The room a zoom buys goes to the sky, not to the moon

Zooming out drew fifty rows DOWN from the world's origin, which put
exactly the same sky on the screen as before with twice as much moon
under it. Measured: 47 per cent rock zoomed in and 71 per cent zoomed
out. A zoom that shows you more of the thing you cannot fly through is
not worth a button.

The eighty column screen is fifty rows and the flyable band is thirty -
the ceiling is eight rows above the origin and the deepest valley is
twenty two below it - so the twenty rows a zoom buys have to go
somewhere. They go above. The wide view starts twenty four rows over the
origin, the ground sits near the bottom, and the whole band is on the
screen: 23 per cent rock instead of 71.

Which needed three things. The moon is drawn from row minus twenty four
rather than from nought, because rows above the origin are sky by
definition and because whatever the shell left in them is otherwise still
there. The row origin comes out of the view block like every other screen
number. And the lander's own Y moves with the view, which meant making
toPixels' answer SIGNED at last: it masks to twelve bits, so a lander
above the origin came back as a large positive number rather than a small
negative one - harmless while such a lander was off the picture either
way, and wrong the moment the view moved up to include it.

That is the point of the button. A lander at the ceiling is off the top
of a forty column screen, which is where the orbit lives and why the
altitude bar had to exist; zoomed out it is at row 149 and you can watch
the whole orbit.

Four checks, and the proportion is deliberately not on its own: measured
alone it passes for a moon floating over a void, because pointing the
view back at the origin leaves the rows under the terrain simply never
drawn, and black counts as sky. Both breaks that matter went straight
through it. What catches them is that the ground has to reach the bottom
of the screen and the sky has to be empty - the latter only on a shell
scrolled a hundred and eighteen lines deep, since that is what it takes
to get anything into the rows the wide view moves into.

The tap fixture also moved to frame 100. Fifty rows of moon take longer
to draw than twenty five, and a six frame tap at frame thirty now lands
before the program is reading a controller at all, which reads exactly
like a button that has stopped working.

