opengl render was freeing all images from the graphics card each update.

with some 4x4k and 4x8k textures this becomes very slow.

only free animated textures (movies and sequences)

source/blender/editors/space_view3d/view3d_draw.c

@@ -1965,7 +1965,10 @@ void ED_view3d_draw_offscreen(Scene *scene, View3D *v3d, ARegion *ar, int winx,
 
 	/* set flags */
 	G.f |= G_RENDER_OGL;
-	GPU_free_images();
+
+	/* free images which can have changed on frame-change
+	 * warning! can be slow so only free animated images - campbell */
+	GPU_free_images_anim();
 
 	/* set background color, fallback on the view background color */
 	if(scene->world) {
@@ -2030,7 +2033,8 @@ void ED_view3d_draw_offscreen(Scene *scene, View3D *v3d, ARegion *ar, int winx,
 	/* draw grease-pencil stuff - needed to get paint-buffer shown too (since it's 2D) */
 	draw_gpencil_view3d_ext(scene, ar, 0);
 
-	GPU_free_images();
+	/* freeing the images again here could be done after the operator runs, leaving for now */
+	GPU_free_images_anim();
 
 	/* restore size */
 	ar->winx= bwinx;

source/blender/gpu/GPU_draw.h

@@ -117,6 +117,7 @@ int GPU_update_image_time(struct Image *ima, double time);
 int GPU_verify_image(struct Image *ima, struct ImageUser *iuser, int tftile, int tfmode, int compare, int mipmap);
 void GPU_free_image(struct Image *ima);
 void GPU_free_images(void);
+void GPU_free_images_anim(void);
 
 /* smoke drawing functions */
 void GPU_free_smoke(struct SmokeModifierData *smd);

source/blender/gpu/intern/gpu_draw.c

@@ -851,6 +851,17 @@ void GPU_free_images(void)
 			GPU_free_image(ima);
 }
 
+/* same as above but only free animated images */
+void GPU_free_images_anim(void)
+{
+	Image* ima;
+
+	if(G.main)
+		for(ima=G.main->image.first; ima; ima=ima->id.next)
+			if(ELEM(ima->type, IMA_SRC_SEQUENCE, IMA_SRC_MOVIE))
+				GPU_free_image(ima);
+}
+
 /* OpenGL Materials */
 
 #define FIXEDMAT	8