Fix window_res related bugs (#6753)

Author: BMagnu

code/graphics/opengl/gropengl.cpp

@@ -130,6 +130,8 @@ void gr_opengl_flip()
 	if (Cmdline_gl_finish)
 		glFinish();
 
+	Assertion(GL_state.ValidForFlip(), "OpenGL state is invalid!");
+
 	current_viewport->swapBuffers();
 
 	opengl_tcache_frame();
@@ -278,7 +280,11 @@ void gr_opengl_print_screen(const char *filename)
 
     _mkdir(os_get_config_path("screenshots").c_str());
 
-//	glReadBuffer(GL_FRONT);
+	GL_state.PushFramebufferState();
+	GL_state.BindFrameBuffer(Cmdline_window_res ? Back_framebuffer : 0, GL_FRAMEBUFFER);
+
+	//Reading from the front buffer here seems to no longer work correctly; that just reads back all zeros
+	glReadBuffer(Cmdline_window_res ? GL_COLOR_ATTACHMENT0 : GL_FRONT);
 
 	// now for the data
 	if (Use_PBOs) {
@@ -292,7 +298,6 @@ void gr_opengl_print_screen(const char *filename)
 		glBindBuffer(GL_PIXEL_PACK_BUFFER, pbo);
 		glBufferData(GL_PIXEL_PACK_BUFFER, (gr_screen.max_w * gr_screen.max_h * 4), NULL, GL_STATIC_READ);
 
-		glReadBuffer(GL_FRONT);
 		glReadPixels(0, 0, gr_screen.max_w, gr_screen.max_h, GL_RGBA, GL_UNSIGNED_INT_8_8_8_8_REV, NULL);
 
 		// map the image data so that we can save it to file
@@ -319,6 +324,8 @@ void gr_opengl_print_screen(const char *filename)
 		glDeleteBuffers(1, &pbo);
 	}
 
+	GL_state.PopFramebufferState();
+
 	if (pixels != NULL) {
 		vm_free(pixels);
 	}
@@ -329,6 +336,12 @@ SCP_string gr_opengl_blob_screen()
 	GLubyte* pixels = nullptr;
 	GLuint pbo = 0;
 
+	GL_state.PushFramebufferState();
+	GL_state.BindFrameBuffer(Cmdline_window_res ? Back_framebuffer : 0, GL_FRAMEBUFFER);
+
+	//Reading from the front buffer here seems to no longer work correctly; that just reads back all zeros
+	glReadBuffer(Cmdline_window_res ? GL_COLOR_ATTACHMENT0 : GL_FRONT);
+
 	// now for the data
 	if (Use_PBOs) {
 		Assert(!pbo);
@@ -341,7 +354,6 @@ SCP_string gr_opengl_blob_screen()
 		glBindBuffer(GL_PIXEL_PACK_BUFFER, pbo);
 		glBufferData(GL_PIXEL_PACK_BUFFER, (gr_screen.max_w * gr_screen.max_h * 4), NULL, GL_STATIC_READ);
 
-		glReadBuffer(GL_FRONT);
 		glReadPixels(0, 0, gr_screen.max_w, gr_screen.max_h, GL_RGBA, GL_UNSIGNED_INT_8_8_8_8_REV, NULL);
 
 		// map the image data so that we can save it to file
@@ -367,6 +379,8 @@ SCP_string gr_opengl_blob_screen()
 		glDeleteBuffers(1, &pbo);
 	}
 
+	GL_state.PopFramebufferState();
+
 	if (pixels != nullptr) {
 		vm_free(pixels);
 	}
@@ -618,7 +632,7 @@ void gr_opengl_get_region(int  /*front*/, int w, int h, ubyte *data)
 
 }
 
-int gr_opengl_save_screen()
+int  gr_opengl_save_screen()
 {
 	int i;
 	ubyte *sptr = NULL, *dptr = NULL;
@@ -640,7 +654,12 @@ int gr_opengl_save_screen()
 	}
 
 	GLboolean save_state = GL_state.DepthTest(GL_FALSE);
-	glReadBuffer(GL_FRONT_LEFT);
+
+	GL_state.PushFramebufferState();
+	GL_state.BindFrameBuffer(Cmdline_window_res ? Back_framebuffer : 0, GL_FRAMEBUFFER);
+
+	//Reading from the front buffer here seems to no longer work correctly; that just reads back all zeros
+	glReadBuffer(Cmdline_window_res ? GL_COLOR_ATTACHMENT0 : GL_FRONT);
 
 	if ( Use_PBOs ) {
 		GLubyte *pixels = NULL;
@@ -713,6 +732,7 @@ int gr_opengl_save_screen()
 		GL_saved_screen_id = bm_create(32, gr_screen.max_w, gr_screen.max_h, GL_saved_screen, 0);
 	}
 
