4GL Access: RW

The BgDisplayPolicy attribute controls the positioning and display of form field background images.

Valid values are:

BDP_DEFAULT
BDP_FIXED
BDP_RELATIVE
BDP_BORDEREDTILED
BDP_BORDEREDSCALED
BDP_CORNERED

BDP_BORDEREDTILED, BDP_BORDEREDSCALED, and BDP_CORNERED require the following companion settings:

Except for BDP_RELATIVE, all settings anchor the background image to the top left corner of the field.

Descriptions of system constant values and their numeric equivalents are listed in BgDisplayPolicy Settings.

When the setting is BDP_RELATIVE, the background image is anchored relative to the closest parent field whose background is fixed. Parent field settings are evaluated regardless of whether they have a background image themselves. If neither the field nor its parents have a fixed setting, the image is anchored relative to the TopForm top left corner.

When the setting is BDP_FIXED, BDP_RELATIVE, or BDP_DEFAULT, the background image is painted at its exact size and tiled, if necessary, to fill the whole field.

When the setting is BDP_BORDEREDTILED, the image's border effect is preserved: the image corners are mapped to the field corners, the image edges are resized to fill the field by corner-to-corner tiling, and the center is resized to fill the remainder of the field by tiling.

When the setting is BDP_BORDEREDSCALED, the image's border effect is preserved: the image corners are mapped to the field corners (any transparency effects are honored), the image edges are resized to fill the field by corner-to-corner rescaling of the edges, and the center is resized to fill the remainder of the field by rescaling.

When the setting is BDP_CORNERED, the effect is identical to BDP_BORDEREDSCALED, except that the corners are modified to follow the cornerradius set for the image.

This value is typically set at runtime by a call to the field's UpdBackground method, passing the desired cornerradius (as the cornersize parameter). For more information about how cornerradius is used with BDP_BORDEREDSCALED and BDP_CORNERED, see the FormField.UpdBackground method (see UpdBackground Method).

When BDP_BORDEREDTILED, BDP_BORDEREDSCALED, and BDP_CORNERED are set, the sizes of the image corners, edges, and center are defined in order of evaluation, as follows:

For fields with a BgDisplayPolicy of BDP_BORDEREDTILED, BDP_BORDEREDSCALED, or BDP_CORNERED, the corner exteriors are always transparent if set to the background bitmap's transparency color. In the remaining background, pixels of this color are treated as transparent only if the field's BgPattern is FP_BITMAPCLEAR. The transparency color is set by the first corner of the bitmap that has one of the allowed transparency colors:

This field's BgBitmap is:

If the corner radius is set to 1 pixel, OpenROAD treats such a bitmap as comprising four corners of 1x1 pixels, four edges of 1x1 pixels, and a central area of 1x1 pixels. When displayed, the edges and the central area expand to fill whatever size the field is set to. For this example, assume that the BDP_CORNERED border width is 0 (BDP_CORNERED borders are non-transparent).

This definition produces the following transparency effects:

If a field's BgBitmap has a foreground shape on a white background, RGB(255,255,255), the white background is automatically interpreted as transparent unless all four corners are recolored, perhaps to RGB(254,255,255):