added option to disable automatic clearing of viewport render buffer

scene/main/viewport.cpp

@@ -972,6 +972,22 @@ bool Viewport::get_render_target_vflip() const{
 	return render_target_vflip;
 }
 
+void Viewport::set_render_target_clear_on_new_frame(bool p_enable) {
+
+	render_target_clear_on_new_frame=p_enable;
+	VisualServer::get_singleton()->viewport_set_render_target_clear_on_new_frame(viewport,p_enable);
+}
+
+bool Viewport::get_render_target_clear_on_new_frame() const{
+
+	return render_target_clear_on_new_frame;
+}
+
+void Viewport::render_target_clear() {
+
+	//render_target_clear=true;
+	VisualServer::get_singleton()->viewport_render_target_clear(viewport);
+}
 
 void Viewport::set_render_target_filter(bool p_enable) {
 
@@ -1264,6 +1280,11 @@ void Viewport::_bind_methods() {
 
 	ObjectTypeDB::bind_method(_MD("set_render_target_vflip","enable"), &Viewport::set_render_target_vflip);
 	ObjectTypeDB::bind_method(_MD("get_render_target_vflip"), &Viewport::get_render_target_vflip);
+	
+	ObjectTypeDB::bind_method(_MD("set_render_target_clear_on_new_frame","enable"), &Viewport::set_render_target_clear_on_new_frame);
+	ObjectTypeDB::bind_method(_MD("get_render_target_clear_on_new_frame"), &Viewport::get_render_target_clear_on_new_frame);
+	
+	ObjectTypeDB::bind_method(_MD("render_target_clear"), &Viewport::render_target_clear);
 
 	ObjectTypeDB::bind_method(_MD("set_render_target_filter","enable"), &Viewport::set_render_target_filter);
 	ObjectTypeDB::bind_method(_MD("get_render_target_filter"), &Viewport::get_render_target_filter);
@@ -1306,6 +1327,7 @@ void Viewport::_bind_methods() {
 	ADD_PROPERTY( PropertyInfo(Variant::BOOL,"transparent_bg"), _SCS("set_transparent_background"), _SCS("has_transparent_background") );
 	ADD_PROPERTY( PropertyInfo(Variant::BOOL,"render_target/enabled"), _SCS("set_as_render_target"), _SCS("is_set_as_render_target") );
 	ADD_PROPERTY( PropertyInfo(Variant::BOOL,"render_target/v_flip"), _SCS("set_render_target_vflip"), _SCS("get_render_target_vflip") );
+	ADD_PROPERTY( PropertyInfo(Variant::BOOL,"render_target/clear_on_new_frame"), _SCS("set_render_target_clear_on_new_frame"), _SCS("get_render_target_clear_on_new_frame") );
 	ADD_PROPERTY( PropertyInfo(Variant::BOOL,"render_target/filter"), _SCS("set_render_target_filter"), _SCS("get_render_target_filter") );
 	ADD_PROPERTY( PropertyInfo(Variant::BOOL,"render_target/gen_mipmaps"), _SCS("set_render_target_gen_mipmaps"), _SCS("get_render_target_gen_mipmaps") );
 	ADD_PROPERTY( PropertyInfo(Variant::INT,"render_target/update_mode",PROPERTY_HINT_ENUM,"Disabled,Once,When Visible,Always"), _SCS("set_render_target_update_mode"), _SCS("get_render_target_update_mode") );
@@ -1344,6 +1366,8 @@ Viewport::Viewport() {
 	render_target_gen_mipmaps=false;
 	render_target=false;
 	render_target_vflip=false;
+	render_target_clear_on_new_frame=true;
+	//render_target_clear=true;
 	render_target_update_mode=RENDER_TARGET_UPDATE_WHEN_VISIBLE;
 	render_target_texture = Ref<RenderTargetTexture>( memnew( RenderTargetTexture(this) ) );
 

scene/main/viewport.h

@@ -114,6 +114,7 @@ friend class RenderTargetTexture;
 
 	bool transparent_bg;
 	bool render_target_vflip;
+	bool render_target_clear_on_new_frame;
 	bool render_target_filter;
 	bool render_target_gen_mipmaps;
 
@@ -220,6 +221,10 @@ public:
 	void set_render_target_vflip(bool p_enable);
 	bool get_render_target_vflip() const;
 
+	void set_render_target_clear_on_new_frame(bool p_enable);
+	bool get_render_target_clear_on_new_frame() const;
+	void render_target_clear();
+
 	void set_render_target_filter(bool p_enable);
 	bool get_render_target_filter() const;
 

servers/visual/visual_server_raster.cpp

@@ -1576,6 +1576,15 @@ void VisualServerRaster::viewport_set_render_target_vflip(RID p_viewport,bool p_
 
 }
 
+void VisualServerRaster::viewport_set_render_target_clear_on_new_frame(RID p_viewport,bool p_enable) {
+
+	Viewport *viewport = viewport_owner.get( p_viewport );
+	ERR_FAIL_COND(!viewport);
+
+	viewport->render_target_clear_on_new_frame=p_enable;
+
+}
+
 void VisualServerRaster::viewport_set_render_target_to_screen_rect(RID p_viewport,const Rect2& p_rect) {
 
