Expose PreviewImage & custom icons to py API.

This commit mainly:

* Exposes PreviewImage struct in RNA, including ways for user to set images data.
* Adds a new kind of PreviewImage, using a file path and IMB_thumb to get image.
* Adds a new kind of custom icon using PreviewImage, unrelated to ID previews system.
* Adds a python API (utils.previews) to allow python scripts to access those custom previews/icons.

Note that loading image from files' thumbnails is done when needed (deferred loading), not
when defining the custom preview/icon.

WARNING: for release addons who would want to use this, please keep it to a strict minimum, really needed level.
We do not want our UI to explode under hundreds of different flashy icons!

For more info, see also the release notes of Blender 2.75 (http://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.75/Addons)
and the example/templates featured with Blender.

Patch by Campbell (ideasman42), Inês (brita) and Bastien (mont29).

Differential Revision: https://developer.blender.org/D1255

9 files changed, 251 insertions, 137 deletions

diff --git a/source/blender/editors/include/ED_render.h b/source/blender/editors/include/ED_render.h
index 2bc0566f4a6..414126cac13 100644
--- a/source/blender/editors/include/ED_render.h
+++ b/source/blender/editors/include/ED_render.h
@@ -60,11 +60,15 @@ struct Scene *ED_render_job_get_current_scene(const struct bContext *C);
  * - PR_BUTS_RENDER: preview is rendered for buttons window
  * - PR_ICON_RENDER: preview is rendered for icons. hopefully fast enough for at least 32x32
  * - PR_NODE_RENDER: preview is rendered for node editor
+ * - PR_ICON_DEFERRED: No render, we just ensure deferred icon data gets generated.
  */
 
-#define PR_BUTS_RENDER  0
-#define PR_ICON_RENDER  1
-#define PR_NODE_RENDER  2
+enum {
+	PR_BUTS_RENDER   = 0,
+	PR_ICON_RENDER   = 1,
+	PR_NODE_RENDER   = 2,
+	PR_ICON_DEFERRED = 3,
+};
 
 void ED_preview_init_dbase(void);
 void ED_preview_free_dbase(void);
diff --git a/source/blender/editors/include/UI_interface_icons.h b/source/blender/editors/include/UI_interface_icons.h
index 9d190fa81c7..92f3b0180c6 100644
--- a/source/blender/editors/include/UI_interface_icons.h
+++ b/source/blender/editors/include/UI_interface_icons.h
@@ -49,7 +49,7 @@ typedef struct IconFile {
 #define ICON_DEFAULT_HEIGHT_SCALE ((int)(UI_UNIT_Y * 0.8f))
 #define ICON_DEFAULT_WIDTH_SCALE  ((int)(UI_UNIT_X * 0.8f))
 
-#define PREVIEW_DEFAULT_HEIGHT 96
+#define PREVIEW_DEFAULT_HEIGHT 128
 
 /*
  * Resizable Icons for Blender
diff --git a/source/blender/editors/interface/interface.c b/source/blender/editors/interface/interface.c
index b63871f5c82..a9cc926b275 100644
--- a/source/blender/editors/interface/interface.c
+++ b/source/blender/editors/interface/interface.c
@@ -3237,6 +3237,18 @@ static uiBut *ui_def_but(
 	return but;
 }
 
+void ui_def_but_icon(uiBut *but, const int icon, const int flag) {
+	if (icon) {
+		ui_icon_ensure_deferred(but->block->evil_C, icon, (flag & UI_BUT_ICON_PREVIEW) != 0);
+	}
+	but->icon = (BIFIconID)icon;
+	but->flag |= flag;
+
+	if (but->str && but->str[0]) {
+		but->drawflag |= UI_BUT_ICON_LEFT;
+	}
+}
+
 static void ui_def_but_rna__disable(uiBut *but)
 {
 	but->flag |= UI_BUT_DISABLED;
@@ -3500,11 +3512,7 @@ static uiBut *ui_def_but_rna(
 		but->rnaindex = 0;
 
 	if (icon) {
-		but->icon = (BIFIconID)icon;
-		but->flag |= UI_HAS_ICON;
-		if (str[0]) {
-			but->drawflag |= UI_BUT_ICON_LEFT;
-		}
+		ui_def_but_icon(but, icon, UI_HAS_ICON);
 	}
 	
 	if ((type == UI_BTYPE_MENU) && (but->dt == UI_EMBOSS_PULLDOWN)) {
@@ -3691,8 +3699,7 @@ int UI_autocomplete_end(AutoComplete *autocpl, char *autoname)
 static void ui_but_update_and_icon_set(uiBut *but, int icon)
 {
 	if (icon) {
-		but->icon = (BIFIconID) icon;
-		but->flag |= UI_HAS_ICON;
+		ui_def_but_icon(but, icon, UI_HAS_ICON);
 	}
 
