Customizing a Control's Appearance

Customizing a Control's Appearance

Custom draw is not a common control; it is a service that many common controls provide. Custom draw services allow an application greater flexibility in customizing a control's appearance. Your application can harness custom draw notifications to easily change the font used to display items or manually draw an item without having to do a full-blown owner draw.

About Custom Draw

Custom Draw With List View and Tree View Controls
Using Custom Draw

Custom Draw Reference

About Custom Draw
This section contains general information about custom draw functionality and provides a conceptual overview of how an application can support custom draw.

Currently, the following controls support custom draw functionality:

Header controls
List view controls
Rebar controls
Toolbar controls
Tooltip controls
Trackbar controls
Tree view controls
Note Custom draw is implemented in version 4.70 and later of Comctl32.dll.

About Custom Draw Notification Messages
All common controls that support custom draw send NM_CUSTOMDRAW notification messages at specific points during drawing operations. These notifications describe drawing operations that apply to the entire control as well as drawing operations specific to items within the control. Like many notification messages, NM_CUSTOMDRAW notifications are sent as WM_NOTIFY messages.

The lParam parameter of a custom draw notification message will be the address of an NMCUSTOMDRAW structure or a control-specific structure that contains an NMCUSTOMDRAW structure as its first member. The following table illustrates the relationship between the controls and the structures they use.

Structure  Used by
NMCUSTOMDRAW Rebar, trackbar, and header controls
NMLVCUSTOMDRAW  List view controls
NMTBCUSTOMDRAW  Toolbar controls
NMTTCUSTOMDRAW  Tooltip controls
NMTVCUSTOMDRAW  Tree view controls

Paint Cycles, Drawing Stages, and Notification Messages
Like all Microsoft® Windows® applications, common controls periodically paint and erase themselves based on messages received from the system or other applications. The process of a control painting or erasing itself is called a paint cycle. Controls that support custom draw send NM_CUSTOMDRAW notification messages periodically through each paint cycle. This notification message is accompanied by an NMCUSTOMDRAW structure or another structure that contains an NMCUSTOMDRAW structure as its first member.

One piece of information that the NMCUSTOMDRAW structure contains is the current stage of the paint cycle. This is referred to as the draw stage and is represented by the value in the structure's dwDrawStage member. A control informs its parent about four basic draw stages. These basic, or global, draw stages are represented in the structure by the following flag values (defined in Commctrl.h).

Global draw stage values Description
CDDS_PREPAINT  Before the paint cycle begins.
CDDS_POSTPAINT  After the paint cycle is complete.
CDDS_PREERASE  Before the erase cycle begins.
CDDS_POSTERASE  After the erase cycle is complete.

Each of the preceding values can be combined with the CDDS_ITEM flag to specify draw stages specific to items. For convenience, Commctrl.h contains the following item-specific values.

Item-specific draw stage values Description
CDDS_ITEMPREPAINT  Before an item is drawn.
CDDS_ITEMPOSTPAINT  After an item has been drawn.
CDDS_ITEMPREERASE  Before an item is erased.
CDDS_ITEMPOSTERASE  After an item has been erased.
CDDS_SUBITEM Version 4.71. Flag combined with CDDS_ITEMPREPAINT or CDDS_ITEMPOSTPAINT if a subitem is being drawn. This will only be set if CDRF_NOTIFYITEMDRAW is returned from CDDS_PREPAINT.

Your application must process the NM_CUSTOMDRAW notification message and then return a specific value that informs the control what it must do. See the following sections for more information about these return values.

Taking Advantage of Custom Draw Services
The key to harnessing custom draw functionality is in responding to the NM_CUSTOMDRAW notification messages that a control sends. The return values your application sends in response to these notifications determine the control's behavior for that paint cycle.

This section contains information about how your application can use NM_CUSTOMDRAW notification return values to determine the control's behavior. Details are broken into the following topics:

Responding to the prepaint notification
Requesting item-specific notifications
Drawing the item yourself
Changing fonts and colors
Responding to the prepaint notification
At the beginning of each paint cycle, the control sends the NM_CUSTOMDRAW notification message, specifying the CDDS_PREPAINT value in the dwDrawStage member of the accompanying NMCUSTOMDRAW structure. The value that your application returns to this first notification dictates how and when the control sends subsequent custom draw notifications for the rest of that paint cycle. Your application can return a combination of the following flags in response to the first notification.

