add much-needed optimizations and enhance the snake example game

Makefile

@@ -16,7 +16,7 @@ run:
 	$(OUT)
 
 build-snake:
-	$(CC) -o $(SNAKE) $(SNAKE_SRC) $(INC) $(LIBS)
+	$(CC) -o $(SNAKE) -O3 -DNDEBUG $(SNAKE_SRC) $(INC) $(LIBS)
 
 run-snake:
 	$(SNAKE)

include/engine.h

@@ -41,6 +41,8 @@ typedef struct {
 	uint32_t framebuffer[WINDOW_WIDTH * WINDOW_HEIGHT];
 	SDL_Event event;
 	bool is_running;
+	bool framebuffer_dirty;
+	SDL_Rect dirty_rect;
 	uint16_t width, height;
 } game_state_t;
 
@@ -88,6 +90,12 @@ clear_framebuffer(
 	uint32_t color
 );
 
+void
+clear_rect(int x, int y, int w, int h, uint32_t color);
+
+void
+mark_dirty_rect(int x, int y, int w, int h);
+
 void
 put_char(
 	char c,

src/engine/engine.c

@@ -3,12 +3,144 @@
 engine_internal_state_t *internal_state = NULL;
 game_state_t *game_state = NULL;
 
+void
+mark_dirty_rect(int x, int y, int w, int h)
+{
+    if (w <= 0 || h <= 0) {
+        return;
+    }
+
+    // clip rectangle to the framebuffer
+    if (x < 0) {
+        w += x;
+        x = 0;
+    }
+
+    if (y < 0) {
+        h += y;
+        y = 0;
+    }
+
+    if (x + w > game_state->width) {
+        w = game_state->width - x;
+    }
+
+    if (y + h > game_state->height) {
+        h = game_state->height - y;
+    }
+
+    if (w <= 0 || h <= 0) {
+        return;
+    }
+
+    SDL_Rect rect = {
+        .x = x,
+        .y = y,
+        .w = w,
+        .h = h
+    };
+
+    if (!game_state->framebuffer_dirty) {
+        game_state->dirty_rect = rect;
+        game_state->framebuffer_dirty = true;
+        return;
+    }
+
+    int left = game_state->dirty_rect.x < rect.x
+        ? game_state->dirty_rect.x
+        : rect.x;
+
+    int top = game_state->dirty_rect.y < rect.y
+        ? game_state->dirty_rect.y
+        : rect.y;
+
+    int old_right =
+        game_state->dirty_rect.x + game_state->dirty_rect.w;
+
+    int new_right = rect.x + rect.w;
+
+    int old_bottom =
+        game_state->dirty_rect.y + game_state->dirty_rect.h;
+
+    int new_bottom = rect.y + rect.h;
+
+    int right = old_right > new_right
+        ? old_right
+        : new_right;
+
+    int bottom = old_bottom > new_bottom
+        ? old_bottom
+        : new_bottom;
+
+    game_state->dirty_rect = (SDL_Rect) {
+        .x = left,
+        .y = top,
+        .w = right - left,
+        .h = bottom - top
+    };
+}
+
+bool
+upload_dirty_texture(void)
+{
+    if (!game_state->framebuffer_dirty) {
+        return true;
+    }
+
+    SDL_Texture *texture =
+        internal_state->sdl_state->texture;
+
+    SDL_Rect rect = game_state->dirty_rect;
+
+    void *locked_pixels = NULL;
+    int locked_pitch = 0;
+
+    if (!SDL_LockTexture(
+            texture,
+            &rect,
+            &locked_pixels,
+            &locked_pitch
+        )) {
+        SDL_Log(
+            "SDL_LockTexture failed: %s",
+            SDL_GetError()
+        );
+        return false;
+    }
+
+    const size_t source_pitch =
+        (size_t)game_state->width * sizeof(uint32_t);
+
+    const size_t row_bytes =
+        (size_t)rect.w * sizeof(uint32_t);
+
+    const uint8_t *source =
+        (const uint8_t *)game_state->framebuffer +
+        (size_t)rect.y * source_pitch +
+        (size_t)rect.x * sizeof(uint32_t);
+
+    uint8_t *destination =
+        (uint8_t *)locked_pixels;
+
+    for (int y = 0; y < rect.h; ++y) {
+        memcpy(
+            destination + (size_t)y * locked_pitch,
+            source + (size_t)y * source_pitch,
+            row_bytes
+        );
+    }
+
+    SDL_UnlockTexture(texture);
+
+    game_state->framebuffer_dirty = false;
+
+    return true;
+}
+
 void
 engine_start() {
 	// main game loop
 	while(game_state->is_running) {
-		uint64_t start = SDL_GetPerformanceCounter();
-
 		// poll events
 		while (SDL_PollEvent(&game_state->event)) {
 			internal_state->engine_poll_events();
@@ -18,11 +150,7 @@ engine_start() {
 		internal_state->engine_update_framebuffer();
 
