Memory saving for large renders:

New option "Save Buffers", in first Output panel of renderbuttons, will not
allocate all render buffers, but instead save the rendered tiles to exr.
For each scene rendered, a single exr file then is created.
After rendering, the files get read, and only then the memory allocation is
done.

The exr files are saved in the temp dir (from user settings), and have
names derived from the filename+scene name. That way these buffers remain
relatively unique, and can be re-used later too.

Saving all render-layers and passes in a single file (as F3 command) will
be done later. Also reading back the current muli-layer exr files is not
supported yet (will read black). The purpose is that these files then can
be used as input for the Compositor.

One fun thing I added; after rendering once with this option, close
Blender, and restart it. If you have a Composite set up press 'R' on an
active RenderResult node. This will refresh the node(s) and load the exr,
so you can composite again without a re-render.

source/blender/imbuf/intern/openexr/openexr_api.cpp

@@ -429,18 +429,20 @@ int IMB_exr_begin_read(void *handle, char *filename, int *width, int *height)
 {
 	ExrHandle *data= (ExrHandle *)handle;
 	
-	data->ifile = new InputFile(filename);
-	if(data->ifile) {
-		Box2i dw = data->ifile->header().dataWindow();
-		data->width= *width  = dw.max.x - dw.min.x + 1;
-		data->height= *height = dw.max.y - dw.min.y + 1;
-		
-		const ChannelList &channels = data->ifile->header().channels();
-		
-		for (ChannelList::ConstIterator i = channels.begin(); i != channels.end(); ++i)
-			IMB_exr_add_channel(data, NULL, i.name());
-		
-		return 1;
+	if(BLI_exists(filename)) {
+		data->ifile = new InputFile(filename);
+		if(data->ifile) {
+			Box2i dw = data->ifile->header().dataWindow();
+			data->width= *width  = dw.max.x - dw.min.x + 1;
+			data->height= *height = dw.max.y - dw.min.y + 1;
+			
+			const ChannelList &channels = data->ifile->header().channels();
+			
+			for (ChannelList::ConstIterator i = channels.begin(); i != channels.end(); ++i)
+				IMB_exr_add_channel(data, NULL, i.name());
+			
+			return 1;
+		}
 	}
 	return 0;
 }

source/blender/makesdna/DNA_scene_types.h

@@ -446,6 +446,8 @@ typedef struct Scene {
 #define R_COMP_CROP			0x0080
 #define R_FREE_IMAGE		0x0100
 #define R_SINGLE_LAYER		0x0200
+#define R_EXR_TILE_FILE		0x0400
+
 
 /* alphamode */
 #define R_ADDSKY		0

source/blender/render/intern/source/pipeline.c

@@ -1224,7 +1224,7 @@ static void render_scene(Render *re, Scene *sce, int cfra)
 	
 	sce->r.cfra= cfra;
 	
-	if(G.rt)
+	if(R_EXR_TILE_FILE)
 		resc->flag |= R_FILEBUFFER;
 	
 	/* makes render result etc */
@@ -1464,7 +1464,7 @@ static int render_initialize_from_scene(Render *re, Scene *scene)
 		disprect.ymax= winy;
 	}
 	
-	if(G.rt) {
+	if(R_EXR_TILE_FILE) {
 		int partx= winx/scene->r.xparts, party= winy/scene->r.yparts;
 		/* stupid exr tiles dont like different sizes */
 		if(winx != partx*scene->r.xparts || winy != party*scene->r.xparts) {

source/blender/src/buttons_scene.c

@@ -1249,6 +1249,8 @@ static void render_panel_output(void)
 			uiDefButBitS(block, TOG, 1<<(3*b+a), 800,"",	(short)(10+18*a),(short)(10+14*b),16,12, &G.winpos, 0, 0, 0, 0, "Render window placement on screen");
 	uiBlockEndAlign(block);
 
+	uiDefButBitS(block, TOG, R_EXR_TILE_FILE, B_NOP, "Save Buffers", 72, 31, 120, 19, &G.scene->r.scemode, 0.0, 0.0, 0, 0, "Save the tiles for all RenderLayers and used SceneNodes to files, to save memory");
+	
 	uiBlockBeginAlign(block);
 	uiDefButS(block, ROW, B_REDR, "DispWin",	72, 10, 60, 20, &G.displaymode, 0.0, (float)R_DISPLAYWIN, 0, 0, "Sets render output to display in a seperate window");
 	uiDefButS(block, ROW, B_REDR, "DispView",	134, 10, 60, 20, &G.displaymode, 0.0, (float)R_DISPLAYVIEW, 0, 0, "Sets render output to display in 3D view");
@@ -1264,7 +1266,7 @@ static void render_panel_output(void)
 	uiDefButBitI(block, TOG, R_EDGE, B_NOP,"Edge",   100, 94, 70, 20, &G.scene->r.mode, 0, 0, 0, 0, "Enable Toon edge shading");
 	uiDefBlockBut(block, edge_render_menu, NULL, "Edge Settings", 170, 94, 140, 20, "Display edge settings");
 	uiBlockEndAlign(block);
-
+	
 	uiDefButBitS(block, TOG, R_FREE_IMAGE, B_NOP, "Free Tex Images", 170, 68, 140, 20, &G.scene->r.scemode, 0.0, 0.0, 0, 0, "Frees all Images used by Textures after each render");
 }
 

source/blender/src/editnode.c

@@ -1864,9 +1864,9 @@ void winqreadnodespace(ScrArea *sa, void *spacedata, BWinEvent *evt)
 		{
 			bNode *node= editnode_get_active(snode->edittree);
 			if(node && node->type==CMP_NODE_R_RESULT) {
-				//RE_ReadRenderResult(G.scene, (Scene *)node->id);
-				//ntreeCompositTagRender(snode->edittree);
-				//snode_handle_recalc(snode);
+				RE_ReadRenderResult(G.scene, (Scene *)node->id);
+				ntreeCompositTagRender(snode->edittree);
+				snode_handle_recalc(snode);
 			}
 		}
 			break;