Return value Effect
CDRF_DODEFAULT The control will draw itself. It will not send additional NM_CUSTOMDRAW notifications for this paint cycle. This flag cannot be used with any other flag.
CDRF_NOTIFYITEMDRAW The control will notify the parent of any item-specific drawing operations. It will send NM_CUSTOMDRAW notification messages before and after it draws items.
CDRF_NOTIFYPOSTPAINT The control will send an NM_CUSTOMDRAW notification when the painting cycle for the entire control is complete.
CDRF_SKIPDEFAULT The control will not perform any painting at all.

Requesting item-specific notifications
If your application returns CDRF_NOTIFYITEMDRAW to the initial prepaint custom draw notification, the control will send notifications for each item it draws during that paint cycle. These item-specific notifications will have the CDDS_ITEMPREPAINT value in the dwDrawStage member of the accompanying NMCUSTOMDRAW structure. You can request that the control send another notification when it is finished drawing the item by returning CDRF_NOTIFYPOSTPAINT to these item-specific notifications. Otherwise, return CDRF_DODEFAULT and the control will not notify the parent window until it starts to draw the next item.

Drawing the item yourself
If your application draws the entire item, return CDRF_SKIPDEFAULT. This allows the control to skip items that it does not need to draw, thereby decreasing system overhead. Keep in mind that returning this value means the control will not draw any portion of the item.

Changing fonts and colors
Your application can use custom draw to change an item's font. Simply select the HFONT you want into the device context specified by the hdc member of the NMCUSTOMDRAW structure associated with the custom draw notification. Since the font you select might have different metrics than the default font, make sure you include the CDRF_NEWFONT bit in the return value for the notification message. For more information on using this functionality, see the sample code in Using Custom Draw. The font that your application specifies is used to display that item when it is not selected. Custom draw does not allow you to change the font attributes for selected items.

To change text colors for all controls that support custom draw except for the list view and tree view, simply set the desired text and background colors in the device context supplied in the custom draw notification structure with the SetTextColor and SetBkColor functions. To modify the text colors in the list view or tree view, you need to place the desired color values in the clrText and clrTextBk members of the NMLVCUSTOMDRAW or NMTVCUSTOMDRAW structure.

Custom Draw With List View and Tree View Controls
Most common controls can be handled in essentially the same way. However, the list view and tree view controls have some features that require a somewhat different approach to custom draw.

For Version 5.0 of the common controls, these two controls may display clipped text if you change the font by returning CDRF_NEWFONT. This behavior is necessary for backward compatibility with earlier versions of the common controls. If you want to change the font of a list view or tree view control, you will get better results if you send a CCM_SETVERSION message with the wParam value set to 5 before adding any items to the control.

Custom Draw With List View Controls
Because list view controls have subitems and multiple display modes, you will need to handle the NM_CUSTOMDRAW notification somewhat differently than for the other common controls.

For report mode:

The first NM_CUSTOMDRAW notification will have the dwDrawStage member of the associated NMCUSTOMDRAW structure set to CDDS_PREPAINT. Return CDRF_NOTIFYITEMDRAW.
You will then receive an NM_CUSTOMDRAW notification with dwDrawStage set to CDDS_ITEMPREPAINT. If you specify new fonts or colors and return CDRF_NEWFONT, all subitems of the item will be changed. If you want instead to handle each subitem separately, return CDRF_NOTIFYSUBITEMDRAW.
If you returned CDRF_NOTIFYITEMDRAW in the previous step, you will then receive an NM_CUSTOMDRAW notification for each subitem with dwDrawStage set to CDDS_SUBITEM | CDDS_PREPAINT. To change the font or color for that subitem, specify a new font or color and return CDRF_NEWFONT.
For the large icon, small icon, and list modes:

The first NM_CUSTOMDRAW notification will have the dwDrawStage member of the associated NMCUSTOMDRAW structure set to CDDS_PREPAINT. Return CDRF_NOTIFYITEMDRAW.
You will then receive an NM_CUSTOMDRAW notification with dwDrawStage set to CDDS_ITEMPREPAINT. You can change the fonts or colors of an item by specifying new fonts and colors and returning CDRF_NEWFONT. Because these modes do not have subitems, you will not receive any additional NM_CUSTOMDRAW notifications.
An example of a list view NM_CUSTOMDRAW notification handler is given in the next section.

