Texture painting:

Do not generate materials/images/UVs if they are missing.

Now we spawn a panel ("Missing Data") with operators to generate the missing data and
pop a warning if user tries to paint without them.

The reason we have reverted this is that it is too easy to end up with more textures
than we wanted. It was impossible to enter texture paint without having textures added,
and code makes too many assumptions about what user may want.

Discussed during Sunday's meeting.

This might be a candidate for 2.72a but I'm not sure how other artists will take this
(and how refined and crash-free it is), better make a few iterations first.

And for interested parties...test please, don't wait until after a release to poke with such issues.

Also, add slot operator now adds a new unconnected image node in cycles. Only
used in the "Missing Data" panel. This should be a separate commit but I am squashing it into the same commit because
it relies too much on changes done here and can be reverted easily if complainstorm occurs again.

4 files changed, 181 insertions, 149 deletions

diff --git a/source/blender/editors/sculpt_paint/paint_image.c b/source/blender/editors/sculpt_paint/paint_image.c
index 87866f764bc..f4189b512e5 100644
--- a/source/blender/editors/sculpt_paint/paint_image.c
+++ b/source/blender/editors/sculpt_paint/paint_image.c
@@ -57,6 +57,7 @@
 
 #include "BKE_context.h"
 #include "BKE_depsgraph.h"
+#include "BKE_DerivedMesh.h"
 #include "BKE_brush.h"
 #include "BKE_image.h"
 #include "BKE_main.h"
@@ -87,6 +88,7 @@
 #include "RNA_enum_types.h"
 
 #include "GPU_draw.h"
+#include "GPU_buffers.h"
 
 #include "BIF_gl.h"
 #include "BIF_glutil.h"
@@ -752,14 +754,16 @@ static PaintOperation *texture_paint_init(bContext *C, wmOperator *op, const flo
 	copy_v2_v2(pop->prevmouse, mouse);
 	copy_v2_v2(pop->startmouse, mouse);
 
-	if ((brush->imagepaint_tool == PAINT_TOOL_FILL) && (brush->flag & BRUSH_USE_GRADIENT)) {
-		pop->cursor = WM_paint_cursor_activate(CTX_wm_manager(C), image_paint_poll, gradient_draw_line, pop);
-	}
-
 	/* initialize from context */
 	if (CTX_wm_region_view3d(C)) {
 		Object *ob = OBACT;
-		paint_proj_mesh_data_ensure(C, ob, op);
+		bool uvs, mat, tex, stencil;
+		if (!BKE_paint_proj_mesh_data_check(scene, ob, &uvs, &mat, &tex, &stencil)) {
+			BKE_paint_data_warning(op->reports, uvs, mat, tex, stencil);
+			MEM_freeN(pop);
+			WM_event_add_notifier(C, NC_SCENE | ND_TOOLSETTINGS, NULL);
+			return NULL;			
+		}
 		pop->mode = PAINT_MODE_3D_PROJECT;
 		pop->custom_paint = paint_proj_new_stroke(C, ob, mouse, mode);
 	}
@@ -773,6 +777,10 @@ static PaintOperation *texture_paint_init(bContext *C, wmOperator *op, const flo
 		return NULL;
 	}
 
+	if ((brush->imagepaint_tool == PAINT_TOOL_FILL) && (brush->flag & BRUSH_USE_GRADIENT)) {
+		pop->cursor = WM_paint_cursor_activate(CTX_wm_manager(C), image_paint_poll, gradient_draw_line, pop);
+	}
+	
 	settings->imapaint.flag |= IMAGEPAINT_DRAWING;
 	ED_undo_paint_push_begin(UNDO_PAINT_IMAGE, op->type->name,
 	                         ED_image_undo_restore, ED_image_undo_free, NULL);
@@ -1381,29 +1389,31 @@ static int texture_paint_toggle_exec(bContext *C, wmOperator *op)
 		 * cache in case we are loading a file */
 		BKE_texpaint_slots_refresh_object(scene, ob);
 
-		paint_proj_mesh_data_ensure(C, ob, op);
-
+		BKE_paint_proj_mesh_data_check(scene, ob, NULL, NULL, NULL, NULL);
+		
 		/* entering paint mode also sets image to editors */
 		if (imapaint->mode == IMAGEPAINT_MODE_MATERIAL) {
 			Material *ma = give_current_material(ob, ob->actcol); /* set the current material active paint slot on image editor */
 
