From bb9c6b6ff3ca196977f9ddd73120897c679e2515 Mon Sep 17 00:00:00 2001
From: Leo Tenenbaum <pommicket@gmail.com>
Date: Mon, 1 Feb 2021 19:58:27 -0500
Subject: cache syntax highlighting

---
 buffer.c | 49 +++++++++++++++++++++++++++++++++++++++----------
 ted.h    |  9 ++++++++-
 2 files changed, 47 insertions(+), 11 deletions(-)

diff --git a/buffer.c b/buffer.c
index a672bdf..0d24d21 100644
--- a/buffer.c
+++ b/buffer.c
@@ -632,6 +632,8 @@ Status buffer_load_file(TextBuffer *buffer, char const *filename) {
 								buffer_clear(buffer);
 								buffer->lines = lines;
 								buffer->nlines = nlines;
+								buffer->frame_earliest_line_modified = 0;
+								buffer->frame_latest_line_modified = nlines - 1;
 								buffer->lines_capacity = lines_capacity;
 								buffer->filename = filename_copy;
 							}
@@ -1270,6 +1272,16 @@ void buffer_cursor_move_to_end_of_file(TextBuffer *buffer) {
 	buffer_cursor_move_to_pos(buffer, buffer_end_of_file(buffer));
 }
 
+
+static void buffer_lines_modified(TextBuffer *buffer, u32 first_line, u32 last_line) {
+	assert(last_line >= first_line);
+	buffer->modified = true;
+	if (first_line < buffer->frame_earliest_line_modified)
+		buffer->frame_earliest_line_modified = first_line;
+	if (last_line > buffer->frame_latest_line_modified)
+		buffer->frame_latest_line_modified = last_line;
+}
+
 // insert `number` empty lines starting at index `where`.
 static Status buffer_insert_lines(TextBuffer *buffer, u32 where, u32 number) {
 	assert(!buffer->is_line_buffer);
@@ -1382,7 +1394,7 @@ BufferPos buffer_insert_text_at_pos(TextBuffer *buffer, BufferPos pos, String32
 	// We need to put this after the end so the emptiness-checking is done after the edit is made.
 	buffer_remove_last_edit_if_empty(buffer);
 
-	buffer->modified = true;
+	buffer_lines_modified(buffer, pos.line, line_idx);
 
 	BufferPos b = {.line = line_idx, .index = index};
 	return b;
@@ -1627,7 +1639,7 @@ void buffer_delete_chars_at_pos(TextBuffer *buffer, BufferPos pos, i64 nchars_)
 	// cursor position could have been invalidated by this edit
 	buffer_validate_cursor(buffer);
 
-	buffer->modified = true;
+	buffer_lines_modified(buffer, line_idx, line_idx);
 }
 
 // Delete characters between the given buffer positions. Returns number of characters deleted.
@@ -2002,27 +2014,44 @@ void buffer_render(TextBuffer *buffer, Rect r) {
 	// scroll <= sel - scrolloff
 	text_state.y -= (float)(buffer->scroll_y - start_line) * char_height;
 
-	SyntaxState syntax_state = {0};
 	Language language = buffer_language(buffer);
 	// dynamic array of character types, to be filled by syntax_highlight
 	SyntaxCharType *char_types = NULL;
 	bool syntax_highlighting = language && settings->syntax_highlighting;
-	if (syntax_highlighting) {
-		for (u32 line_idx = 0; line_idx < start_line; ++line_idx) {
-			Line *line = &lines[line_idx];
-			syntax_highlight(&syntax_state, language, line->str, line->len, NULL);
-		}
-	} else {
+	if (!syntax_highlighting) {
 		gl_color_rgba(colors[COLOR_TEXT]);
 	}
 
+	if (buffer->frame_latest_line_modified >= buffer->frame_earliest_line_modified) {
+		// update syntax cache
+		Line *earliest = &buffer->lines[buffer->frame_earliest_line_modified];
+		Line *latest = &buffer->lines[buffer->frame_latest_line_modified];
+		Line *buffer_last_line = &buffer->lines[buffer->nlines - 1];
+		Line *start = earliest == buffer->lines ? earliest : earliest - 1;
+
+		for (Line *line = start; line != buffer_last_line; ++line) {
+			SyntaxState syntax = line->syntax;
+			syntax_highlight(&syntax, language, line->str, line->len, NULL);
+			if (line > latest && line[1].syntax == syntax) {
+				// no further necessary changes to the cache
+				break;
+			} else {
+				line[1].syntax = syntax;
+			}
+		}
+	}
+	buffer->frame_earliest_line_modified = U32_MAX;
+	buffer->frame_latest_line_modified = 0;
+
 	for (u32 line_idx = start_line; line_idx < nlines; ++line_idx) {
 		Line *line = &lines[line_idx];
 		if (arr_len(char_types) < line->len) {
 			arr_set_len(char_types, line->len);
 		}
-		if (language)
+		if (syntax_highlighting) {
+			SyntaxState syntax_state = line->syntax;
 			syntax_highlight(&syntax_state, language, line->str, line->len, char_types);
+		}
 		for (u32 i = 0; i < line->len; ++i) {
 			char32_t c = line->str[i];
 			if (syntax_highlighting) {
diff --git a/ted.h b/ted.h
index a88c460..df41766 100644
--- a/ted.h
+++ b/ted.h
@@ -18,7 +18,7 @@ enum {
 	SYNTAX_STATE_STRING = 1<<SYNTAX_STATE_STRING_SHIFT,
 };
 
-typedef u16 SyntaxState;
+typedef u8 SyntaxState;
 
 ENUM_U16 {
 	LANG_NONE,
@@ -89,6 +89,7 @@ typedef struct {
 } BufferPos;
 
 typedef struct {
+	SyntaxState syntax;
 	u32 len;
 	u32 capacity;
 	char32_t *str;
@@ -116,6 +117,12 @@ typedef struct {
 	float x1, y1, x2, y2;
 	u32 nlines;
 	u32 lines_capacity;
+
+	// to cache syntax highlighting properly, it is important to keep track of the
+	// first and last line modified since last frame.
+	u32 frame_earliest_line_modified;
+	u32 frame_latest_line_modified;
+
 	Line *lines;
 	char error[256];
 	BufferEdit *undo_history; // dynamic array of undo history
-- 
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