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authorKartik Agaram <vc@akkartik.com>2021-01-22 19:57:33 -0800
committerKartik Agaram <vc@akkartik.com>2021-01-22 19:57:33 -0800
commit121a9eba56d62ef6bd9900bcd771647c0c58e718 (patch)
tree29b19ce63ea7f3e9c733ed847141189e452daf11 /baremetal
parentc316a11ffa6fa184c9c62dc6fccbc0a6aa6c8f63 (diff)
downloadmu-121a9eba56d62ef6bd9900bcd771647c0c58e718.tar.gz
7540 - baremetal: cursor
I spent over a week agonizing over this.

* I had to come to terms with the fact that I don't really know how to
make pixel graphics testable. ASCII art on a pixel by pixel basis feels
inhuman. Just focus on text mode for now.

* I had to set aside the problem of non-English family languages.
Languages like Arabic that can stack complex graphemes together likely
can't be fixed-width. But I don't know enough at the moment to solve for
them.

* I spent a while trying to juggle two cursors, one invisible output
cursor for tracking the most recent print, and one visible one that's
just a hint to the user of what the next keystroke will do. But it looks
like I can fold both into a single cursor. Drawing things updates the
location of the cursor but doesn't display it. Explicitly moving the
cursor displays it, but future drawing can overwrite the cursor.
Diffstat (limited to 'baremetal')
-rw-r--r--baremetal/103grapheme.subx24
-rw-r--r--baremetal/mu-init.subx4
2 files changed, 19 insertions, 9 deletions
diff --git a/baremetal/103grapheme.subx b/baremetal/103grapheme.subx
index 5b160bfe..97a44315 100644
--- a/baremetal/103grapheme.subx
+++ b/baremetal/103grapheme.subx
@@ -96,8 +96,8 @@ cursor-position-on-real-screen:  # -> _/eax: int, _/ecx: int
     55/push-ebp
     89/<- %ebp 4/r32/esp
     # TODO: support fake screen; we currently assume 'screen' is always 0 (real)
-    8b/-> *Default-next-x 0/r32/eax
-    8b/-> *Default-next-y 1/r32/ecx
+    8b/-> *Real-screen-cursor-x 0/r32/eax
+    8b/-> *Real-screen-cursor-y 1/r32/ecx
 $cursor-position-on-real-screen:end:
     # . epilogue
     89/<- %esp 5/r32/ebp
@@ -110,11 +110,13 @@ set-cursor-position-on-real-screen:  # x: int, y: int
     89/<- %ebp 4/r32/esp
     # . save registers
     50/push-eax
+    #
+    (draw-grapheme-on-real-screen 0x20 *(ebp+8) *(ebp+0xc) 0 7)
     # TODO: support fake screen; we currently assume 'screen' is always 0 (real)
     8b/-> *(ebp+8) 0/r32/eax
-    89/<- *Default-next-x 0/r32/eax
+    89/<- *Real-screen-cursor-x 0/r32/eax
     8b/-> *(ebp+0xc) 0/r32/eax
-    89/<- *Default-next-y 0/r32/eax
+    89/<- *Real-screen-cursor-y 0/r32/eax
 $set-cursor-position-on-real-screen:end:
     # . restore registers
     58/pop-to-eax
@@ -125,8 +127,16 @@ $set-cursor-position-on-real-screen:end:
 
 == data
 
-Default-next-x:
+# The cursor is where certain Mu functions (usually of the form
+# 'draw*cursor*') print to by default. It becomes visible on
+# set-cursor-position, but further drawing might overwrite it.
+# We don't bother displaying the cursor when drawing text. It's up to
+# applications to display the cursor before waiting for a key, and to ensure
+# its location appropriately suggests the effect keystrokes will have.
+#
+# There's no low-level support for blinking, etc. We aren't using any
+# hardware-supported text mode here.
+Real-screen-cursor-x:
   0/imm32
-
-Default-next-y:
+Real-screen-cursor-y:
   0/imm32
diff --git a/baremetal/mu-init.subx b/baremetal/mu-init.subx
index 0ed4f085..26b83451 100644
--- a/baremetal/mu-init.subx
+++ b/baremetal/mu-init.subx
@@ -16,8 +16,8 @@ bd/copy-to-ebp 0/imm32
   3d/compare-eax-and 0/imm32
   75/jump-if-!= break/disp8
   (clear-real-screen)
-  c7 0/subop/copy *Default-next-x 0/imm32
-  c7 0/subop/copy *Default-next-y 0/imm32
+  c7 0/subop/copy *Real-screen-cursor-x 0/imm32
+  c7 0/subop/copy *Real-screen-cursor-y 0/imm32
   (main)
 }