by Mohsen Alshayef 24 Oct 2008
BBC BASIC for Windows provides keywords to perform graphics operations, such as plotting points, lines and circles, etc. These operations are performed using graphics coordinates into the graphics screen.
Irrespective of the graphics or display mode your programme is in, the reference graphics screen is made of a fixed coordinate system of -32768 to +32767 in the x- and y- directions.
The display mode selected then becomes a window into this large graphics screen. The example below illustrates mode 8 which has graphics units of 1280 x 1024.
In the example, a line is drawn between (-2500,-2000) and (2500,2500) using:
and what would appear on the screen is only the portion of the line which crosses the window region.
Graphics Units should not be confused with Graphics Pixels (graphics resolution). The actual resolution (Graphics Pixels) of the screen modes is less than the corresponding Graphics Units. Typically, each graphics pixel translates into two (2) Graphics Units. An example of some screen modes are:
| Mode|| Graphaphics Units|| Graphics Pixels
| 8|| 1280 x 1024|| 640 x 512
| 14|| 2560 x 2048|| 1280 x 1024
| 20|| 1600 x 1200|| 800 x 600
| 22|| 2048 x 1536|| 1024 x 768
| 31|| 3200 x 2400|| 1600 x 1200
In the standard modes, each pixel translates into 2 Graphics Units wide and 2 Graphics Units High.
Details of screen modes may be found in the Manual at Graphics and Colours.