From 422ebaf88c5a04900beb0a68162213ebc94e37c2 Mon Sep 17 00:00:00 2001
From: Kartik Agaram <vc@akkartik.com>
Date: Wed, 13 Jan 2021 00:02:35 -0800
Subject: [PATCH] 7508

This is the right way to be direction-independent. Don't save the cursor
when drawing a single grapheme. Where the next char goes is just a
property of the direction-oriented primitives.
---
 baremetal/103grapheme.subx | 25 +++++++++++++++++++------
 baremetal/400.mu           |  1 +
 baremetal/501draw-text.mu  | 38 ++++++++++++++++++++------------------
 baremetal/ex6.mu           |  7 +++++++
 4 files changed, 47 insertions(+), 24 deletions(-)

diff --git a/baremetal/103grapheme.subx b/baremetal/103grapheme.subx
index 053cd497..a536bfed 100644
--- a/baremetal/103grapheme.subx
+++ b/baremetal/103grapheme.subx
@@ -58,12 +58,6 @@ draw-grapheme:  # screen: (addr screen), g: grapheme, x: int, y: int, color: int
       #
       eb/jump loop/disp8
     }
-    # Save default coordinates for a future call to draw-grapheme
-    8b/-> *(ebp+0x10) 0/r32/eax
-    81 0/subop/add %eax 8/imm32
-    89/<- *Default-next-x 0/r32/eax
-    8b/-> *(ebp+0x14) 0/r32/eax
-    89/<- *Default-next-y 0/r32/eax
 $draw-grapheme:end:
     # . restore registers
     5e/pop-to-esi
@@ -89,6 +83,25 @@ $cursor-position:end:
     5d/pop-to-ebp
     c3/return
 
+set-cursor-position:  # screen: (addr screen), x: int, y: int
+    # . prologue
+    55/push-ebp
+    89/<- %ebp 4/r32/esp
+    # . save registers
+    50/push-eax
+    # TODO: support fake screen; we currently assume 'screen' is always 0 (real)
+    8b/-> *(ebp+0xc) 0/r32/eax
+    89/<- *Default-next-x 0/r32/eax
+    8b/-> *(ebp+0x10) 0/r32/eax
+    89/<- *Default-next-y 0/r32/eax
+$set-cursor-position:end:
+    # . restore registers
+    58/pop-to-eax
+    # . epilogue
+    89/<- %esp 5/r32/ebp
+    5d/pop-to-ebp
+    c3/return
+
 == data
 
 Default-next-x:
diff --git a/baremetal/400.mu b/baremetal/400.mu
index c32497b8..dd494ecf 100644
--- a/baremetal/400.mu
+++ b/baremetal/400.mu
@@ -2,6 +2,7 @@ sig pixel screen: (addr screen), x: int, y: int, color: int
 sig read-key kbd: (addr keyboard) -> _/eax: byte
 sig draw-grapheme screen: (addr screen), g: grapheme, x: int, y: int, color: int
 sig cursor-position screen: (addr screen) -> _/eax: int, _/ecx: int
+sig set-cursor-position screen: (addr screen), x: int, y: int
 sig clear-stream f: (addr stream _)
 sig rewind-stream f: (addr stream _)
 sig write f: (addr stream byte), s: (addr array byte)
diff --git a/baremetal/501draw-text.mu b/baremetal/501draw-text.mu
index 63e41728..5ddb4bf5 100644
--- a/baremetal/501draw-text.mu
+++ b/baremetal/501draw-text.mu
@@ -32,6 +32,7 @@ fn draw-text-rightward screen: (addr screen), text: (addr array byte), x: int, x
     xcurr <- add 8  # font-width
     loop
   }
+  set-cursor-position screen, xcurr, y
   return xcurr
 }
 
@@ -92,6 +93,7 @@ fn draw-text-wrapping-right-then-down screen: (addr screen), text: (addr array b
     }
     loop
   }
+  set-cursor-position screen, xcurr, ycurr
   return xcurr, ycurr
 }
 
@@ -106,16 +108,14 @@ fn draw-text-wrapping-right-then-down-from-cursor screen: (addr screen), text: (
   var cursor-x/eax: int <- copy 0
   var cursor-y/ecx: int <- copy 0
   cursor-x, cursor-y <- cursor-position screen
-  # we could wrap around if we're too far to the right, but that feels like it
-  # makes assumptions about text direction
-#?   var end-x/edx: int <- copy cursor-x
-#?   end-x <- add 8  # font-width
-#?   compare end-x, xmax
-#?   {
-#?     break-if-<
-#?     cursor-x <- copy xmin
-#?     cursor-y <- add 0x10  # font-height
-#?   }
+  var end-x/edx: int <- copy cursor-x
+  end-x <- add 8  # font-width
+  compare end-x, xmax
+  {
+    break-if-<
+    cursor-x <- copy xmin
+    cursor-y <- add 0x10  # font-height
+  }
   cursor-x, cursor-y <- draw-text-wrapping-right-then-down screen, text, xmin, ymin, xmax, ymax, cursor-x, cursor-y, color
   return cursor-x, cursor-y
 }
@@ -163,6 +163,7 @@ fn draw-text-downward screen: (addr screen), text: (addr array byte), x: int, y:
     ycurr <- add 0x10  # font-height
     loop
   }
+  set-cursor-position screen, x, ycurr
   return ycurr
 }
 
@@ -223,6 +224,7 @@ fn draw-text-wrapping-down-then-right screen: (addr screen), text: (addr array b
     }
     loop
   }
+  set-cursor-position screen, xcurr, ycurr
   return xcurr, ycurr
 }
 
@@ -237,14 +239,14 @@ fn draw-text-wrapping-down-then-right-from-cursor screen: (addr screen), text: (
   var cursor-x/eax: int <- copy 0
   var cursor-y/ecx: int <- copy 0
   cursor-x, cursor-y <- cursor-position screen
-#?   var end-y/edx: int <- copy cursor-y
-#?   end-y <- add 0x10  # font-height
-#?   compare end-y, ymax
-#?   {
-#?     break-if-<
-#?     cursor-x <- add 8  # font-width
-#?     cursor-y <- copy ymin
-#?   }
+  var end-y/edx: int <- copy cursor-y
+  end-y <- add 0x10  # font-height
+  compare end-y, ymax
+  {
+    break-if-<
+    cursor-x <- add 8  # font-width
+    cursor-y <- copy ymin
+  }
   cursor-x, cursor-y <- draw-text-wrapping-down-then-right screen, text, xmin, ymin, xmax, ymax, cursor-x, cursor-y, color
   return cursor-x, cursor-y
 }
diff --git a/baremetal/ex6.mu b/baremetal/ex6.mu
index 00fefe60..587720d5 100644
--- a/baremetal/ex6.mu
+++ b/baremetal/ex6.mu
@@ -22,4 +22,11 @@ fn main {
   # drawing at the cursor in multiple directions
   x, y <- draw-text-wrapping-down-then-right-from-cursor-over-full-screen 0, "abc", 0xa
   x, y <- draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0, "def", 0xa
+
+  # test drawing near the edge
+  x <- draw-text-rightward 0, "R", 0x3f8, 0x400, 0x100, 0xa
+  x, y <- draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0, "wrapped from R", 0xa
+
+  x <- draw-text-downward 0, "D", 0x100, 0x2f0, 0x300, 0xa
+  x, y <- draw-text-wrapping-down-then-right-from-cursor-over-full-screen 0, "wrapped from D", 0xa
 }