From c38e418286c5cc2e8af7f68de9483d9cdcf95dce Mon Sep 17 00:00:00 2001
From: Leo Tenenbaum <pommicket@gmail.com>
Date: Sun, 27 Dec 2020 15:48:59 -0500
Subject: only render visible lines

---
 base.h   |  7 ++++---
 buffer.c | 15 ++++++++++++---
 main.c   |  9 +++++++--
 3 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/base.h b/base.h
index c9306a3..9b0c805 100644
--- a/base.h
+++ b/base.h
@@ -77,19 +77,20 @@ typedef unsigned long long ullong;
 
 #if DEBUG
 #if __unix__
-#define debug_println(...) printf(__VA_ARGS__), printf("\n")
+#define debug_print(...) printf(__VA_ARGS__)
 #else // __unix__
-static void debug_println(char const *fmt, ...) {
+static void debug_print(char const *fmt, ...) {
 	char buf[256];
 	va_list args;
 	va_start(args, fmt);
 	vsprintf_s(buf, sizeof buf, fmt, args);
 	va_end(args);
 	OutputDebugStringA(buf);
-	OutputDebugStringA("\n");
 }
 #endif // __unix__
+#define debug_println(...) debug_print(__VA_ARGS__), debug_print("\n")
 #else // DEBUG
+#define debug_print(...)
 #define debug_println(...)
 #endif
 
diff --git a/buffer.c b/buffer.c
index fac72af..7f9d810 100644
--- a/buffer.c
+++ b/buffer.c
@@ -787,10 +787,12 @@ void buffer_render(TextBuffer *buffer, float x1, float y1, float x2, float y2) {
 
 	u32 column = 0;
 
-	// @TODO: make this better (we should figure out where to start rendering, etc.)
-	text_state.y -= (float)buffer->scroll_y * char_height;
+	u32 start_line = (u32)buffer->scroll_y; // line to start rendering from
+	text_state.y -= (float)(buffer->scroll_y - start_line) * char_height;
 
-	for (u32 line_idx = 0; line_idx < nlines; ++line_idx) {
+	//debug_print("Rendering from " U32_FMT, start_line);
+
+	for (u32 line_idx = start_line; line_idx < nlines; ++line_idx) {
 		Line *line = &lines[line_idx];
 		for (char32_t *p = line->str, *end = p + line->len; p != end; ++p) {
 			char32_t c = *p;
@@ -813,9 +815,16 @@ void buffer_render(TextBuffer *buffer, float x1, float y1, float x2, float y2) {
 
 		// next line
 		text_state.x = render_start_x;
+		if (text_state.y > text_state.max_y) {
+			// made it to the bottom of the buffer view.
+			//debug_println(" to " U32_FMT ".", line_idx);
+			break;
+		}
 		text_state.y += text_font_char_height(font);
 		column = 0;
 	}
+	
+
 	text_chars_end(font);
 
 	{ // render cursor
diff --git a/main.c b/main.c
index ae197ac..763decd 100644
--- a/main.c
+++ b/main.c
@@ -76,13 +76,17 @@ int main(void) {
 	TextBuffer text_buffer;
 	buffer_create(&text_buffer, font);
 
-	if (!buffer_load_file(&text_buffer, "test.txt"))
+	if (!buffer_load_file(&text_buffer, "buffer.c"))
 		die("Error loading file: %s", buffer_geterr(&text_buffer));
 
 
 	Uint32 time_at_last_frame = SDL_GetTicks();
 
 	while (!quit) {
+	#if DEBUG
+		printf("\033[H\033[2J"); fflush(stdout);
+	#endif
+
 		SDL_Event event;
 		Uint8 const *keyboard_state = SDL_GetKeyboardState(NULL);
 		bool ctrl = keyboard_state[SDL_SCANCODE_LCTRL] || keyboard_state[SDL_SCANCODE_RCTRL];
@@ -216,10 +220,11 @@ int main(void) {
 			}
 		}
 
+	#if DEBUG
 		//buffer_print_debug(&text_buffer);
 		buffer_check_valid(&text_buffer);
-		printf("\033[H\033[2J"); fflush(stdout);
 		buffer_print_undo_history(&text_buffer);
+	#endif
 
 		SDL_GL_SwapWindow(window);
 	}
-- 
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