' RANMERGE.BAS -- by Gary Neal, Jr. (garyneal@geeocities.com)
'
' Merged RANGRAPH.BAS, FGRAPH.BI, and FGRAPH.BAS files for use in QBasic.

DECLARE SUB DrawCircle (xOffset%, yOffset%, radius%, C%)
DECLARE SUB DrawLine (X1%, Y1%, X2%, Y2%, C%)

DIM SHARED angleIncr AS SINGLE

SCREEN 13

' Random pixels
WHILE INKEY$ = ""
    PSET (RND * 320, RND * 200), RND * 256
WEND

' Clear keyboard
WHILE INKEY$ <> "": WEND
CLS

' Random lines
WHILE INKEY$ = ""
    DrawLine RND * 320, RND * 200, RND * 320, RND * 200, RND * 256
WEND

' Clear keyboard
WHILE INKEY$ <> "": WEND
CLS

' Set angle increments directly in this program.
angleIncr = .5

DrawCircle 160, 100, 90, 15

' Wait for keypress
WHILE INKEY$ = "": WEND

' Clear the keyboard
WHILE INKEY$ <> "": WEND

' Clean up and exit
SCREEN 0, 0, 0
END    ' You can use SYSTEM also.

' DrawCircle
' Draws a circle on the graphics screen using floating point math.
'
SUB DrawCircle (xOffset%, yOffset%, radius%, C%)
     DIM xPlot!, yPlot!     ' Current pixel being plotted.
     DIM angle!, angleRad!  ' Current angle in degrees & radiens.

     IF angleIncr < 1! THEN angleIncr = .5

     FOR angle! = 0! TO 360! STEP angleIncr

          ' Convert degrees to radiens.
          angleRad! = angle! * (3.141592654# / 180!)

          ' Convert polar to rectangular coordinates.
          xPlot! = (radius% * COS(angleRad!)) + xOffset%
          yPlot! = (radius% * SIN(angleRad!)) + yOffset%

          ' Check boundaries.
          IF xPlot! < 0 THEN
              xPlot! = 0
          ELSEIF xPlot! > 319 THEN
              xPlot! = 319
          END IF

          IF yPlot! < 0 THEN
              yPlot! = 0
          ELSEIF yPlot! > 199 THEN
              yPlot! = 199
          END IF

          ' Plot the pixel on the graphics screen.
          PSET (xPlot!, yPlot!), C%
     NEXT angle!
END SUB

' Line function
'
' Draws a line on the graphics screen using floating point math.
'
SUB DrawLine (X1%, Y1%, X2%, Y2%, C%)
    DIM currX!, currY!            ' Current pixel to be plotted
    DIM deltaX!, deltaY!, slope!  ' 2 deltas and slope

    deltaX! = X2% - X1%           ' Get value for delta X
    deltaY! = Y2% - Y1%           ' Get value for delta Y

    IF ABS(deltaY!) > ABS(deltaX!) THEN

        ' |slope| > 1
        IF Y2% < Y1% THEN
            SWAP Y2%, Y1%         ' Swap coordinates
            SWAP X2%, X1%         ' Y1 must be < Y2
        END IF

        ' Compute the slope off the vertical axis
        slope! = deltaX! / deltaY!

        ' Plot each pixel starting at (X1, X2)
        currX! = X1%
        FOR currY! = Y1% TO Y2%
            PSET (currX!, currY!), C%

            ' Increment X by slope
            currX! = currX! + slope!
        NEXT currY!
        EXIT SUB

    ELSEIF deltaX! <> 0! OR deltaY! <> 0! THEN

        ' |slope| < 1
        IF X2% < X1% THEN
            SWAP X2%, X1%         ' Swap coordinates
            SWAP Y2%, Y1%         ' X1 must be < X2
        END IF

        ' Compute the slope off the horizontal axis
        slope! = deltaY! / deltaX!

        ' Plot each pixel starting at (X1, X2)
        currY! = Y1%
        FOR currX! = X1% TO X2%
            PSET (currX!, currY!), C%

            ' Increment X by slope
            currY! = currY! + slope!
        NEXT currX!
        EXIT SUB

    ELSE

        ' Set a single pixel because X1 = X2 and Y1 = Y2
        PSET (X1%, X2%), C%

    END IF
END SUB