KWin/Shadow: Difference between revisions

Latest revision as of 11:25, 4 February 2013

TODO: document the current shadow system

KWin Shadows

The ideas for a new shadow system originated from the disadvantages of the old system. The old code shows serious bugs in conjunction with blur effect, slows down the system, is mostly obsoleted by the decoration shadows and not consistent with the overall look'n'feel. The widget style has no influence in the shadow.

Giving control to the Widget Style

The new system should give the control to the widget style. A shadow is part of the overall light model. The compositor does not know about the light model or about things like the Oxygen glow.

Nevertheless the decoration shadows should be kept and the new shadow system should only be used if the decoration does not provide shadows. The new system is therefore mostly meant for unmanaged windows such as menus, tooltips, dropdown menus, etc. but can also be used for "normal" windows with a legacy decoration. In future we could think about allowing an ARGB deco to not use the decoration shadows any more, but the new system. For decorations like Aurorae we will still need the decoration shadows. Nevertheless for decorations direct API calls are to be preferred over using any X property based systems!

The shadow elements

The shadow elements are inspired by Plasma's FrameSvg borders. There will be eight pixmaps defining the shadow:

* top
* top-right
* right
* bottom-right
* bottom
* bottom-left
* left
* top-left

The center element is not required as we do not want to have shadows behind the window.

The compositor announces support for the shadows through adding _KDE_NET_WM_SHADOW to _NET_SUPPORTED

Requesting Shadow for a Window

To set a shadow for a window the toolkit/widget style should set the property _KDE_NET_WM_SHADOW. The structure of the property is the X11 ids of the pixmaps defining the shadow elements followed by the padding in the various directions starting from top in clockwise direction. 4 padding elements are required, corresponding to the 4 sides of the shadow:

* padding in y-pixels for TOP
* padding in x-pixels for RIGHT
* padding in y-pixels for BOTTOM
* padding in x-pixels for LEFT

Padding for the corners is derived from the 4 values above.

An example for a shadow of 10 pixels in all directions and 20 pixels on the bottom and tiled borders: _KDE_NET_WM_SHADOW=#top, #top-right, #right, #bottom-right, #bottom, #bottom-left, #left, #top-left, 10, 10, 20, 10

The pixmaps start from the offsets derived from the 4 padding values above and are painted in their complete size. For the borders the pixmaps are stretched in the respective direction, the other size is fixed.

It is the task of the toolkit/widget style to ensure that the pixmaps are valid, namely that they have been created and exist in memory as an X11 pixmap. If the shadow changes the pixmaps can be updated and the compositor needs to respond to damage events on the pixmaps. A toolkit/widget style may share the pixmaps between various processes and this is also recommended to do, if possible.

Implementation in KWin

Shadows are moved directly into the compositor following the approach of the decoration shadows. Window quads for each of the shadow areas are added and rendered before the window (if it is RGB) or rendered together with the window in case of RGBA (for Oxygen the latter case will always be the case).

Moving the shadows directly into the compositor and not in an effect should provide the required performance and should not show the visual bugs seen before with e.g. blur effect. The shadow belongs to the window, so even wobbly shadows should work better ;-)

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+TODO: document the current shadow system
 == KWin Shadows ==
 The ideas for a new shadow system originated from the disadvantages of the old system. The old code shows serious bugs in conjunction with blur effect, slows down the system, is mostly obsoleted by the decoration shadows and not consistent with the overall look'n'feel. The widget style has no influence in the shadow.
@@ Line 22: / Line 24: @@
 === Requesting Shadow for a Window ===
-To set a shadow for a window the toolkit/widget style should set the property _KDE_NET_WM_SHADOW. The structure of the property is the padding in the various directions starting from top in clockwise direction. For border elements only one element is required, for corner elements x and y padding is required, that is 12 elements:
+To set a shadow for a window the toolkit/widget style should set the property _KDE_NET_WM_SHADOW. The structure of the property is the X11 ids of the pixmaps defining the shadow elements followed by the padding in the various directions starting from top in clockwise direction. 4 padding elements are required, corresponding to the 4 sides of the shadow:
   * padding in y-pixels for TOP
- * padding in x-pixels for TOP-RIGHT
- * padding in y-pixels for TOP-RIGHT
   * padding in x-pixels for RIGHT
- * ...
+  * padding in y-pixels for BOTTOM
-  * padding in x-pixels for TOP-LEFT
+  * padding in x-pixels for LEFT
-  * padding in y-pixels for TOP-LEFT
-Two additional values are required: the first to specify if borders need to be stretched or tiled: zero represents stretched, any non-zero represents tiled. The second value specifies whether the generic of (un)focused shadow should be used: zero represents generic, any non-zero value represents the (un)focused shadow. An additional third parameter for the (un)focused shadow can be specified to provide the duration of a transition animation from focused to unfocused state (and vice versa) in msec. If not specified or 0 no transition animation is used.
+Padding for the corners is derived from the 4 values above.
-An example for a shadow of 10 pixels in all directions and 20 pixels on the bottom, tiled with (un)focused shadow and a 200 msec transition animation would look like the following:
+An example for a shadow of 10 pixels in all directions and 20 pixels on the bottom and tiled borders:
-_KDE_NET_WM_SHADOW=10, 10, 10, 10, 10, 20, 20, 10, 20, 10, 10, 10, 1, 1, 200
+_KDE_NET_WM_SHADOW=#top, #top-right, #right, #bottom-right, #bottom, #bottom-left, #left, #top-left, 10, 10, 20, 10
-The pixmaps start from the offset and are painted in there complete size. For the borders the pixmaps are either tiled or stretched in the respective direction, the other size is fixed.
+The pixmaps start from the offsets derived from the 4 padding values above and are painted in their complete size. For the borders the pixmaps are stretched in the respective direction, the other size is fixed.
+It is the task of the toolkit/widget style to ensure that the pixmaps are valid, namely that they have been created and exist in memory as an X11 pixmap. If the shadow changes the pixmaps can be updated and the compositor needs to respond to damage events on the pixmaps. A toolkit/widget style may share the pixmaps between various processes and this is also recommended to do, if possible.
 === Implementation in KWin ===
@@ Line 42: / Line 43: @@
 Moving the shadows directly into the compositor and not in an effect should provide the required performance and should not show the visual bugs seen before with e.g. blur effect. The shadow belongs to the window, so even wobbly shadows should work better ;-)
-=== Ideas for Future Improvements ===
-It should be possible to set shadow pixmaps on a per-window level (though global shadows on the root window should be preferred for performance reasons).