Draw continuous lines

So that the application is actually usable in shitty terminals.

autistdraw.c

@@ -497,6 +497,14 @@ make_place_for_point (app_context_t *app, int x, int y)
 static void
 draw_point (app_context_t *app, int x, int y, uint8_t color)
 {
+	// We don't actually draw anything immediately in client mode,
+	// instead we wait for confirmation from the server
+	if (app->mode == NETWORK_MODE_CLIENT)
+	{
+		send_draw_point_request (app, x, y, color);
+		return;
+	}
+
 	make_place_for_point (app, x, y);
 	BITMAP_PIXEL (app, x - app->bitmap_x, y - app->bitmap_y) = color;
 
@@ -516,6 +524,50 @@ draw_point (app_context_t *app, int x, int y, uint8_t color)
 			send_draw_point_response (iter, x, y, color);
 }
 
+static void
+draw_line (app_context_t *app, int x0, int x1, int y0, int y1, uint8_t color)
+{
+	// Integer version of Bresenham's line drawing algorithm,
+	// loosely based on code from libcaca because screw math
+	int dx = abs (x1 - x0);
+	int dy = abs (y1 - y0);
+
+	bool steep = dx < dy;
+	if (steep)
+	{
+		// Flip the coordinate system on input
+		int tmp;
+		tmp = x0; x0 = y0; y0 = tmp;
+		tmp = x1; x1 = y1; y1 = tmp;
+		tmp = dx; dx = dy; dy = tmp;
+	}
+
+	int step_x = x0 > x1 ? -1 : 1;
+	int step_y = y0 > y1 ? -1 : 1;
+
+	int dpr = dy * 2;
+	int delta = dpr - dx;
+	int dpru = delta - dx;
+
+	while (dx-- >= 0)
+	{
+		// Unflip the coordinate system on output
+		if (steep)
+			draw_point (app, y0, x0, color);
+		else
+			draw_point (app, x0, y0, color);
+
+		x0 += step_x;
+		if (delta > 0)
+		{
+			y0 += step_y;
+			delta += dpru;
+		}
+		else
+			delta += dpr;
+	}
+}
+
 // --- Exports -----------------------------------------------------------------
 
 static bool
@@ -854,10 +906,16 @@ on_mouse (app_context_t *app, termo_key_t *key)
 
 	if (screen_y >= TOP_BAR_CUTOFF)
 	{
-		if (app->mode == NETWORK_MODE_CLIENT)
+		if (event == TERMO_MOUSE_DRAG)
-			send_draw_point_request (app, canvas_x, canvas_y, *color);
+			draw_line (app,
+				app->move_saved_x, canvas_x,
+				app->move_saved_y, canvas_y,
+				*color);
 		else
 			draw_point (app, canvas_x, canvas_y, *color);
+
+		app->move_saved_x = canvas_x;
+		app->move_saved_y = canvas_y;
 	}
 	else if (screen_y > 0 && event != TERMO_MOUSE_DRAG)
 	{