Allow viewport to move past the top-left edge of the map.

src/tileiterator.cpp

@@ -1,19 +1,31 @@
 #include "tileiterator.hpp"
 #include "worldviewport.hpp"
 #include "worldgrid.hpp"
+#include "compatibility.h"
 #include <cassert>
 #include <ciso646>
 
 namespace curry {
+	namespace {
+		vec2i first_col_starting_pixel (const vec2i& parViewportPos, const vec2i& parTileSize) a_pure;
+
+		vec2i first_col_starting_pixel (const vec2i& parViewportPos, const vec2i& parTileSize) {
+			const auto& pos = parViewportPos;
+			const auto& ts = parTileSize;
+
+			return vec2i(
+				(pos.x() > 0 ? -pos.x() % ts.x() : -pos.x()),
+				(pos.y() > 0 ? -pos.y() % ts.y() : -pos.y())
+			);
+		}
+	} //unnamed namespace
+
 	TileIterator::TileIterator (WorldViewport* parViewport, bool parEnd) :
 		m_viewport(parViewport),
 		m_index(parEnd ? -1 : 0)
 	{
 		assert(m_viewport);
-		m_pixel_pos = vec2i(
+		m_pixel_pos = first_col_starting_pixel(m_viewport->position(), m_viewport->world()->tile_size());
-			-m_viewport->position().x() % m_viewport->world()->tile_size().x(),
-			-m_viewport->position().y() % m_viewport->world()->tile_size().y()
-		);
 	}
 
 	void TileIterator::increment() {
@@ -21,9 +33,9 @@ namespace curry {
 
 		const WorldGrid& world = *m_viewport->world();
 		vec2i tile_size(world.tile_size());
-		auto first_tile_pos = vec2i(
+		auto first_tile_pos = first_col_starting_pixel(
-			-m_viewport->position().x() % tile_size.x(),
+			m_viewport->position(),
-			-m_viewport->position().y() % tile_size.y()
+			m_viewport->world()->tile_size()
 		);
 		vec2i pos(tile_size * m_index + first_tile_pos);