-			if (ma->texpaintslot)
+			if (ma && ma->texpaintslot)
 				ima = ma->texpaintslot[ma->paint_active_slot].ima;
 		}
 		else if (imapaint->mode == IMAGEPAINT_MODE_MATERIAL) {
 			ima = imapaint->canvas;
 		}	
 		
-		for (sc = bmain->screen.first; sc; sc = sc->id.next) {
-			ScrArea *sa;
-			for (sa = sc->areabase.first; sa; sa = sa->next) {
-				SpaceLink *sl;
-				for (sl = sa->spacedata.first; sl; sl = sl->next) {
-					if (sl->spacetype == SPACE_IMAGE) {
-						SpaceImage *sima = (SpaceImage *)sl;
-						
-						if (!sima->pin)
-							ED_space_image_set(sima, scene, scene->obedit, ima);
+		if (ima) {
+			for (sc = bmain->screen.first; sc; sc = sc->id.next) {
+				ScrArea *sa;
+				for (sa = sc->areabase.first; sa; sa = sa->next) {
+					SpaceLink *sl;
+					for (sl = sa->spacedata.first; sl; sl = sl->next) {
+						if (sl->spacetype == SPACE_IMAGE) {
+							SpaceImage *sima = (SpaceImage *)sl;
+							
+							if (!sima->pin)
+								ED_space_image_set(sima, scene, scene->obedit, ima);
+						}
 					}
 				}
 			}
@@ -1420,7 +1430,7 @@ static int texture_paint_toggle_exec(bContext *C, wmOperator *op)
 		toggle_paint_cursor(C, 1);
 	}
 
-	DAG_id_tag_update(&ob->id, OB_RECALC_DATA);
+	GPU_drawobject_free(ob->derivedFinal);
 	WM_event_add_notifier(C, NC_SCENE | ND_MODE, scene);
 
 	return OPERATOR_FINISHED;
diff --git a/source/blender/editors/sculpt_paint/paint_image_proj.c b/source/blender/editors/sculpt_paint/paint_image_proj.c
index be9a614a6fe..352e633218a 100644
--- a/source/blender/editors/sculpt_paint/paint_image_proj.c
+++ b/source/blender/editors/sculpt_paint/paint_image_proj.c
@@ -74,6 +74,7 @@
 #include "BKE_material.h"
 #include "BKE_mesh.h"
 #include "BKE_mesh_mapping.h"
+#include "BKE_node.h"
 #include "BKE_paint.h"
 #include "BKE_report.h"
 #include "BKE_scene.h"
@@ -84,6 +85,7 @@
 
 #include "ED_image.h"
 #include "ED_mesh.h"
+#include "ED_node.h"
 #include "ED_paint.h"
 #include "ED_screen.h"
 #include "ED_uvedit.h"
@@ -362,7 +364,7 @@ static TexPaintSlot *project_paint_face_paint_slot(const ProjPaintState *ps, int
 {
 	MFace *mf = ps->dm_mface + face_index;
 	Material *ma = ps->dm->mat[mf->mat_nr];
-	return ma->texpaintslot + ma->paint_active_slot;
+	return ma ? ma->texpaintslot + ma->paint_active_slot : NULL;
 }
 
 static Image *project_paint_face_paint_image(const ProjPaintState *ps, int face_index)
@@ -373,7 +375,7 @@ static Image *project_paint_face_paint_image(const ProjPaintState *ps, int face_
 	else {
 		MFace *mf = ps->dm_mface + face_index;
 		Material *ma = ps->dm->mat[mf->mat_nr];
-		TexPaintSlot *slot = ma->texpaintslot + ma->paint_active_slot;
+		TexPaintSlot *slot = ma ? ma->texpaintslot + ma->paint_active_slot : NULL;
 		return slot ? slot->ima : ps->canvas_ima;
 	}
 }
@@ -382,14 +384,14 @@ static TexPaintSlot *project_paint_face_clone_slot(const ProjPaintState *ps, int
 {
 	MFace *mf = ps->dm_mface + face_index;
 	Material *ma = ps->dm->mat[mf->mat_nr];
-	return ma->texpaintslot + ma->paint_clone_slot;
+	return ma ? ma->texpaintslot + ma->paint_clone_slot : NULL;
 }
 
 static Image *project_paint_face_clone_image(const ProjPaintState *ps, int face_index)
 {
 	MFace *mf = ps->dm_mface + face_index;
 	Material *ma = ps->dm->mat[mf->mat_nr];
-	TexPaintSlot *slot = ma->texpaintslot + ma->paint_clone_slot;
+	TexPaintSlot *slot = ma ? ma->texpaintslot + ma->paint_clone_slot : NULL;
 	return slot ? slot->ima : ps->clone_ima;
 }
 
