- Restored "dither" option for conversion from float -> byte images.

This now is a post-process option only (used to be in render).
  It is only handled within the Imbuf/ module, on conversions from float
  to byte rect, which atm mostly happens on saving images.

- Small fix: when using Scene RenderLayer nodes, the speed vectors for
  these nodes were not created when that scene had "Do Composite" off.

source/blender/imbuf/IMB_imbuf_types.h

@@ -96,6 +96,7 @@ typedef struct ImBuf{
 	unsigned int   encodedbuffersize; /**< Size of encodedbuffer */
 
 	float *rect_float;		/**< floating point Rect equivilant */
+	float dither;			/**< random dither value, for conversion from float -> byte rect */
 	
 	struct MEM_CacheLimiterHandle_s * c_handle; /**< handle for cache limiter */
 	int refcounter;                /**< Refcounter for multiple users */

source/blender/imbuf/intern/divers.c

@@ -33,6 +33,7 @@
  */
 
 #include "BLI_blenlib.h"
+#include "BLI_rand.h"
 
 #include "imbuf.h"
 #include "imbuf_patch.h"
@@ -172,6 +173,7 @@ void IMB_rect_from_float(struct ImBuf *ibuf)
 {
 	/* quick method to convert floatbuf to byte */
 	float *tof = ibuf->rect_float;
+	float dither= ibuf->dither;
 	int i;
 	unsigned char *to = (unsigned char *) ibuf->rect;
 	
@@ -181,8 +183,8 @@ void IMB_rect_from_float(struct ImBuf *ibuf)
 		to = (unsigned char *) ibuf->rect;
 	}
 	
-	for (i = ibuf->x * ibuf->y; i > 0; i--) 
-	{
+	if(dither==0.0f) {
+		for (i = ibuf->x * ibuf->y; i > 0; i--) {
 			to[0] = FTOCHAR(tof[0]);
 			to[1] = FTOCHAR(tof[1]);
 			to[2] = FTOCHAR(tof[2]);
@@ -191,6 +193,25 @@ void IMB_rect_from_float(struct ImBuf *ibuf)
 			tof += 4;
 		}
 	}
+	else {
+		float dither_value, col;
+		dither= dither/255.0f;
+		for (i = ibuf->x * ibuf->y; i > 0; i--) {
+			dither_value = (BLI_frand()-0.5)*dither; 
+			col= tof[0] + dither_value;
+			to[0] = FTOCHAR(col);
+			col= tof[1] + dither_value;
+			to[1] = FTOCHAR(col);
+			col= tof[2] + dither_value;
+			to[2] = FTOCHAR(col);
+			col= tof[3] + dither_value;
+			to[3] = FTOCHAR(col);
+
+			to += 4; 
+			tof += 4;
+		}
+	}
+}
 
 void IMB_float_from_rect(struct ImBuf *ibuf)
 {

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

@@ -936,6 +936,9 @@ static void do_render_scene_node(Render *re, Scene *sce, int cfra)
 	/* makes render result etc */
 	RE_InitState(resc, &sce->r, re->winx, re->winy, &re->disprect);
 	
+	/* this to enable this scene to create speed vectors */
+	resc->r.scemode |= R_DOCOMP;
+	
 	/* now use renderdata and camera to set viewplane */
 	if(sce->camera==NULL) return;
 	RE_SetCamera(resc, sce->camera);
@@ -1222,10 +1225,14 @@ static void do_write_image_or_movie(Render *re, Scene *scene, bMovieHandle *mh)
 
                 /* if not exists, BKE_write_ibuf makes one */
 		ibuf->rect= rres.rect32;    
-
 		ibuf->rect_float= rres.rectf;
 		ibuf->zbuf_float= rres.rectz;
+		
+		/* float factor for random dither, imbuf takes care of it */
+		ibuf->dither= scene->r.dither_intensity;
+
 		ok= BKE_write_ibuf(ibuf, name, scene->r.imtype, scene->r.subimtype, scene->r.quality);
+		
 		if(ok==0) {
 			printf("Render error: cannot save %s\n", name);
 			G.afbreek=1;

source/blender/src/writeimage.c

@@ -136,6 +136,9 @@ static void save_rendered_image_cb_real(char *name, int zbuf)
 			ibuf->zbuf_float= rres.rectz;
 		}
 		
+		/* float factor for random dither, imbuf takes care of it */
+		ibuf->dither= G.scene->r.dither_intensity;
+		
 		BKE_write_ibuf(ibuf, str, G.scene->r.imtype, G.scene->r.subimtype, G.scene->r.quality);
 		IMB_freeImBuf(ibuf);	/* imbuf knows rects are not part of ibuf */