 	ui_but_update(but);
@@ -4066,7 +4073,7 @@ void UI_but_drag_set_value(uiBut *but)
 void UI_but_drag_set_image(uiBut *but, const char *path, int icon, struct ImBuf *imb, float scale)
 {
 	but->dragtype = WM_DRAG_PATH;
-	but->icon = icon; /* no flag UI_HAS_ICON, so icon doesnt draw in button */
+	ui_def_but_icon(but, icon, 0);  /* no flag UI_HAS_ICON, so icon doesnt draw in button */
 	but->dragpoin = (void *)path;
 	but->imb = imb;
 	but->imb_scale = scale;
@@ -4220,8 +4227,7 @@ uiBut *uiDefIconTextMenuBut(uiBlock *block, uiMenuCreateFunc func, void *arg, in
 {
 	uiBut *but = ui_def_but(block, UI_BTYPE_PULLDOWN, 0, str, x, y, width, height, arg, 0.0, 0.0, 0.0, 0.0, tip);
 
-	but->icon = (BIFIconID) icon;
-	but->flag |= UI_HAS_ICON;
+	ui_def_but_icon(but, icon, UI_HAS_ICON);
 
 	but->drawflag |= UI_BUT_ICON_LEFT;
 	but->flag |= UI_BUT_ICON_SUBMENU;
@@ -4236,8 +4242,7 @@ uiBut *uiDefIconMenuBut(uiBlock *block, uiMenuCreateFunc func, void *arg, int ic
 {
 	uiBut *but = ui_def_but(block, UI_BTYPE_PULLDOWN, 0, "", x, y, width, height, arg, 0.0, 0.0, 0.0, 0.0, tip);
 
-	but->icon = (BIFIconID) icon;
-	but->flag |= UI_HAS_ICON;
+	ui_def_but_icon(but, icon, UI_HAS_ICON);
 	but->drawflag &= ~UI_BUT_ICON_LEFT;
 
 	but->menu_create_func = func;
@@ -4253,7 +4258,7 @@ uiBut *uiDefIconTextBlockBut(uiBlock *block, uiBlockCreateFunc func, void *arg,
 	
 	/* XXX temp, old menu calls pass on icon arrow, which is now UI_BUT_ICON_SUBMENU flag */
 	if (icon != ICON_RIGHTARROW_THIN) {
-		but->icon = (BIFIconID) icon;
+		ui_def_but_icon(but, icon, 0);
 		but->drawflag |= UI_BUT_ICON_LEFT;
 	}
 	but->flag |= UI_HAS_ICON;
@@ -4270,9 +4275,8 @@ uiBut *uiDefIconBlockBut(uiBlock *block, uiBlockCreateFunc func, void *arg, int
 {
 	uiBut *but = ui_def_but(block, UI_BTYPE_BLOCK, retval, "", x, y, width, height, arg, 0.0, 0.0, 0.0, 0.0, tip);
 	
-	but->icon = (BIFIconID) icon;
-	but->flag |= UI_HAS_ICON;
-	
+	ui_def_but_icon(but, icon, UI_HAS_ICON);
+
 	but->drawflag |= UI_BUT_ICON_LEFT;
 	
 	but->block_create_func = func;
@@ -4305,9 +4309,8 @@ uiBut *uiDefSearchBut(uiBlock *block, void *arg, int retval, int icon, int maxle
 {
 	uiBut *but = ui_def_but(block, UI_BTYPE_SEARCH_MENU, retval, "", x, y, width, height, arg, 0.0, maxlen, a1, a2, tip);
 	
-	but->icon = (BIFIconID) icon;
-	but->flag |= UI_HAS_ICON;
-	
+	ui_def_but_icon(but, icon, UI_HAS_ICON);
+
 	but->drawflag |= UI_BUT_ICON_LEFT | UI_BUT_TEXT_LEFT;
 	
 	ui_but_update(but);
diff --git a/source/blender/editors/interface/interface_icons.c b/source/blender/editors/interface/interface_icons.c
index 6536c0a869e..7c05d5f4378 100644
--- a/source/blender/editors/interface/interface_icons.c
+++ b/source/blender/editors/interface/interface_icons.c
@@ -55,6 +55,7 @@
 
 #include "IMB_imbuf.h"
 #include "IMB_imbuf_types.h"
+#include "IMB_thumbs.h"
 
 #include "BIF_gl.h"
 #include "BIF_glutil.h"
@@ -904,10 +905,13 @@ void UI_icons_init(int first_dyn_id)
 static int preview_render_size(enum eIconSizes size)
 {
 	switch (size) {
-		case ICON_SIZE_ICON:    return 32;
-		case ICON_SIZE_PREVIEW: return PREVIEW_DEFAULT_HEIGHT;
+		case ICON_SIZE_ICON:
+			return ICON_RENDER_DEFAULT_HEIGHT;
+		case ICON_SIZE_PREVIEW:
+			return PREVIEW_RENDER_DEFAULT_HEIGHT;
+		default:
+			return 0;
 	}
-	return 0;
 }
 