+	GL_state.PopFramebufferState();
 	GL_state.DepthTest(save_state);
 
 	return GL_saved_screen_id;

code/graphics/opengl/gropenglstate.cpp

@@ -193,7 +193,7 @@ void opengl_state::init()
 	current_program = 0;
 	glUseProgram(0);
 
-	current_framebuffer = 0;
+	current_framebuffer = {0, 0};
 	glBindFramebuffer(GL_FRAMEBUFFER, 0);
 
 	framebuffer_stack.clear();
@@ -552,22 +552,56 @@ bool opengl_state::IsCurrentProgram(GLuint program) {
 	return current_program == program;
 }
 void opengl_state::BindFrameBuffer(GLuint name, GLenum mode) {
-	if (current_framebuffer != name) {
-		glBindFramebuffer(mode, name);
-		current_framebuffer = name;
+	switch(mode) {
+		case GL_FRAMEBUFFER:
+			if (current_framebuffer.first != current_framebuffer.second || current_framebuffer.first != name) {
+				glBindFramebuffer(mode, name);
+				current_framebuffer = {name, name};
+			}
+			break;
+		case GL_READ_FRAMEBUFFER:
+			if (current_framebuffer.first != name) {
+				glBindFramebuffer(mode, name);
+				current_framebuffer.first = name;
+			}
+			break;
+		case GL_DRAW_FRAMEBUFFER:
+			if (current_framebuffer.second != name) {
+				glBindFramebuffer(mode, name);
+				current_framebuffer.second = name;
+			}
+			break;
+		default:
+			UNREACHABLE("Invalid BindFrameBuffer mode!");
+	}
+}
+void opengl_state::BindFrameBufferBoth(GLuint read, GLuint draw) {
+	if (read != current_framebuffer.first) {
+		glBindFramebuffer(GL_READ_FRAMEBUFFER, read);
+		current_framebuffer.first = read;
+	}
+	if (draw != current_framebuffer.second) {
+		glBindFramebuffer(GL_DRAW_FRAMEBUFFER, draw);
+		current_framebuffer.second = draw;
 	}
 }
 void opengl_state::PushFramebufferState() {
 	framebuffer_stack.push_back(current_framebuffer);
 }
 void opengl_state::PopFramebufferState() {
-	Assertion(framebuffer_stack.size() > 0, "Tried to pop the framebuffer state stack while it was empty!");
+	Assertion(!framebuffer_stack.empty(), "Tried to pop the framebuffer state stack while it was empty!");
 
-	auto restoreBuffer = framebuffer_stack.back();
+	auto [restoreBufferRead, restoreBufferDraw] = framebuffer_stack.back();
 	framebuffer_stack.pop_back();
 
-	BindFrameBuffer(restoreBuffer);
+	BindFrameBufferBoth(restoreBufferRead, restoreBufferDraw);
 }
+
+bool opengl_state::ValidForFlip() const {
+	//Check everything that may put the state into an invalid state for rendering
+	return framebuffer_stack.empty() && current_framebuffer.first == 0 && current_framebuffer.second == 0;
+}
+
 void opengl_state::BindVertexArray(GLuint vao) {
 	if (current_vao == vao) {
 		return;

code/graphics/opengl/gropenglstate.h

@@ -241,9 +241,9 @@ class opengl_state
 
 		GLuint current_program;
 
-		// The framebuffer state actually consists of draw and read buffers but we only use both at the same time
-		GLuint current_framebuffer;
-		SCP_vector<GLuint> framebuffer_stack;
+		// The first is the read buffer, the second is the draw buffer
+		std::pair<GLuint, GLuint> current_framebuffer;
+		SCP_vector<std::pair<GLuint, GLuint>> framebuffer_stack;
 
 		GLuint current_vao = 0;
 	public:
@@ -291,11 +291,14 @@ class opengl_state
 		bool IsCurrentProgram(GLuint program);
 
 		void BindFrameBuffer(GLuint name, GLenum mode = GL_FRAMEBUFFER);
+		void BindFrameBufferBoth(GLuint read, GLuint draw);
 
 		void PushFramebufferState();
 		void PopFramebufferState();
 
 		void BindVertexArray(GLuint vao);
+
+		bool ValidForFlip() const;
 };
 
 inline GLenum opengl_state::FrontFaceValue(GLenum new_val)