@@ -4665,13 +4667,18 @@ static int texture_paint_camera_project_exec(bContext *C, wmOperator *op)
 	IDProperty *idgroup;
 	IDProperty *view_data = NULL;
 	Object *ob = OBACT;
+	bool uvs, mat, tex;
 
 	if (ob == NULL || ob->type != OB_MESH) {
 		BKE_report(op->reports, RPT_ERROR, "No active mesh object");
 		return OPERATOR_CANCELLED;
 	}
 
-	paint_proj_mesh_data_ensure(C, ob, op);
+	if (!BKE_paint_proj_mesh_data_check(scene, ob, &uvs, &mat, &tex, NULL)) {
+		BKE_paint_data_warning(op->reports, uvs, mat, tex, true);
+		WM_event_add_notifier(C, NC_SCENE | ND_TOOLSETTINGS, NULL);
+		return OPERATOR_CANCELLED;		
+	}
 
 	project_state_init(C, ob, &ps, BRUSH_STROKE_NORMAL);
 
@@ -4863,110 +4870,78 @@ void PAINT_OT_image_from_view(wmOperatorType *ot)
  * Data generation for projective texturing  *
  * *******************************************/
 
+void BKE_paint_data_warning(struct ReportList *reports, bool uvs, bool mat, bool tex, bool stencil)
+{
+	BKE_reportf(reports, RPT_WARNING, "Missing%s%s%s%s detected!", 
+	           !uvs ? " UVs," : "",
+	           !mat ? " Materials," : "",
+	           !tex ? " Textures," : "",
+	           !stencil ? " Stencil," : ""
+	           );
+}
 
 /* Make sure that active object has a material, and assign UVs and image layers if they do not exist */
-void paint_proj_mesh_data_ensure(bContext *C, Object *ob, wmOperator *op)
+bool BKE_paint_proj_mesh_data_check(Scene *scene, Object *ob, bool *uvs, bool *mat, bool *tex, bool *stencil)
 {
 	Mesh *me;
 	int layernum;
-	ImagePaintSettings *imapaint = &(CTX_data_tool_settings(C)->imapaint);
-	bScreen *sc;
-	Scene *scene = CTX_data_scene(C);
-	Main *bmain = CTX_data_main(C);
+	ImagePaintSettings *imapaint = &scene->toolsettings->imapaint;
 	Brush *br = BKE_paint_brush(&imapaint->paint);
+	bool hasmat = true;
+	bool hastex = true;
+	bool hasstencil = true;
+	bool hasuvs = true;
 
+	imapaint->missing_data = 0;
+	
 	BLI_assert(ob->type == OB_MESH);
 
-	/* no material, add one */
-	if (ob->totcol == 0) {
-		Material *ma = BKE_material_add(CTX_data_main(C), "Material");
-		/* no material found, just assign to first slot */
-		assign_material(ob, ma, 1, BKE_MAT_ASSIGN_USERPREF);
-		proj_paint_add_slot(C, ma, NULL);
-	}
-	else {
-		/* there may be material slots but they may be empty, check */
-		int i;
-		
-		for (i = 1; i < ob->totcol + 1; i++) {
-			Material *ma = give_current_material(ob, i);
-
-			if (ma) {
-				if (imapaint->mode == IMAGEPAINT_MODE_MATERIAL) {
+	if (imapaint->mode == IMAGEPAINT_MODE_MATERIAL) {
+		/* no material, add one */
+		if (ob->totcol == 0) {
+			hasmat = false;
+			hastex = false;
+		}
+		else {
+			/* there may be material slots but they may be empty, check */
+			int i;
+			hasmat = false;
+			hastex = false;
+			
+			for (i = 1; i < ob->totcol + 1; i++) {
+				Material *ma = give_current_material(ob, i);
+				
+				if (ma) {
+					hasmat = true;
 					if (!ma->texpaintslot) {
 						/* refresh here just in case */
 						BKE_texpaint_slot_refresh_cache(scene, ma);				
 						