 /* Create rect for the icon
@@ -923,12 +927,49 @@ static void icon_create_rect(struct PreviewImage *prv_img, enum eIconSizes size)
 	else if (!prv_img->rect[size]) {
 		prv_img->w[size] = render_size;
 		prv_img->h[size] = render_size;
-		prv_img->changed[size] = 1;
+		prv_img->flag[size] |= PRV_CHANGED;
 		prv_img->changed_timestamp[size] = 0;
 		prv_img->rect[size] = MEM_callocN(render_size * render_size * sizeof(unsigned int), "prv_rect");
 	}
 }
 
+void ui_icon_ensure_deferred(const bContext *C, const int icon_id, const bool big)
+{
+	Icon *icon = BKE_icon_get(icon_id);
+
+	if (icon) {
+		DrawInfo *di = (DrawInfo *)icon->drawinfo;
+
+		if (!di) {
+			di = icon_create_drawinfo();
+
+			icon->drawinfo = di;
+			icon->drawinfo_free = UI_icons_free_drawinfo;
+		}
+
+		if (di) {
+			if (di->type == ICON_TYPE_PREVIEW) {
+				PreviewImage *prv = (icon->type != 0) ? BKE_previewimg_id_ensure((ID *)icon->obj) : icon->obj;
+
+				if (prv) {
+					const int size = big ? ICON_SIZE_PREVIEW : ICON_SIZE_ICON;
+
+					if (!prv->use_deferred || prv->rect[size] || (prv->flag[size] & PRV_USER_EDITED)) {
+						return;
+					}
+
+					icon_create_rect(prv, size);
+
+					/* Always using job (background) version. */
+					ED_preview_icon_job(C, prv, NULL, prv->rect[size], prv->w[size], prv->h[size]);
+
+					prv->flag[size] &= ~PRV_CHANGED;
+				}
+			}
+		}
+	}
+}
+
 /* only called when icon has changed */
 /* only call with valid pointer from UI_icon_draw */
 static void icon_set_image(
@@ -940,6 +981,11 @@ static void icon_set_image(
 		return;
 	}
 
+	if (prv_img->flag[size] & PRV_USER_EDITED) {
+		/* user-edited preview, do not auto-update! */
+		return;
+	}
+
 	icon_create_rect(prv_img, size);
 
 	if (use_job) {
@@ -961,22 +1007,32 @@ PreviewImage *UI_icon_to_preview(int icon_id)
 	
 	if (icon) {
 		DrawInfo *di = (DrawInfo *)icon->drawinfo;
-		if (di && di->data.buffer.image) {
-			ImBuf *bbuf;
-			
-			bbuf = IMB_ibImageFromMemory(di->data.buffer.image->datatoc_rect, di->data.buffer.image->datatoc_size, IB_rect, NULL, "<matcap buffer>");
-			if (bbuf) {
-				PreviewImage *prv = BKE_previewimg_create();
-				
-				prv->rect[0] = bbuf->rect;
+		if (di) {
+			if (di->type == ICON_TYPE_PREVIEW) {
+				PreviewImage *prv = (icon->type != 0) ? BKE_previewimg_id_ensure((ID *)icon->obj) : icon->obj;
 
-				prv->w[0] = bbuf->x;
-				prv->h[0] = bbuf->y;
-				
-				bbuf->rect = NULL;
-				IMB_freeImBuf(bbuf);
-				
-				return prv;
+				if (prv) {
+					return BKE_previewimg_copy(prv);
+				}
+			}
+			else if (di->data.buffer.image) {
+				ImBuf *bbuf;
+
+				bbuf = IMB_ibImageFromMemory(di->data.buffer.image->datatoc_rect, di->data.buffer.image->datatoc_size,
+				                             IB_rect, NULL, __func__);
+				if (bbuf) {
+					PreviewImage *prv = BKE_previewimg_create();
+
+					prv->rect[0] = bbuf->rect;
+
+					prv->w[0] = bbuf->x;
+					prv->h[0] = bbuf->y;
+
+					bbuf->rect = NULL;
+					IMB_freeImBuf(bbuf);
+
+					return prv;
+				}
 			}
 		}
 	}
@@ -987,6 +1043,10 @@ static void icon_draw_rect(float x, float y, int w, int h, float UNUSED(aspect),
                            unsigned int *rect, float alpha, const float rgb[3], const bool is_preview)
 {
 	ImBuf *ima = NULL;
+	int draw_w = w;
+	int draw_h = h;
+	int draw_x = x;
+	int draw_y = y;
 
 	/* sanity check */
 	if (w <= 0 || h <= 0 || w > 2000 || h > 2000) {
@@ -1006,21 +1066,34 @@ static void icon_draw_rect(float x, float y, int w, int h, float UNUSED(aspect),
 	}
 
