Merge (large!).

1 files changed, 173 insertions, 86 deletions

diff --git a/doc/dw-images-and-backgrounds.doc b/doc/dw-images-and-backgrounds.doc
index 356652a6..8f07766a 100644
--- a/doc/dw-images-and-backgrounds.doc
+++ b/doc/dw-images-and-backgrounds.doc
@@ -1,10 +1,11 @@
 /** \page dw-images-and-backgrounds Images and Backgrounds in Dw
 
-<h2>General</h2>
+Image Buffers
+=============
 
-Representation of the image data is delegated to dw::core::Imgbuf, see
-there for details. Drawing is delegated to dw::core::View
-(dw::core::View::drawImgbuf).
+Representation of the image data is done by dw::core::Imgbuf, see
+there for details. Drawing is done by dw::core::View
+(dw::core::View::drawImage).
 
 Since dw::core::Imgbuf provides memory management based on reference
 counting, there may be an 1-to-n relation from image renderers (image
@@ -15,61 +16,73 @@ dw::core::Imgbuf::copyRow) notify all renderers connected to the
 buffer.
 
 
-<h2>Images</h2>
+Image Renderer
+==============
+
+Generally, there are no restrictions on how to manage
+dw::core::Imgbuf; but to handle image data from web resources, the
+interface dw::core::ImgRenderer should be implemented. It is again
+wrapped by DilloImage (to make access from the C part possible, since
+dw::core::ImgRenderer is written in C++), which is referenced by
+DilloWeb. There are two positions where retrieving image data is
+initiated:
+
+- Html_load_image: for embedded images (implemented by dw::Image,
+  which implements dw::core::ImgRenderer);
+- StyleEngine::apply (search for "case
+  CSS_PROPERTY_BACKGROUND_IMAGE"): for backgrond images; there are
+  some implementations of dw::core::ImgRenderer within the context of
+  dw::core::style::StyleImage.
+
+Both are described in detail below. Notice that the code is quite
+similar; only the implementation of dw::core::ImgRenderer differs.
+
+At this time, dw::core::ImgRenderer has got two methods (see more
+documentation there):
+
+- dw::core::ImgRenderer::setBuffer,
+- dw::core::ImgRenderer::drawRow,
+- dw::core::ImgRenderer::finish, and
+- dw::core::ImgRenderer::fatal.
+
+
+Images
+======
 
 This is the simplest renderer, displaying an image. For each row to be
 drawn,
 
-<ol>
-<li> first dw::core::Imgbuf::copyRow, and then
-<li> for each dw::Image, dw::Image::drawRow must be called, with the same
-     argument (no scaling is necessary).
-</ol>
+- first dw::core::Imgbuf::copyRow, and then
+- for each dw::Image, dw::Image::drawRow must be called, with the same
+  argument (no scaling is necessary).
 
 dw::Image automatically scales the dw::core::Imgbuf, the root buffer
 should be passed to dw::Image::setBuffer.
 
 \see dw::Image for more details.
 
-<h2>Future Extensions</h2>
 
-(This is not implemented yet.) Rendering itself (image widgets and
-background) will be abstracted, by a new interface
-dw::core::ImageRenderer.  In the current code for image decoding, this
-interface will replace references to dw::Image, which implements
-dw::core::ImageRenderer, in most cases.
+Background Images
+=================
 
-<h2>Backgrounds</h2>
+Since background images are style resources, they are associated with
+dw::core::style::Style, as dw::core::style::StyleImage, which is
+handled in a similar way (reference counting etc.) as
+dw::core::style::Color and dw::core::style::Font, although it is
+concrete and not platform-dependant.
 
-(This is based on future extensions described above.) Since background
-are style resources, they are associated with
-dw::core::style::Style. For backgrounds, another level is needed,
-because of the 1-to-n relation from dw::core::style::Style to
-dw::core::Widget:
+The actual renderer (passed to Web) is an instance of
+dw::core::ImgRendererDist (distributes all calls to a set of other
+instances of dw::core::ImgRenderer), which contains two kinds of
+renderers:
 
-\dot
-digraph G {
-   node [shape=record, fontname=Helvetica, fontsize=10];
-   edge [arrowhead="open", dir="both", arrowtail="none",
-         labelfontname=Helvetica, labelfontsize=10, color="#404040",
-         labelfontcolor="#000080"];
-   fontname=Helvetica; fontsize=10;
-
-   "background renderer (as a part of style)" -> "image buffer" [headlabel="*",
-                                                                taillabel="1"];
-   "widget (or a part of it)" -> "background renderer (as a part of style)"
-      [headlabel="*", taillabel="1"];
-}
-\enddot
-
-Unlike dw::Image, dw::core::style::BgRenderer is not associated with a
-certain rectangle on the canvas. Instead, widgets, or parts of widgets
-take this role. This is generally represented by an implementation of
-the interface dw::core::style::BgAllocation, which is implemented by
-dw::core::Widget, but also by all parts of widget implementation,
-which may have an own background image.
+- one instance of dw::core::style::StyleImage::StyleImgRenderer, which
+  does everything needed for dw::core::style::StyleImage, and
+- other renderers, used externally (widgets etc.), which are added by
+  dw::core::style::StyleImage::putExternalImgRenderer (and removed by
+  dw::core::style::StyleImage::removeExternalImgRenderer).
 
