From 66540ff86f59039770476fdfd42c4d543b893bb7 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Mon, 3 Jun 2019 21:56:53 -0400
Subject: [PATCH] Permits end_data only after a begin_data.

---
 Outputs/OpenGL/ScanTarget.cpp | 8 ++++++--
 Outputs/OpenGL/ScanTarget.hpp | 1 +
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/Outputs/OpenGL/ScanTarget.cpp b/Outputs/OpenGL/ScanTarget.cpp
index be44733a6..08e1d4fbc 100644
--- a/Outputs/OpenGL/ScanTarget.cpp
+++ b/Outputs/OpenGL/ScanTarget.cpp
@@ -208,7 +208,8 @@ uint8_t *ScanTarget::begin_data(size_t required_length, size_t required_alignmen
 		return nullptr;
 	}
 
-	// Everything checks out, return the pointer.
+	// Everything checks out, note expectation of a future end_data and return the pointer.
+	data_is_allocated_ = true;
 	vended_write_area_pointer_ = write_pointers_.write_area = TextureAddress(aligned_start_x, output_y);
 	return &write_area_texture_[size_t(write_pointers_.write_area) * data_type_size_];
 
@@ -217,7 +218,7 @@ uint8_t *ScanTarget::begin_data(size_t required_length, size_t required_alignmen
 }
 
 void ScanTarget::end_data(size_t actual_length) {
-	if(allocation_has_failed_) return;
+	if(allocation_has_failed_ || !data_is_allocated_) return;
 
 	// Bookend the start of the new data, to safeguard for precision errors in sampling.
 	memcpy(
@@ -234,6 +235,9 @@ void ScanTarget::end_data(size_t actual_length) {
 		&write_area_texture_[size_t(write_pointers_.write_area - 1) * data_type_size_],
 		&write_area_texture_[size_t(write_pointers_.write_area - 2) * data_type_size_],
 		data_type_size_);
+
+	// Record that no further end_data calls are expected.
+	data_is_allocated_ = false;
 }
 
 void ScanTarget::will_change_owner() {
diff --git a/Outputs/OpenGL/ScanTarget.hpp b/Outputs/OpenGL/ScanTarget.hpp
index 5a5dde05e..ce7d671a7 100644
--- a/Outputs/OpenGL/ScanTarget.hpp
+++ b/Outputs/OpenGL/ScanTarget.hpp
@@ -186,6 +186,7 @@ class ScanTarget: public Outputs::Display::ScanTarget {
 		int vended_write_area_pointer_ = 0;
 
 		// Track allocation failures.
+		bool data_is_allocated_ = false;
 		bool allocation_has_failed_ = false;
 		bool line_allocation_has_failed_ = false;