Garbo/Garbo.cdr/mac/progrmng/qbgrphcs.sit/antialias.bas/antialias.bas

BASIC Source File | 1991-06-05 | 5.4 KB | 202 lines | [TEXT/MSBB]

'------------------------------------------------------------------------------
' TITLE:    antialias.bas
' DATE:     February 19, 1991
' AUTHOR: R. Gonzalez
'
' DESCRIPTION:    Draw circles using various techniques, including antialiasing.
'     REQUIRES COLOR OR GRAY-SCALE MONITOR.
'
' COMPILING:    Remove STATIC declarations, uncomment indicated lines
'     Check: Include MBPCs & MBLCs, Include runtime code, Make all arrays static,
'     Use default window & menu, (if available: Generate 68020 & 68881 code).
'
' (MODIFICATION HISTORY)
' DATE:
' AUTHOR:
' DESCRIPTION:
'------------------------------------------------------------------------------

' these variables may be shared among several subprograms:
DIM SHARED TRUE%,FALSE%,PI,white%,light.gray%,gray%,black%

'------------------------------------------------------------------------------
' main procedure
'------------------------------------------------------------------------------
'MAIN

    DIM window.width%,window.height%,x%,y%,radius%

    TRUE% = -1
    FALSE% = 0
    PI = 3.14159
    white% = 30
    light.gray% = 273
    gray% = 137
    black% = 33
    forecolor white%
    backcolor black%

    window.width% = WINDOW(2)
    window.height% = WINDOW(3)
    radius% = 50
    y% = INT(window.height%/2)

    CLS
    x% = INT(window.width%/4)
    CIRCLE (x%,y%),radius%
    x% = INT(window.width%/2)
    draw.circle x%,y%,radius%,FALSE%
    x% = INT(3*window.width%/4)
    draw.circle x%,y%,radius%,TRUE%

    pause

END

'------------------------------------------------------------------------------
' pause until mouse or any key is pressed
'------------------------------------------------------------------------------
SUB pause STATIC

    WHILE INKEY$ = "" AND MOUSE(0) <> 1
    WEND

END SUB

'------------------------------------------------------------------------------
' draw circle using line-drawing routine, either antialiased or not
'------------------------------------------------------------------------------
SUB draw.circle (x%,y%,radius%,anti%) STATIC

    'for compiler only:
'    dim increment,angle,x1,y1,x2,y2

    increment = .1
    x1 = radius%+x%
    y1 = y%

    FOR angle = 0 TO 2*PI+increment STEP increment
        x2 = radius%*COS(angle)+x%
        y2 = radius%*SIN(angle)+y%
        draw.line x1,y1,x2,y2,anti%
        x1 = x2
        y1 = y2
    NEXT

END SUB

'------------------------------------------------------------------------------
' draw plain line using white or antialiased line using white and grays.  Use
' floating-point arguments so that antialiasing procedure will work properly
' with very short lines, e.g. when drawing curves.
'------------------------------------------------------------------------------
SUB draw.line (x1.param,y1.param,x2.param,y2.param,anti%) STATIC

    'for compiler only:
'    dim m,yp,x1,y1,x2,y2
'    dim x%,ya%,yb%,switch.xy%,color.a%,color.b%

    ' local variables because of call-by-reference:
    x1 = x1.param
    y1 = y1.param
    x2 = x2.param
    y2 = y2.param

    convert.line x1,y1,x2,y2,m,switch.xy%

    FOR x% = INT(x1+.5) TO INT(x2+.5)
        yp = m*(x%-x1)+y1
        ya% = INT(yp+.5)
        IF NOT anti% THEN
            color.a% = white%
        ELSE
            IF ya%<yp THEN
                yb% = ya% + 1
            ELSE
                yb% = ya% - 1
            END IF
            ' For efficiency it may be better to later use inline code rather than a
            ' subprogram call here, since we are in a critical loop:
            select.anti.colors ABS(ya%-yp),color.a%,color.b%
            forecolor color.b%
            IF switch.xy% THEN
                PSET (yb%,x%)
            ELSE
                PSET (x%,yb%)
            END IF
        END IF
        forecolor color.a%
        IF switch.xy% THEN
            PSET (ya%,x%)
        ELSE
            PSET (x%,ya%)
        END IF
    NEXT

END SUB

'------------------------------------------------------------------------------
' convert line if necessary so that slope<=1 and x1<x2.  If switch.xy% is set to TRUE
' then the calling routine should switch x and y coordinates when drawing the line.
'------------------------------------------------------------------------------
SUB convert.line (x1,y1,x2,y2,m,switch.xy%) STATIC

    'for compiler only:
'    dim temp

    IF ABS(x2-x1)<.000001 THEN
        m = 1000000!
    ELSE
        m = (y2-y1)/(x2-x1)
    END IF

    IF ABS(m) > 1 THEN
        temp = x1
        x1 = y1
        y1 = temp
        temp = x2
        x2 = y2
        y2 = temp
        IF ABS(x2-x1)<.000001 THEN
            m = 1000000!
        ELSE
            m = (y2-y1)/(x2-x1)
        END IF
        switch.xy% = TRUE%
    ELSE
        switch.xy% = FALSE%
    END IF

    IF x1 > x2 THEN
        temp = x1
        x1 = x2
        x2 = temp
        temp = y1
        y1 = y2
        y2 = temp
    END IF

END SUB

'------------------------------------------------------------------------------
' select pixel colors for antialiasing line.
'------------------------------------------------------------------------------
SUB select.anti.colors (distance,color.a%,color.b%) STATIC

    SELECT CASE distance
        CASE 0 TO .1
            color.a% = white%
            color.b% = black%
        CASE .1 TO .25
            color.a% = white%
            color.b% = gray%
        CASE .25 TO .4
            color.a% = white%
            color.b% = light.gray%
        CASE ELSE
            color.a% = light.gray%
            color.b% = light.gray%
    END SELECT

END SUB