Attempt a line output shader.

OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj

@@ -1237,6 +1237,7 @@
 		4BF0BC722973318E00CCA2B5 /* RP5C01.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BF0BC6F2973318E00CCA2B5 /* RP5C01.cpp */; };
 		4BF437EE209D0F7E008CBD6B /* SegmentParser.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BF437EC209D0F7E008CBD6B /* SegmentParser.cpp */; };
 		4BF437EF209D0F7E008CBD6B /* SegmentParser.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BF437EC209D0F7E008CBD6B /* SegmentParser.cpp */; };
+		4BF64D672F33D27B001EB900 /* LineOutputShader.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BF64D662F33D27B001EB900 /* LineOutputShader.cpp */; };
 		4BF701A026FFD32300996424 /* AmigaBlitterTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4BF7019F26FFD32300996424 /* AmigaBlitterTests.mm */; };
 		4BF8D4C82516E27A00BBE21B /* Accelerate.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 4BB8617024E22F4900A00E03 /* Accelerate.framework */; };
 		4BF8D4D5251C11DD00BBE21B /* 65816Storage.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BF8D4D4251C11DD00BBE21B /* 65816Storage.cpp */; };
@@ -2577,6 +2578,8 @@
 		4BF437F0209D112F008CBD6B /* Sector.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Sector.hpp; sourceTree = "<group>"; };
 		4BF4A2D91F534DB300B171F4 /* TargetPlatforms.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = TargetPlatforms.hpp; sourceTree = "<group>"; };
 		4BF52672218E752E00313227 /* ScanTarget.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = ScanTarget.hpp; sourceTree = "<group>"; };
+		4BF64D652F33D27B001EB900 /* LineOutputShader.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = LineOutputShader.hpp; sourceTree = "<group>"; };
+		4BF64D662F33D27B001EB900 /* LineOutputShader.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = LineOutputShader.cpp; sourceTree = "<group>"; };
 		4BF6606A1F281573002CB053 /* ClockReceiver.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = ClockReceiver.hpp; sourceTree = "<group>"; };
 		4BF7019F26FFD32300996424 /* AmigaBlitterTests.mm */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.objcpp; path = AmigaBlitterTests.mm; sourceTree = "<group>"; };
 		4BF8D4CD251C0C9C00BBE21B /* 65816.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = 65816.hpp; sourceTree = "<group>"; };
@@ -5411,12 +5414,14 @@
 				4BD235BF2F312C0C0094AFAE /* CompositionShader.cpp */,
 				4BD235C12F312C0C0094AFAE /* CopyShader.cpp */,
 				4BD235CB2F32A4C80094AFAE /* KernelShaders.cpp */,
+				4BF64D662F33D27B001EB900 /* LineOutputShader.cpp */,
 				4BD235C62F312C3A0094AFAE /* Rectangle.cpp */,
 				4BD235C92F32A2780094AFAE /* CommonAtrributes.hpp */,
 				4BD235BE2F312C0C0094AFAE /* CompositionShader.hpp */,
 				4BD235C02F312C0C0094AFAE /* CopyShader.hpp */,
 				4BD235C82F326A280094AFAE /* DirtyZone.hpp */,
 				4BD235CA2F32A4C80094AFAE /* KernelShaders.hpp */,
+				4BF64D652F33D27B001EB900 /* LineOutputShader.hpp */,
 				4BD235C52F312C3A0094AFAE /* Rectangle.hpp */,
 			);
 			path = Shaders;
@@ -6502,6 +6507,7 @@
 				4B302185208A550100773308 /* DiskII.cpp in Sources */,
 				42EB81292B23AAC300429AF4 /* IMD.cpp in Sources */,
 				4B051CB1267C1CA200CA44E8 /* Keyboard.cpp in Sources */,
+				4BF64D672F33D27B001EB900 /* LineOutputShader.cpp in Sources */,
 				4B8855A72E84D51B00E251DD /* SAA5050.cpp in Sources */,
 				4B0F1BB32602645900B85C66 /* StaticAnalyser.cpp in Sources */,
 				4B055A931FAE85B50060FFFF /* BinaryDump.cpp in Sources */,

Outputs/OpenGL/ScanTarget.cpp

@@ -14,6 +14,7 @@
 #include "Outputs/OpenGL/Shaders/CompositionShader.hpp"
 #include "Outputs/OpenGL/Shaders/CopyShader.hpp"
 #include "Outputs/OpenGL/Shaders/KernelShaders.hpp"
+#include "Outputs/OpenGL/Shaders/LineOutputShader.hpp"
 
 #include <algorithm>
 #include <cassert>
@@ -127,6 +128,7 @@ ScanTarget::ScanTarget(const API api, const GLuint target_framebuffer, const flo
 	unprocessed_line_texture_(api, LineBufferWidth, LineBufferHeight, UnprocessedLineBufferTextureUnit, GL_NEAREST, false),
 	full_display_rectangle_(api, -1.0f, -1.0f, 2.0f, 2.0f),
 	scans_(scan_buffer_),
+	lines_(line_buffer_),
 	dirty_zones_(dirty_zones_buffer_) {
 
 	set_scan_buffer(scan_buffer_.data(), scan_buffer_.size());
@@ -327,8 +329,18 @@ void ScanTarget::setup_pipeline() {
 				dirty_zones_,
 				is_svideo(modals.display_type) ? CompositionTextureUnit : SeparationTextureUnit
 			);
+
+			line_output_shader_ = OpenGL::line_output_shader(
+				api_,
+				buffer_width, 2048,
+				modals.expected_vertical_lines,
+				modals.output_scale.x, modals.output_scale.y,
+				lines_,
+				DemodulationTextureUnit
+			);
 		} else {
 			demodulation_shader_.reset();
+			line_output_shader_.reset();
 		}
 	}
 

Outputs/OpenGL/ScanTarget.hpp

@@ -164,6 +164,7 @@ private:
 	std::array<DirtyZone, 2> dirty_zones_buffer_{};
 
 	VertexArray scans_;
+	VertexArray lines_;
 	VertexArray dirty_zones_;
 
 	Texture source_texture_;
@@ -175,6 +176,7 @@ private:
 	Shader composition_shader_;
 	Shader separation_shader_;
 	Shader demodulation_shader_;
+	Shader line_output_shader_;
 	CopyShader copy_shader_;
 };
 

Outputs/OpenGL/Shaders/CommonAtrributes.hpp

@@ -40,4 +40,14 @@ inline std::vector<std::string> dirty_zone_attributes() {
 	};
 }
 
+inline std::vector<std::string> line_attributes() {
+	return std::vector<std::string>{
+		"lineEndpoint0Position",
+		"lineEndpoint0CyclesSinceRetrace",
+		"lineEndpoint1Position",
+		"lineEndpoint1CyclesSinceRetrace",
+		"lineLine",
+	};
+}
+
 }

Outputs/OpenGL/Shaders/LineOutputShader.cpp

@@ -0,0 +1,125 @@
+//
+//  LineOutputShader.cpp
+//  Clock Signal Kiosk
+//
+//  Created by Thomas Harte on 04/02/2026.
+//  Copyright © 2026 Thomas Harte. All rights reserved.
+//
+
+#include "LineOutputShader.hpp"
+
+#include "CommonAtrributes.hpp"
+#include "Outputs/ScanTargets/BufferingScanTarget.hpp"
+
+namespace {
+
+constexpr char vertex_shader[] = R"glsl(
+
+uniform mediump vec2 sourceSize;
+uniform highp vec2 positionScale;
+uniform mediump float lineHeight;
+
+// TODO: programmable crop should affect scaling via uniforms.
+
+in highp vec2 lineEndpoint0Position;
+in highp float lineEndpoint0CyclesSinceRetrace;
+
+in highp vec2 lineEndpoint1Position;
+in highp float lineEndpoint1CyclesSinceRetrace;
+
+in highp float lineLine;
+
+out mediump vec2 coordinate;
+
+void main(void) {
+	float lateral = float(gl_VertexID & 1);
+	float longitudinal = float((gl_VertexID & 2) >> 1);
+
+	coordinate = vec2(
+		mix(
+			lineEndpoint0CyclesSinceRetrace,
+			lineEndpoint1CyclesSinceRetrace,
+			lateral
+		),
+		lineLine + 0.5
+	) / sourceSize;
+
+	vec2 tangent = normalize(lineEndpoint1Position - lineEndpoint0Position);
+	vec2 normal = vec2(tangent.y, -tangent.x);
+
+	vec2 centre =
+		mix(
+			lineEndpoint0Position,
+			lineEndpoint1Position,
+			lateral
+		) / positionScale;
+	gl_Position =
+		vec4(
+			centre + (longitudinal - 0.5) * normal,
+			0.0,
+			1.0
+		);
+}
+
+)glsl";
+
+constexpr char fragment_shader[] = R"glsl(
+
+uniform lowp sampler2D source;
+in mediump vec2 coordinate;
+
+out lowp vec4 outputColour;
+
+void main(void) {
+	outputColour = texture(source, coordinate);
+}
+
+)glsl";
+
+}
+
+using namespace Outputs::Display;
+
+OpenGL::Shader OpenGL::line_output_shader(
+	const API api,
+	const int source_width,
+	const int source_height,
+	const int expected_vertical_lines,
+	const int scale_x,
+	const int scale_y,
+	const VertexArray &vertex_array,
+	const GLenum source_texture_unit
+) {
+	auto shader = OpenGL::Shader(
+		api,
+		vertex_shader,
+		fragment_shader,
+		line_attributes()
+	);
+
+	BufferingScanTarget::Line line;
+	vertex_array.bind_all();
+	const auto enable = [&](const std::string &name, uint16_t &element, const GLint size) {
+		shader.enable_vertex_attribute_with_pointer(
+			name,
+			size,
+			GL_UNSIGNED_SHORT,
+			GL_FALSE,
+			sizeof(line),
+			reinterpret_cast<void *>((reinterpret_cast<uint8_t *>(&element) - reinterpret_cast<uint8_t *>(&line))),
+			1
+		);
+	};
+	enable("lineEndpoint0Position", line.end_points[0].x, 2);
+	enable("lineEndpoint0CyclesSinceRetrace", line.end_points[0].cycles_since_end_of_horizontal_retrace, 1);
+	enable("lineEndpoint1Position", line.end_points[1].x, 2);
+	enable("lineEndpoin10CyclesSinceRetrace", line.end_points[1].cycles_since_end_of_horizontal_retrace, 1);
+	enable("lineLine", line.line, 1);
+
+	shader.set_uniform("lineHeight", 1.0f / float(expected_vertical_lines));
+	shader.set_uniform("positionScale", float(scale_x), float(scale_y));
+	shader.set_uniform("sourceSize", float(source_width), float(source_height));
+	shader.set_uniform("source", GLint(source_texture_unit - GL_TEXTURE0));
+
+	return shader;
+}

Outputs/OpenGL/Shaders/LineOutputShader.hpp

@@ -0,0 +1,30 @@
+//
+//  LineOutputShader.hpp
+//  Clock Signal Kiosk
+//
+//  Created by Thomas Harte on 04/02/2026.
+//  Copyright © 2026 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include "Outputs/OpenGL/Primitives/VertexArray.hpp"
+#include "Outputs/OpenGL/Primitives/Shader.hpp"
+
+namespace Outputs::Display::OpenGL {
+
+/*!
+	Using `Line`s as input, draws output spans.
+*/
+Shader line_output_shader(
+	API,
+	int source_width,
+	int source_height,
+	int expected_vertical_lines,
+	int scale_x,
+	int scale_y,
+	const VertexArray &,
+	GLenum source_texture_unit
+);
+
+}

Outputs/ScanTargets/BufferingScanTarget.hpp

@@ -74,6 +74,7 @@ public:
 		uint8_t composite_amplitude;
 		uint16_t line;
 	};
+	static_assert(sizeof(Line) == 20);
 
 	/// Provides additional metadata about lines; this is separate because it's unlikely to be of
 	/// interest to the GPU, unlike the fields in Line.

cmake/CLK_SOURCES.cmake

@@ -166,6 +166,7 @@ set(CLK_SOURCES
 	Outputs/OpenGL/Shaders/CompositionShader.cpp
 	Outputs/OpenGL/Shaders/CopyShader.cpp
 	Outputs/OpenGL/Shaders/KernelShaders.cpp
+	Outputs/OpenGL/Shaders/LineOutputShader.cpp
 	Outputs/OpenGL/Shaders/Rectangle.cpp
 	Outputs/OpenGL/ScanTarget.cpp
 	Outputs/OpenGL/ScanTargetGLSLFragments.cpp