Behavior changes

• The desktop background image is no longer smeared to fill the screen. If it's too small, it will be too small. (#1464)

Bug fixes

• Fix sometimes window property changes aren't reflected in picom.
• Fix shadow-opacity being applied twice. You may need to adjust your shadow-opacity settings.
• Properly fix the longstanding "request too big" problem when uploading shadow images. (Previous workaround: 69b3eee76b6f3ec6be1d2402151d8882279a74a4) (#257)
• Fix window frames not being blended correctly when using frame-opacity with saved-image-blend.
• Fix shadow not being correctly masked when scaled. (#1389)
• Fix misaligned shadow and window when they are scaled. (#1389)
• Fix unexpected relative movement between shadow and window when they are scaled. (#1389)
• background blur does not cover the entire background if the window has rounded corner and is scaled.
• Fix shaders in window-shader-fg-rule being erroneously reported as failed to load.
• Fix --blur-background-fixed having no effect. (#1402)
• Fix assertion failure when running with some window managers (e.g. qtile) and no window is focused (#1384)

Other changes

• Hide picom from menus by default (#1155)

Internal changes

• Breaking change to backend API, to allow better image creation, and applying tints to windows.
• Refactor shadow rendering, preparing for dynamic shadow colors.
• Backend API 2.0 breaking change, backend_mask_image.origin is now a vec2.
• Backend API 2.0 breaking change, backend_blur_args now has source_mask_scale.
• Backend API 2.0 breaking change, backend_blit_args.shader is now shader_handle instead of void *.