 						/* if still no slots, we have to add */
-						if (!ma->texpaintslot) {
-							proj_paint_add_slot(C, ma, NULL);
-							
-							if (ma->texpaintslot) {
-								for (sc = bmain->screen.first; sc; sc = sc->id.next) {
-									ScrArea *sa;
-									for (sa = sc->areabase.first; sa; sa = sa->next) {
-										SpaceLink *sl;
-										for (sl = sa->spacedata.first; sl; sl = sl->next) {
-											if (sl->spacetype == SPACE_IMAGE) {
-												SpaceImage *sima = (SpaceImage *)sl;
-												
-												if (!sima->pin)
-													ED_space_image_set(sima, scene, scene->obedit, ma->texpaintslot[0].ima);
-											}
-										}
-									}
-								}
-							}							
+						if (ma->texpaintslot) {							
+							hastex = true;
+							break;						
 						}
 					}
+					else {
+						hastex = true;
+						break;						
+					}
 				}
 			}
-			else {
-				Material *ma = BKE_material_add(CTX_data_main(C), "Material");
-				/* no material found, just assign to first slot */
-				assign_material(ob, ma, i, BKE_MAT_ASSIGN_USERPREF);
-				proj_paint_add_slot(C, ma, NULL);
-			}
 		}
 	}
-	
-	if (imapaint->mode == IMAGEPAINT_MODE_IMAGE) {
+	else if (imapaint->mode == IMAGEPAINT_MODE_IMAGE) {
 		if (imapaint->canvas == NULL) {
-			int width;
-			int height;
-			Main *bmain = CTX_data_main(C);
-			float color[4] = {0.0, 0.0, 0.0, 1.0};
-
-			width = 1024;
-			height = 1024;
-			imapaint->canvas = BKE_image_add_generated(bmain, width, height, "Canvas", 32, false, IMA_GENTYPE_BLANK, color);
-			
-			GPU_drawobject_free(ob->derivedFinal);
-			
-			for (sc = bmain->screen.first; sc; sc = sc->id.next) {
-				ScrArea *sa;
-				for (sa = sc->areabase.first; sa; sa = sa->next) {
-					SpaceLink *sl;
-					for (sl = sa->spacedata.first; sl; sl = sl->next) {
-						if (sl->spacetype == SPACE_IMAGE) {
-							SpaceImage *sima = (SpaceImage *)sl;
-							
-							if (!sima->pin)
-								ED_space_image_set(sima, scene, scene->obedit, imapaint->canvas);
-						}
-					}
-				}
-			}			
+			hastex = false;
 		}		
 	}
-		
+	
 	me = BKE_mesh_from_object(ob);
 	layernum = CustomData_number_of_layers(&me->pdata, CD_MTEXPOLY);
 
 	if (layernum == 0) {
-		BKE_reportf(op->reports, RPT_WARNING, "Object did not have UV map, manual unwrap recommended");
-
-		ED_mesh_uv_texture_add(me, "UVMap", true);
+		hasuvs = false;
 	}
 
 	/* Make sure we have a stencil to paint on! */
@@ -4974,16 +4949,29 @@ void paint_proj_mesh_data_ensure(bContext *C, Object *ob, wmOperator *op)
 		imapaint->flag |= IMAGEPAINT_PROJECT_LAYER_STENCIL;
 
 		if (imapaint->stencil == NULL) {
-			int width;
-			int height;
-			Main *bmain = CTX_data_main(C);
-			float color[4] = {0.0, 0.0, 0.0, 1.0};
-
-			width = 1024;
-			height = 1024;
-			imapaint->stencil = BKE_image_add_generated(bmain, width, height, "Stencil", 32, false, IMA_GENTYPE_BLANK, color);
+			hasstencil = false;
 		}
 	}
+
+	if (!hasuvs) imapaint->missing_data |= IMAGEPAINT_MISSING_UVS;
+	if (!hasmat) imapaint->missing_data |= IMAGEPAINT_MISSING_MATERIAL;
+	if (!hastex) imapaint->missing_data |= IMAGEPAINT_MISSING_TEX;
+	if (!hasstencil) imapaint->missing_data |= IMAGEPAINT_MISSING_STENCIL;
+	
+	if (uvs) {
+		*uvs = hasuvs;
+	}
+	if (mat) {
+		*mat = hasmat;
+	}
+	if (tex) {
+		*tex = hastex;
+	}
+	if (stencil) {
+		*stencil = hasstencil;
+	}
+	
+	return hasuvs && hasmat && hastex && hasstencil;
 }
 
