VidMem v1.5 (Copyright 1991 by Geoff Speicher) -
Access to video memory (320x200x256 mode only) through Turbo
VidMem v1.5 has been rewritten in assembler for maximum speed and
compatibility with different versions of TP.
The following are the procedures and functions in the VIDMEM.OBJ
This puts your system into it's 320x200x256 graphics mode. A VGA
or MCGA card is required. ----- Procedure DeInitMCGAMode;
This puts your system back into text mode.
WriteVidMem(OfsVal: LongInt; Value: Byte);
This writes a value directly to video memory, and thus, is the
core of the graphics routines you will be using. The two
parameters are set as follows:
OfsVal - Offset, or location on the screen at which the pixel
will be written. You have to imagine the screen as
being a large array of bytes. Byte 0 is the upper left
corner. Byte 64000 is the lower right. So, the center
of the screen would be 32099. An easy rule to follow is
this: Add 320 to a number, and it will move down exactly
one scan line. Subtract 320, and it will move up one
line. Add 1 and the location moves to the right 1
pixel. Of course, subtract 1 and the location moves 1
pixel to the left.
Value - Value to be written at the specific location of video
memory. In other words, the color you want the pixel to
be. This can be set from 0 to 255.
Procedure ReadVidMem(OfsVal: LongInt; var Color: Byte);
Reads the color of a pixel at a specific video location. Set
OfsVal the same way you would if writing a pixel. The color
(0-255) will be returned in ReadVidMem.
SetPaletteColorRGB(Number, RedVal, GreenVal, BlueVal: Byte);
Sets an individual palette color. Number is the palette color
(0-255). RedVal, GreenVal, and BlueVal are the Red, Green, and
Blue shades that compose the color. Setting RedVal to 255, and
GreenVal and BlueVal to 0 will produce a bright Red. The same is
true for GreenVal and BlueVal. You can mix any combination of
these three colors (setting all three to 255 will give you bright
white). You can make almost any color using different
combinations. The lower you set the value, the darker the color
var RedVal, GreenVal, BlueVal: Byte);
Will return the red, green, and blue values for a certain palette
color in RedVal, GreenVal, and BlueVal. Number is the palette
WriteImage(TopLeft, ImageSeg, ImageOfs, ImageSize: LongInt;
This will write a predefined image to the screen. The image MUST
be defined as an array of bytes. This array can be as large or
small as you want. Each byte value will be interpreted as the
color to write on the screen. Here is an example of defining an
ManyColors: Array[1..20] of Byte = (16,17,18,19,20,21,22,23,24,
TopLeft is the screen location for the upper left corner of the
image. ImageSeg is the segment of the image. ImageOfs is the
offset, ImageSize is the size, and Width is the width of the
image, in pixels. You could display the above image like this:
The best way to get familiar with this procedure is to just fool
around with it. And experiment with different images and width
settings. For example, setting the width in the above to 20
would draw a horizontal line. However, setting the width to 1
would draw a vertical line!
ReadImage(TopLeft, ImageSeg, ImageOfs, ImageSize: LongInt;
Does the exact opposite of WriteImage. Pass the parameters the
same way, and you've got it made!
New procedures/functions to v1.5
WritePixel(X,Y: Integer; Color: Byte);
This will perform the same operation as WriteVidMem, but you can
use an X,Y system of coordinates to name the pixel.
ReadPixel(X,Y: Integer; var Color: Byte);
Same idea as WritePixel...
XYtoVM(X,Y: Integer): Word;
Returns the single number (0-63999) equivalence of a set of X,Y
coordinates passed to it. This enables you to use X,Y
coordinates with other procedures, such as ReadImage and
That's it! Be on the lookout for future versions and updates!
Any questions or comments can be sent to me by:
1) FidoNet Mail. Send it to Net/Node 1:268/310, addressed to
2) EMail. If you don't want to wait for NetMail, you can call up
my BBS: GROUND ZER0!!! BBS (717)876-5869 14.4k bps HST. And
leave EMail to the Sysop (that's me).
3) If you're not really looking for a response, and don't like
the first two methods, you can send a "real" letter to:
P.O. Box 163
Archbald, Pa 18403