Orbit, and two bars that answer instead of reporting
Going sideways lifts the moon off you. Not because gravity weakened - because at speed the surface falls away underneath as fast as the lander falls towards it, which is what an orbit is. A GRADIENT OUT OF INTEGER ARITHMETIC. Gravity is one sixteenth of a pixel a tick and there is nothing between that and nothing, so it cannot be scaled down. Instead four times the sideways speed goes into a byte every tick and the tick's gravity is skipped whenever that byte carries: the fraction cancelled is the speed over 64, smoothly, with no multiply and no divide. At four pixels a frame it carries every time. That is the linear approximation; the honest one is the square, and wants a table. It did nothing at all for its first two versions. Once because the relief was a 256th a tick, so orbit wanted a speed no lander would reach; and once because A IS THE HIGH HALF of the shift register, so multiplying by four left the answer in A while the code read B, which is nought. The same trap as the scroll register and the pixel conversion before it. And a bar for the vertical speed beside the one for drift, both GREEN WHILE A LANDING WOULD SURVIVE AND RED WHILE IT WOULD NOT. That turns two numbers into one question - can I put down - and answers it at a glance. WHAT THIS COST: the flown delivery check. A recording is a list of buttons and not a flight, so replaying it under different gravity flies somewhere else; the delivery became a crash two columns short. The fixture is still there and is still a faithful record of what somebody did, and is no longer a record of what happens. That is the standing cost of a flown fixture, and it is worse than the transcript tests dropped earlier: those broke when an output moved, and this breaks whenever a NUMBER moves. Making the delivery reachable without flying - a way to start already carrying, or at a chosen base - is what would fix it properly. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
This commit is contained in:
Anachronaut
co-authored by
Claude Opus 5
Claude Opus 5
parent
4b1c3d8e3f
commit
a069ee7a00
@@ -96,6 +96,7 @@ everyFrame:
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CALL touchdown
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CALL showLander
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CALL showDrift
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CALL showFall
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CALL showFuel
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SETD.0 Flying
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LDA.0
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@@ -660,6 +661,62 @@ fall:
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SETD.0 Landed
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LDA.0
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BNA fallResting
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; ---- Orbit ----
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;
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; The faster it is going sideways, the less of the moon it feels. Not because gravity got
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; weaker - because at speed the surface is falling away underneath as fast as the lander is
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; falling towards it, which is what an orbit IS.
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;
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; A GRADIENT OUT OF INTEGER ARITHMETIC. Gravity is one sixteenth of a pixel a tick and there
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; is nothing between that and nothing, so it cannot simply be scaled down. Instead the
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; sideways speed is added into a byte every tick and the tick's gravity is skipped whenever
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; that byte carries - so the fraction of ticks cancelled is the speed over 256, smoothly,
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; with no multiply and no divide. At 256 sixteenths a frame it carries every time and the
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; lander is in orbit.
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;
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; That is the linear approximation. The honest one is the square of the speed, which wants a
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; multiply this machine has not got; a table would give the curve if the feel ever asks for
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; it. What is here is one add and one branch.
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SETD.0 SpeedAcross
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CALL magnitude
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SETD.0 DriftHigh
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LDA.0
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BNA fallResting ; A whole high byte of it is far past orbital speed.
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; ---- Four times the speed, and orbit at sixty four ----
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;
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; The speed alone made the relief a 256th a tick, so orbit wanted a lateral speed no lander
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; would ever reach and the whole thing was invisible. Times four puts it at 64 sixteenths -
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; four pixels a frame, which crosses the moon in about three seconds and takes ten seconds
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; of holding a thruster to build. Something worked up to rather than stumbled into.
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SETD.0 DriftLow
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LDA.0
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INIB 0d64
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CCF
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SUB
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BNC fallOrbiting ; No borrow, so it is at orbital speed and gravity is gone.
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LDA.0 ; DP0 is still DriftLow, from the comparison above.
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RSTB
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SHL
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SHL ; ---- Times four, and it comes out in A ----
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;
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; A is the HIGH half of the shift register, so a value in A with
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; nothing in B is already that value times 256 - and rotating left
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; twice makes it times 1024, whose top byte is the value times
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; four. Written the other way first, reading B out of it, which is
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; nought every time: the relief was always none and the whole
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; mechanic did nothing at all.
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SETD.1 OrbitAt
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LDB.1
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CCF
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ADD
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STQ.1
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BRC fallResting ; Carried, so this tick's pull is what the speed cancelled.
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BRI fallPulled
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fallOrbiting:
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BRI fallResting
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fallPulled:
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SETD.0 SpeedDown
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SETD.1 Gravity
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CALL addWord
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@@ -809,6 +866,33 @@ showLander:
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OUTA 0xE9
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RET
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; ---- Green if it would survive, red if it would not ----
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;
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; The magnitude is in DriftLow and DriftHigh and DP1 names the limit. Q comes back the
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; attribute to draw with, which turns a bar from a number into an ANSWER: a person aiming at a
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; pad does not want to know their speed, they want to know whether they can put it down.
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barColour:
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SETD.0 DriftHigh
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LDA.0
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BNA barColourFast ; A whole high byte of speed is past any limit worth having.
