Allows a CRT machine owner to set the target frame buffer for OpenGL output, breaking the assumption that it'll be zero.

OSBindings/Mac/Clock Signal/Machine/CSMachine.mm

@@ -170,6 +170,7 @@ struct MachineDelegate: CRTMachine::Machine::Delegate, public LockProtectedDeleg
 
 	// Since OS X v10.6, Macs have had a gamma of 2.2.
 	_machine->get_crt()->set_output_gamma(2.2f);
+	_machine->get_crt()->set_target_framebuffer(0);
 }
 
 - (void)drawViewForPixelSize:(CGSize)pixelSize onlyIfDirty:(BOOL)onlyIfDirty {

OSBindings/SDL/main.cpp

@@ -11,6 +11,7 @@
 #include <cstdio>
 
 #include <SDL2/SDL.h>
+#include <SDL2/SDL_opengl.h>
 
 #include "../../StaticAnalyser/StaticAnalyser.hpp"
 #include "../../Machines/Utility/MachineForTarget.hpp"
@@ -175,6 +176,9 @@ int main(int argc, char *argv[]) {
 	SDL_GLContext gl_context = SDL_GL_CreateContext(window);
 	SDL_GL_MakeCurrent(window, gl_context);
 
+	GLint target_framebuffer = 0;
+	glGetIntegerv(GL_FRAMEBUFFER_BINDING, &target_framebuffer);
+
 	// For vanilla SDL purposes, assume system ROMs can be found in one of:
 	//
 	//	/usr/local/share/CLK/[system]; or
@@ -221,6 +225,7 @@ int main(int argc, char *argv[]) {
 	// Setup output, assuming a CRT machine for now, and prepare a best-effort updater.
 	machine->crt_machine()->setup_output(4.0 / 3.0);
 	machine->crt_machine()->get_crt()->set_output_gamma(2.2f);
+	machine->crt_machine()->get_crt()->set_target_framebuffer(target_framebuffer);
 
 	// For now, lie about audio output intentions.
 	auto speaker = machine->crt_machine()->get_speaker();

Outputs/CRT/CRT.hpp

@@ -241,6 +241,13 @@ class CRT {
 			openGL_output_builder_.draw_frame(output_width, output_height, only_if_dirty);
 		}
 
+		/*! Sets the OpenGL framebuffer to which output is drawn. */
+		inline void set_target_framebuffer(GLint framebuffer) {
+			enqueue_openGL_function( [framebuffer, this] {
+				openGL_output_builder_.set_target_framebuffer(framebuffer);
+			});
+		}
+
 		/*!	Sets the gamma exponent for the simulated screen. */
 		void set_input_gamma(float gamma);
 

Outputs/CRT/Internals/CRTOpenGL.cpp

@@ -75,6 +75,10 @@ bool OpenGLOutputBuilder::get_is_television_output() {
 	return output_device_ == OutputDevice::Television || !rgb_input_shader_program_;
 }
 
+void OpenGLOutputBuilder::set_target_framebuffer(GLint target_framebuffer) {
+	target_framebuffer_ = target_framebuffer;
+}
+
 void OpenGLOutputBuilder::draw_frame(unsigned int output_width, unsigned int output_height, bool only_if_dirty) {
 	// lock down any other draw_frames
 	draw_mutex_.lock();
@@ -219,7 +223,7 @@ void OpenGLOutputBuilder::draw_frame(unsigned int output_width, unsigned int out
 
 	// copy framebuffer to the intended place
 	glDisable(GL_BLEND);
-	glBindFramebuffer(GL_FRAMEBUFFER, 0);
+	glBindFramebuffer(GL_FRAMEBUFFER, static_cast<GLuint>(target_framebuffer_));
 	glViewport(0, 0, (GLsizei)output_width, (GLsizei)output_height);
 
 	glActiveTexture(pixel_accumulation_texture_unit);

Outputs/CRT/Internals/CRTOpenGL.hpp

@@ -50,6 +50,7 @@ class OpenGLOutputBuilder {
 		// Other things the caller may have provided.
 		std::string composite_shader_;
 		std::string rgb_shader_;
+		GLint target_framebuffer_ = 0;
 
 		// Methods used by the OpenGL code
 		void prepare_output_shader();
@@ -146,6 +147,7 @@ class OpenGLOutputBuilder {
 				composite_src_output_y_++;
 		}
 	
+		void set_target_framebuffer(GLint target_framebuffer);
 		void draw_frame(unsigned int output_width, unsigned int output_height, bool only_if_dirty);
 		void set_openGL_context_will_change(bool should_delete_resources);
 		void set_composite_sampling_function(const std::string &shader);