 	/* rect contains image in 'rendersize', we only scale if needed */
-	if (rw != w && rh != h) {
+	if (rw != w || rh != h) {
+		/* preserve aspect ratio and center */
+		if (rw > rh) {
+			draw_w = w;
+			draw_h = (int)(((float)rh / (float)rw) * (float)w);
+			draw_y += (h - draw_h) / 2;
+		}
+		else if (rw < rh) {
+			draw_w = (int)(((float)rw / (float)rh) * (float)h);
+			draw_h = h;
+			draw_x += (w - draw_w) / 2;
+		}
+		/* if the image is squared, the draw_ initialization values are good */
+
 		/* first allocate imbuf for scaling and copy preview into it */
 		ima = IMB_allocImBuf(rw, rh, 32, IB_rect);
 		memcpy(ima->rect, rect, rw * rh * sizeof(unsigned int));
-		IMB_scaleImBuf(ima, w, h); /* scale it */
+		IMB_scaleImBuf(ima, draw_w, draw_h); /* scale it */
 		rect = ima->rect;
 	}
 
 	/* draw */
 	if (is_preview) {
-		glaDrawPixelsSafe(x, y, w, h, w, GL_RGBA, GL_UNSIGNED_BYTE, rect);
+		glaDrawPixelsSafe(draw_x, draw_y, draw_w, draw_h, draw_w, GL_RGBA, GL_UNSIGNED_BYTE, rect);
 	}
 	else {
-		glRasterPos2f(x, y);
-		glDrawPixels(w, h, GL_RGBA, GL_UNSIGNED_BYTE, rect);
+		glRasterPos2f(draw_x, draw_y);
+		glDrawPixels(draw_w, draw_h, GL_RGBA, GL_UNSIGNED_BYTE, rect);
 	}
 
 	if (ima)
@@ -1081,10 +1154,13 @@ static void icon_draw_texture(
 static int get_draw_size(enum eIconSizes size)
 {
 	switch (size) {
-		case ICON_SIZE_ICON: return ICON_DEFAULT_HEIGHT;
-		case ICON_SIZE_PREVIEW: return PREVIEW_DEFAULT_HEIGHT;
+		case ICON_SIZE_ICON:
+			return ICON_DEFAULT_HEIGHT;
+		case ICON_SIZE_PREVIEW:
+			return PREVIEW_DEFAULT_HEIGHT;
+		default:
+			return 0;
 	}
-	return 0;
 }
 
 
@@ -1147,9 +1223,12 @@ static void icon_draw_size(
 		glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 	}
 	else if (di->type == ICON_TYPE_PREVIEW) {
-		PreviewImage *pi = BKE_previewimg_get((ID *)icon->obj);
+		PreviewImage *pi = (icon->type != 0) ? BKE_previewimg_id_ensure((ID *)icon->obj) : icon->obj;
 
 		if (pi) {
+			/* Do deferred loading/generation if needed. */
+//			BKE_previewimg_ensure(pi, size);
+
 			/* no create icon on this level in code */
 			if (!pi->rect[size]) return;  /* something has gone wrong! */
 			
@@ -1164,17 +1243,17 @@ static void icon_draw_size(
 static void ui_id_preview_image_render_size(
         const bContext *C, Scene *scene, ID *id, PreviewImage *pi, int size, const bool use_job)
 {
-	if ((pi->changed[size] || !pi->rect[size])) { /* changed only ever set by dynamic icons */
+	if (((pi->flag[size] & PRV_CHANGED) || !pi->rect[size])) { /* changed only ever set by dynamic icons */
 		/* create the rect if necessary */
 		icon_set_image(C, scene, id, pi, size, use_job);
 
-		pi->changed[size] = 0;
+		pi->flag[size] &= ~PRV_CHANGED;
 	}
 }
 
 void UI_id_icon_render(const bContext *C, Scene *scene, ID *id, const bool big, const bool use_job)
 {
-	PreviewImage *pi = BKE_previewimg_get(id);
+	PreviewImage *pi = BKE_previewimg_id_ensure(id);
 
 	if (pi) {
 		if (big)
@@ -1186,7 +1265,7 @@ void UI_id_icon_render(const bContext *C, Scene *scene, ID *id, const bool big,
 
 static void ui_id_brush_render(const bContext *C, ID *id)
 {
-	PreviewImage *pi = BKE_previewimg_get(id); 
+	PreviewImage *pi = BKE_previewimg_id_ensure(id);
 	enum eIconSizes i;
 	
