The class styles define additional elements of the window class.
Two or more styles can be combined by using the bitwise OR (|) operator.
To assign a style to a window class, assign the style to the style member
of the WNDCLASSEX structure. The class styles are as follows.

Style Action
CS_BYTEALIGNCLIENT Aligns the window‘s client area on a byte boundary
(in the x direction) to enhance performance during
drawing operations. This style affects the width of
the window and its horizontal placement on the display.

CS_BYTEALIGNWINDOW Aligns the window on a byte boundary (in the x
direction) to enhance performance during operations
that involve moving or sizing the window.
This style affects the width of the window and its
horizontal placement on the display.

CS_CLASSDC Allocates one device context to be shared by all
windows in the class. For more information about
device contexts, see Class and Private Device Contexts
and Device Contexts.

CS_DBLCLKS Instructs Windows to send a double-click message to
the window procedure when the user double-clicks the
mouse while the cursor is within a window belonging to the class.
For more information about double-clicks, see Mouse Input.

CS_GLOBALCLASS Specifies that the window class is an application
global class. For more information, see Application
Global Classes.

CS_HREDRAW Specifies that the entire window is to be redrawn if
a movement or size adjustment changes the width of the
client area.

CS_NOCLOSE Disables the Close command on the System menu.
CS_OWNDC Allocates a unique device context for each window in
the class. For more information about device contexts,
see Class and Private Device Contexts and Device Contexts.

CS_PARENTDC Sets the clipping rectangle of the child window to that of the parent
window so that the child can draw on the parent. A window with the
CS_PARENTDC style bit receives a regular device context from the
system‘s cache of device contexts. It does not give the child the
parent‘s device context or device context settings. Specifying
CS_PARENTDC enhances an application‘s performance. For more information
about device contexts, see Class and Private Device Contexts and Device
Contexts.

CS_SAVEBITS Saves, as a bitmap, the portion of the screen image obscured by a
window. Windows uses the saved bitmap to re-create the screen image
when the window is removed. Windows displays the bitmap at its original
location and does not send WM_PAINT messages to windows obscured by
the window if other screen actions have not invalidated the stored
image. Use this style for small windows that are displayed briefly and
then removed before other screen activity takes place (for example,
menus or dialog boxes). This style increases the time required to
display the window, because the operating system must first allocate
memory to store the bitmap.

CS_VREDRAW Specifies that the entire window is to be redrawn if
a movement or size adjustment changes the height of
the client area.

Class Styles