Spotted error was in texture target all along. This now gets as far as showing something a lot like the correct display, but precision is way off. Way off.

OSBindings/Mac/Clock Signal/Base.lproj/ElectronDocument.xib

@@ -31,7 +31,7 @@
             </connections>
         </window>
         <window title="Options" allowsToolTipsWhenApplicationIsInactive="NO" autorecalculatesKeyViewLoop="NO" hidesOnDeactivate="YES" oneShot="NO" releasedWhenClosed="NO" showsToolbarButton="NO" visibleAtLaunch="NO" frameAutosaveName="" animationBehavior="default" id="ZW7-Bw-4RP" customClass="NSPanel">
-            <windowStyleMask key="styleMask" titled="YES" closable="YES" utility="YES" nonactivatingPanel="YES" HUD="YES"/>
+            <windowStyleMask key="styleMask" titled="YES" closable="YES" utility="YES" HUD="YES"/>
             <windowPositionMask key="initialPositionMask" leftStrut="YES" rightStrut="YES" topStrut="YES" bottomStrut="YES"/>
             <rect key="contentRect" x="83" y="102" width="200" height="83"/>
             <rect key="screenRect" x="0.0" y="0.0" width="1366" height="768"/>

Outputs/CRT/CRT.cpp

@@ -77,7 +77,6 @@ CRT::CRT(unsigned int cycles_per_line, unsigned int common_output_divisor, unsig
 CRT::CRT(unsigned int cycles_per_line, unsigned int common_output_divisor, DisplayType displayType, unsigned int buffer_depth) : CRT(common_output_divisor)
 {
 	_openGL_output_builder = std::unique_ptr<OpenGLOutputBuilder>(new OpenGLOutputBuilder(buffer_depth));
-
 	set_new_display_type(cycles_per_line, displayType);
 }
 
@@ -238,6 +237,9 @@ void CRT::advance_cycles(unsigned int number_of_cycles, unsigned int source_divi
 				output_lateral(2) = 1;
 				output_frame_id(0) = output_frame_id(1) = output_frame_id(2) = (uint8_t)_openGL_output_builder->get_current_field();
 
+//				printf("%d", _horizontal_flywheel->get_current_output_position());
+//				if(_is_writing_composite_run) printf("\n"); else printf(" -> ");
+
 				_openGL_output_builder->complete_output_run(3);
 				_is_writing_composite_run ^= true;
 			}

Outputs/CRT/Internals/CRTOpenGL.cpp

@@ -176,6 +176,8 @@ void OpenGLOutputBuilder::draw_frame(unsigned int output_width, unsigned int out
 
 	// upload more source pixel data if any; we'll always resubmit the last line submitted last
 	// time as it may have had extra data appended to it
+	glActiveTexture(GL_TEXTURE0 + first_supplied_buffer_texture_unit);
+	glBindTexture(GL_TEXTURE_2D, textureName);
 	if(_buffer_builder->_next_write_y_position < _buffer_builder->last_uploaded_line)
 	{
 		glTexSubImage2D(	GL_TEXTURE_2D, 0,
@@ -201,8 +203,7 @@ void OpenGLOutputBuilder::draw_frame(unsigned int output_width, unsigned int out
 	{
 		composite_input_shader_program->bind();
 
-//		compositeTexture->bind_framebuffer();
+		compositeTexture->bind_framebuffer();
-		glBindFramebuffer(GL_FRAMEBUFFER, defaultFramebuffer);
 		glBindVertexArray(source_vertex_array);
 
 		glDisable(GL_BLEND);
@@ -230,7 +231,9 @@ void OpenGLOutputBuilder::draw_frame(unsigned int output_width, unsigned int out
 		}
 
 		// transfer to screen
-//		perform_output_stage(output_width, output_height, rgb_shader_program.get());
+		glBindFramebuffer(GL_FRAMEBUFFER, defaultFramebuffer);
+		compositeTexture->bind_texture();
+		perform_output_stage(output_width, output_height, rgb_shader_program.get());
 	}
 	else
 		perform_output_stage(output_width, output_height, rgb_shader_program.get());
@@ -244,6 +247,7 @@ void OpenGLOutputBuilder::draw_frame(unsigned int output_width, unsigned int out
 
 	_input_texture_data = (uint8_t *)glMapBufferRange(GL_PIXEL_UNPACK_BUFFER, 0, _input_texture_array_size, GL_MAP_WRITE_BIT | GL_MAP_UNSYNCHRONIZED_BIT);
 
