A.14. wl_surface - an onscreen surface
A surface is a rectangular area that is displayed on the screen. It has a location, size and pixel contents.
The size of a surface (and relative positions on it) is described in surface local coordinates, which may differ from the buffer local coordinates of the pixel content, in case a buffer_transform or a buffer_scale is used.
Surfaces are also used for some special purposes, e.g. as cursor images for pointers, drag icons, etc.
A.14.1. Requests provided by wl_surface
A.14.1.1. wl_surface::destroy - delete surface
Deletes the surface and invalidates its object ID.
A.14.1.2. wl_surface::attach - set the surface contents
Set a buffer as the content of this surface.
The new size of the surface is calculated based on the buffer size transformed by the inverse buffer_transform and the inverse buffer_scale. This means that the supplied buffer must be an integer multiple of the buffer_scale.
The x and y arguments specify the location of the new pending buffer's upper left corner, relative to the current buffer's upper left corner, in surface local coordinates. In other words, the x and y, combined with the new surface size define in which directions the surface's size changes.
Surface contents are double-buffered state, see wl_surface.commit.
The initial surface contents are void; there is no content. wl_surface.attach assigns the given wl_buffer as the pending wl_buffer. wl_surface.commit makes the pending wl_buffer the new surface contents, and the size of the surface becomes the size calculated from the wl_buffer, as described above. After commit, there is no pending buffer until the next attach.
Committing a pending wl_buffer allows the compositor to read the pixels in the wl_buffer. The compositor may access the pixels at any time after the wl_surface.commit request. When the compositor will not access the pixels anymore, it will send the wl_buffer.release event. Only after receiving wl_buffer.release, the client may re-use the wl_buffer. A wl_buffer that has been attached and then replaced by another attach instead of committed will not receive a release event, and is not used by the compositor.
Destroying the wl_buffer after wl_buffer.release does not change the surface contents. However, if the client destroys the wl_buffer before receiving the wl_buffer.release event, the surface contents become undefined immediately.
If wl_surface.attach is sent with a NULL wl_buffer, the following wl_surface.commit will remove the surface content.
wl_surface::attach arguments
- buffer
Type: object
- x
Type: int
- y
Type: int
A.14.1.3. wl_surface::damage - mark part of the surface damaged
This request is used to describe the regions where the pending buffer is different from the current surface contents, and where the surface therefore needs to be repainted. The pending buffer must be set by wl_surface.attach before sending damage. The compositor ignores the parts of the damage that fall outside of the surface.
Damage is double-buffered state, see wl_surface.commit.
The damage rectangle is specified in surface local coordinates.
The initial value for pending damage is empty: no damage. wl_surface.damage adds pending damage: the new pending damage is the union of old pending damage and the given rectangle.
wl_surface.commit assigns pending damage as the current damage, and clears pending damage. The server will clear the current damage as it repaints the surface.
wl_surface::damage arguments
- x
Type: int
- y
Type: int
- width
Type: int
- height
Type: int
A.14.1.4. wl_surface::frame - request repaint feedback
Request notification when the next frame is displayed. Useful for throttling redrawing operations, and driving animations. The frame request will take effect on the next wl_surface.commit. The notification will only be posted for one frame unless requested again.
A server should avoid signalling the frame callbacks if the surface is not visible in any way, e.g. the surface is off-screen, or completely obscured by other opaque surfaces.
A client can request a frame callback even without an attach, damage, or any other state changes. wl_surface.commit triggers a display update, so the callback event will arrive after the next output refresh where the surface is visible.
The object returned by this request will be destroyed by the compositor after the callback is fired and as such the client must not attempt to use it after that point.
wl_surface::frame arguments
- callback
Type: new_id
A.14.1.5. wl_surface::set_opaque_region - set opaque region
This request sets the region of the surface that contains opaque content.
The opaque region is an optimization hint for the compositor that lets it optimize out redrawing of content behind opaque regions. Setting an opaque region is not required for correct behaviour, but marking transparent content as opaque will result in repaint artifacts.
The opaque region is specified in surface local coordinates.
The compositor ignores the parts of the opaque region that fall outside of the surface.
Opaque region is double-buffered state, see wl_surface.commit.
wl_surface.set_opaque_region changes the pending opaque region. wl_surface.commit copies the pending region to the current region. Otherwise, the pending and current regions are never changed.
The initial value for opaque region is empty. Setting the pending opaque region has copy semantics, and the wl_region object can be destroyed immediately. A NULL wl_region causes the pending opaque region to be set to empty.
wl_surface::set_opaque_region arguments
- region
Type: object
A.14.1.7. wl_surface::commit - commit pending surface state
Surface state (input, opaque, and damage regions, attached buffers, etc.) is double-buffered. Protocol requests modify the pending state, as opposed to current state in use by the compositor. Commit request atomically applies all pending state, replacing the current state. After commit, the new pending state is as documented for each related request.
On commit, a pending wl_buffer is applied first, all other state second. This means that all coordinates in double-buffered state are relative to the new wl_buffer coming into use, except for wl_surface.attach itself. If there is no pending wl_buffer, the coordinates are relative to the current surface contents.
All requests that need a commit to become effective are documented to affect double-buffered state.
Other interfaces may add further double-buffered surface state.
A.14.1.9. wl_surface::set_buffer_scale - sets the buffer scaling factor
This request sets an optional scaling factor on how the compositor interprets the contents of the buffer attached to the window.
Buffer scale is double-buffered state, see wl_surface.commit.
A newly created surface has its buffer scale set to 1.
The purpose of this request is to allow clients to supply higher resolution buffer data for use on high resolution outputs. Its intended that you pick the same buffer scale as the scale of the output that the surface is displayed on.This means the compositor can avoid scaling when rendering the surface on that output.
Note that if the scale is larger than 1, then you have to attach a buffer that is larger (by a factor of scale in each dimension) than the desired surface size.
wl_surface::set_buffer_scale arguments
- scale
Type: int