 		// update the texture with the modified framebuffer
-		SDL_UpdateTexture(
-			internal_state->sdl_state->texture, 
-			NULL, game_state->framebuffer, 
-			internal_state->sdl_state->width * sizeof(uint32_t)
-		);
+		upload_dirty_texture();
 
 		SDL_RenderClear(
 			internal_state->sdl_state->renderer
@@ -37,17 +165,6 @@ engine_start() {
 		SDL_RenderPresent(
 			internal_state->sdl_state->renderer
 		);
-
-		uint64_t end = SDL_GetPerformanceCounter();
-
-		double elapsed = 
-			(double)(end - start) / 
-			(double)SDL_GetPerformanceFrequency();
-
-		// cap the framerate at '1.0/TARGET_FRAME' fps
-		if (elapsed < TARGET_FRAME) {
-			SDL_Delay((TARGET_FRAME - elapsed) * 1000);
-		}
 	}
 }
 

src/engine/engine_init.c

@@ -65,6 +65,11 @@ engine_sdl_init_renderer(
 		return RCODE_FAILURE;
 	}
 
+	// enable VSync
+	if (!SDL_SetRenderVSync(state->renderer, 1)) {
+	    eprintf("SDL_SetRenderVSync failed: %s\n", SDL_GetError());
+	}
+
 	return RCODE_SUCCESS;
 }
 
@@ -127,9 +132,16 @@ engine_init(
 ) {
 	internal_state = (engine_internal_state_t *)
 		malloc(sizeof(engine_internal_state_t));
+	if (internal_state == NULL) {
+		return RCODE_FAILURE;
+	}
 
 	game_state = (game_state_t *)
 		malloc(sizeof(game_state_t));
+	if (game_state == NULL) {
+		free(internal_state);
+		return RCODE_FAILURE;
+	}
 
 	internal_state->engine_poll_events
 		= engine_poll_events;
@@ -138,11 +150,22 @@ engine_init(
 		= engine_update_framebuffer;
 
 	internal_state->sdl_state = engine_sdl_init();
+	if (internal_state->sdl_state == NULL) {
+		free(internal_state);
+		free(game_state);
+		return RCODE_FAILURE;
+	}
 
 	game_state->is_running = true;
+	game_state->framebuffer_dirty = true;
+	game_state->dirty_rect = (SDL_Rect) {
+	    .x = 0,
+	    .y = 0,
+	    .w = game_state->width,
+	    .h = game_state->height
+	};
 	game_state->width = internal_state->sdl_state->width;
 	game_state->height = internal_state->sdl_state->height;
 
-	return (game_state == NULL || internal_state == NULL) 
-		? RCODE_FAILURE : RCODE_SUCCESS;
+	return RCODE_SUCCESS;
 }

src/engine/render.c

@@ -20,6 +20,8 @@ put_pixel(
 	} else {
 		game_state->framebuffer[game_state->width * y + x]
 			= color;
+
+	    mark_dirty_rect(x, y, 1, 1);
 	}
 }
 
@@ -40,18 +42,43 @@ put_rect(
 			put_pixel(i, j, color);
 		}
 	}
+	mark_dirty_rect(x, y, w, h);
 }
 
 // fill the entire framebuffer with a given color
-void 
+void
 clear_framebuffer(
 	uint32_t color
 ) {
-	uint16_t w = game_state->width;
-	uint16_t h = game_state->height;
+    for (size_t i = 0;
+         i < (size_t)game_state->width * game_state->height;
+         ++i) {
+        game_state->framebuffer[i] = color;
+    }
 
-	for (int i = 0; i < w * h; i++) {
-		game_state->framebuffer[i] = color;
-	}
+    mark_dirty_rect(
+        0,
+        0,
+        game_state->width,
+        game_state->height
+    );
 }
 
+void
+clear_rect(int x, int y, int w, int h, uint32_t color)
+{
+    for (int py = y; py < y + h; ++py) {
+        for (int px = x; px < x + w; ++px) {
+            if (px >= 0 &&
+                px < game_state->width &&
+                py >= 0 &&
+                py < game_state->height) {
+                game_state->framebuffer[
+                    py * game_state->width + px
+                ] = color;
+            }
+        }
+    }
+
+    mark_dirty_rect(x, y, w, h);
+}

src/engine/text.c

@@ -112,6 +112,8 @@ put_char(
             );
         }
     }
+
+    mark_dirty_rect(x, y, size, size);
 }
 
 void

src/examples/snake.c

@@ -11,7 +11,7 @@ typedef struct {
 	int32_t y;
 } v2;
 