Programs/CosmOS/README.md

@@ -727,7 +727,7 @@ from every assembly file in it. Several are old programs written for the bare ma
 | Grid | The first program to use the screen as a screen. Redefines a tile above the font, fills all 128 map rows, and scrolls it diagonally a pixel at a time. |
 | Sprite | Moves a ball across the shell's own text, writing not one byte of the map to do it. It leaves the sprite in the table on the way out, because clearing them is the system's job - see below. |
 | Pad | Says what the controllers are doing, printing a line whenever one changes. It tells apart the three things that look identical from inside a game that is not responding: a pad nobody noticed, a pad mapped to nothing, and a mapping that is wrong. |
-| Lander | Lunar Porter, rung one: a lander over a moon that wraps. Flown with a controller if there is one - a held thruster burns every tick it is held for - and with the arrow keys if there is not, where one press is one burn and that is the most the console can say. A bar at the bottom is the sideways drift, drawn as a sprite stretched to the speed - a moon has no air, so a drift never stops by itself and stopping one means cancelling it exactly, which is hard to do blind. It lands or crashes on arrival, and what decides is the speed at the moment it touches: gentler than three quarters of a pixel a frame downwards and half of one sideways, or it is a lander on its side. A fuel gauge sits in the window layer, where the moon turning underneath cannot scroll it away, and every thruster costs a unit of fuel every tick it fires. An empty tank is not an ending: it is a lander still flying that can no longer do anything about where. Four landing pads are carved into the moon after it is generated, levelled to whatever height their first column happened to have, and marked in cyan by an attribute rather than a tile of their own. The lander starts above one, because that is where a porter's day begins. Each pad is a base, told apart by the colour it is drawn in, and landing at one either loads cargo for the base across the moon or delivers what is aboard and pays eighty units of fuel. A landing is not an ending: the lander rests where it is until the throttle opens again, and A or Start says "read it" as readily as a key does. What a base says goes in the window rather than out of the console: the console draws into the map, so a message printed while flying is one the lander then flies over, and printing scrolls the whole world up a row. Opening the throttle wipes the line. Two bars read the speeds and are green while a landing would survive and red while it would not, so "can I put down" is a glance rather than a sum. A third runs up the left edge and is how much sky is under the lander, half a pixel of bar to a pixel of it; it reads nought the moment the lander is down, and it exists because the orbit takes the lander off the top of the screen and a panel that only works while the ground is in sight is no use above it. And gravity here is the pull MINUS the swing outwards, which is what makes an orbit rather than a one way trip: under four pixels a frame sideways the pull wins and the lander falls, over it the swing wins and the lander climbs, and at it they cancel and it circles. Falling buys sideways speed and climbing spends it - at a rate set by the product of the two, so the trade stops by itself as the sideways speed runs out - and that is the cycle: a fall carries the lander past orbital speed and becomes a climb, the climb pays it back and becomes a fall, periapse and apoapse, round and round. Orbital speed is marked on the drift bar, sixty four pixels either side of the middle, because a number nothing points at is folklore. Gravity never falls off and the moon wraps, so a circular orbit is the same length at any height and one orbital speed serves everywhere. There is a ceiling sixty four pixels above the screen, which pins rather than ends: leaving upward is recoverable, so the lander is held there and told so, and one sideways is spent every tick it tries to climb - without that the pin wiped the climb, the trade saw neither fall nor climb, and the speed pushing it up never changed. What kills you out here is running dry a long way from the ground. B, or z on the keyboard, swaps the screen between forty columns and eighty, which is the same map, the same cells and the same engine at half the size: nearly two thirds of the moon at once for the orbit, and twice as big for the landing. |
+| Lander | Lunar Porter, rung one: a lander over a moon that wraps. Flown with a controller if there is one - a held thruster burns every tick it is held for - and with the arrow keys if there is not, where one press is one burn and that is the most the console can say. A bar at the bottom is the sideways drift, drawn as a sprite stretched to the speed - a moon has no air, so a drift never stops by itself and stopping one means cancelling it exactly, which is hard to do blind. It lands or crashes on arrival, and what decides is the speed at the moment it touches: gentler than three quarters of a pixel a frame downwards and half of one sideways, or it is a lander on its side. A fuel gauge sits in the window layer, where the moon turning underneath cannot scroll it away, and every thruster costs a unit of fuel every tick it fires. An empty tank is not an ending: it is a lander still flying that can no longer do anything about where. Four landing pads are carved into the moon after it is generated, levelled to whatever height their first column happened to have, and marked in cyan by an attribute rather than a tile of their own. The lander starts above one, because that is where a porter's day begins. Each pad is a base, told apart by the colour it is drawn in, and landing at one either loads cargo for the base across the moon or delivers what is aboard and pays eighty units of fuel. A landing is not an ending: the lander rests where it is until the throttle opens again, and A or Start says "read it" as readily as a key does. What a base says goes in the window rather than out of the console: the console draws into the map, so a message printed while flying is one the lander then flies over, and printing scrolls the whole world up a row. Opening the throttle wipes the line. Two bars read the speeds and are green while a landing would survive and red while it would not, so "can I put down" is a glance rather than a sum. A third runs up the left edge and is how much sky is under the lander, half a pixel of bar to a pixel of it; it reads nought the moment the lander is down, and it exists because the orbit takes the lander off the top of the screen and a panel that only works while the ground is in sight is no use above it. And gravity here is the pull MINUS the swing outwards, which is what makes an orbit rather than a one way trip: under four pixels a frame sideways the pull wins and the lander falls, over it the swing wins and the lander climbs, and at it they cancel and it circles. Falling buys sideways speed and climbing spends it - at a rate set by the product of the two, so the trade stops by itself as the sideways speed runs out - and that is the cycle: a fall carries the lander past orbital speed and becomes a climb, the climb pays it back and becomes a fall, periapse and apoapse, round and round. Orbital speed is marked on the drift bar, sixty four pixels either side of the middle, because a number nothing points at is folklore. Gravity never falls off and the moon wraps, so a circular orbit is the same length at any height and one orbital speed serves everywhere. There is a ceiling sixty four pixels above the screen, which pins rather than ends: leaving upward is recoverable, so the lander is held there and told so, and one sideways is spent every tick it tries to climb - without that the pin wiped the climb, the trade saw neither fall nor climb, and the speed pushing it up never changed. What kills you out here is running dry a long way from the ground. B, or z on the keyboard, swaps the screen between forty columns and eighty, which is the same map, the same cells and the same engine at half the size: nearly two thirds of the moon at once for the orbit, and twice as big for the landing. The twenty extra rows that buys go to the SKY and not to the moon - the wide view starts twenty four rows above the world's origin rather than at it, so the ground sits near the bottom and the whole flyable band is on the screen. Drawn down from the origin instead it was 71 per cent rock, which is a zoom that shows you more of the thing you cannot fly through. A lander at the ceiling is off the top of a forty column screen, which is where the orbit lives and why the altitude bar had to exist; zoomed out it is in the picture. |
 | Depth | Four pillars at four distances and a ball walking past them, behind the near ones and in front of the far ones. The ball is sprite nought and every pillar is numbered after it, so table order puts it in front of all four - what actually decides is the depth buffer, asked a column at a time. |
 | Flip | Draws a whole screen into the bank that is not being shown, waits, and then shows it in one byte out of one port. It writes nothing else at all - not a tile, not a colour - so it does not ask for the screen to be saved, and the line it printed is still there when it comes back. It deliberately does not put the displayed screen back either, because that is the system's to restore: a program that faulted while flipped could not have. |
 | Edit | A line editor. |