 	if (!pi)
@@ -1195,9 +1274,9 @@ static void ui_id_brush_render(const bContext *C, ID *id)
 	for (i = 0; i < NUM_ICON_SIZES; i++) {
 		/* check if rect needs to be created; changed
 		 * only set by dynamic icons */
-		if ((pi->changed[i] || !pi->rect[i])) {
+		if (((pi->flag[i] & PRV_CHANGED) || !pi->rect[i])) {
 			icon_set_image(C, NULL, id, pi, i, true);
-			pi->changed[i] = 0;
+			pi->flag[i] &= ~PRV_CHANGED;
 		}
 	}
 }
@@ -1208,7 +1287,7 @@ static int ui_id_brush_get_icon(const bContext *C, ID *id)
 	Brush *br = (Brush *)id;
 
 	if (br->flag & BRUSH_CUSTOM_ICON) {
-		BKE_icon_getid(id);
+		BKE_icon_id_ensure(id);
 		ui_id_brush_render(C, id);
 	}
 	else {
@@ -1270,7 +1349,7 @@ int ui_id_icon_get(const bContext *C, ID *id, const bool big)
 		case ID_IM: /* fall through */
 		case ID_WO: /* fall through */
 		case ID_LA: /* fall through */
-			iconid = BKE_icon_getid(id);
+			iconid = BKE_icon_id_ensure(id);
 			/* checks if not exists, or changed */
 			UI_id_icon_render(C, NULL, id, big, true);
 			break;
diff --git a/source/blender/editors/interface/interface_intern.h b/source/blender/editors/interface/interface_intern.h
index a3192d3b8d0..9461547a164 100644
--- a/source/blender/editors/interface/interface_intern.h
+++ b/source/blender/editors/interface/interface_intern.h
@@ -465,6 +465,8 @@ extern bool ui_but_string_set(struct bContext *C, uiBut *but, const char *str) A
 extern bool ui_but_string_set_eval_num(struct bContext *C, uiBut *but, const char *str, double *value) ATTR_NONNULL();
 extern int  ui_but_string_get_max_length(uiBut *but);
 extern uiBut *ui_but_drag_multi_edit_get(uiBut *but);
+
+void ui_def_but_icon(uiBut *but, const int icon, const int flag);
 extern uiButExtraIconType ui_but_icon_extra_get(uiBut *but);
 
 extern void ui_but_default_set(struct bContext *C, const bool all, const bool use_afterfunc);
@@ -673,6 +675,7 @@ void ui_draw_preview_item(struct uiFontStyle *fstyle, rcti *rect, const char *na
 void uiStyleInit(void);
 
 /* interface_icons.c */
+void ui_icon_ensure_deferred(const struct bContext *C, const int icon_id, const bool big);
 int ui_id_icon_get(const struct bContext *C, struct ID *id, const bool big);
 
 /* resources.c */
diff --git a/source/blender/editors/interface/interface_templates.c b/source/blender/editors/interface/interface_templates.c
index fe1a1b9096d..9a34e4be980 100644
--- a/source/blender/editors/interface/interface_templates.c
+++ b/source/blender/editors/interface/interface_templates.c
@@ -430,8 +430,8 @@ static void template_ID(
 
 		but = uiDefBlockButN(block, id_search_menu, MEM_dupallocN(template), "", 0, 0, UI_UNIT_X * 6, UI_UNIT_Y * 6,
 		                     TIP_(template_id_browse_tip(type)));
-		but->icon = id ? ui_id_icon_get(C, id, true) : RNA_struct_ui_icon(type);
-		UI_but_flag_enable(but, UI_HAS_ICON | UI_BUT_ICON_PREVIEW);
+		ui_def_but_icon(but, id ? ui_id_icon_get(C, id, true) : RNA_struct_ui_icon(type),
+		                UI_HAS_ICON | UI_BUT_ICON_PREVIEW);
 
 		if ((idfrom && idfrom->lib) || !editable)
 			UI_but_flag_enable(but, UI_BUT_DISABLED);
@@ -441,10 +441,9 @@ static void template_ID(
 	else if (flag & UI_ID_BROWSE) {
 		but = uiDefBlockButN(block, id_search_menu, MEM_dupallocN(template), "", 0, 0, UI_UNIT_X * 1.6, UI_UNIT_Y,
 		                     TIP_(template_id_browse_tip(type)));
-		but->icon = RNA_struct_ui_icon(type);
+		ui_def_but_icon(but, RNA_struct_ui_icon(type), UI_HAS_ICON);
 		/* default dragging of icon for id browse buttons */
 		UI_but_drag_set_id(but, id);
-		UI_but_flag_enable(but, UI_HAS_ICON);
 		UI_but_drawflag_enable(but, UI_BUT_ICON_LEFT);
 
 		if ((idfrom && idfrom->lib) || !editable)
@@ -1666,9 +1665,9 @@ static uiBlock *ui_icon_view_menu_cb(bContext *C, ARegion *ar, void *arg_litem)
 		
 		icon = item[a].icon;
 		value = item[a].value;
-		but = uiDefIconButR_prop(block, UI_BTYPE_ROW, 0, icon, x, y, UI_UNIT_X * 5, UI_UNIT_Y * 5,
+		but = uiDefIconButR_prop(block, UI_BTYPE_ROW, 0, ICON_NONE, x, y, UI_UNIT_X * 5, UI_UNIT_Y * 5,
 		                         &cb.ptr, cb.prop, -1, 0, value, -1, -1, NULL);
-		UI_but_flag_enable(but, UI_HAS_ICON | UI_BUT_ICON_PREVIEW);
+		ui_def_but_icon(but, icon, UI_HAS_ICON | UI_BUT_ICON_PREVIEW);
 	}
 
