From 6025516f9f49455935b5dabfa9fc5e1df73efc77 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sun, 20 Jun 2021 14:31:02 -0400
Subject: [PATCH] Ensure addresses increment even when there's no target for
 pixels.

---
 Machines/Enterprise/Nick.cpp | 19 ++++++++++++++++++-
 Machines/Enterprise/Nick.hpp |  1 +
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/Machines/Enterprise/Nick.cpp b/Machines/Enterprise/Nick.cpp
index 17fc34805..f8272c5fe 100644
--- a/Machines/Enterprise/Nick.cpp
+++ b/Machines/Enterprise/Nick.cpp
@@ -161,6 +161,8 @@ void Nick::run_for(Cycles duration) {
 
 				switch(mode_) {
 					default:
+						assert(false);
+					case Mode::Vsync:
 					break;
 
 					// NB: LSBALT/MSBALT and ALTIND0/ALTIND1 appear to have opposite effects on palette selection.
@@ -178,6 +180,9 @@ void Nick::run_for(Cycles duration) {
 
 						alt_ind_palettes[1] = alt_ind_palettes[0] + ((line_parameters_[2] & 0x40) ? 4 : 0);
 						alt_ind_palettes[3] = alt_ind_palettes[2] + ((line_parameters_[2] & 0x40) ? 4 : 0);
+
+						line_data_per_column_increments_[0] = 1 + (mode_ == Mode::Pixel);
+						line_data_per_column_increments_[1] = 0;
 					break;
 
 					case Mode::CH64:
@@ -192,6 +197,14 @@ void Nick::run_for(Cycles duration) {
 
 						alt_ind_palettes[1] = alt_ind_palettes[0] + ((line_parameters_[3] & 0x80) ? 4 : 0);
 						alt_ind_palettes[3] = alt_ind_palettes[2] + ((line_parameters_[3] & 0x80) ? 4 : 0);
+
+						line_data_per_column_increments_[0] = 1;
+						line_data_per_column_increments_[1] = 0;
+					break;
+
+					case Mode::Attr:
+						line_data_per_column_increments_[0] = 1;
+						line_data_per_column_increments_[1] = 1;
 					break;
 				}
 			}
@@ -284,7 +297,10 @@ void Nick::run_for(Cycles duration) {
 								}
 								columns_remaining -= output_duration;
 							} else {
-								// TODO: advance line pointers.
+								// Ensure line data pointers are advanced as if there hadn't been back pressure on
+								// pixel rendering.
+								line_data_pointer_[0] += columns_remaining * line_data_per_column_increments_[0];
+								line_data_pointer_[1] += columns_remaining * line_data_per_column_increments_[1];
 
 								// Advance pixel pointer, so as to be able to supply something
 								// convincing to the CRT as to the number of samples that would have
@@ -518,6 +534,7 @@ template <int bpp, int index_bits> void Nick::output_character(uint16_t *target,
 		switch(bpp) {
 			default:
 				assert(false);
+				// TODO: other BPPs are supported for character modes, I think.
 			break;
 
 			case 1: {
diff --git a/Machines/Enterprise/Nick.hpp b/Machines/Enterprise/Nick.hpp
index 31cf03be9..cb8f7431b 100644
--- a/Machines/Enterprise/Nick.hpp
+++ b/Machines/Enterprise/Nick.hpp
@@ -77,6 +77,7 @@ class Nick {
 		int bpp_ = 0;
 		int column_size_ = 0;
 		bool interrupt_line_ = true;
+		int line_data_per_column_increments_[2] = {0, 0};
 
 		// An accumulator for border output regions.
 		int border_duration_ = 0;