-The following diagram gives a total overview:
+This diagram gives an comprehensive overview:
 
 \dot
 digraph G {
@@ -79,70 +92,144 @@ digraph G {
          labelfontcolor="#000080"];
    fontname=Helvetica; fontsize=10;
 
-   "DICache Entry";
-
-   subgraph cluster_dw_images {
+   subgraph cluster_dw_style {
       style="dashed"; color="#000080"; fontname=Helvetica; fontsize=10;
-      label="Dw Images";
 
-      ImageRenderer [URL="\ref dw::core::ImageRenderer", color="#ff8080"];
-      Imgbuf [URL="\ref dw::core::Imgbuf", color="#ff8080"];
+      Style [URL="\ref dw::core::style::Style"];
+      StyleImage [URL="\ref dw::core::style::StyleImage"];
+      Imgbuf [URL="\ref dw::core::Imgbuf", color="#a0a0a0"];
+      StyleImgRenderer
+         [URL="\ref dw::core::style::StyleImage::StyleImgRenderer"];
+      ImgRenderer [URL="\ref dw::core::ImgRenderer", color="#ff8080"];
+      ImgRendererDist [URL="\ref dw::core::ImgRendererDist"];
+      ExternalImgRenderer
+         [URL="\ref dw::core::style::StyleImage::ExternalImgRenderer",
+          color="#a0a0a0"];
+      ExternalWidgetImgRenderer
+         [URL="\ref dw::core::style::StyleImage::ExternalWidgetImgRenderer",
+          color="#a0a0a0"];
    }
 
-   subgraph cluster_widgets {
+   subgraph cluster_dw_layout {
       style="dashed"; color="#000080"; fontname=Helvetica; fontsize=10;
-      label="Widgets";
 
-      Widget [URL="\ref dw::core::Widget", color="#a0a0a0"];
-      Textblock [URL="\ref dw::Textblock"];
-      "Textblock::Word" [URL="\ref dw::Textblock::Word"];
-      Table [URL="\ref dw::Table"];
-      "Table::Row" [URL="\ref dw::Table::Row"];
-      Image [URL="\ref dw::Image"];
+      Layout [URL="\ref dw::core::Layout"];
+      LayoutImgRenderer [URL="\ref dw::core::Layout::LayoutImgRenderer"];
    }
 
-   subgraph cluster_style {
+   subgraph cluster_dw_widget {
       style="dashed"; color="#000080"; fontname=Helvetica; fontsize=10;
-      label="dw::core::style";
 
-      Style [URL="\ref dw::core::style::Style"];
-      BgRenderer [URL="\ref dw::core::style::BgRenderer"];
-      BgAllocation [URL="\ref dw::core::style::BgAllocation", color="#ff8080"];
+      Widget [URL="\ref dw::core::Widget", color="#a0a0a0"];
+      WidgetImgRenderer [URL="\ref dw::core::Widget::WidgetImgRenderer"];
    }
 
-   "DICache Entry" -> ImageRenderer [headlabel="*", taillabel="1"];
-   "DICache Entry" -> Imgbuf [headlabel="1", taillabel="1"];
-
-   BgRenderer -> Imgbuf [headlabel="1", taillabel="*"];
-   BgRenderer -> BgAllocation [headlabel="*", taillabel="1"];
-   ImageRenderer -> BgRenderer [arrowhead="none", arrowtail="empty", dir="both",
-                                style="dashed"];
-   ImageRenderer -> Image [arrowhead="none", arrowtail="empty", dir="both",
-                           style="dashed"];
-
-   Style -> BgRenderer [headlabel="0..1", taillabel="1"];
+   subgraph cluster_dw_textblock {
+      style="dashed"; color="#000080"; fontname=Helvetica; fontsize=10;
 
-   Widget -> Textblock [arrowhead="none", arrowtail="empty", dir="both"];
-   Textblock -> "Textblock::Word" [headlabel="*", taillabel="1"];
-   Widget -> Table [arrowhead="none", arrowtail="empty", dir="both"];
-   Table -> "Table::Row" [headlabel="*", taillabel="1"];
-   Widget -> Image [arrowhead="none", arrowtail="empty", dir="both"];
+      Textblock [URL="\ref dw::Textblock"];
+      Word [URL="\ref dw::Textblock::Word"];
+      WordImgRenderer [URL="\ref dw::Textblock::WordImgRenderer"];
+      SpaceImgRenderer [URL="\ref dw::Textblock::SpaceImgRenderer"];
+   }
 