 /* Add layer operator */
@@ -5006,30 +4994,74 @@ static EnumPropertyItem layer_type_items[] = {
 	{0, NULL, 0, NULL, NULL}
 };
 
-bool proj_paint_add_slot(bContext *C, Material *ma, wmOperator *op)
+static Image *proj_paint_image_create(wmOperator *op, Main *bmain)
+{
+	Image *ima;
+	float color[4] = {0.0f, 0.0f, 0.0f, 1.0f};
+	char imagename[MAX_ID_NAME - 2] = "Material Diffuse Color";
+	int width = 1024;
+	int height = 1024;
+	bool use_float = false;
+	short gen_type = IMA_GENTYPE_BLANK;
+	bool alpha = false;
+
+	if (op) {
+		width = RNA_int_get(op->ptr, "width");
+		height = RNA_int_get(op->ptr, "height");
+		use_float = RNA_boolean_get(op->ptr, "float");
+		gen_type = RNA_enum_get(op->ptr, "generated_type");
+		RNA_float_get_array(op->ptr, "color", color);
+		alpha = RNA_boolean_get(op->ptr, "alpha");
+		RNA_string_get(op->ptr, "name", imagename);
+	}
+	ima = BKE_image_add_generated(bmain, width, height, imagename, alpha ? 32 : 24, use_float,
+	                                               gen_type, color);
+	
+	return ima;
+}
+
+static bool proj_paint_add_slot(bContext *C, wmOperator *op)
 {
 	Object *ob = CTX_data_active_object(C);
 	Scene *scene = CTX_data_scene(C);
+	Material *ma;
 	bool is_bi = BKE_scene_uses_blender_internal(scene);
+	Image *ima = NULL;
 
 	if (!ob)
 		return false;
 
-	if (!ma)
-		ma = give_current_material(ob, ob->actcol);
+	ma = give_current_material(ob, ob->actcol);
 
 	if (ma) {
+		Main *bmain = CTX_data_main(C);
+
+		if (!is_bi && BKE_scene_use_new_shading_nodes(scene)) {
+			bNode *imanode;
+			bNodeTree *ntree = ma->nodetree;
 
-		if (!is_bi || ma->use_nodes) {
-			/* not supported for now */
+			if (!ntree) {
+				ED_node_shader_default(C, &ma->id);
+				ntree = ma->nodetree;
+			}
+			
+			ma->use_nodes = true;
+						
+			/* try to add an image node */
+			imanode = nodeAddStaticNode(C, ntree, SH_NODE_TEX_IMAGE);
+			
+			ima = proj_paint_image_create(op, bmain);
+			imanode->id = &ima->id;
+			
+			nodeSetActive(ntree, imanode);
+					
+			ntreeUpdateTree(CTX_data_main(C), ntree);
 		}
 		else {
 			MTex *mtex = add_mtex_id(&ma->id, -1);
 
 			/* successful creation of mtex layer, now create set */
 			if (mtex) {
-				Main *bmain = CTX_data_main(C);
-				Image *ima;
 				int type = MAP_COL;
 				int type_id = 0;
 
@@ -5049,47 +5081,33 @@ bool proj_paint_add_slot(bContext *C, Material *ma, wmOperator *op)
 				mtex->mapto = type;
 
 				if (mtex->tex) {
-					float color[4] = {0.0f, 0.0f, 0.0f, 1.0f};
-					char imagename[MAX_ID_NAME - 2] = "Material Diffuse Color";
-					int width = 1024;
-					int height = 1024;
-					bool use_float = false;
-					short gen_type = IMA_GENTYPE_BLANK;
-					bool alpha = false;
-
-					if (op) {
-						width = RNA_int_get(op->ptr, "width");
-						height = RNA_int_get(op->ptr, "height");
-						use_float = RNA_boolean_get(op->ptr, "float");
-						gen_type = RNA_enum_get(op->ptr, "generated_type");
-						RNA_float_get_array(op->ptr, "color", color);
-						alpha = RNA_boolean_get(op->ptr, "alpha");
-						RNA_string_get(op->ptr, "name", imagename);
-					}
-
-					ima = mtex->tex->ima = BKE_image_add_generated(bmain, width, height, imagename, alpha ? 32 : 24, use_float,
-					                                               gen_type, color);
-
-					BKE_texpaint_slot_refresh_cache(scene, ma);
-					BKE_image_signal(ima, NULL, IMA_SIGNAL_USER_NEW_IMAGE);
-					WM_event_add_notifier(C, NC_TEXTURE | NA_ADDED, mtex->tex);
-					WM_event_add_notifier(C, NC_IMAGE | NA_ADDED, ima);
-					DAG_id_tag_update(&ma->id, 0);
-					ED_area_tag_redraw(CTX_wm_area(C));
+					ima = mtex->tex->ima = proj_paint_image_create(op, bmain);
 				}
 