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SETD.0 DriftLow
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LDA.0
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LDB.1
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CCF
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SUB
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BNC barColourFast ; No borrow, so it is at or over the limit.
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INIA 0x02
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RSTB
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CCF
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ADD ; Scheme two, green, which is within tolerance.
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RET
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barColourFast:
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INIA 0x01
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RSTB
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CCF
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ADD ; Scheme one, red, which is not.
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RET
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; ---- How fast sideways, as a bar ----
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;
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; A moon has no air, so a drift never stops by itself and stopping one means cancelling the
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@@ -862,6 +946,10 @@ magnitudeDone:
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showDrift:
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SETD.0 SpeedAcross
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CALL magnitude
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SETD.1 GentleAcross
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CALL barColour
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SETD.1 DriftColour
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STQ.1
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; ---- Clamped, because a bar wider than the screen says nothing a full one does not ----
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;
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; And because a target width is sixteen bits: an unclamped one would be asking the device to
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@@ -921,8 +1009,9 @@ driftAt:
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OUTA 0xE5 ; Sprite one begins sixteen bytes in.
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INIA 0xC8
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OUTA 0xE9 ; The ground block, which is a solid tile.
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INIA 0x01
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OUTA 0xE9 ; Attribute one, so the bar is not the colour of the moon.
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SETD.0 DriftColour
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LDA.0
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OUTA 0xE9 ; Green while this drift could be landed with, red while not.
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SETD.0 DriftAt
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LDA.0
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OUTA 0xE9
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@@ -1285,6 +1374,102 @@ payFuelFull:
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STA.0
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RET
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; ---- How fast downwards, as a bar down the side ----
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;
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; The same idea stood on its end. Sprite two, three pixels wide, growing DOWN from the middle
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; of the screen while falling and UP while climbing - so which way is as plain as how fast,
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; and a lander holding its height has no bar at all.
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;
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; Two bars and two limits is the whole instrument panel: when both are green the lander can be
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; put down, and that is a question a person can answer at a glance instead of by counting.
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showFall:
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SETD.0 SpeedDown
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CALL magnitude
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SETD.1 GentleDown
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CALL barColour
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SETD.1 FallColour
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STQ.1
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; Clamped, and to less than the drift bar because there is half a screen either way.
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SETD.0 DriftHigh
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LDA.0
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BNA fallBarWide
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SETD.0 DriftLow
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LDA.0
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INIB 0d90
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CCF
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SUB
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BRC fallBarReady
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fallBarWide:
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INIA 0d90
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SETD.0 DriftLow
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STA.0
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fallBarReady:
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; No tiles at all when there is nothing to show, which is the off switch: a target size of
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; nought is the NATURAL size, not an empty sprite.
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SETD.0 DriftLow
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LDA.0
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BRA fallBarEmpty
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INIA 0x11
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BRI fallBarSized
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fallBarEmpty:
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RSTA
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fallBarSized:
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SETD.1 FallSize
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STA.1
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; Where it starts: the middle going down, and that much back going up.
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INIA 0d100
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SETD.0 DriftLeftward
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LDB.0
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BRB fallBarAt ; Nought is downward, so it starts at the middle.
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SETD.0 DriftLow
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LDB.0
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CCF
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SUB
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MVQA
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fallBarAt:
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SETD.1 FallAt
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STA.1
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INIA 0d4
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OUTA 0xE3
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INIA 0xC0
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OUTA 0xE4
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INIA 0x20
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OUTA 0xE5 ; Sprite two begins thirty two bytes in.
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INIA 0xC8
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OUTA 0xE9 ; The solid block.
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SETD.0 FallColour
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LDA.0
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OUTA 0xE9
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INIA 0x2C
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OUTA 0xE9
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INIA 0x01
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OUTA 0xE9 ; X is 300, which is two bytes: the screen is wider than one.
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SETD.0 FallAt
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LDA.0
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OUTA 0xE9
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RSTA
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OUTA 0xE9 ; Y.
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SETD.0 FallSize
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LDA.0
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OUTA 0xE9
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RSTA
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OUTA 0xE9 ; No flags.
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INIA 0x03
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OUTA 0xE9
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RSTA
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OUTA 0xE9 ; Three pixels wide.
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SETD.0 DriftLow
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LDA.0
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OUTA 0xE9
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RSTA
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OUTA 0xE9 ; And as tall as the lander is fast.
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OUTA 0xE9 ; No depth.
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RET
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; ---- Sums ----
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;
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; DP0 names the two byte value being changed, low half first, and DP1 the one being added to
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@@ -1455,6 +1640,14 @@ DriftAt:
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0x00
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DriftSize:
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0x00
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DriftColour:
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0x00
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FallColour:
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0x00
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FallSize:
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0x00
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FallAt:
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0x00
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; ---- The tank ----
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;
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@@ -1534,6 +1727,11 @@ LandColumn:
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0x00
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AtBase:
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0x00
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; Where the orbit sum has got to. The sideways speed goes in here every tick and the carry out
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; of it is a tick of gravity that never happened.
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OrbitAt:
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0x00
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SayAt:
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0x00
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