From c5d8d9127b501294ebba04ca6d584eab68264bf7 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sun, 21 Jun 2020 18:25:38 -0400
Subject: [PATCH] Rejigs ScanTarget relationship from pull to push, so it can
 be set whenever it is safe.

---
 OSBindings/Qt/mainwindow.cpp       |  2 +-
 OSBindings/Qt/scantargetwidget.cpp | 32 +++++++++++++++++++++---------
 OSBindings/Qt/scantargetwidget.h   |  7 ++++++-
 3 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/OSBindings/Qt/mainwindow.cpp b/OSBindings/Qt/mainwindow.cpp
index 03eec545c..781a2a007 100644
--- a/OSBindings/Qt/mainwindow.cpp
+++ b/OSBindings/Qt/mainwindow.cpp
@@ -217,7 +217,7 @@ void MainWindow::launchMachine() {
 			// TODO: in the future, hypothetically, deal with non-scan producers.
 			const auto scan_producer = machine->scan_producer();
 			if(scan_producer) {
-				scan_producer->set_scan_target(ui->openGLWidget->getScanTarget());
+				ui->openGLWidget->setScanProducer(scan_producer);
 			}
 
 			// Install audio output if required.
diff --git a/OSBindings/Qt/scantargetwidget.cpp b/OSBindings/Qt/scantargetwidget.cpp
index 4d2804008..a9aab5e32 100644
--- a/OSBindings/Qt/scantargetwidget.cpp
+++ b/OSBindings/Qt/scantargetwidget.cpp
@@ -20,7 +20,26 @@ void ScanTargetWidget::initializeGL() {
 
 void ScanTargetWidget::paintGL() {
 	glClear(GL_COLOR_BUFFER_BIT);
-	if(isConnected) {
+
+	// Gmynastics ahoy: if a producer has been specified or previously connected then:
+	//
+	//	(i) if it's a new producer, generate a new scan target and pass it on;
+	//	(ii) in any case, check whether the underlyiung framebuffer has changed; and
+	//	(iii) draw.
+	//
+	// The slightly convoluted scan target forwarding arrangement works around an issue
+	// with QOpenGLWidget under macOS, which I did not fully diagnose, in which creating
+	// a scan target in ::initializeGL did not work (and no other arrangement really works
+	// with regard to starting up).
+	if(isConnected || producer) {
+		if(producer) {
+			isConnected = true;
+			framebuffer = defaultFramebufferObject();
+			scanTarget = std::make_unique<Outputs::Display::OpenGL::ScanTarget>(framebuffer);
+			producer->set_scan_target(scanTarget.get());
+			producer = nullptr;
+		}
+
 		// Qt reserves the right to change the framebuffer object due to window resizes or if setParent is called;
 		// therefore check whether it has changed.
 		const auto newFramebuffer = defaultFramebufferObject();
@@ -52,12 +71,7 @@ void ScanTargetWidget::resizeGL(int w, int h) {
 	glViewport(0, 0, w, h);
 }
 
-Outputs::Display::OpenGL::ScanTarget *ScanTargetWidget::getScanTarget() {
-	makeCurrent();
-	if(!scanTarget) {
-		isConnected = true;
-		framebuffer = defaultFramebufferObject();
-		scanTarget = std::make_unique<Outputs::Display::OpenGL::ScanTarget>(framebuffer);
-	}
-	return scanTarget.get();
+void ScanTargetWidget::setScanProducer(MachineTypes::ScanProducer *producer) {
+	this->producer = producer;
+	repaint();
 }
diff --git a/OSBindings/Qt/scantargetwidget.h b/OSBindings/Qt/scantargetwidget.h
index e3204707e..520df2153 100644
--- a/OSBindings/Qt/scantargetwidget.h
+++ b/OSBindings/Qt/scantargetwidget.h
@@ -4,6 +4,8 @@
 #include <QOpenGLWidget>
 
 #include "../../Outputs/OpenGL/ScanTarget.hpp"
+#include "../../Machines/ScanProducer.hpp"
+
 #include "../../ClockReceiver/VSyncPredictor.hpp"
 
 class ScanTargetWidget : public QOpenGLWidget
@@ -12,7 +14,9 @@ class ScanTargetWidget : public QOpenGLWidget
 		ScanTargetWidget(QWidget *parent = nullptr);
 		~ScanTargetWidget();
 
-		Outputs::Display::OpenGL::ScanTarget *getScanTarget();
+		// Sets the current scan producer; this scan producer will be
+		// handed a suitable scan target as soon as one exists.
+		void setScanProducer(MachineTypes::ScanProducer *);
 
 	protected:
 		void initializeGL() override;
@@ -26,6 +30,7 @@ class ScanTargetWidget : public QOpenGLWidget
 		Time::VSyncPredictor vsyncPredictor;
 		bool isConnected = false;
 		GLuint framebuffer = 0;
+		MachineTypes::ScanProducer *producer = nullptr;
 
 	private slots:
 		void vsync();