Article: Q51412
Product(s): See article
Version(s): 1.00 1.01 1.02 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S890822-40 B_MQUICKB B_BASICCOM B_BasicInt B_GWBasicI | mspl13_basic
Last Modified: 12-DEC-1989
This article describes the format with which the graphics GET
statement stores graphics in an array.
This article applies to Microsoft GW-BASIC Interpreter Versions 3.20,
3.22, 3.23 for MS-DOS, Microsoft BASIC Compiler Versions 6.00 and
6.00b for MS-DOS and MS OS/2, Microsoft QuickBASIC Versions 1.00,
1.01, 1.02, 2.00, 2.01, 3.00, 4.00, 4.00b and 4.50 for MS-DOS,
Microsoft QuickBASIC Version 1.00 for the Apple Macintosh, Microsoft
BASIC Compiler Version 1.00 for the Apple Macintosh, and Microsoft
BASIC Interpreter Versions 1.00, 1.01, 2.00, 2.10, and 3.00 for the
Apple Macintosh.
This internal product information is provided as is, and may be
subject to change or nondisclosure in future versions of BASIC.
The graphics GET statement transfers a screen image into a specified
array. The first 4 bytes in the array are two integers which specify
how wide and long the stored image is in pixels, while the rest of the
data stored in the array is a binary representation of the stored
screen image, as shown in the following diagram:
+------------+------------+
| image width, in pixels | <-- 2-byte integer number
+------------+------------+
| image length, in pixels | <-- 2-byte integer number
+--------+--------+--------+--------+--------+--------+
| | | < binary image data > | |
+--------+--------+--------+--------+--------+--------+
byte #5 byte #6 byte #7
The binary image data depends on the screen mode of the graphic image
and is stored linearly in memory by pixel rows and columns. The GET
statement scans the screen image by row from left to right and stores
the bit representation of each pixel. Each row of the stored data will
be padded out to an even byte boundary by NULL bytes (ASCII 0). The
following is an example.
Take a square box drawn on the screen and stored with the following
program:
SCREEN 2 ' Delete this statement for Macintosh BASICs
DIM box%(1 to 5)
LINE (1, 1)-(10, 3), ,B
GET (1, 1)-(10, 3), box%
The first 4 bytes of box% will be as follows:
box%(1) = 10 ' The box is 10 pixels wide
box%(2) = 3 ' The box is 3 pixels long
The binary representation of the remaining bytes in the box% array
is as follows:
box%(3) = 11111111 11000000 <- Note padding of each row of bits
box%(4) = 10000000 01000000 <- Also note how the 1's form a box.
box%(5) = 11111111 11000000
How GET Stores Color on an IBM PC or Compatible
-----------------------------------------------
On an IBM PC or compatible, the way the graphics GET statement stores
color information depends upon the characteristics of the display
mode. For screen modes with a single color plane (SCREENs 1, 2, 3,
11, and 13), each pixel is represented by the number of bits per pixel
per plane for the particular display mode. The following is an
example.
If the square box given above were drawn in SCREEN mode 1 (2 bits
per pixel per plane) with the following program,
SCREEN 1
DIM box%(1 to 7)
LINE (1, 1)-(10, 3), ,B
GET (1, 1)-(10, 3), box%
then the binary representation of the image data bytes (after the
4-byte width and length header) would be as follows:
11111111 11111111 11110000
11000000 00000000 00110000 <- Notice 2 bits per pixel
11111111 11111111 11110000
Since no color was specified, the default color (white) was used
(thus all of the color bits were turned on).
For SCREEN modes with multiple color pages (SCREENs 7, 8, 9, 10, and
12), GET stores each display page separately by screen row. GET
stores the binary information for one row of the graphics on the first
color page and then the same row of graphics on the next color page,
padding each row of color page information to an even byte boundary.
The following is an example:
If the same square box were drawn in SCREEN mode 12 (four color
planes) in red with the following program,
SCREEN 12
COLOR 4 ' select red color
DIM box%(1 to 14)
LINE (1, 1)-(10, 3), ,B
GET (1, 1)-(10, 3), box%
then the binary representation of the image data bytes (again after
the 4-byte header) would be as follows:
00000000 00000000 <- blue plane
00000000 00000000 <- green plane
11111111 11000000 <- red plane (note padding to byte boundary)
00000000 00000000 <- intensity plane - first row finished
00000000 00000000 <- blue
00000000 00000000 <- green
10000000 01000000 <- red
00000000 00000000 < - intensity - second row
00000000 00000000
00000000 00000000
11111111 11000000
00000000 00000000 <- last row
GET Doesn't Preserve Color in QuickBASIC for the Macintosh
----------------------------------------------------------
The graphics GET statement in Microsoft QuickBASIC Version 1.00 for
the Macintosh does not preserve the colors of graphics in its array
argument, and a subsequent graphics PUT using that array will draw in
monochrome, using only the current foreground and background colors.
The following list shows how the GET statement translates pixel colors
on the screen and stores them in the array:
1. White (or current background color) <= yellow, magenta, cyan, white
2. Black (or current foreground color) <= red, green, blue, black
The GET statement captures screen information as a bitmap only. Only
the on or off status of each pixel -- not the color information -- is
stored in the array.
The ForeColor and BackColor MBLC routines built into QuickBASIC let
you change the color used by subsequent graphics statements. Invoking
ForeColor and BackColor will cause a subsequent graphics PUT to use
that new foreground and background for all pixels drawn.
Note that the earlier products, Microsoft BASIC Compiler Version 1.00
for the Apple Macintosh and Microsoft BASIC Interpreter Versions 1.00,
1.01, 2.00, 2.10, and 3.00 for the Apple Macintosh, do not support
ForeColor or BackColor, or any color capabilities.