diff --git a/c++/perspective/src/generator.cpp b/c++/perspective/src/generator.cpp
index 83bf8aa..4e0f23a 100644
--- a/c++/perspective/src/generator.cpp
+++ b/c++/perspective/src/generator.cpp
@@ -348,7 +348,7 @@ Generator::generate(GenSurface &target, const GenSurface &source) const {
 
 
 void
-Generator::generate(Surface &target, const Pair2 &bounds) const {
+Generator::generate(Surface &target, const Pair2 &bounds, bool checks) const {
 	if (target.empty()) return;
 	
 	const int w = target.width();
@@ -365,6 +365,9 @@ Generator::generate(Surface &target, const Pair2 &bounds) const {
 	d.x /= w;
 	d.y /= h;
 	const Vector2 precision(fabs(d.x/2.0), fabs(d.x/2.0));
+	const Vector2 precision_inv(
+		1/std::max(precision.x, real_precision),
+		1/std::max(precision.y, real_precision) );
 	const Real precision_max = std::max(precision.x, precision.y);
 	
 	Color gray(0.5, 0.5, 0.5, 0.5);
@@ -419,15 +422,29 @@ Generator::generate(Surface &target, const Pair2 &bounds) const {
 		ULongInt rr = (ULongInt(round(p.y*one)) - offset.y)/step;
 		assert(rr < gen_surface.height());
 		
+		const Real ay = checks ? checks_value(p.y, precision_inv.y) : 1;
 		for(int c = 0; c < target.width(); ++c, ++pixel, p.x += d.x) {
 			ULongInt cc = (ULongInt(round(p.x*one)) - offset.x)/step;
 			assert(cc < gen_surface.width());
 			
+			const Real ax = checks ? checks_value(p.x, precision_inv.x) : 1;
+			const Real a = (ax*ay + 1)*0.5;
+			
 			const Vector4 &v = gen_surface[rr][cc];
-			*pixel = Color( flip_clamp((v.x + 1)*0.5),
-							flip_clamp((v.y + 1)*0.5),
-							flip_clamp((v.z + 1)*0.5),
-							flip_clamp((v.w + 1)*0.5) )*alpha + gray;
+			const Color color = Color( flip_clamp((v.x + 1)*0.5),
+									   flip_clamp((v.y + 1)*0.5),
+									   flip_clamp((v.z + 1)*0.5),
+									   flip_clamp((v.w + 1)*0.5) )*alpha + gray;
+			if (a + real_precision >= 1) {
+				*pixel = color;
+			} else {
+				const Color back_color = Color(1 - color.r, 1 - color.g, 1 - color.b, 1 - color.a);
+				if (a - real_precision <= 0) {
+					*pixel = back_color;
+				} else {
+					*pixel = color*a + back_color*(1 - a);
+				}
+			}
 		}
 	}
 }
diff --git a/c++/perspective/src/generator.h b/c++/perspective/src/generator.h
index b79519a..6718ac5 100644
--- a/c++/perspective/src/generator.h
+++ b/c++/perspective/src/generator.h
@@ -114,7 +114,7 @@ public:
 	
 	Vector4 generate(const ULongIntVector2 &coord, bool shrink_cache = true) const;
 	Vector4 generate(const Vector2 &coord, const Vector2 &precision) const;
-	void generate(Surface &target, const Pair2 &bounds) const;
+	void generate(Surface &target, const Pair2 &bounds, bool checks = false) const;
 
 	void generate(GenSurface &target) const;
 	void generate(GenSurface &target, const GenSurface &source) const;
diff --git a/c++/perspective/src/mainwindow.cpp b/c++/perspective/src/mainwindow.cpp
index 85632e0..d40780d 100644
--- a/c++/perspective/src/mainwindow.cpp
+++ b/c++/perspective/src/mainwindow.cpp
@@ -10,7 +10,8 @@
 #include "mainwindow.h"
 
 
-const bool checks = true;
+const bool checks = false;
+const bool checks_on_generator = true;
 const bool paint_outside_bounds = true;
 
 
@@ -114,7 +115,7 @@ MainWindow::update_src_surface() {
 	} else {
 		DataSurface surface(w, h);
 		if (checks) generator.generate_checks(surface, rect);
-			   else generator.generate(surface, rect);
+			   else generator.generate(surface, rect, checks_on_generator);
 		src_surface = surface.to_cairo_surface();
 	}
 
@@ -205,7 +206,7 @@ MainWindow::update_dst_surface() {
 	for(Perspective::LayerList::const_iterator i = layers.begin(); i != layers.end(); ++i) {
 		DataSurface layer_surface(i->src_size.x, i->src_size.y);
 		if (checks) generator.generate_checks(layer_surface, i->src_bounds);
-			   else generator.generate(layer_surface, i->src_bounds);
+			   else generator.generate(layer_surface, i->src_bounds, checks_on_generator);
 		layer_surface.mult_alpha();
 		Perspective::add_premulted(*i, layer_surface, surface);
 	}