Using Custom Draw
The following code fragment is a portion of a WM_NOTIFY handler that illustrates how to handle custom draw notifications sent to a list view control:

LPNMLISTVIEW  pnm    = (LPNMLISTVIEW)lParam;

switch (pnm->hdr.code){
...
case NM_CUSTOMDRAW:

    LPNMLVCUSTOMDRAW  lplvcd = (LPNMLVCUSTOMDRAW)lParam;

    switch(lplvcd->nmcd.dwDrawStage) {
    case CDDS_PREPAINT :
        return CDRF_NOTIFYITEMDRAW;
   
    case CDDS_ITEMPREPAINT:
        SelectObject(lplvcd->nmcd.hdc,
                     GetFontForItem(lplvcd->nmcd.dwItemSpec,
                                    lplvcd->nmcd.lItemlParam) );
        lplvcd->clrText = GetColorForItem(lplvcd->nmcd.dwItemSpec,
                                          lplvcd->nmcd.lItemlParam);
        lplvcd->clrTextBk = GetBkColorForItem(lplvcd->nmcd.dwItemSpec,
                                              lplvcd->nmcd.lItemlParam);

/* At this point, you can change the background colors for the item
and any subitems and return CDRF_NEWFONT. If the list view control
is in report mode, you can simply return CDRF_NOTIFYSUBITEMREDRAW
to customize the item's subitems individually */

        ...
        return CDRF_NEWFONT;
 //  or return CDRF_NOTIFYSUBITEMREDRAW;
 
    case CDDS_SUBITEM | CDDS_ITEMPREPAINT:
        SelectObject(lplvcd->nmcd.hdc,
                     GetFontForSubItem(lplvcd->nmcd.dwItemSpec,
                                       lplvcd->nmcd.lItemlParam,
                                       lplvcd->iSubItem));
        lplvcd->clrText = GetColorForSubItem(lplvcd->nmcd.dwItemSpec,
                                             lplvcd->nmcd.lItemlParam,
                                             lplvcd->iSubItem));
        lplvcd->clrTextBk = GetBkColorForSubItem(lplvcd->nmcd.dwItemSpec,
                                                 lplvcd->nmcd.lItemlParam,
                                                 lplvcd->iSubItem));

/* This notification is received only if you are in report mode and
returned CDRF_NOTIFYSUBITEMREDRAW in the previous step. At
this point, you can change the background colors for the
subitem and return CDRF_NEWFONT.*/

        ...
        return CDRF_NEWFONT;   
    }
...
}

The first NM_CUSTOMDRAW notification has the dwDrawStage member of the NMCUSTOMDRAW structure set to CDDS_PREPAINT. The handler returns CDRF_NOTIFYITEMDRAW to indicate that it wishes to modify one or more items individually. The control then sends an NM_CUSTOMDRAW notification with dwDrawStage set to CDDS_PREPAINT for each item. The handler returns CDRF_NOTIFYITEMDRAW to indicate that it wishes to modify the item.

If CDRF_NOTIFYITEMDRAW was returned in the previous step, the next NM_CUSTOMDRAW notification has dwDrawStage set to CDDS_ITEMPREPAINT. The handler gets the current color and font values. At this point, you can specify new values for small icon, large icon, and list modes. If the control is in report mode, you can also specify new values that will apply to all subitems of the item. If you have changed anything, return CDRF_NEWFONT. If the control is in report mode and you want to handle the subitems individually, return CDRF_NOTIFYSUBITEMREDRAW.

The final notification is only sent if the control is in report mode and you returned CDRF_NOTIFYSUBITEMREDRAW in the previous step. The procedure for changing fonts and colors is the same as that step, but it only applies to a single subitem. Return CDRF_NEWFONT to notify the control if the color or font was changed.