(!!) Only render when draw-dependency props change

This is a very large change and probably breaks most applications not
built to work with it. (Obviously, I'm not really being that responsible
with this sort of thing.) I've tested with mtui and it works fine, but
some elements may need tweaks before being 100% adjusted to the new
scheduled-render system we're using with this commit. Also, any elements
which have custom draw behavior will likely need updating so that they
appropriately schedule renders.

1 files changed, 16 insertions, 5 deletions

diff --git a/util/ansi.js b/util/ansi.js
index c786db5..ac511ed 100644
--- a/util/ansi.js
+++ b/util/ansi.js
@@ -182,7 +182,8 @@ const ansi = {
 
   interpret(text, scrRows, scrCols, {
     oldChars = null, oldLastChar = null,
-    oldCursorRow = 0, oldCursorCol = 0, oldShowCursor = true
+    oldScrRows = null, oldScrCols = null,
+    oldCursorRow = 1, oldCursorCol = 1, oldShowCursor = true
   } = {}) {
     // Interprets the given ansi code, more or less.
 
@@ -193,9 +194,17 @@ const ansi = {
 
     const chars = new Array(scrRows * scrCols).fill(blank)
 
-    let showCursor = true
-    let cursorRow = 1
-    let cursorCol = 1
+    if (oldChars) {
+      for (let row = 0; row < scrRows && row < oldScrRows; row++) {
+        for (let col = 0; col < scrCols && col < oldScrCols; col++) {
+          chars[row * scrCols + col] = oldChars[row * oldScrCols + col]
+        }
+      }
+    }
+
+    let showCursor = oldShowCursor
+    let cursorRow = oldCursorRow
+    let cursorCol = oldCursorCol
     let attributes = []
 
     for (let charI = 0; charI < text.length; charI++) {
@@ -475,10 +484,12 @@ const ansi = {
 
     return {
       oldChars: newChars.slice(),
+      oldLastChar: Object.assign({}, lastChar),
+      oldScrRows: scrRows,
+      oldScrCols: scrCols,
       oldCursorRow: cursorRow,
       oldCursorCol: cursorCol,
       oldShowCursor: showCursor,
-      oldLastChar: Object.assign({}, lastChar),
       screen: result.join('')
     }
   }