 	UI_block_bounds_set_normal(block, 0.3f * U.widget_unit);
@@ -1708,8 +1707,7 @@ void uiTemplateIconView(uiLayout *layout, PointerRNA *ptr, const char *propname)
 
 	but = uiDefBlockButN(block, ui_icon_view_menu_cb, cb, "", 0, 0, UI_UNIT_X * 6, UI_UNIT_Y * 6, "");
 
-	but->icon = icon;
-	UI_but_flag_enable(but, UI_HAS_ICON | UI_BUT_ICON_PREVIEW);
+	ui_def_but_icon(but, icon, UI_HAS_ICON | UI_BUT_ICON_PREVIEW);
 
 	if (free_items) {
 		MEM_freeN(items);
diff --git a/source/blender/editors/render/render_preview.c b/source/blender/editors/render/render_preview.c
index 65d4c2301a9..5112cd84d09 100644
--- a/source/blender/editors/render/render_preview.c
+++ b/source/blender/editors/render/render_preview.c
@@ -79,7 +79,7 @@
 
 #include "IMB_imbuf.h"
 #include "IMB_imbuf_types.h"
-
+#include "IMB_thumbs.h"
 
 #include "BIF_gl.h"
 #include "BIF_glutil.h"
@@ -128,7 +128,7 @@ ImBuf *get_brush_icon(Brush *brush)
 				}
 
 				if (brush->icon_imbuf)
-					BKE_icon_changed(BKE_icon_getid(&brush->id));
+					BKE_icon_changed(BKE_icon_id_ensure(&brush->id));
 			}
 		}
 	}
@@ -935,65 +935,87 @@ static void set_alpha(char *cp, int sizex, int sizey, char alpha)
 static void icon_preview_startjob(void *customdata, short *stop, short *do_update)
 {
 	ShaderPreview *sp = customdata;
-	ID *id = sp->id;
-	short idtype = GS(id->name);
-	
-	if (idtype == ID_IM) {
-		Image *ima = (Image *)id;
-		ImBuf *ibuf = NULL;
-		ImageUser iuser = {NULL};
 
-		/* ima->ok is zero when Image cannot load */
-		if (ima == NULL || ima->ok == 0)
-			return;
+	if (sp->pr_method == PR_ICON_DEFERRED) {
+		PreviewImage *prv = sp->owner;
+		ImBuf *thumb;
+		char *deferred_data = PRV_DEFERRED_DATA(prv);
+		int source =  deferred_data[0];
+		char *path = &deferred_data[1];
 
-		/* setup dummy image user */
-		iuser.ok = iuser.framenr = 1;
-		iuser.scene = sp->scene;
-		
-		/* elubie: this needs to be changed: here image is always loaded if not
-		 * already there. Very expensive for large images. Need to find a way to 
-		 * only get existing ibuf */
-		ibuf = BKE_image_acquire_ibuf(ima, &iuser, NULL);
-		if (ibuf == NULL || ibuf->rect == NULL) {
-			BKE_image_release_ibuf(ima, ibuf, NULL);
-			return;
-		}
-		
-		icon_copy_rect(ibuf, sp->sizex, sp->sizey, sp->pr_rect);
+//		printf("generating deferred %d×%d preview for %s\n", sp->sizex, sp->sizey, path);
+
+		thumb = IMB_thumb_manage(path, THB_LARGE, source);
 
-		*do_update = true;
+		if (thumb) {
+			/* PreviewImage assumes premultiplied alhpa... */
+			IMB_premultiply_alpha(thumb);
 
-		BKE_image_release_ibuf(ima, ibuf, NULL);
+			icon_copy_rect(thumb, sp->sizex, sp->sizey, sp->pr_rect);
+			IMB_freeImBuf(thumb);
+		}
 	}
-	else if (idtype == ID_BR) {
-		Brush *br = (Brush *)id;
+	else {
+		ID *id = sp->id;
+		short idtype = GS(id->name);
+
+		if (idtype == ID_IM) {
+			Image *ima = (Image *)id;
+			ImBuf *ibuf = NULL;
+			ImageUser iuser = {NULL};
+
+			/* ima->ok is zero when Image cannot load */
+			if (ima == NULL || ima->ok == 0)
+				return;
+
+			/* setup dummy image user */
+			iuser.ok = iuser.framenr = 1;
+			iuser.scene = sp->scene;
+
+			/* elubie: this needs to be changed: here image is always loaded if not
+			 * already there. Very expensive for large images. Need to find a way to
+			 * only get existing ibuf */
+			ibuf = BKE_image_acquire_ibuf(ima, &iuser, NULL);
+			if (ibuf == NULL || ibuf->rect == NULL) {
+				BKE_image_release_ibuf(ima, ibuf, NULL);
+				return;
+			}
 
