Fix cairo surface flushing and marking in create_surface

visor.c

@@ -355,8 +355,7 @@ void plane_resize(GtkWidget *widget)
 
 void create_surface(GtkWidget *widget)
 {
-	cairo_t *cr;
+	// Stop all current drawers
-
 	pthread_mutex_lock(&pixmapMutex);
 	pixmapAvailable = false; // Mark drawing area as unavailable
 	pthread_mutex_unlock(&pixmapMutex);
@@ -367,9 +366,24 @@ void create_surface(GtkWidget *widget)
 		for (int32_t i = 0; i < thread_count; i++) {
 			if (threads[i].drawing) {
 				allWritersStopped = false;
+				break;
 			}
 		}
 	} while (!allWritersStopped);
+
+	// If all drawers hadn't completed, we need to call
+	// cairo_surface_mark_dirty in the main thread
+	bool allWritersHadCompleted = true;
+	for (int32_t i = 0; i < thread_count; i++) {
+		if (!threads[i].complete) {
+			allWritersHadCompleted = false;
+			break;
+		}
+	}
+	if (!allWritersHadCompleted && surface != NULL) {
+		cairo_surface_mark_dirty(surface);
+	}
+
 	for (int32_t i = 0; i < thread_count; i++) {
 		threads[i].complete = false;
 	}
@@ -382,20 +396,21 @@ void create_surface(GtkWidget *widget)
 			gtk_widget_get_width(widget),
 			gtk_widget_get_height(widget));
 
-	cr = cairo_create(surface);
-
-	cairo_surface_flush(surface);
 	int h = cairo_image_surface_get_height(surface);
 	int w = cairo_image_surface_get_width(surface);
 	mandelbrot.height = h;
 	mandelbrot.width = w;
-	pixmap = cairo_image_surface_get_data(surface);
-	cairo_surface_mark_dirty(surface);
 
+	// Mark the surface as ready to be drawn by memory access
+	// Then notify other threads to start drawing
+	// One of these threads will make the corresponding call using
+	// cairo_surface_mark_dirty, to notify they are all done drawing
+	cairo_surface_flush(surface);
+	pixmap = cairo_image_surface_get_data(surface);
+
+	// This lock is unnecessary since all other threads are stopped already
 	pthread_mutex_lock(&pixmapMutex);
 	pixmapAvailable = true;
 	pthread_mutex_unlock(&pixmapMutex);
 	pthread_cond_broadcast(&pixmapCond);
-
-	cairo_destroy(cr);
 }