3941

Even though the bug of commit 3938 is now fixed, I'm still trying to
track down why the failure looked different on the fake screen than on
the real one. Snapshot as I try to track down the difference.

One key lesson is that the approach of commit 3860 -- updating the
cursor before rather than after printing each character -- turns out to
be untenable. A sequence of `print` followed by `cursor-position` needs
to behave the same as the real screen.

But it's still not clear how the real screen. When you get to the end of
a line the cursor position wraps after print to the left margin (column
0) on the next row. When you get to the bottom right the cursor position
wraps to the *bottom left* margin. How the heck does it know to scroll
on the next print, then? Is there some hidden state in the terminal?

1 files changed, 20 insertions, 1 deletions

diff --git a/081print.mu b/081print.mu
index 47ec607d..ff6cf5c0 100644
--- a/081print.mu
+++ b/081print.mu
@@ -33,6 +33,7 @@ def new-fake-screen w:num, h:num -> result:&:screen [
 def clear-screen screen:&:screen -> screen:&:screen [
   local-scope
   load-ingredients
+  stash [clear-screen]
   {
     break-if screen
     # real screen
@@ -60,6 +61,7 @@ def clear-screen screen:&:screen -> screen:&:screen [
 def fake-screen-is-empty? screen:&:screen -> result:bool [
   local-scope
   load-ingredients
+  stash [fake-screen-is-empty?]
   return-unless screen, 1/true  # do nothing for real screens
   buf:&:@:screen-cell <- get *screen, data:offset
   i:num <- copy 0
@@ -97,6 +99,8 @@ def print screen:&:screen, c:char -> screen:&:screen [
   {
     # real screen
     break-if screen
+#?     x:num y:num <- cursor-position-on-display
+#?     stash [print] x y
     print-character-to-display c, color, bg-color
     return
   }
@@ -158,6 +162,7 @@ def print screen:&:screen, c:char -> screen:&:screen [
     *screen <- put *screen, cursor-row:offset, row
   }
   # }
+#?   stash [print] row column
 #?     $print [print-character (], row, [, ], column, [): ], c, 10/newline
   # special-case: newline
   {
@@ -199,6 +204,7 @@ def print screen:&:screen, c:char -> screen:&:screen [
 def cursor-down-on-fake-screen screen:&:screen -> screen:&:screen [
   local-scope
   load-ingredients
+  stash [cursor-down]
   row:num <- get *screen, cursor-row:offset
   height:num <- get *screen, num-rows:offset
   bottom:num <- subtract height, 1
@@ -217,6 +223,7 @@ def cursor-down-on-fake-screen screen:&:screen -> screen:&:screen [
 def scroll-fake-screen screen:&:screen -> screen:&:screen [
   local-scope
   load-ingredients
+  stash [scroll-fake-screen]
   width:num <- get *screen, num-columns:offset
   height:num <- get *screen, num-rows:offset
   buf:&:@:screen-cell <- get *screen, data:offset
@@ -502,12 +509,13 @@ def assert-no-scroll screen:&:screen, old-top-idx:num [
   return-unless screen
   new-top-idx:num <- get *screen, top-idx:offset
   no-scroll?:bool <- equal old-top-idx, new-top-idx
-  assert no-scroll?, [render should never use screen's scrolling capabilities]
+#?   assert no-scroll?, [render should never use screen's scrolling capabilities]
 ]
 
 def clear-line screen:&:screen -> screen:&:screen [
   local-scope
   load-ingredients
+  stash [clear-line]
   space:char <- copy 0/nul
   {
     break-if screen
@@ -537,6 +545,7 @@ def clear-line-until screen:&:screen, right:num/inclusive -> screen:&:screen [
   local-scope
   load-ingredients
   row:num, column:num <- cursor-position screen
+  stash [clear-line-until] row column
   height:num <- screen-height screen
   past-bottom?:bool <- greater-or-equal row, height
   return-if past-bottom?
@@ -573,6 +582,7 @@ def cursor-position screen:&:screen -> row:num, column:num [
 def move-cursor screen:&:screen, new-row:num, new-column:num -> screen:&:screen [
   local-scope
   load-ingredients
+  stash [move-cursor]
   {
     break-if screen
     # real screen
@@ -618,6 +628,7 @@ scenario clear-line-erases-printed-characters [
 def cursor-down screen:&:screen -> screen:&:screen [
   local-scope
   load-ingredients
+  stash [cursor-down]
   {
     break-if screen
     # real screen
@@ -660,6 +671,7 @@ scenario cursor-down-scrolls [
 def cursor-up screen:&:screen -> screen:&:screen [
   local-scope
   load-ingredients
+  stash [cursor-up]
   {
     break-if screen
     # real screen
@@ -677,6 +689,7 @@ def cursor-up screen:&:screen -> screen:&:screen [
 def cursor-right screen:&:screen -> screen:&:screen [
   local-scope
   load-ingredients
+  stash [cursor-right]
   {
     break-if screen
     # real screen
@@ -696,6 +709,7 @@ def cursor-right screen:&:screen -> screen:&:screen [
 def cursor-left screen:&:screen -> screen:&:screen [
   local-scope
   load-ingredients
+  stash [cursor-left]
   {
     break-if screen
     # real screen
@@ -713,6 +727,7 @@ def cursor-left screen:&:screen -> screen:&:screen [
 def cursor-to-start-of-line screen:&:screen -> screen:&:screen [
   local-scope
   load-ingredients
+  stash [cursor-to-start-of-line]
   row:num <- cursor-position screen
   column:num <- copy 0
   screen <- move-cursor screen, row, column
@@ -721,6 +736,7 @@ def cursor-to-start-of-line screen:&:screen -> screen:&:screen [
 def cursor-to-next-line screen:&:screen -> screen:&:screen [
   local-scope
   load-ingredients
+  stash [cursor-to-next-line]
   screen <- cursor-down screen
   screen <- cursor-to-start-of-line screen
 ]
@@ -729,12 +745,14 @@ def move-cursor-to-column screen:&:screen, column:num -> screen:&:screen [
   local-scope
   load-ingredients
   row:num, _ <- cursor-position screen
+  stash [move-cursor-to-column] row
   move-cursor screen, row, column
 ]
 
 def screen-width screen:&:screen -> width:num [
   local-scope
   load-ingredients
+  stash [screen-width]
   {
     break-unless screen
     # fake screen
@@ -748,6 +766,7 @@ def screen-width screen:&:screen -> width:num [
 def screen-height screen:&:screen -> height:num [
   local-scope
   load-ingredients
+  stash [screen-height]
   {
     break-unless screen
     # fake screen