overlay Subroutine

Purpose

Sets the number of user-defined bitplanes used for overlay drawing.

Libraries

Graphics Library

C (libgl.a)

FORTRAN (libfgl.a)

C Syntax

void overlay(Int32 planes)

FORTRAN Syntax

SUBROUTINE OVERLA(planes)
INTEGER*4 planes

Description

The overlay subroutine sets the number of user-defined bitplanes used for overlay colors to 0, 2, or 4, depending on the installed adapter. An overlay color is the color that is placed on top of the standard pixel contents. The overlay color appears whenever any of its bits are nonzero. The system has either two or four bitplanes that can be allocated as either underlay or overlay. Call the overlay subroutine to set them as overlay bitplanes.

The High-Performance 8-bit 3-D Color Graphics Processor can be configured with either 0 or 2 overlay planes. The 8-bit adapter has a total of 2 auxiliary planes, which can be configured into 2/0 or 0/2 overlay/underlay. For example, setting the number of overlay planes to 2 forces the number of underlay planes to 0.

The High-Performance 24-bit 3-D Color Graphics Processor can be configured with either 0, 2, or 4 overlay planes. The 24-bit adapter has a total of 4 auxiliary planes, which can be configured into 4/0, 2/2, or 0/4 overlay/underlay. For example, setting the number of overlay planes to 4 forces the number of underlay planes to 0.

The POWER GXT1000 adapter has 8 overlay planes, all of which are nonmodifiable.

Call the gconfig subroutine after the overlay subroutine to activate the overlay setting.

When the drawing mode is OVERDRAW, all drawing occurs in the overlay bitplanes. In OVERDRAW mode, FLAT is the only available shading model.

Notes:

1. The operation of this subroutine for the Supergraphics Processor Subsystem is modified. (See "Understanding the Adapter")
2. This subroutine cannot be used to add to a display list.

Parameter

Example

The example C language program overlay.c uses the overlay subroutine to set the number of overlay bitplanes to two.

Implementation Specifics

This subroutine is part of GL in the AIXwindows Environment/6000 Version 1, Release 2 with AIXwindows/3D Feature.

The POWER Gt4, and POWER Gt4x, and POWER GXT1000 adapters do not support hidden-line and hidden-surface removal when rendering into the overlay planes. The z-buffer is automatically disabled when drawmode (OVERDRAW) is specified. The z-buffer is automatically enabled when drawmode (NORMALDRAW) is specified.

Files

Related Information

Specifying the target frame buffer for drawing subroutines with the drawmode subroutine.

Reconfiguring the system with the gconfig subroutine.

Setting the number of bitplanes used for underlay colors with the underlay subroutine.

Configuring the Frame Buffer, and Writemasks and Logical Operations.