From 467ee8710ebc75826c3022f1f3b628f70d99e580 Mon Sep 17 00:00:00 2001
From: "Michael D. Lowis" <mike@mdlowis.com>
Date: Sun, 11 Jun 2017 20:08:50 -0400
Subject: [PATCH] optimized syntax highlighting for *real* this time

---
 lib/colors.c | 34 +++++++++++++++-------------------
 lib/view.c   | 14 +++++++++++++-
 2 files changed, 28 insertions(+), 20 deletions(-)

diff --git a/lib/colors.c b/lib/colors.c
index 8fb27bf..cb79fff 100644
--- a/lib/colors.c
+++ b/lib/colors.c
@@ -67,6 +67,8 @@ static SyntaxSpan* mkspan(size_t beg, size_t end, size_t clr, SyntaxSpan* span)
 
 SyntaxSpan* colors_scan(SyntaxDef* syntax, SyntaxSpan* spans, Buf* buf, size_t beg, size_t end) {
     SyntaxSpan* firstspan = spans;
+    SyntaxSpan* currspan  = spans;
+
     if (!syntax) return firstspan;
     for (size_t off = beg; off < end; off++) {
         size_t start = off;
@@ -75,33 +77,27 @@ SyntaxSpan* colors_scan(SyntaxDef* syntax, SyntaxSpan* spans, Buf* buf, size_t b
         else if (matches(buf, &off, syntax->comments.multi_beg))
             for (; off < end && !matches(buf, &off, syntax->comments.multi_end); off++);
         if (start != off)
-            spans = mkspan(start, --off, CLR_Comment, spans);
-        if (!firstspan && spans)
-            firstspan = spans;
+            currspan = mkspan(start, --off, CLR_Comment, currspan);
+        if (!firstspan && currspan)
+            firstspan = currspan;
     }
+
     return firstspan;
 }
 
 SyntaxSpan* colors_rewind(SyntaxSpan* spans, size_t first) {
-    /* rewind to the first span that start before visible space */
-    while (spans && spans->beg >= first && spans->prev)
-        spans = spans->prev;
+    SyntaxSpan *curr = spans, *next = (spans ? spans->next : NULL);
+    while (curr && curr->end > first)
+        next = curr, curr = curr->prev;
 
-    /* if we're on the first one, setup to return NULL, otherwise return the
-       previous one because we're about to regenerate the current one and
-       everything after it */
-    SyntaxSpan* ret = (spans ? spans->prev : NULL);
+    if (curr) curr->next = NULL;
 
-    /* ok now free the rest of the list */
-    while (spans) {
-        SyntaxSpan* dead = spans;
-        spans = dead->next;
+    for (SyntaxSpan* span = next; span;) {
+        SyntaxSpan* dead = span;
+        span = dead->next;
+        if (span) span->prev = NULL;
         free(dead);
     }
-
-    /* make sure we clear out the next link */
-    if (ret) ret->next = NULL;
-
-    return ret;
+    return curr;
 }
 
diff --git a/lib/view.c b/lib/view.c
index 5ee56bf..4ddff64 100644
--- a/lib/view.c
+++ b/lib/view.c
@@ -103,12 +103,16 @@ void view_update(View* view, size_t* csrx, size_t* csry) {
         view_scrollto(view, csr);
     /* locate the cursor if visible */
     find_cursor(view, csrx, csry);
+
     /* synchronize, scan for, and apply highlighted regions */
+    if (!view->syntax) return;
+
     size_t first = (view->nrows ? view->rows[0]->off : 0),
            last  = buf_end(&(view->buffer));
     if (view->nrows)
         last = view->rows[view->nrows-1]->off + view->rows[view->nrows-1]->rlen;
     view->spans = colors_rewind(view->spans, first);
+    first = (view->spans ? view->spans->end : 0);
     view->spans = colors_scan(view->syntax, view->spans, &(view->buffer), first, last+1);
     apply_colors(view);
 }
@@ -674,7 +678,16 @@ static void sync_line_numbers(View* view) {
 }
 
 static void apply_colors(View* view) {
+    /* fast forward the span list to the first span that ends on screen if there
+       is one. We take care to not go past the last item because we need to
+       ensure newly scanned items are poperly appended next time around */
+    size_t first = (view->nrows ? view->rows[0]->off : 0);
     SyntaxSpan* curr = view->spans;
+    for (; curr && curr->next && curr->end < first; curr = curr->next);
+    view->spans = curr;
+
+    /* ok, now for each row, scan the columns and apply the colors for the span
+       that each rune is a member of. */
     for (size_t r = 0; curr && r < view->nrows; r++) {
         Row* row = view->rows[r];
         size_t off = row->off, col = 0;
@@ -693,5 +706,4 @@ static void apply_colors(View* view) {
                 col++;
         }
     }
-
 }
-- 
2.49.0