Cache solid alpha pictures at 256 discrete levels - #48
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…erver round-trips Creating a solid alpha picture via solid_picture() involves multiple X server round-trips: XCreatePixmap, XRenderCreatePicture, XRenderFillRectangle. Currently, every window with opacity < OPAQUE creates its own alpha picture in paint_all(), and determine_mode() destroys it when the mode changes. For a desktop with many translucent windows, this means dozens of redundant picture creations per frame. Add a global cache of 256 discrete alpha levels (indexed by opacity>>24). When a window needs an alpha picture, it reuses the cached one instead of creating a new one. The border alpha picture (for frame opacity) is also cached once. Since the pictures are now shared across windows, they must never be freed per-window. determine_mode() and finish_destroy_win() now only null the pointers, never calling XRenderFreePicture(). This fixes the double-free that would otherwise occur when two windows share the same cached picture. Impact: eliminates redundant alpha picture creation/destruction, reducing server round-trips especially for desktops with many translucent windows.
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Summary
Caches solid alpha pictures at 256 discrete levels to eliminate redundant X server round-trips for translucent windows. Also fixes a double-free bug that would occur if the cached pictures were freed per-window.
Problem
Creating a solid alpha picture via
solid_picture()involves multiple X server round-trips:XCreatePixmap,XRenderCreatePicture,XRenderFillRectangle. Every window with opacity <OPAQUEcreates its own alpha picture inpaint_all(), anddetermine_mode()destroys it when the mode changes. For a desktop with many translucent windows, this means dozens of redundant picture creations per frame.Solution
Global cache
g_alpha_pict_cache[256]— indexed byopacity >> 24(0-255). Each level is created on first demand and reused for all windows with that opacity level.g_border_alpha_pict— cached once for frame opacity (shared across all windows with frame opacity).No per-window free
Since the pictures are now shared across windows, they must never be freed per-window:
determine_mode()now only nulls the pointers, never callingXRenderFreePicture()finish_destroy_win()now only nulls the pointersThis fixes the double-free that would occur when two windows share the same cached picture.
Changes
fastcompmgr.cis touchedmake clean && makeproduces zero warnings, zero errorsImpact
Eliminates redundant alpha picture creation/destruction, reducing server round-trips especially for desktops with many translucent windows.