Added the option for both intermediate and output shaders to use only a portion of the input/output texture; made an attempt to pick an appropriate proportion in order to align signal sampling with the colour subcarrier.

Outputs/CRT/Internals/CRTOpenGL.cpp

@@ -381,11 +381,40 @@ void OpenGLOutputBuilder::set_timing_uniforms()
 		extends = true;
 	}
 
-	if(output_shader_program_) output_shader_program_->set_timing(height_of_display_, cycles_per_line_, horizontal_scan_period_, vertical_scan_period_, vertical_period_divider_);
-
 	float colour_subcarrier_frequency = (float)colour_cycle_numerator_ / (float)colour_cycle_denominator_;
-	if(composite_separation_filter_program_)			composite_separation_filter_program_->set_separation_frequency(cycles_per_line_, colour_subcarrier_frequency);
-	if(composite_y_filter_shader_program_)				composite_y_filter_shader_program_->set_filter_coefficients(cycles_per_line_, colour_subcarrier_frequency * 0.25f);
-	if(composite_chrominance_filter_shader_program_)	composite_chrominance_filter_shader_program_->set_filter_coefficients(cycles_per_line_, colour_subcarrier_frequency * 0.5f);
-	if(rgb_filter_shader_program_)						rgb_filter_shader_program_->set_filter_coefficients(cycles_per_line_, (float)input_frequency_ * 0.5f);
+	float output_width = ((float)colour_cycle_numerator_ * 4.0f) / (float)(colour_cycle_denominator_ * IntermediateBufferWidth);
+
+	if(composite_separation_filter_program_)
+	{
+		composite_separation_filter_program_->set_width_scalers(output_width, output_width);
+		composite_separation_filter_program_->set_separation_frequency(cycles_per_line_, colour_subcarrier_frequency);
+	}
+	if(composite_y_filter_shader_program_)
+	{
+		composite_y_filter_shader_program_->set_width_scalers(output_width, output_width);
+		composite_y_filter_shader_program_->set_filter_coefficients(cycles_per_line_, colour_subcarrier_frequency * 0.25f);
+	}
+	if(composite_chrominance_filter_shader_program_)
+	{
+		composite_chrominance_filter_shader_program_->set_width_scalers(output_width, output_width);
+		composite_chrominance_filter_shader_program_->set_filter_coefficients(cycles_per_line_, colour_subcarrier_frequency * 0.5f);
+	}
+	if(rgb_filter_shader_program_)
+	{
+		rgb_filter_shader_program_->set_width_scalers(output_width, output_width);
+		rgb_filter_shader_program_->set_filter_coefficients(cycles_per_line_, (float)input_frequency_ * 0.5f);
+	}
+	if(output_shader_program_)
+	{
+		output_shader_program_->set_input_width_scaler(output_width);
+		output_shader_program_->set_timing(height_of_display_, cycles_per_line_, horizontal_scan_period_, vertical_scan_period_, vertical_period_divider_);
+	}
+	if(composite_input_shader_program_)
+	{
+		composite_input_shader_program_->set_width_scalers(1.0f, output_width);
+	}
+	if(rgb_input_shader_program_)
+	{
+		rgb_input_shader_program_->set_width_scalers(1.0f, output_width);
+	}
 }

Outputs/CRT/Internals/Shaders/IntermediateShader.cpp

@@ -45,6 +45,7 @@ std::unique_ptr<IntermediateShader> IntermediateShader::make_shader(const char *
 		"uniform float extension;"
 		"uniform %s texID;"
 		"uniform float offsets[5];"
+		"uniform vec2 widthScalers;"
 
 		"out vec2 phaseAndAmplitudeVarying;"
 		"out vec2 inputPositionsVarying[11];"
@@ -59,8 +60,8 @@ std::unique_ptr<IntermediateShader> IntermediateShader::make_shader(const char *
 			// inputPosition.x is either inputStart.x or ends.x, depending on whether it is on the left or the right;
 			// outputPosition.x is either outputStart.x or ends.y;
 			// .ys are inputStart.y and outputStart.y respectively
-			"vec2 inputPosition = vec2(mix(inputStart.x, ends.x, extent), inputStart.y);"
-			"vec2 outputPosition = vec2(mix(outputStart.x, ends.y, extent), outputStart.y);"
+			"vec2 inputPosition = vec2(mix(inputStart.x, ends.x, extent)*widthScalers[0], inputStart.y);"
+			"vec2 outputPosition = vec2(mix(outputStart.x, ends.y, extent)*widthScalers[1], outputStart.y);"
 
