRAPHIC 5` had to throw them all away
periodically; eight are now spent once and never again.
Three mistakes worth recording, because each was silent:
- **The bricks were registered and then immediately thrown away.**
`GOSUB BUILDLIVE` sat *after* the fill loop in `SETUPLEVEL` and meant "rebuild
the list of what is standing"; replaced in place by a bare `SOLID`, it meant
"retire everything" and ran after all sixty had been registered. Nothing
failed -- the ball simply passed through the wall.
- **The handler tested the wrong bits.** `BUMP` is a mask by *sprite*, and the
balls are sprites 5, 6 and 7, so their bits are 16, 32 and 64. Testing 1, 2 and
4 asked about the HUD and field sprites that no longer exist.
- **The eraser stamps were undeclared**, so `SSHAPE` filled them inside
`DRAWPROTOS` and they were empty everywhere else -- exactly the scope trap
chapter 17 Step 3 is about, found by printing the handle inside the routine and
again outside it.
Verified by driving it: a copy with a tracking paddle and auto-relaunch breaks
thirteen bricks in sixty seconds with no error line, and the shipped listing runs
clean. Both suites green.
Chapter 18 still describes the architecture this commit removed; that is the rest
of section 6 item 39.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EwxGB6TdoVvZ11KQQME9cL
Andrew Kesterson
39d1d0c80c
