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Implement this interface to handle events when window rendering is disabled (off-screen rendering). The methods of this class will be called on the UI thread. In order to create windowless browsers the windowless_rendering_enabled setting must be set to true.

Table of contents:

• Examples
• Notes
• Callbacks
  • GetRootScreenRect
  • GetViewRect
  • GetScreenPoint
  • GetScreenInfo
  • OnPopupShow
  • OnPopupSize
  • OnPaint
  • OnCursorChange
  • OnScrollOffsetChanged
  • OnTextSelectionChanged
  • StartDragging
  • UpdateDragCursor

Off-screen rendering examples:

• Kivy
• Panda3D - tested with v31
• pygame + PyOpenGL - tested with v31, more info on this example on the Forum in this post
• cefpython_offscreen_no_UI_framework.py - most basic usage of OSR to take a screenshot of a page

Callbacks available in upstream CEF, but not yet exposed in CEF Python (see src/include/cef_render_handler.h):

• OnImeCompositionRangeChanged

Called to retrieve the root window rectangle in screen coordinates. Return true if the rectangle was provided.

Called to retrieve the view rectangle which is relative to screen coordinates. Return true if the rectangle was provided.

Called to retrieve the translation from view coordinates to actual screen coordinates. Return true if the screen coordinates were provided.

Called to allow the client to fill in the screen info with appropriate values. Return true if screen_info_out was modified, false to let CEF use defaults.

Fill screen_info_out with any of the following keys (all optional):

If neither rect nor available_rect is supplied, CEF falls back to the rectangle returned by GetViewRect (popups may be misplaced if the rectangle ends up empty).

HiDPI handling: set device_scale_factor to match the host display (e.g. 2.0 on a Retina/4K screen, 1.5 for 150% fractional scaling). The factor is applied to the OnPaint buffer: with a view rect of 800x600 and device_scale_factor=2.0, OnPaint receives a 1600x1200 BGRA buffer while width/height arguments equal the buffer's pixel dimensions. Always upload the buffer at its actual pixel size and lay it out at the view's logical size to avoid blurry output. Call Browser.NotifyScreenInfoChanged when the device scale factor or display geometry changes (e.g. the window moved to a different monitor) so CEF re-queries this callback.

Called when the browser wants to show or hide the popup widget. The popup should be shown if |show| is true and hidden if|show| is false.

Called when the browser wants to move or resize the popup widget. |rect_out| contains the new location and size.

Called when an element should be painted. Pixel values passed to this method are scaled relative to view coordinates based on the value of CefScreenInfo.device_scale_factor returned from GetScreenInfo. |type| indicates whether the element is the view or the popup widget. |buffer| contains the pixel data for the whole image. |dirty_rects| contains the set of rectangles in pixel coordinates that need to be repainted. |buffer| will be |width|*|height|*4 bytes in size and represents a BGRA image with an upper-left origin.

Important: Do not keep reference to |paint_buffer| after this method returns.

PaintElementType enum:

• cef.PET_VIEW
• cef.PET_POPUP

Called when the browser's cursor has changed. If |type| is CT_CUSTOM then |custom_cursor_info| will be populated with the custom cursor information.

CursorHandle is an int pointer.

Called when the scroll offset has changed.

Description from upstream CEF:

Called when text selection has changed for the specified |browser|. |selected_text| is the currently selected text and |selected_range| is the character range.

NOTE: this callback seems to be called only when selecting text with a mouse. When selecting text programmatically using javascript code it doesn't get called.

Description from upstream CEF:

Called when the user starts dragging content in the web view. Contextual information about the dragged content is supplied by |drag_data|. (|x|, |y|) is the drag start location in screen coordinates. OS APIs that run a system message loop may be used within the StartDragging call.

Return false to abort the drag operation. Don't call any of CefBrowserHost::DragSourceEnded methods after returning false.

Return true to handle the drag operation. Call CefBrowserHost::DragSourceEndedAt and DragSourceSystemDragEnded either synchronously or asynchronously to inform the web view that the drag operation has ended.

Description from upstream CEF:

Called when the web view wants to update the mouse cursor during a drag & drop operation. |operation| describes the allowed operation (none, move, copy, link).

See Browser.DragSourceEndedAt for a list of values for the operation enum.