+//	printf("%04x\n", glGetError());
 	_output_mutex->unlock();
 }
 
@@ -251,16 +255,18 @@ void OpenGLOutputBuilder::perform_output_stage(unsigned int output_width, unsign
 {
 	if(shader)
 	{
-		shader->bind();
+		// definitively establish the viewport
-
-		// update uniforms
-		push_size_uniforms(output_width, output_height);
 		glViewport(0, 0, (GLsizei)output_width, (GLsizei)output_height);
 
 		// Ensure we're back on the output framebuffer, drawing from the output array buffer
 		glBindFramebuffer(GL_FRAMEBUFFER, defaultFramebuffer);
 		glBindVertexArray(output_vertex_array);
 
+		shader->bind();
+
+		// update uniforms
+		push_size_uniforms(output_width, output_height);
+
 		// clear the buffer
 		glClear(GL_COLOR_BUFFER_BIT);
 		glEnable(GL_BLEND);
@@ -426,7 +432,7 @@ char *OpenGLOutputBuilder::get_output_vertex_shader()
 		"uniform vec2 positionConversion;"
 		"uniform vec2 scanNormal;"
 
-		"uniform usampler2D texID;"
+		"uniform sampler2D texID;"
 //		"uniform sampler2D shadowMaskTexID;"
 
 //		"const float shadowMaskMultiple = 600;"
@@ -492,14 +498,18 @@ char *OpenGLOutputBuilder::get_output_fragment_shader(const char *sampling_funct
 
 		"out vec4 fragColour;"
 
-		"uniform usampler2D texID;"
+//		"uniform usampler2D texID;"
+		"uniform sampler2D texID;"
 //		"uniform sampler2D shadowMaskTexID;"
 
 		"\n%s\n"
 
 		"void main(void)"
 		"{"
-			"fragColour = vec4(rgb_sample(texID, srcCoordinatesVarying, iSrcCoordinatesVarying), clamp(alpha, 0.0, 1.0)*sin(lateralVarying));" //
+//			"fragColour = vec4(srcCoordinatesVarying.rg, 0.0, 1.0);" //
+			"fragColour = texture(texID, srcCoordinatesVarying).rgba;" //
+//			"fragColour = vec4(srcCoordinatesVarying.y / 4.0, 0.0, 0.0, 1.0);"//texture(texID, srcCoordinatesVarying).rgba;" //
+//			"fragColour = vec4(rgb_sample(texID, srcCoordinatesVarying, iSrcCoordinatesVarying), clamp(alpha, 0.0, 1.0)*sin(lateralVarying));" //
 		"}"
 	, sampling_function);
 }

Outputs/CRT/Internals/Shader.cpp

@@ -47,6 +47,22 @@ Shader::Shader(const char *vertex_shader, const char *fragment_shader)
 	glAttachShader(_shader_program, vertex);
 	glAttachShader(_shader_program, fragment);
 	glLinkProgram(_shader_program);
+
+#if defined(DEBUG)
+	GLint didLink = 0;
+	glGetProgramiv(_shader_program, GL_LINK_STATUS, &didLink);
+	if(didLink == GL_FALSE)
+	{
+		GLint logLength;
+		glGetProgramiv(_shader_program, GL_INFO_LOG_LENGTH, &logLength);
+		if (logLength > 0) {
+			GLchar *log = (GLchar *)malloc((size_t)logLength);
+			glGetProgramInfoLog(_shader_program, logLength, &logLength, log);
+			printf("Link log:\n%s\n", log);
+			free(log);
+		}
+	}
+#endif
 }
 
 Shader::~Shader()

Outputs/CRT/Internals/TextureTarget.cpp

@@ -17,10 +17,9 @@ TextureTarget::TextureTarget(GLsizei width, GLsizei height) : _width(width), _he
 
 	glGenTextures(1, &_texture);
 	glBindTexture(GL_TEXTURE_2D, _texture);
-
+	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, (GLsizei)width, (GLsizei)height, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
-	uint8_t *emptySpace = new uint8_t[width*height*3];
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
-	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, (GLsizei)width, (GLsizei)height, 0, GL_RGB, GL_UNSIGNED_BYTE, emptySpace);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
-	delete[] emptySpace;
 
 	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, _texture, 0);