The Cybiko is a very capable graphics machine. In this section we cover the non-bitmapped graphics commands. B2C has 5 basic graphic commands with which to draw on the screen.
Cls – Clear screen
Cls stands for Clear Screen. It will turn all pixels on the display to the background color (usually white). It will also erase all text on the screen. Cls takes no parameters
Cls
Paper – set the color of the background
B2C has a concept of a foreground color and a background color. The background color is set with the Paper command. Whenever you do a Cls – the entire display is set to the color defined by the Paper command. There are 4 colors to chose from. Color 0 is white. Color 1 is light grey. Color 2 is dark grey. Color 3 is black. There are constants defined for your use:
0 – White 1 – LtGrey 2 - DkGrey 3 - Black Paper Black ' set the background color to black Cls ' color the screen with the background color
Ink – set the color of the foreground
B2C's foreground color is used to draw text (Print) and lines (Line). There are constants defined for your use:
0 – White 1 – LtGrey 2 - DkGrey 3 - Black Paper White ' set the background to White Ink Black ' set the foreground to black Cls ' clear the background line -80, -50, 80, 50 ' draw a diagonal line
Line – draw a line on the screen
The B2C display area is an X/Y coordinate system. You place a line on the screen by telling B2C to position the cursor at a horizontal (X) coordinate and a vertical (Y) coordinate. The valid values for the screen coordinates are –80 to 79 in the X (horizontal) direction, and –50 to 49 in the Y (vertical) direction. You may specify values as large as +/- 20,000 in either direction, but only the pixels, which are in the screen coordinates (-80 to 79 and –50 to 49), will be displayed.
Paper White ' set the background to White Ink Black ' set the foreground to black Cls ' clear the background line -80, -50, 80, 50 ' draw a diagonal line
It is possible to use a different coordinate system. The so-called 'C' coordinate system runs from 0 to 159 in the X direction and from 0 to 99 in the Y direction. You can switch to this system by placing
OPTION C_COORDS
at the top of your program.
Point – draw a single pixel on the screen
Draw a single pixel at the x/y coordinates (see Line, above).
Paper White ' set the background to White Ink Black ' set the foreground to black Cls ' clear the background Point 0, 0 ' draw a dot in the center
Example Program
DO THIS |
| Copy the
file "c:\…\B2Cv5\tutorial\ch13.b2c" to "C:\…\B2Cv5\ch13.b2c".
Then execute the command "build ch13.bld". Download the ch13.app file
to the cybiko.
This program is like the old Microsoft Windows screen saver. A set of bouncing lines chase after each other: 'chapter 13 'qix line drawing 'requires B2C-2 'see below for B2C-1 dim n as int print "Number of lines" input n dim n1 as int dim n2 as int n1=n-1 n2=n1-1 dim x0[n] as int dim y0[n] as int dim x1[n] as int dim y1[n] as int dim dx0 as int dim dy0 as int dim dx1 as int dim dy1 as int dim seed as int sub newdirection(j as int) if (x0[j] < -80 or x0[j] > 80) then dx0 = -dx0 end if if (x1[j] < -80 or x1[j] > 80) then dx1 = -dx1 end if if (y0[j] < -43 or y0[j] > 43) then dy0 = -dy0 end if if (y1[j] < -80 or y1[j] > 80) then dy1 = -dy1 end if end sub ' for B2C1 do the following ' dx0=-3 ' dx1=-1 ' dy0=1 ' dy1=2 'and remove the while loops... ' select random motion offsets while dx0=0 dx0 = 4-rnd(9) wend while dx1=0 dx1 = 4-rnd(9) wend while dy0=0 dy0 = 4-rnd(9) wend while dy1=0 dy1 = 4-rnd(9) wend 'select initial random line x0[0] = rnd(80) x1[0] = rnd(80) y0[0] = rnd(43) y1[0] = rnd(43) line x0[0], y0[0], x1[0], y1[0] cls 'fill up queue with trailing lines and print them for i=1 to n-1 x0[i] = x0[i-1] + dx0 x1[i] = x0[i-1] + dx1 y0[i] = y0[i-1] + dy0 y1[i] = y1[i-1] + dy1 line x0[i], y0[i], x1[i], y1[i] newdirection(i) next for i=0 to 1 step 0 ink 0 line x0[0], y0[0], x1[0], y1[0] ink 3 for j=1 to n-1 x0[j-1] = x0[j] x1[j-1] = x1[j] y0[j-1] = y0[j] y1[j-1] = y1[j] next x0[n1] = x0[n2] + dx0 y0[n1] = y0[n2] + dy0 x1[n1] = x1[n2] + dx1 y1[n1] = y1[n2] + dy1 line x0[n1], y0[n1], x1[n1], y1[n1] newdirection(n1) next
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