let the document know about the current adjustments

The document object now has functions to set and get the position and
the viewport size.

The position is a relative position with respect to the size of the
entire document, i.e. position_y=0 means top of the document and
position_y=1 bottom.

The viewport size is stored in screen coordinates, in pixels.

document.c

@@ -52,9 +52,13 @@ struct zathura_document_s {
   int page_offset; /**< Page offset */
   double cell_width; /**< width of a page cell in the document (not ransformed by scale and rotation) */
   double cell_height; /**< height of a page cell in the document (not ransformed by scale and rotation) */
+  unsigned int view_width; /**< width of current viewport */
+  unsigned int view_height; /**< height of current viewport */
   unsigned int pages_per_row; /**< number of pages in a row */
   unsigned int first_page_column; /**< column of the first page */
   unsigned int page_padding; /**< padding between pages */
+  double position_x; /**< X adjustment */
+  double position_y; /**< Y adjustment */
 
   /**
    * Document pages
@@ -131,6 +135,10 @@ zathura_document_open(zathura_plugin_manager_t* plugin_manager, const char*
   document->adjust_mode = ZATHURA_ADJUST_NONE;
   document->cell_width  = 0.0;
   document->cell_height = 0.0;
+  document->view_height = 0;
+  document->view_width  = 0;
+  document->position_x  = 0.0;
+  document->position_y  = 0.0;
 
   /* open document */
   zathura_plugin_functions_t* functions = zathura_plugin_get_functions(plugin);
@@ -326,6 +334,46 @@ zathura_document_set_current_page_number(zathura_document_t* document, unsigned
   document->current_page_number = current_page;
 }
 
+double
+zathura_document_get_position_x(zathura_document_t* document)
+{
+  if (document == NULL) {
+    return 0;
+  }
+
+  return document->position_x;
+}
+
+double
+zathura_document_get_position_y(zathura_document_t* document)
+{
+  if (document == NULL) {
+    return 0;
+  }
+
+  return document->position_y;
+}
+
+void
+zathura_document_set_position_x(zathura_document_t* document, double position_x)
+{
+  if (document == NULL) {
+    return;
+  }
+
+  document->position_x = position_x;
+}
+
+void
+zathura_document_set_position_y(zathura_document_t* document, double position_y)
+{
+  if (document == NULL) {
+    return;
+  }
+
+  document->position_y = position_y;
+}
+
 double
 zathura_document_get_scale(zathura_document_t* document)
 {
@@ -416,6 +464,33 @@ zathura_document_set_page_offset(zathura_document_t* document, unsigned int page
   document->page_offset = page_offset;
 }
 
+void
+zathura_document_set_viewport_width(zathura_document_t* document, unsigned int width)
+{
+  if (document == NULL) {
+    return;
+  }
+  document->view_width = width;
+}
+
+void
+zathura_document_set_viewport_height(zathura_document_t* document, unsigned int height)
+{
+  if (document == NULL) {
+    return;
+  }
+  document->view_height = height;
+}
+
+void
+zathura_document_get_viewport_size(zathura_document_t* document,
+                                   unsigned int *height, unsigned int* width)
+{
+  g_return_if_fail(document != NULL && height != NULL && width != NULL);
+  *height = document->view_height;
+  *width = document->view_width;
+}
+
 void
 zathura_document_get_cell_size(zathura_document_t* document,
                                unsigned int* height, unsigned int* width)

document.h

@@ -97,6 +97,42 @@ unsigned int zathura_document_get_current_page_number(zathura_document_t* docume
 void zathura_document_set_current_page_number(zathura_document_t* document, unsigned
     int current_page);
 
+/**
+ * Returns the X position, as a value relative to the document width (0=left,
+ * 1=right).
+ *
+ * @param document The document
+ * @return X adjustment
+ */
+double zathura_document_get_position_x(zathura_document_t* document);
+
+/**
+ * Returns the Y position as value relative to the document height (0=top,
+ * 1=bottom)
+ *
+ * @param document The document
+ * @return Y adjustment
+ */
+double zathura_document_get_position_y(zathura_document_t* document);
+
+/**
+ * Sets the X position as a value relative to the document width (0=left,
+ * 1=right)
+ *
+ * @param document The document
+ * @param position_x the X adjustment
+ */
+void zathura_document_set_position_x(zathura_document_t* document, double position_x);
+
+/**
+ * Sets the Y position as a value relative to the document height (0=top,
+ * 1=bottom)
+ *
+ * @param document The document
+ * @param position_y the Y adjustment
+ */
+void zathura_document_set_position_y(zathura_document_t* document, double position_y);
+
 /**
  * Returns the current scale value of the document
  *
@@ -178,9 +214,37 @@ void* zathura_document_get_data(zathura_document_t* document);
 void zathura_document_set_data(zathura_document_t* document, void* data);
 
 /**
- * Return the size of a cell in the document's layout table, assuming that
+ * Sets the width of the viewport in pixels.
- * the table is homogeneous (i.e. every cell has the same dimensions). It takes
+ *
- * the current scale into account.
+ * @param[in] document     The document instance
+ * @param[in] width        The width of the viewport
+ */
+void
+zathura_document_set_viewport_width(zathura_document_t* document, unsigned int width);
+
+/**
+ * Sets the height of the viewport in pixels.
+ *
+ * @param[in] document     The document instance
+ * @param[in] height       The height of the viewport
+ */
+void
+zathura_document_set_viewport_height(zathura_document_t* document, unsigned int height);
+
+/**
+ * Return the size of the viewport in pixels.
+ *
+ * @param[in]  document     The document instance
+ * @param[out] height,width The width and height of the viewport
+ */
+void
+zathura_document_get_viewport_size(zathura_document_t* document,
+                                   unsigned int *height, unsigned int* width);
+
+/**
+ * Return the size of a cell from the document's layout table in pixels. Assumes
+ * that the table is homogeneous (i.e. every cell has the same dimensions). It
+ * takes the current scale into account.
  *
  * @param[in]  document     The document instance
  * @param[out] height,width The computed height and width of the cell
@@ -189,10 +253,9 @@ void zathura_document_get_cell_size(zathura_document_t* document,
                                     unsigned int* height, unsigned int* width);
 
 /**
- * Compute the size of the entire document to be displayed (in pixels), taking
+ * Compute the size of the entire document to be displayed in pixels. Takes into
- * into account the scale, the layout of the pages, and the padding between
+ * account the scale, the layout of the pages, and the padding between them. It
- * them. It should be equal to the allocation of zathura->ui.page_widget once
+ * should be equal to the allocation of zathura->ui.page_widget once it's shown.
- * it's shown.
  *
  * @param[in]  document               The document
  * @param[out] height,width           The height and width of the document