-   BgAllocation -> Widget [arrowhead="none", arrowtail="empty", dir="both",
-                           style="dashed"];
-   BgAllocation -> "Textblock::Word" [arrowhead="none", arrowtail="empty",
+   Style -> StyleImage [headlabel="*", taillabel="1"];
+   StyleImage -> Imgbuf [headlabel="*", taillabel="1"];
+   StyleImage -> StyleImgRenderer [headlabel="1", taillabel="1"];
+   StyleImage -> ImgRendererDist [headlabel="1", taillabel="1"];
+   ImgRendererDist -> StyleImgRenderer [headlabel="1", taillabel="1"];
+   ImgRendererDist -> ImgRenderer [headlabel="1", taillabel="*"];
+
+   ImgRenderer -> ImgRendererDist [arrowhead="none", arrowtail="empty",
+                                   dir="both", style="dashed"];
+   ImgRenderer -> StyleImgRenderer [arrowhead="none", arrowtail="empty",
+                                   dir="both", style="dashed"];
+   ImgRenderer -> ExternalImgRenderer [arrowhead="none", arrowtail="empty",
                                       dir="both", style="dashed"];
-   BgAllocation -> "Table::Row" [arrowhead="none", arrowtail="empty",
-                                 dir="both", style="dashed"];
+   ExternalImgRenderer -> ExternalWidgetImgRenderer [arrowhead="none",
+                                 arrowtail="empty", dir="both", style="dashed"];
+
+   Layout -> LayoutImgRenderer [headlabel="1", taillabel="0..1"];
+   ExternalImgRenderer -> LayoutImgRenderer [arrowhead="none",
+                                 arrowtail="empty", dir="both", style="dashed"];
+
+   Widget -> WidgetImgRenderer [headlabel="1", taillabel="0..1"];
+   ExternalWidgetImgRenderer -> WidgetImgRenderer [arrowhead="none",
+                                 arrowtail="empty", dir="both", style="dashed"];
+
+   Textblock -> Word [headlabel="1", taillabel="*"];
+   Word -> WordImgRenderer [headlabel="1", taillabel="0..1"];
+   Word -> SpaceImgRenderer [headlabel="1", taillabel="0..1"];
+   ExternalWidgetImgRenderer -> WordImgRenderer [arrowhead="none",
+                                 arrowtail="empty", dir="both", style="dashed"];
+   WordImgRenderer -> SpaceImgRenderer [arrowhead="none", arrowtail="empty",
+                                        dir="both", style="dashed"];
 }
 \enddot
 
 <center>[\ref uml-legend "legend"]</center>
 
 
-<h2>Integration into dillo</h2>
+Memory management
+-----------------
+
+dw::core::style::StyleImage extends lout::signal::ObservedObject, so
+that deleting this instance can be connected to code dealing with
+cache clients etc. See StyleImageDeletionReceiver and how it is
+attached in StyleEngine::apply ("case CSS_PROPERTY_BACKGROUND_IMAGE").
+
+
+Bugs and Things Needing Improvement
+===================================
+
+(Mostly related to image backgrounds, when not otherwise mentioned.)
+
+High Priority
+-------------
+
+**Configurability, security/privacy aspects, etc.,** which are
+currently available for image widgets, should be adopted. Perhaps some
+more configuration options specially for background images.
+
+
+Medium Priority
+---------------
+
+**Background-attachment** is not yet implemented, and will be postponed.
+
+**Calls to dw::core::ImgRenderer::fatal** are incomplete. As an
+example, it is not called, when connecting to a server fails. (And so,
+as far as I see, no cache client is started.)
+
+
+Low Priority
+------------
+
+**Alpha support:** (not related to image backgrounds) currently alpha
+support (and also colormap management) is done in dicache, while
+dw::Image is only created with type RGB. This leads to several problems:
+
+- One dicache entry (representing an image related to the same URL),
+  which has only one background color, may refer to different images
+  with different background colors.
+- The dicache only handles background colors, not background images.
+
+The solution is basicly simple: keep alpha support out of dicache;
+instead implement RGBA in dw::Image. As it seems, the main problem is
+alpha support in FLTK/X11.
+
+
+Solved (Must Be Documented)
+---------------------------
 
-\todo Add some references.
+*Drawing background images row by row may become slow. As an
+alternative, dw::core::ImgRenderer::finish could be used. However,
+drawing row by row could become an option.* There is now
+dw::core::style::drawBackgroundLineByLine, which can be changed in the
+code, and is set to *false*. The old code still exists, so changing
+this to *true* activates again drawing line by line.
 
+(For image widgets, this could also become an option: in contexts,
+when image data is retrieved in a very fast way.)
 
 */