 			// extension is the amount to extend both the input and output by to add a full colour cycle at each end
 			"vec2 extensionVector = vec2(extension, 0.0) * 2.0 * (extent - 0.5);"
@@ -477,3 +478,8 @@ void IntermediateShader::set_colour_conversion_matrices(float *fromRGB, float *t
 	set_uniform_matrix("lumaChromaToRGB", 3, false, toRGB);
 	set_uniform_matrix("rgbToLumaChroma", 3, false, fromRGB);
 }
+
+void IntermediateShader::set_width_scalers(float input_scaler, float output_scaler)
+{
+	set_uniform("widthScalers", input_scaler, output_scaler);
+}

Outputs/CRT/Internals/Shaders/IntermediateShader.hpp

@@ -88,6 +88,12 @@ public:
 	*/
 	void set_colour_conversion_matrices(float *fromRGB, float *toRGB);
 
+	/*!
+		Sets the proportions of the input and output areas that should be considered the whole width — 1.0 means use all available
+		space, 0.5 means use half, etc.
+	*/
+	void set_width_scalers(float input_scaler, float output_scaler);
+
 private:
 	static std::unique_ptr<IntermediateShader> make_shader(const char *fragment_shader, bool use_usampler, bool input_is_inputPosition);
 };

Outputs/CRT/Internals/Shaders/OutputShader.cpp

@@ -38,6 +38,7 @@ std::unique_ptr<OutputShader> OutputShader::make_shader(const char *fragment_met
 		"uniform vec2 positionConversion;"
 		"uniform vec2 scanNormal;"
 		"uniform %s texID;"
+		"uniform float inputScaler;"
 
 		"out float lateralVarying;"
 		"out vec2 srcCoordinatesVarying;"
@@ -54,7 +55,7 @@ std::unique_ptr<OutputShader> OutputShader::make_shader(const char *fragment_met
 			"vec2 vSrcCoordinates = vec2(x, vertical.y);"
 			"ivec2 textureSize = textureSize(texID, 0);"
 			"iSrcCoordinatesVarying = vSrcCoordinates;"
-			"srcCoordinatesVarying = vec2(vSrcCoordinates.x / textureSize.x, (vSrcCoordinates.y + 0.5) / textureSize.y);"
+			"srcCoordinatesVarying = vec2(inputScaler * vSrcCoordinates.x / textureSize.x, (vSrcCoordinates.y + 0.5) / textureSize.y);"
 
 			"vec2 vPosition = vec2(x, vertical.x);"
 			"vec2 floatingPosition = (vPosition / positionConversion) + lateral * scanNormal;"
@@ -117,3 +118,8 @@ void OutputShader::set_timing(unsigned int height_of_display, unsigned int cycle
 	set_uniform("scanNormal", scan_normal[0], scan_normal[1]);
 	set_uniform("positionConversion", (GLfloat)horizontal_scan_period, (GLfloat)vertical_scan_period / (GLfloat)vertical_period_divider);
 }
+
+void OutputShader::set_input_width_scaler(float input_scaler)
+{
+	set_uniform("inputScaler", input_scaler);
+}

Outputs/CRT/Internals/Shaders/OutputShader.hpp

@@ -58,6 +58,12 @@ public:
 		to occur upon the next `bind`.
 	*/
 	void set_timing(unsigned int height_of_display, unsigned int cycles_per_line, unsigned int horizontal_scan_period, unsigned int vertical_scan_period, unsigned int vertical_period_divider);
+
+	/*!
+		Sets the proportion of the input area that should be considered the whole width — 1.0 means use all available
+		space, 0.5 means use half, etc.
+	*/
+	void set_input_width_scaler(float input_scaler);
 };
 
 }

Outputs/CRT/Internals/Shaders/Shader.cpp

@@ -156,7 +156,8 @@ void Shader::set_uniform(const std::string &name, GLint value1, GLint value2)
 void Shader::set_uniform(const std::string &name, GLfloat value1, GLfloat value2)
 {
 	enqueue_function([name, value1, value2, this] {
-		glUniform2f(location(), value1, value2);
+		GLint location = location();
+		glUniform2f(location, value1, value2);
 	});
 }