From 83231821cfc8d3bb09db9893040eb01ebb4b7201 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 5 Feb 2026 17:12:39 -0500
Subject: [PATCH] Introduce line blending.

---
 .../xcschemes/Clock Signal Kiosk.xcscheme             |  6 +++---
 Outputs/OpenGL/ScanTarget.cpp                         |  5 ++++-
 Outputs/OpenGL/Shaders/LineOutputShader.cpp           | 11 +++++++----
 Outputs/OpenGL/Shaders/LineOutputShader.hpp           |  1 +
 4 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal Kiosk.xcscheme b/OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal Kiosk.xcscheme
index 2cf3e5c7b..20bb6f405 100644
--- a/OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal Kiosk.xcscheme	
+++ b/OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal Kiosk.xcscheme	
@@ -58,7 +58,7 @@
          </CommandLineArgument>
          <CommandLineArgument
             argument = "&quot;/Users/thomasharte/Library/Mobile Documents/com~apple~CloudDocs/Soft/Master System/Alex Kidd in Miracle World (US).sms&quot;"
-            isEnabled = "NO">
+            isEnabled = "YES">
          </CommandLineArgument>
          <CommandLineArgument
             argument = "&quot;/Users/thomasharte/Library/Mobile\ Documents/com\~apple\~CloudDocs/Soft/Archimedes/Lemmings.adf&quot;"
@@ -66,11 +66,11 @@
          </CommandLineArgument>
          <CommandLineArgument
             argument = "--new=amstradcpc"
-            isEnabled = "YES">
+            isEnabled = "NO">
          </CommandLineArgument>
          <CommandLineArgument
             argument = "--display=CompositeColour"
-            isEnabled = "NO">
+            isEnabled = "YES">
          </CommandLineArgument>
          <CommandLineArgument
             argument = "/Users/thomasharte/Downloads/Program/Program.prg"
diff --git a/Outputs/OpenGL/ScanTarget.cpp b/Outputs/OpenGL/ScanTarget.cpp
index 130061199..670032ea3 100644
--- a/Outputs/OpenGL/ScanTarget.cpp
+++ b/Outputs/OpenGL/ScanTarget.cpp
@@ -244,6 +244,7 @@ void ScanTarget::setup_pipeline() {
 				modals.expected_vertical_lines,
 				modals.output_scale.x,
 				modals.output_scale.y,
+				0.64f,
 				lines_,
 				DemodulationTextureUnit
 			);
@@ -415,7 +416,7 @@ void ScanTarget::update(const int output_width, const int output_height) {
 				output_buffer_height,
 				OutputTextureUnit,
 				GL_NEAREST,
-				false	// TODO: should probably be true, if I'm going to use stencil (?)
+				true
 			);
 		}
 
@@ -493,7 +494,9 @@ void ScanTarget::update(const int output_width, const int output_height) {
 			// Output new lines.
 			line_output_shader_.bind();
 			output_buffer_.bind_framebuffer();
+			test_gl([&]{ glEnable(GL_BLEND); });
 			test_gl([&]{ glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, GLsizei(new_lines)); });
+			test_gl([&]{ glDisable(GL_BLEND); });
 
 			// TODO: end-of-frame blanking of untouched areas.
 
diff --git a/Outputs/OpenGL/Shaders/LineOutputShader.cpp b/Outputs/OpenGL/Shaders/LineOutputShader.cpp
index 9f2ee908e..d716cc83a 100644
--- a/Outputs/OpenGL/Shaders/LineOutputShader.cpp
+++ b/Outputs/OpenGL/Shaders/LineOutputShader.cpp
@@ -66,12 +66,13 @@ void main(void) {
 constexpr char fragment_shader[] = R"glsl(
 
 uniform lowp sampler2D source;
+uniform lowp float alpha;
 in mediump vec2 coordinate;
 
 out lowp vec4 outputColour;
 
 void main(void) {
-	outputColour = texture(source, coordinate);
+	outputColour = texture(source, coordinate) * vec4(1.0, 1.0, 1.0, alpha);
 }
 
 )glsl";
@@ -88,6 +89,7 @@ OpenGL::Shader OpenGL::line_output_shader(
 	const int expected_vertical_lines,
 	const int scale_x,
 	const int scale_y,
+	const float alpha,
 	const VertexArray &vertex_array,
 	const GLenum source_texture_unit
 ) {
@@ -117,10 +119,11 @@ OpenGL::Shader OpenGL::line_output_shader(
 	enable("lineEndpoint1CyclesSinceRetrace", line.end_points[1].cycles_since_end_of_horizontal_retrace, 1);
 	enable("lineLine", line.line, 1);
 
-	shader.set_uniform("lineHeight", 1.05f / float(expected_vertical_lines));
-	shader.set_uniform("positionScale", float(scale_x), float(scale_y));
-	shader.set_uniform("sourceSize", float(source_width) / cycle_multiplier, float(source_height));
+	shader.set_uniform("lineHeight", 1.05f / GLfloat(expected_vertical_lines));
+	shader.set_uniform("positionScale", GLfloat(scale_x), GLfloat(scale_y));
+	shader.set_uniform("sourceSize", GLfloat(source_width) / cycle_multiplier, GLfloat(source_height));
 	shader.set_uniform("source", GLint(source_texture_unit - GL_TEXTURE0));
+	shader.set_uniform("alpha", GLfloat(alpha));
 
 	return shader;
 }
diff --git a/Outputs/OpenGL/Shaders/LineOutputShader.hpp b/Outputs/OpenGL/Shaders/LineOutputShader.hpp
index 891044973..2f0104bdd 100644
--- a/Outputs/OpenGL/Shaders/LineOutputShader.hpp
+++ b/Outputs/OpenGL/Shaders/LineOutputShader.hpp
@@ -24,6 +24,7 @@ Shader line_output_shader(
 	int expected_vertical_lines,
 	int scale_x,
 	int scale_y,
+	float alpha,
 	const VertexArray &,
 	GLenum source_texture_unit
 );