-		br->icon_imbuf = get_brush_icon(br);
+			icon_copy_rect(ibuf, sp->sizex, sp->sizey, sp->pr_rect);
 
-		memset(sp->pr_rect, 0x88, sp->sizex * sp->sizey * sizeof(unsigned int));
+			*do_update = true;
 
-		if (!(br->icon_imbuf) || !(br->icon_imbuf->rect))
-			return;
+			BKE_image_release_ibuf(ima, ibuf, NULL);
+		}
+		else if (idtype == ID_BR) {
+			Brush *br = (Brush *)id;
 
-		icon_copy_rect(br->icon_imbuf, sp->sizex, sp->sizey, sp->pr_rect);
+			br->icon_imbuf = get_brush_icon(br);
 
-		*do_update = true;
-	}
-	else {
-		/* re-use shader job */
-		shader_preview_startjob(customdata, stop, do_update);
+			memset(sp->pr_rect, 0x88, sp->sizex * sp->sizey * sizeof(unsigned int));
+
+			if (!(br->icon_imbuf) || !(br->icon_imbuf->rect))
+				return;
 
-		/* world is rendered with alpha=0, so it wasn't displayed 
-		 * this could be render option for sky to, for later */
-		if (idtype == ID_WO) {
-			set_alpha((char *)sp->pr_rect, sp->sizex, sp->sizey, 255);
+			icon_copy_rect(br->icon_imbuf, sp->sizex, sp->sizey, sp->pr_rect);
+
+			*do_update = true;
 		}
-		else if (idtype == ID_MA) {
-			Material *ma = (Material *)id;
+		else {
+			/* re-use shader job */
+			shader_preview_startjob(customdata, stop, do_update);
 
-			if (ma->material_type == MA_TYPE_HALO)
+			/* world is rendered with alpha=0, so it wasn't displayed
+			 * this could be render option for sky to, for later */
+			if (idtype == ID_WO) {
 				set_alpha((char *)sp->pr_rect, sp->sizex, sp->sizey, 255);
+			}
+			else if (idtype == ID_MA) {
+				Material *ma = (Material *)id;
+
+				if (ma->material_type == MA_TYPE_HALO)
+					set_alpha((char *)sp->pr_rect, sp->sizex, sp->sizey, 255);
+			}
 		}
 	}
 }
@@ -1005,7 +1027,7 @@ static void common_preview_startjob(void *customdata, short *stop, short *do_upd
 {
 	ShaderPreview *sp = customdata;
 
-	if (sp->pr_method == PR_ICON_RENDER)
+	if (ELEM(sp->pr_method, PR_ICON_RENDER, PR_ICON_DEFERRED))
 		icon_preview_startjob(customdata, stop, do_update);
 	else
 		shader_preview_startjob(customdata, stop, do_update);
@@ -1041,29 +1063,34 @@ static void icon_preview_startjob_all_sizes(void *customdata, short *stop, short
 	const bool use_new_shading = BKE_scene_use_new_shading_nodes(ip->scene);
 
 	while (cur_size) {
+		PreviewImage *prv = ip->owner;
 		ShaderPreview *sp = MEM_callocN(sizeof(ShaderPreview), "Icon ShaderPreview");
+		const bool is_render = !prv->use_deferred;
 
 		/* construct shader preview from image size and previewcustomdata */
 		sp->scene = ip->scene;
 		sp->owner = ip->owner;
 		sp->sizex = cur_size->sizex;
 		sp->sizey = cur_size->sizey;
-		sp->pr_method = PR_ICON_RENDER;
+		sp->pr_method = is_render ? PR_ICON_RENDER : PR_ICON_DEFERRED;
 		sp->pr_rect = cur_size->rect;
 		sp->id = ip->id;
 
-		if (use_new_shading) {
-			/* texture icon rendering is hardcoded to use BI,
-			 * so don't even think of using cycle's bmain for
-			 * texture icons
-			 */
-			if (GS(ip->id->name) != ID_TE)
-				sp->pr_main = G_pr_main_cycles;
-			else
+		if (is_render) {
+			BLI_assert(ip->id);
+			if (use_new_shading) {
+				/* texture icon rendering is hardcoded to use BI,
+				 * so don't even think of using cycle's bmain for
+				 * texture icons
+				 */
+				if (GS(ip->id->name) != ID_TE)
+					sp->pr_main = G_pr_main_cycles;
+				else
+					sp->pr_main = G_pr_main;
+			}
+			else {
 				sp->pr_main = G_pr_main;
-		}
-		else {
-			sp->pr_main = G_pr_main;
+			}
 		}
 
 		common_preview_startjob(sp, stop, do_update, progress);
@@ -1145,7 +1172,7 @@ void ED_preview_icon_job(const bContext *C, void *owner, ID *id, unsigned int *r
 