 				WM_event_add_notifier(C, NC_TEXTURE, CTX_data_scene(C));
-				return true;
 			}
+			WM_event_add_notifier(C, NC_TEXTURE | NA_ADDED, mtex->tex);				
+		}
+		
+		if (ima) {
+			BKE_texpaint_slot_refresh_cache(scene, ma);
+			BKE_image_signal(ima, NULL, IMA_SIGNAL_USER_NEW_IMAGE);
+			WM_event_add_notifier(C, NC_IMAGE | NA_ADDED, ima);
+			DAG_id_tag_update(&ma->id, 0);
+			ED_area_tag_redraw(CTX_wm_area(C));
+			
+			return true;			
 		}
 	}
-
+	
 	return false;
 }
 
 static int texture_paint_add_texture_paint_slot_exec(bContext *C, wmOperator *op)
 {
-	return proj_paint_add_slot(C, NULL, op);
+	if(proj_paint_add_slot(C, op))
+		return OPERATOR_FINISHED;
+	else return OPERATOR_CANCELLED;
 }
 
 
@@ -5100,6 +5118,12 @@ static int texture_paint_add_texture_paint_slot_invoke(bContext *C, wmOperator *
 	Material *ma = give_current_material(ob, ob->actcol);
 	int type = RNA_enum_get(op->ptr, "type");
 
+	if (!ma) {
+		ma = BKE_material_add(CTX_data_main(C), "Material");
+		/* no material found, just assign to first slot */
+		assign_material(ob, ma, ob->actcol, BKE_MAT_ASSIGN_USERPREF);		
+	}
+	
 	type = RNA_enum_from_value(layer_type_items, type);
 
 	/* get the name of the texture layer type */
diff --git a/source/blender/editors/sculpt_paint/paint_intern.h b/source/blender/editors/sculpt_paint/paint_intern.h
index 5e1ac0cf8a8..c3b7ec60e71 100644
--- a/source/blender/editors/sculpt_paint/paint_intern.h
+++ b/source/blender/editors/sculpt_paint/paint_intern.h
@@ -169,8 +169,6 @@ void *paint_proj_new_stroke(struct bContext *C, struct Object *ob, const float m
 void paint_proj_stroke(const struct bContext *C, void *ps, const float prevmval_i[2], const float mval_i[2], const bool eraser, float pressure, float distance, float size);
 void paint_proj_redraw(const struct bContext *C, void *pps, bool final);
 void paint_proj_stroke_done(void *ps);
-void paint_proj_mesh_data_ensure(bContext *C, struct Object *ob, struct wmOperator *op);
-bool proj_paint_add_slot(bContext *C, struct Material *ma, struct wmOperator *op);
 
 void paint_brush_color_get(struct Scene *scene, struct Brush *br, bool color_correction, bool invert, float distance, float pressure, float color[3], struct ColorManagedDisplay *display);
 bool paint_use_opacity_masking(struct Brush *brush);
diff --git a/source/blender/editors/sculpt_paint/paint_utils.c b/source/blender/editors/sculpt_paint/paint_utils.c
index f34d0ff3f7b..e03c8a5f106 100644
--- a/source/blender/editors/sculpt_paint/paint_utils.c
+++ b/source/blender/editors/sculpt_paint/paint_utils.c
@@ -395,7 +395,7 @@ static Image *imapaint_face_image(DerivedMesh *dm, int face_index)
 	Image *ima;
 	MFace *mf = dm->getTessFaceArray(dm) + face_index;
 	Material *ma = dm->mat[mf->mat_nr];
-	ima = ma->texpaintslot[ma->paint_active_slot].ima;
+	ima = ma ? ma->texpaintslot[ma->paint_active_slot].ima : NULL;
 
 	return ima;
 }