-#define SNAKE_MAX_LENGTH 64
+#define SNAKE_MAX_LENGTH 10
 
 typedef struct {
 	// position of the head of the snake in the framebuffer
@@ -32,6 +32,9 @@ typedef struct {
 } snake_state_t;
 
 snake_state_t snake;
+bool put_string_game_over;
+bool put_string_win;
+bool redraw = false;
 
 bool
 is_opposite_direction(v2 a, v2 b)
@@ -156,11 +159,17 @@ calculate_snake_death_collisions()
 {
 	for (int i = 1; i < snake.length; i++) {
 		if (v2_eq(snake.body[0], snake.body[i])) {
-			game_state->is_running = false;
+			put_string_game_over = true;
 		}
 	}
 }
 
+void
+evaluate_win()
+{
+	put_string_win = (snake.length >= SNAKE_MAX_LENGTH);
+}
+
 /**
  * performed every frame
  * runs on a separate worker thread - you can take advantage
@@ -171,7 +180,7 @@ client_update_framebuffer()
 {
 	uint64_t now = SDL_GetTicks();
 
-	if (now >= snake.next_move_time) {
+	if (now >= snake.next_move_time && !put_string_game_over) {
 		
 		// ------- business logic --------
 
@@ -183,7 +192,62 @@ client_update_framebuffer()
 
 		calculate_snake_death_collisions();
 
+		evaluate_win();
+
+		v2 old_head = snake.body[0];
+		v2 old_tail = snake.body[snake.length - 1];
+
 		advance_snake_pos();
+
+		v2 new_head = snake.body[0];
+
+		clear_rect(
+		    old_tail.x,
+		    old_tail.y,
+		    snake.size,
+		    snake.size,
+		    0x000000
+		);
+
+		if (snake.length > 1) {
+			put_rect(
+			    old_head.x,
+			    old_head.y,
+			    snake.size,
+			    snake.size,
+			    0x00AA00
+			);
+		}
+
+		put_rect(
+		    new_head.x,
+		    new_head.y,
+		    snake.size,
+		    snake.size,
+		    0x00FF00
+		);
+
+		mark_dirty_rect(
+		    old_tail.x,
+		    old_tail.y,
+		    snake.size,
+		    snake.size
+		);
+
+		mark_dirty_rect(
+		    old_head.x,
+		    old_head.y,
+		    snake.size,
+		    snake.size
+		);
+
+		mark_dirty_rect(
+		    new_head.x,
+		    new_head.y,
+		    snake.size,
+		    snake.size
+		);
+
 		
 		// -------------------------------
 		
@@ -193,8 +257,11 @@ client_update_framebuffer()
 	    	snake.next_move_time = now + snake.move_interval;
 		}
 
-		clear_framebuffer(0x000000);
+		redraw = true;
+		game_state->framebuffer_dirty = true;
+	}
 
+	if (redraw) {
 		// draw the apple
 		if (snake.is_apple_alive) {
 			put_rect_v2(
@@ -210,6 +277,7 @@ client_update_framebuffer()
 			snake.body[0].x, snake.body[0].y, 
 			snake.size, snake.size, 0x00FF00
 		);
+
 		// draw the tail
 		for (int i = 1; i < snake.length; i++) {
 			put_rect(
@@ -217,6 +285,21 @@ client_update_framebuffer()
 				snake.size, snake.size, 0x00AA00
 			);
 		}
+
+		// draw the splash texts
+		if (put_string_game_over) {
+			put_string("GAME OVER!\n<q> to quit", 
+				0, 0, 5, 2, 3, 0xFF0000, 0x000000
+			);
+		}
+
+		if (put_string_win) {
+			put_string("YOU WIN!\n<q> to quit", 
+				0, 100, 5, 2, 3, 0x00FF00, 0x000000
+			);
+		}
+
+		redraw = false;
 	}
 }
 
@@ -230,11 +313,14 @@ snake_init()
 	snake.dir = (v2){1, 0};
 	snake.length = 1;
 	snake.size = 20;
-	snake.move_interval = 300;
+	snake.move_interval = 50;
 	snake.next_move_time = snake.move_interval;
 	snake.is_apple_alive = false;
 	snake.pending_dir = snake.dir;
 	snake.direction_pending = false;
+
+	put_string_game_over = false;
+	put_string_win = false;
 }
 
 int