 	/* customdata for preview thread */
 	ip->scene = CTX_data_scene(C);
-	ip->owner = id;
+	ip->owner = owner;
 	ip->id = id;
 
 	icon_preview_add_size(ip, rect, sizex, sizey);
diff --git a/source/blender/editors/render/render_update.c b/source/blender/editors/render/render_update.c
index d3d5cb12ac8..dedcbb144aa 100644
--- a/source/blender/editors/render/render_update.c
+++ b/source/blender/editors/render/render_update.c
@@ -270,7 +270,7 @@ static void material_changed(Main *bmain, Material *ma)
 	int texture_draw = false;
 
 	/* icons */
-	BKE_icon_changed(BKE_icon_getid(&ma->id));
+	BKE_icon_changed(BKE_icon_id_ensure(&ma->id));
 
 	/* glsl */
 	if (ma->gpumaterial.first)
@@ -285,7 +285,7 @@ static void material_changed(Main *bmain, Material *ma)
 			continue;
 		}
 
-		BKE_icon_changed(BKE_icon_getid(&parent->id));
+		BKE_icon_changed(BKE_icon_id_ensure(&parent->id));
 
 		if (parent->gpumaterial.first)
 			GPU_material_free(&parent->gpumaterial);
@@ -325,7 +325,7 @@ static void lamp_changed(Main *bmain, Lamp *la)
 	Material *ma;
 
 	/* icons */
-	BKE_icon_changed(BKE_icon_getid(&la->id));
+	BKE_icon_changed(BKE_icon_id_ensure(&la->id));
 
 	/* glsl */
 	for (ob = bmain->object.first; ob; ob = ob->id.next)
@@ -361,7 +361,7 @@ static void texture_changed(Main *bmain, Tex *tex)
 	bool texture_draw = false;
 
 	/* icons */
-	BKE_icon_changed(BKE_icon_getid(&tex->id));
+	BKE_icon_changed(BKE_icon_id_ensure(&tex->id));
 
 	/* paint overlays */
 	for (scene = bmain->scene.first; scene; scene = scene->id.next)
@@ -372,7 +372,7 @@ static void texture_changed(Main *bmain, Tex *tex)
 		if (!material_uses_texture(ma, tex))
 			continue;
 
-		BKE_icon_changed(BKE_icon_getid(&ma->id));
+		BKE_icon_changed(BKE_icon_id_ensure(&ma->id));
 
 		if (ma->gpumaterial.first)
 			GPU_material_free(&ma->gpumaterial);
@@ -403,7 +403,7 @@ static void texture_changed(Main *bmain, Tex *tex)
 			continue;
 		}
 
-		BKE_icon_changed(BKE_icon_getid(&wo->id));
+		BKE_icon_changed(BKE_icon_id_ensure(&wo->id));
 		
 		if (wo->gpumaterial.first)
 			GPU_material_free(&wo->gpumaterial);		
@@ -451,7 +451,7 @@ static void world_changed(Main *bmain, World *wo)
 	Material *ma;
 
 	/* icons */
-	BKE_icon_changed(BKE_icon_getid(&wo->id));
+	BKE_icon_changed(BKE_icon_id_ensure(&wo->id));
 	
 	/* glsl */
 	for (ma = bmain->mat.first; ma; ma = ma->id.next)
@@ -470,7 +470,7 @@ static void image_changed(Main *bmain, Image *ima)
 	Tex *tex;
 
 	/* icons */
-	BKE_icon_changed(BKE_icon_getid(&ima->id));
+	BKE_icon_changed(BKE_icon_id_ensure(&ima->id));
 
 	/* textures */
 	for (tex = bmain->tex.first; tex; tex = tex->id.next)
diff --git a/source/blender/editors/space_image/image_ops.c b/source/blender/editors/space_image/image_ops.c
index 75e6f77ba49..ddb1cec9180 100644
--- a/source/blender/editors/space_image/image_ops.c
+++ b/source/blender/editors/space_image/image_ops.c
@@ -1346,7 +1346,7 @@ static int image_replace_exec(bContext *C, wmOperator *op)
 	/* XXX unpackImage frees image buffers */
 	ED_preview_kill_jobs(CTX_wm_manager(C), CTX_data_main(C));
 	
-	BKE_icon_changed(BKE_icon_getid(&sima->image->id));
+	BKE_icon_changed(BKE_icon_id_ensure(&sima->image->id));
 	BKE_image_signal(sima->image, &sima->iuser, IMA_SIGNAL_RELOAD);
 	WM_event_add_notifier(C, NC_IMAGE | NA_EDITED, sima->image);