 	Viewport *viewport = viewport_owner.get( p_viewport );
@@ -1594,6 +1603,23 @@ bool VisualServerRaster::viewport_get_render_target_vflip(RID p_viewport) const{
 
 }
 
+bool VisualServerRaster::viewport_get_render_target_clear_on_new_frame(RID p_viewport) const{
+
+	const Viewport *viewport = viewport_owner.get( p_viewport );
+	ERR_FAIL_COND_V(!viewport,false);
+
+	return viewport->render_target_clear_on_new_frame;
+
+}
+
+void VisualServerRaster::viewport_render_target_clear(RID p_viewport) {
+
+	Viewport *viewport = viewport_owner.get( p_viewport );
+	ERR_FAIL_COND(!viewport);
+
+	viewport->render_target_clear=true;
+
+}
 
 void VisualServerRaster::viewport_queue_screen_capture(RID p_viewport) {
 
@@ -6605,7 +6631,10 @@ void VisualServerRaster::_draw_viewport(Viewport *p_viewport,int p_ofs_x, int p_
 	} else if (true /*|| !p_viewport->canvas_list.empty()*/){
 
 		//clear the viewport black because of no camera? i seriously should..
-		rasterizer->clear_viewport(clear_color);
+		if (p_viewport->render_target_clear_on_new_frame || p_viewport->render_target_clear) {
+			rasterizer->clear_viewport(clear_color);
+			p_viewport->render_target_clear=false;
+		}
 	}
 
 	if (!p_viewport->hide_canvas) {

servers/visual/visual_server_raster.h

@@ -468,6 +468,8 @@ class VisualServerRaster : public VisualServer {
 		bool transparent_bg;
 		bool queue_capture;
 		bool render_target_vflip;
+		bool render_target_clear_on_new_frame;
+		bool render_target_clear;
 		Image capture;
 
 		bool rendered_in_prev_frame;
@@ -494,7 +496,7 @@ class VisualServerRaster : public VisualServer {
 
 		SelfList<Viewport> update_list;
 
-		Viewport() : update_list(this) { transparent_bg=false; render_target_update_mode=RENDER_TARGET_UPDATE_WHEN_VISIBLE; queue_capture=false; rendered_in_prev_frame=false; render_target_vflip=false;}
+		Viewport() : update_list(this) { transparent_bg=false; render_target_update_mode=RENDER_TARGET_UPDATE_WHEN_VISIBLE; queue_capture=false; rendered_in_prev_frame=false; render_target_vflip=false; render_target_clear_on_new_frame=true; render_target_clear=true;}
 	};
 
 	SelfList<Viewport>::List viewport_update_list;
@@ -957,6 +959,9 @@ public:
 	virtual RID viewport_get_render_target_texture(RID p_viewport) const;
 	virtual void viewport_set_render_target_vflip(RID p_viewport,bool p_enable);
 	virtual bool viewport_get_render_target_vflip(RID p_viewport) const;
+	virtual void viewport_set_render_target_clear_on_new_frame(RID p_viewport,bool p_enable);
+	virtual bool viewport_get_render_target_clear_on_new_frame(RID p_viewport) const;
+	virtual void viewport_render_target_clear(RID p_viewport);
 	virtual void viewport_set_render_target_to_screen_rect(RID p_viewport,const Rect2& p_rect);
 
 	virtual void viewport_queue_screen_capture(RID p_viewport);

servers/visual/visual_server_wrap_mt.h

@@ -967,6 +967,10 @@ public:
 	FUNC2(viewport_set_render_target_vflip,RID,bool);
 	FUNC1RC(bool,viewport_get_render_target_vflip,RID);
 	FUNC2(viewport_set_render_target_to_screen_rect,RID,const Rect2&);
+	
+	FUNC2(viewport_set_render_target_clear_on_new_frame,RID,bool);
+	FUNC1RC(bool,viewport_get_render_target_clear_on_new_frame,RID);
+	FUNC1(viewport_render_target_clear,RID);
 
 	FUNC1(viewport_queue_screen_capture,RID);
 	FUNC1RC(Image,viewport_get_screen_capture,RID);

servers/visual_server.h

@@ -684,6 +684,9 @@ public:
 	virtual RID viewport_get_render_target_texture(RID p_viewport) const=0;
 	virtual void viewport_set_render_target_vflip(RID p_viewport,bool p_enable)=0;
 	virtual bool viewport_get_render_target_vflip(RID p_viewport) const=0;
+	virtual void viewport_set_render_target_clear_on_new_frame(RID p_viewport,bool p_enable)=0;
+	virtual bool viewport_get_render_target_clear_on_new_frame(RID p_viewport) const=0;
+	virtual void viewport_render_target_clear(RID p_viewport)=0;
 
 	virtual void viewport_queue_screen_capture(RID p_viewport)=0;
 	virtual Image viewport_get_screen_capture(RID p_viewport) const=0;