[evince] ev-pixbuf-cache: schedule prev or next jobs first depending on the scroll direction

[Carlos Garcia Campos <carlosgc src gnome org>]

commit b6f27b6890ead6b190147c321aad206c8a4c4422
Author: Carlos Garcia Campos <carlosgc gnome org>
Date:   Mon Jul 1 21:16:27 2013 +0200

    ev-pixbuf-cache: schedule prev or next jobs first depending on the scroll direction
    
    If we are scrolling down schedule next pages first, otherwise schedule
    the previous pages first.

 libview/ev-pixbuf-cache.c |   88 ++++++++++++++++++++++++++++++++++++--------
 1 files changed, 72 insertions(+), 16 deletions(-)
---
diff --git a/libview/ev-pixbuf-cache.c b/libview/ev-pixbuf-cache.c
index cb8b22c..2f68215 100644
--- a/libview/ev-pixbuf-cache.c
+++ b/libview/ev-pixbuf-cache.c
@@ -3,6 +3,11 @@
 #include "ev-job-scheduler.h"
 #include "ev-view-private.h"
 
+typedef enum {
+        SCROLL_DIRECTION_DOWN,
+        SCROLL_DIRECTION_UP
+} ScrollDirection;
+
 typedef struct _CacheJobInfo
 {
        EvJob *job;
@@ -40,6 +45,7 @@ struct _EvPixbufCache
        EvDocumentModel *model;
        int start_page;
        int end_page;
+        ScrollDirection scroll_direction;
        gboolean inverted_colors;
 
        gsize max_size;
@@ -706,6 +712,44 @@ add_job_if_needed (EvPixbufCache *pixbuf_cache,
 }
 
 static void
+add_prev_jobs_if_needed (EvPixbufCache *pixbuf_cache,
+                         gint           rotation,
+                         gfloat         scale)
+{
+        CacheJobInfo *job_info;
+        int page;
+        int i;
+
+        for (i = pixbuf_cache->preload_cache_size - 1; i >= FIRST_VISIBLE_PREV(pixbuf_cache); i--) {
+                job_info = (pixbuf_cache->prev_job + i);
+                page = pixbuf_cache->start_page - pixbuf_cache->preload_cache_size + i;
+
+                add_job_if_needed (pixbuf_cache, job_info,
+                                   page, rotation, scale,
+                                   EV_JOB_PRIORITY_LOW);
+        }
+}
+
+static void
+add_next_jobs_if_needed (EvPixbufCache *pixbuf_cache,
+                         gint           rotation,
+                         gfloat         scale)
+{
+        CacheJobInfo *job_info;
+        int page;
+        int i;
+
+        for (i = 0; i < VISIBLE_NEXT_LEN(pixbuf_cache); i++) {
+                job_info = (pixbuf_cache->next_job + i);
+                page = pixbuf_cache->end_page + 1 + i;
+
+                add_job_if_needed (pixbuf_cache, job_info,
+                                   page, rotation, scale,
+                                   EV_JOB_PRIORITY_LOW);
+        }
+}
+
+static void
 ev_pixbuf_cache_add_jobs_if_needed (EvPixbufCache *pixbuf_cache,
                                    gint           rotation,
                                    gfloat         scale)
@@ -723,24 +767,33 @@ ev_pixbuf_cache_add_jobs_if_needed (EvPixbufCache *pixbuf_cache,
                                   EV_JOB_PRIORITY_URGENT);
        }
 
-        for (i = pixbuf_cache->preload_cache_size - 1; i >= FIRST_VISIBLE_PREV(pixbuf_cache); i--) {
-               job_info = (pixbuf_cache->prev_job + i);
-               page = pixbuf_cache->start_page - pixbuf_cache->preload_cache_size + i;
+        if (pixbuf_cache->scroll_direction == SCROLL_DIRECTION_UP) {
+                add_prev_jobs_if_needed (pixbuf_cache, rotation, scale);
+                add_next_jobs_if_needed (pixbuf_cache, rotation, scale);
+        } else {
+                add_next_jobs_if_needed (pixbuf_cache, rotation, scale);
+                add_prev_jobs_if_needed (pixbuf_cache, rotation, scale);
+        }
+}
 
-               add_job_if_needed (pixbuf_cache, job_info,
-                                  page, rotation, scale,
-                                  EV_JOB_PRIORITY_LOW);
-       }
+static ScrollDirection
+ev_pixbuf_cache_get_scroll_direction (EvPixbufCache *pixbuf_cache,
+                                      gint           start_page,
+                                      gint           end_page)
+{
+        if (start_page < pixbuf_cache->start_page)
+                return SCROLL_DIRECTION_UP;
 
-       for (i = 0; i < VISIBLE_NEXT_LEN(pixbuf_cache); i++) {
-               job_info = (pixbuf_cache->next_job + i);
-               page = pixbuf_cache->end_page + 1 + i;
+        if (end_page > pixbuf_cache->end_page)
+                return SCROLL_DIRECTION_DOWN;
 
-               add_job_if_needed (pixbuf_cache, job_info,
-                                  page, rotation, scale,
-                                  EV_JOB_PRIORITY_LOW);
-       }
+        if (start_page > pixbuf_cache->start_page)
+                return SCROLL_DIRECTION_DOWN;
 
+        if (end_page < pixbuf_cache->end_page)
+                return SCROLL_DIRECTION_UP;
+
+        return pixbuf_cache->scroll_direction;
 }
 
 void
@@ -749,8 +802,9 @@ ev_pixbuf_cache_set_page_range (EvPixbufCache  *pixbuf_cache,
                                gint            end_page,
                                GList          *selection_list)
 {
-       gdouble scale = ev_document_model_get_scale (pixbuf_cache->model);
-       gint    rotation = ev_document_model_get_rotation (pixbuf_cache->model);
+       gdouble         scale = ev_document_model_get_scale (pixbuf_cache->model);
+       gint            rotation = ev_document_model_get_rotation (pixbuf_cache->model);
+        ScrollDirection direction;
 
        g_return_if_fail (EV_IS_PIXBUF_CACHE (pixbuf_cache));
 
@@ -758,6 +812,8 @@ ev_pixbuf_cache_set_page_range (EvPixbufCache  *pixbuf_cache,
        g_return_if_fail (end_page >= 0 && end_page < ev_document_get_n_pages (pixbuf_cache->document));
        g_return_if_fail (end_page >= start_page);
 
+        pixbuf_cache->scroll_direction = ev_pixbuf_cache_get_scroll_direction (pixbuf_cache, start_page, 
end_page);
+
        /* First, resize the page_range as needed.  We cull old pages
         * mercilessly. */
        ev_pixbuf_cache_update_range (pixbuf_cache, start_page, end_page, rotation, scale);