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

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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.
This commit is contained in:
Anachronaut
2026-09-03 22:14:02 -04:00
parent 437ddf8ebe
commit 32559ce872
13 changed files with 178 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files
Programs/CosmOS/Apps/Lander.asm
+69 -13
View File
@@ -52,7 +52,6 @@ start:
SETD.0 Wide
LDA.0
OUTA 0x31 ; Forty columns to start in. B swaps to eighty and back.
RSTA
; ---- And the view put back to the top of the map ----
;
@@ -66,7 +65,10 @@ start:
;
; The column origin and the fine offsets are set every frame by follow, so they need no
; help. The row origin is set once, here, because nothing scrolls vertically after this.
SETD.0 ScrollRow
LDA.0
OUTA 0x34
RSTA
OUTA 0x38 ; No fraction of a cell downwards either.
CALL mulReady ; The quarter square table, once. The orbit below needs a product.
@@ -344,8 +346,22 @@ randomTap:
; are next to each other, so the address is named once and the controller's Data port steps
; through 128 of them. Cells down a COLUMN are a page apart, and doing it that way would mean
; naming an address for every one of the 3,200 cells.
; ---- Drawn from twenty four rows above the world, not from the world's top ----
;
; 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 extra twenty
; rows a zoom buys have to go SOMEWHERE, and the first version gave them all to rock - it
; drew fifty rows down from the origin, which put the same sky on the screen as before with
; twice as much moon under it. Measured: 47 per cent moon zoomed in and 71 per cent zoomed
; out, which is a zoom that shows you less of what you are flying in.
;
; They go above instead. The rows run from minus twenty four to twenty five, which is the
; whole band with the ground near the bottom of it, and negative rows are sky by definition
; because nothing has a surface up there. In forty columns the ones above the origin are not
; on the screen at all, and drawing them anyway costs a startup and clears whatever the shell
; left in them.
drawMoon:
RSTA
INIA 0xE8 ; Minus twenty four.
SETD.1 Row
STA.1
drawRow:
@@ -353,6 +369,9 @@ drawRow:
OUTA 0xE3
SETD.1 Row
LDA.1
INIB 0x7F
AND
MVQA ; Round the ring of 128, so minus twenty four is row 104.
INIB 0x40
CCF
ADD
@@ -364,12 +383,18 @@ drawRow:
SETD.1 Column
STA.1 ; A is still the nought that went to DestLow.
drawCell:
; Above the world's origin, where no column has a surface, so there is nothing to compare.
SETD.1 Row
LDA.1
INIB 0x80
AND
BNQ drawSky
; ---- Ground at the surface row and everything under it ----
;
; ROW MINUS HEIGHT and not the other way round, which matters at the surface itself: the
; two are equal there, equal does not borrow, and the row a column's surface is on has to
; be ground rather than the last of the sky.
SETD.1 Row
LDA.1
LDB.2
CCF
@@ -422,11 +447,10 @@ drawNextCell:
LDA.1
INCA
STA.1
SETD.2 MoonRows
LDB.2
INIB 0d26
CCF
SUB
BNQ drawRow
BNQ drawRow ; Fifty rows, from minus twenty four up to and including 25.
RET
; ---- The lander, as a sprite ----
@@ -1162,6 +1186,24 @@ follow:
showLander:
SETD.0 DownLow
CALL toPixels
; ---- Signed, which it did not have to be while the view never moved ----
;
; toPixels shifts a sixteen bit position down four and masks what is left to twelve bits, so
; a lander above the world's origin comes back as a large POSITIVE number rather than a small
; negative one. That was harmless while the top of the screen was the origin: such a lander
; was off the picture either way. Now that the wide view starts twenty four rows higher it is
; on the picture, and it has to be on the right part of it.
SETD.0 PixelHigh
LDA.0
INIB 0x08
AND
BRQ showLanderDown
LDA.0
INIB 0xF0
OR
STQ.0 ; The twelfth bit was the sign, so the top nibble is too.
showLanderDown:
INIA 0d4
OUTA 0xE3
INIA 0xC0
@@ -1170,10 +1212,17 @@ showLander:
OUTA 0xE5 ; Y is bytes four and five of the entry.
SETD.0 PixelLow
LDA.0
OUTA 0xE9
SETD.1 ShipYAdd
LDB.1
CCF
ADD
OUTQ 0xE9
SETD.0 PixelHigh
LDA.0
OUTA 0xE9
INCD.1
LDB.1
ADD ; And the carry, which is the other half of the shift.
OUTQ 0xE9
RET
; ---- Green if it would survive, red if it would not ----
@@ -1722,7 +1771,7 @@ setView:
SETD.0 ViewWide
setViewFrom:
SETD.1 View
INIA 0d15
INIA 0d17
SETD.2 ViewLeft
STA.2
setViewByte:
@@ -1752,6 +1801,9 @@ toggleView:
SETD.0 Wide
LDA.0
OUTA 0x31
SETD.0 ScrollRow
LDA.0
OUTA 0x34 ; The wide view starts higher up, which is where the sky is.
CALL drawMoon
CALL putLander
CALL putGauge
@@ -2368,8 +2420,10 @@ HeightFoot:
0xB4 0x00
RowCells:
0d40
MoonRows:
0d25
ScrollRow:
0d0
ShipYAdd:
0x00 0x00
ViewLeft:
0x00 ; How much of the block is still to copy.
@@ -2383,7 +2437,8 @@ ViewNarrow:
0d100 ; Half the height, which is where the fall bar starts.
0xB4 0x00 ; The height bar's foot.
0d40 ; Cells to a window row.
0d25 ; Rows of moon to draw.
0d0 ; The map row the top of the screen is, and
0x00 0x00 ; how far the lander's own Y has to move with it.
; Eighty columns: 640 by 400, the same cells at half the size, so twice as much moon either
; way. Every screen number doubles except the ones measured from an edge, which are the edge
@@ -2397,7 +2452,8 @@ ViewWide:
0d200
0x7C 0x01 ; 380.
0d80
0d50
0d104 ; Twenty four rows ABOVE the world's origin, which is the point.
0xC0 0x00 ; So the lander's Y moves 192 pixels down to match.
; Which of the two is up. Nought is forty columns, which is what the program starts in.
Wide: