Add a copy shader, which will always be the final stage of output.

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

@@ -1164,6 +1164,7 @@
 		4BD191F52191180E0042E144 /* ScanTarget.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BD191F22191180E0042E144 /* ScanTarget.cpp */; };
 		4BD235B42F27AC680094AFAE /* CompositionShader.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BD235B32F27AC680094AFAE /* CompositionShader.cpp */; };
 		4BD235B72F2C11A40094AFAE /* VertexArray.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BD235B62F2C11A40094AFAE /* VertexArray.cpp */; };
+		4BD235BA2F2C22280094AFAE /* CopyShader.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BD235B92F2C22280094AFAE /* CopyShader.cpp */; };
 		4BD388882239E198002D14B5 /* 68000Tests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4BD388872239E198002D14B5 /* 68000Tests.mm */; };
 		4BD424E02193B5340097291A /* TextureTarget.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BD424DD2193B5340097291A /* TextureTarget.cpp */; };
 		4BD424E62193B5830097291A /* Shader.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BD424E12193B5820097291A /* Shader.cpp */; };
@@ -2466,6 +2467,8 @@
 		4BD235B32F27AC680094AFAE /* CompositionShader.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = CompositionShader.cpp; sourceTree = "<group>"; };
 		4BD235B52F2C11A40094AFAE /* VertexArray.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = VertexArray.hpp; sourceTree = "<group>"; };
 		4BD235B62F2C11A40094AFAE /* VertexArray.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = VertexArray.cpp; sourceTree = "<group>"; };
+		4BD235B82F2C22280094AFAE /* CopyShader.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = CopyShader.hpp; sourceTree = "<group>"; };
+		4BD235B92F2C22280094AFAE /* CopyShader.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = CopyShader.cpp; sourceTree = "<group>"; };
 		4BD388411FE34E010042B588 /* 9918Base.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = 9918Base.hpp; sourceTree = "<group>"; };
 		4BD388872239E198002D14B5 /* 68000Tests.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = 68000Tests.mm; sourceTree = "<group>"; };
 		4BD424DD2193B5340097291A /* TextureTarget.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = TextureTarget.cpp; sourceTree = "<group>"; };
@@ -5383,10 +5386,12 @@
 			isa = PBXGroup;
 			children = (
 				4BD235B32F27AC680094AFAE /* CompositionShader.cpp */,
+				4BD235B92F2C22280094AFAE /* CopyShader.cpp */,
 				4BD191F22191180E0042E144 /* ScanTarget.cpp */,
 				4BD5D2672199148100DDF17D /* ScanTargetGLSLFragments.cpp */,
 				4BA3AF5C2EF252320088C3BC /* API.hpp */,
 				4BD235B22F27AC680094AFAE /* CompositionShader.hpp */,
+				4BD235B82F2C22280094AFAE /* CopyShader.hpp */,
 				4BD191D9219113B80042E144 /* OpenGL.hpp */,
 				4BD191F32191180E0042E144 /* ScanTarget.hpp */,
 				4B961408222760E0001A7BF2 /* Screenshot.hpp */,
@@ -6270,6 +6275,7 @@
 				4B2E86D025D8D8C70024F1E9 /* Keyboard.cpp in Sources */,
 				4B89452F201967B4007DE474 /* StaticAnalyser.cpp in Sources */,
 				4B894531201967B4007DE474 /* StaticAnalyser.cpp in Sources */,
+				4BD235BA2F2C22280094AFAE /* CopyShader.cpp in Sources */,
 				4BB5057B2B962DDF0031C43C /* Electron.cpp in Sources */,
 				4B0ACC2D23775819008902D0 /* IntelligentKeyboard.cpp in Sources */,
 				4B894539201967B4007DE474 /* Tape.cpp in Sources */,

Outputs/OpenGL/CopyShader.cpp

@@ -0,0 +1,90 @@
+//
+//  CopyShader.cpp
+//  Clock Signal Kiosk
+//
+//  Created by Thomas Harte on 29/01/2026.
+//  Copyright © 2026 Thomas Harte. All rights reserved.
+//
+
+#include "CopyShader.hpp"
+
+namespace {
+
+constexpr char vertex_shader[] = R"glsl(
+
+out mediump vec2 coordinate;
+
+void main(void) {
+	float lateral = float(gl_VertexID & 1);
+	float longitudinal = float((gl_VertexID & 2) >> 1);
+
+	gl_Position = vec4)
+		lateral * 2.0 - 1.0,
+		longitudinal * 2.0 - 1.0,
+		0.0,
+		1.0
+	);
+}
+
+)glsl";
+
+
+constexpr char fragment_shader[] = R"glsl(
+
+uniform sampler2D source;
+uniform float brightness;
+uniform float gamma;
+
+in mediump vec2 coordinate;
+
+out lowp vec4 outputColour;
+
+void main(void) {
+	outputColour = texture(source, coordinate);
+
+#ifdef APPLY_BRIGHTNESS
+	outputColour *= brightness;
+#endif
+
+#ifdef APPLY_GAMMA
+	outputColour = pow(outputColour, gamma);
+#endif
+}
+
+)glsl";
+
+}
+
+using namespace Outputs::Display;
+
+OpenGL::Shader OpenGL::copy_shader(
+	const OpenGL::API api,
+	const GLenum source_texture_unit,
+	std::optional<float> brightness,
+	std::optional<float> gamma
+) {
+	std::string prefix;
+
+	if(brightness) {
+		prefix += "#define APPLY_BRIGHTNESS\n";
+	}
+	if(gamma) {
+		prefix += "#define APPLY_GAMMA\n";
+	}
+
+	auto shader = OpenGL::Shader(
+		api,
+		prefix + vertex_shader,
+		prefix + fragment_shader
+	);
+
+	shader.set_uniform("source", GLint(source_texture_unit - GL_TEXTURE0));
+	if(brightness) {
+		shader.set_uniform("brightness", *brightness);
+	}
+	if(gamma) {
+		shader.set_uniform("gamma", *gamma);
+	}
+
+	return shader;
+}

Outputs/OpenGL/CopyShader.hpp

@@ -0,0 +1,28 @@
+//
+//  CopyShader.hpp
+//  Clock Signal Kiosk
+//
+//  Created by Thomas Harte on 29/01/2026.
+//  Copyright © 2026 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include "Outputs/OpenGL/Primitives/Shader.hpp"
+
+#include <optional>
+
+namespace Outputs::Display::OpenGL {
+
+/*!
+	Copies a source texture in its entirety to a destination, optionally applying
+	a change in brightness and a gamma adjustment.
+*/
+Shader copy_shader(
+	API,
+	const GLenum source_texture_unit,
+	std::optional<float> brightness,
+	std::optional<float> gamma
+);
+
+}

cmake/CLK_SOURCES.cmake

@@ -164,6 +164,7 @@ set(CLK_SOURCES
 	Outputs/OpenGL/Primitives/TextureTarget.cpp
 	Outputs/OpenGL/Primitives/VertexArray.cpp
 	Outputs/OpenGL/CompositionShader.cpp
+	Outputs/OpenGL/CopyShader.cpp
 	Outputs/OpenGL/ScanTarget.cpp
 	Outputs/OpenGL/ScanTargetGLSLFragments.cpp
 	Outputs/ScanTarget.cpp