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Epson Research and Development
Vancouver Design Center
5 Virtual Displays
This section discusses the concept of a virtual display and covers navigation within a virtual
display using panning and scrolling.
5.1 Virtual Display
Virtual display is where the image to be viewed is larger than the physical display. This can
be in the horizontal, vertical or both dimensions. To view the image, the display is used as
a window (or viewport) into the display buffer. At any given time only a portion of the
image is visible. Panning and scrolling are used to view the full image. For further infor-
mation on panning and scrolling, see Section 5.2, “Panning and Scrolling” on page 30.
The Memory Address Offset registers determine the number of horizontal pixels in the
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virtual image. The offset registers can be set for a maximum of 2 or 2048 words. At a
color depth of 4 bpp, 2048 words cover 8,192 pixels. At a color depth of 16 bpp, 2048 words
cover 2048 pixels.
The maximum number of lines of the virtual image is the size of the display buffer divided
by the number of bytes per horizontal line. The number of bytes per line equals the number
of words in the offset register multiplied by two. At the maximum horizontal size, the
greatest number of lines that can be displayed using 2M bytes of display memory is 512.
Reducing the horizontal size makes more display buffer available, thus increasing the
available virtual vertical size.
In addition to the calculated limit, the virtual vertical size is limited by the size and location
of the Dual Panel Buffer and the Ink Layer/Hardware Cursor (if present).
The maximum horizontal/vertical sizes are seldom used. Figure 5-1: “Viewport Inside a
Virtual Display,” shows a more typical use of a virtual display. With a display panel of
320x240 pixels, an image of 640x480 pixels can be viewed by navigating a 320x240 pixel
viewport around the image using panning and scrolling.
320x240
Viewport
640x480
“Virtual” Display
Figure 5-1: Viewport Inside a Virtual Display
S1D13506
X25B-G-003-03
Programming Notes and Examples
Issue Date: 01/02/06
EPSON [ EPSON COMPANY ]
