From 0116b00e0334b692d662c065ec5d77df636b1bc5 Mon Sep 17 00:00:00 2001
From: the lemons <citrons@mondecitronne.com>
Date: Mon, 6 Feb 2023 22:47:44 -0600
Subject: improve performance

---
 core.c    | 10 +++++++---
 memview.c | 26 ++++++++++++++++++++++----
 memview.h |  2 +-
 3 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/core.c b/core.c
index 97e0288..97953b0 100644
--- a/core.c
+++ b/core.c
@@ -146,18 +146,22 @@ static void handle_events() {
 				switch (e.key.keysym.sym) {
 					case SDLK_RIGHT:
 						next_map();
+						refresh = true;
 						break;
 					case SDLK_LEFT:
 						prev_map();
+						refresh = true;
+						break;
+					default:
 						break;
 				}
 			default:
 				break;
 		}
 	}
-	render_pages(viewer, pos_x, pos_y,
-			screen_width, screen_height, scale, refresh);
-	SDL_RenderPresent(renderer);
+	if (render_pages(viewer, pos_x, pos_y,
+			screen_width, screen_height, scale, refresh))
+		SDL_RenderPresent(renderer);
 }
 
 void cleanup() {
diff --git a/memview.c b/memview.c
index c2af3ac..9acdd22 100644
--- a/memview.c
+++ b/memview.c
@@ -93,7 +93,18 @@ static void render_page(SDL_Texture *tex, uint8_t *data) {
 	SDL_UnlockTexture(tex);
 }
 
-void render_pages(struct viewer *v,
+static uint64_t fnv(uint8_t *data, size_t size) {
+	uint64_t hash = 0xcbf29ce484222325;
+	for (size_t i = 0; i < size; i++) {
+		hash ^= data[i];
+		hash *= 0x100000001b3;
+	}
+	return hash;
+}
+
+static uint64_t hashes[1024] = {0};
+
+bool render_pages(struct viewer *v,
 		int x, int y, int width, int height, double scale, bool refresh) {
 	int page_x = x / PAGE_WIDTH;
 	int page_y = y / PAGE_HEIGHT;
@@ -107,6 +118,7 @@ void render_pages(struct viewer *v,
 	int view_width = width / page_width;
 	int view_height = height / page_height;
 
+	bool present = false;
 	for (int draw_y = -1; draw_y <= view_height + 1; draw_y++) {
 		for (int draw_x = -1; draw_x <= view_width + 1; draw_x++) {
 			SDL_Rect src = {0, 0, PAGE_WIDTH, PAGE_HEIGHT};
@@ -116,9 +128,15 @@ void render_pages(struct viewer *v,
 			};
 			uintptr_t page = zorder(page_x + draw_x, page_y + draw_y);
 			bool success = read_page(v->fd, page, v->page_buffer) != -1;
-			// TODO: unless refresh is true, do not redraw if page unaltered
-			render_page(v->page_texture, success ? v->page_buffer : NULL);
-			SDL_RenderCopy(v->renderer, v->page_texture, &src, &dest);
+
+			uint64_t hash = fnv(v->page_buffer, success ? PAGE_SIZE : 0);
+			if (refresh || hashes[page % 1024] != hash) {
+				render_page(v->page_texture, success ? v->page_buffer : NULL);
+				SDL_RenderCopy(v->renderer, v->page_texture, &src, &dest);
+				present = true;
+			}
+			hashes[page % 1024] = hash;
 		}
 	}
+	return present;
 }
diff --git a/memview.h b/memview.h
index 186bfa8..2a73ec4 100644
--- a/memview.h
+++ b/memview.h
@@ -21,7 +21,7 @@ struct viewer;
 struct viewer *create_viewer(int fd, SDL_Renderer *renderer);
 void destroy_viewer(struct viewer *v);
 
-void render_pages(struct viewer *v,
+bool render_pages(struct viewer *v,
 		int x, int y, int width, int height, double scale, bool refresh);
 void pencil(struct viewer *v, int x1, int y1, int x2, int y2, bool bit);
 
-- 
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