diff --git a/Machines/Amiga/Blitter.cpp b/Machines/Amiga/Blitter.cpp
index c5e45271f..f26bc8cda 100644
--- a/Machines/Amiga/Blitter.cpp
+++ b/Machines/Amiga/Blitter.cpp
@@ -139,41 +139,64 @@ bool Blitter::advance() {
 		//		* bit 3 = 1 => major variable negative; otherwise positive;
 		//		* bit 2 = 1 => minor variable negative; otherwise positive.
 
+		//
+		// Implementation below is heavily based on the documentation found
+		// at https://github.com/niklasekstrom/blitter-subpixel-line/blob/master/Drawing%20lines%20using%20the%20Amiga%20blitter.pdf
+
 		printf("!!! Line %08x\n", pointer_[3]);
 
 		int error = int(pointer_[0]) * line_sign_;
+		bool draw_ = true;
 		while(height_--) {
 
-			// plot(x, y)
-			c_ = ram_[pointer_[3] & ram_mask_];
-			ram_[pointer_[3] & ram_mask_] =
-				apply_minterm<uint16_t>(
-					a_ >> shifts_[0],
-					0xffff,	// TODO: b_ & (0x8000 >> shifts_[1]) but not that.
-					c_, minterms_);
-			shifts_[1] = (shifts_[1] + 1) & 15;
+			if(draw_) {
+				c_ = ram_[pointer_[3] & ram_mask_];
+//				c_ |= a_ >> shifts_[0];					// TODO: there's an XOR mode, I think?
+				ram_[pointer_[3] & ram_mask_] =
+					apply_minterm<uint16_t>(a_ >> shifts_[0], b_, c_, minterms_);
+				draw_ &= !one_dot_;
+			}
 
-			// Assumed for now: direction 0.
-			pointer_[3] += modulos_[2];
-			if(error > 0) {
+			constexpr int LEFT	= 1 << 0;
+			constexpr int RIGHT	= 1 << 1;
+			constexpr int UP	= 1 << 2;
+			constexpr int DOWN	= 1 << 3;
+			int step = (line_direction_ & 4) ?
+				((line_direction_ & 1) ? LEFT : RIGHT) :
+				((line_direction_ & 1) ? UP : DOWN);
+
+			if(error < 0) {
+				error += modulos_[1];
+			} else {
+				step |=
+					(line_direction_ & 4) ?
+						((line_direction_ & 2) ? UP : DOWN) :
+						((line_direction_ & 2) ? LEFT : RIGHT);
+
+				error += modulos_[0];
+			}
+
+			if(step & LEFT) {
+				--shifts_[0];
+				if(shifts_[0] == -1) {
+					--pointer_[3];
+				}
+			} else if(step & RIGHT) {
 				++shifts_[0];
 				if(shifts_[0] == 16) {
-					shifts_[0] = 0;
 					++pointer_[3];
 				}
-
-				error -= modulos_[0] - modulos_[1];
 			}
-			error += modulos_[1];
+			shifts_[0] &= 15;
 
-			// plot(x, y)
-			// if error > 0 {
-			//		++y
-			//		error -= 2*dx
-			// }
-			// d += 2*dy
+			if(step & UP) {
+				pointer_[3] -= modulos_[2];
+				draw_ = true;
+			} else if(step & DOWN) {
+				pointer_[3] += modulos_[2];
+				draw_ = true;
+			}
 		}
-//		ram_[pointer_[3] & ram_mask_] = 0xffff;
 	} else {
 		// Copy mode.
 		printf("!!! Copy %08x\n", pointer_[3]);
diff --git a/Machines/Amiga/Chipset.cpp b/Machines/Amiga/Chipset.cpp
index 0bb00723f..b0c78254b 100644
--- a/Machines/Amiga/Chipset.cpp
+++ b/Machines/Amiga/Chipset.cpp
@@ -241,11 +241,11 @@ template <int cycle, bool stop_if_cpu> bool Chipset::perform_cycle() {
 	//
 	// TODO: figure out how the hard stops factor into this.
 	//
-	// TODO: eliminate hard-coded 300 below. There's clearly something
+	// TODO: eliminate hard-coded 320 below. There's clearly something
 	// (well, probably many things) I don't yet understand about the
 	// fetch window.
 	fetch_horizontal_ |= (cycle << 1) == fetch_window_[0];
-	fetch_horizontal_ &= (cycle << 1) != (fetch_window_[0] + 300);
+	fetch_horizontal_ &= (cycle << 1) != (fetch_window_[0] + 320);
 //	fetch_horizontal_ &= (cycle << 1) != fetch_window_[1];
 	//fetch_window_[1];
 
@@ -253,7 +253,7 @@ template <int cycle, bool stop_if_cpu> bool Chipset::perform_cycle() {
 	if((dma_control_ & BitplaneFlag) == BitplaneFlag) {
 		// TODO: offer a cycle for bitplane collection.
 		// Probably need to indicate odd or even?
-		if(fetch_horizontal_ && fetch_vertical_ && bitplanes_.advance(cycle)) {	// TODO: cycle should be relative to start of collection.
+		if(fetch_horizontal_ && fetch_vertical_ && bitplanes_.advance(cycle - (fetch_window_[0] >> 1))) {	// TODO: cycle should be relative to start of collection.
 			did_fetch_ = true;
 			return false;
 		}
@@ -774,10 +774,6 @@ void Chipset::perform(const CPU::MC68000::Microcycle &cycle) {
 // MARK: - Bitplanes.
 
 bool Chipset::Bitplanes::advance(int cycle) {
-	// TODO: possibly dispatch a BitplaneData.
-	// The chipset has responsibility for applying a delay,
-	// and the pixel-level start/stop boundaries.
-
 #define BIND_CYCLE(offset, plane)								\
 	case offset:												\
 		if(plane_count_ > plane) {								\
@@ -822,6 +818,8 @@ bool Chipset::Bitplanes::advance(int cycle) {
 	}
 
 	return false;
+
+#undef BIND_CYCLE
 }
 
 void Chipset::Bitplanes::do_end_of_line() {