DRAW - QB64Official/qb64 GitHub Wiki

The DRAW statement uses a STRING expression to draw lines on the screen.

Syntax

DRAW drawString$

Description

  • The drawString$ can be DRAW instructions in quotation marks or a STRING variable using DRAW instructions.

  • DRAW starting coordinates can be set using PSET, PRESET, CIRCLE or LINE ending positions.

  • Other graphic objects can be located at or relative to the last DRAW position using STEP.

  • DRAW can inherit colors from other graphic statements such as PSET, LINE and CIRCLE.

  • Draw strings use letters followed by the number of pixels to move, an angle, coordinate or a color value.

  • Draw strings are flexible with spacing. Spacing is not required. DRAW will look for a number value after a valid letter.

  • DRAW statements are not case sensitive.

    • "B" (blind) before a line move designates that the line move will be hidden. Use to offset from a "P" or PAINT border.
    • "C n" designates the color attribute or _RGB STR$ numerical color value to be used in the draw statement immediately after.
    • "M x, y" can move to another coordinate area of the screen. When a + or - sign is used before a coordinate, it is a relative coordinate move similar to using the STEP graphics keyword. DRAW "M+=" + VARPTR$(variable%)
    • "N" before a line move designates that the graphic cursor will return to the starting position after the line is drawn.
    • "P f [, b]" is used to PAINT enclosed objects. f denotes the fill color and b the border color, if needed.
    • "S n" changes the pixel move size of the lines. Default is 4 (1 pixel) minimum. "S8" would double the pixel line moves.
    • "X" + VARPTR$(value) can draw another substring.

  • Certain letter designations create line moves on the SCREEN. Each move is followed by the number of pixels:

    • "D n" draws a line vertically DOWN n pixels.
    • "E n" draws a diagonal / line going UP and RIGHT n pixels each direction.
    • "F n" draws a diagonal \ line going DOWN and RIGHT n pixels each direction.
    • "G n" draws a diagonal / LINE going DOWN and LEFT n pixels each direction.
    • "H n" draws a diagonal \ LINE going UP and LEFT n pixels each direction.
    • "L n" draws a line horizontally LEFT n pixels.
    • "R n" draws a line horizontally RIGHT n pixels.
    • "U n" draws a line vertically UP n pixels.

  • Angles are used to rotate all subsequent draw moves.

    • "A n" can use values of 1 to 3 to rotate up to 3 90 degree(270) angles.
    • TA n" can use any n angle from -360 to 0 to 360 to rotate a DRAW (Turn Angle). "TA0" resets to normal.
    • When VARPTR$ is used, DRAW functions such as TA angles use an equal sign: "TA=" + VARPTR$(angle%)

  • The graphic cursor is set to the center of the program window on program start for STEP relative coordinates.

  • DRAW can be used in any graphic screen mode, but cannot be used in the default screen mode 0 as it is text only.

Example(s)

Placing an octagon shape DRAW across the the screen using PSET.


SCREEN 12
octagon$ = "C12 R10 F10 D10 G10 L10 H10 U10 E10"  'create a DRAW string value
SCREEN 12
FOR i% = 1 TO 11
  PSET (i% * 50, 100), 15
  _DELAY .5         ' delay for demo
  DRAW octagon$     ' DRAW the octagon using variable
  _DELAY .5         ' delay for demo 
NEXT i%

Explanation: Once a DRAW string variable is created, it can be used to draw a shape throughout the program at any time.

Creating an analog clock's hour markers using "TA=" + VARPTR$(angle).


SCREEN 12
FOR angle = 0 TO 360 STEP 30             ' 360/12 hour circles = 30 degrees apart  
  PSET (175, 250), 6 ' stay at center point of clock
  DRAW "TA=" + VARPTR$(angle) + "BU100" ' move invisibly to set next circle's center point
  CIRCLE STEP(0, 0), 5, 12 ' circle placed at end of blind line
  DRAW "P9, 12" ' paint inside of circle 
  SLEEP 1     ' slowed for demo only
NEXT

Explanation: To place 12 circles in a circle each move is 30 degrees. PSET sets the center of the circular path every loop. TA moves counter-clockwise with positive degree angles. Once TA sets the angle a blind Up move is at that angle. The hour circles use the end point of the blind line as centers using the STEP relative coordinates of 0. After the circles are drawn, a draw "P" string paints the circle centers. DRAW paint strings use the last coordinate position also.

Creating a moving second hand for the clock above (SCREEN 12). (See TIME$ example 1)


DO: sec$ = RIGHT$(TIME$, 2) ' get actual seconds from TIME$ function
  degree$ = STR$(VAL(sec$) * -6) ' 60 second moves. TA uses negative angles for clockwise moves
  PSET (175, 250), 9 ' stay at clock center
  DRAW "TA" + degree$ + "U90" ' up becomes TA directional line
  DO: LOOP UNTIL RIGHT$(TIME$, 2) <> sec$ ' wait for a new second value
  IF INKEY$ <> "" THEN EXIT DO ' any key exit
  PSET (175, 250), 0 ' set at clock center to erase line
  DRAW "TA" + degree$ + "U90" ' erases old second hand line using color 0 from PSET
LOOP

Explanation: The degrees to move from the original UP line move is calculated by dividing 360/60 seconds in a full rotation. That value of 6 is made negative to use TA correctly and multiplied by the VALue of seconds from the TIME$ function. The degree angle is converted by STR$ to a string and added to the DRAW string using the STRING concatenation + operator. Do not use semicolons to create DRAW strings. Once the second hand is placed on the screen, a loop waits for the second value to change. It then erases the hand and it repeats the process again.

Creating digital displays using DRAW format strings to create the LED segments. (See SELECT CASE example 5)


SCREEN 12
DO
  LOCATE 1, 1: INPUT "Enter a number 0 to 9: ", num
  CLS
  SELECT CASE num
    CASE 0, 2, 3, 5 TO 9: PSET (20, 20), 12
      DRAW "E2R30F2G2L30H2BR5P12,12" 'top horiz
  END SELECT

  SELECT CASE num
    CASE 0, 4 TO 6, 8, 9: PSET (20, 20), 12
      DRAW "F2D30G2H2U30E2BD5P12,12" 'left top vert
  END SELECT

  SELECT CASE num
    CASE 0, 2, 6, 8: PSET (20, 54), 12
      DRAW "F2D30G2H2U30E2BD5P12, 12" 'left bot vert
  END SELECT

  SELECT CASE num
    CASE 2 TO 6, 8, 9: PSET (20, 54), 12
      DRAW "E2R30F2G2L30H2BR5P12, 12" 'middle horiz
  END SELECT

  SELECT CASE num
    CASE 0 TO 4, 7 TO 9: PSET (54, 20), 12
      DRAW "F2D30G2H2U30E2BD5P12,12" 'top right vert
  END SELECT

  SELECT CASE num
    CASE 0, 1, 3 TO 9: PSET (54, 54), 12
      DRAW "F2D30G2H2U30E2BD5P12,12" 'bottom right vert
  END SELECT

  SELECT CASE num
    CASE 0, 2, 3, 5, 6, 8: PSET (20, 88), 12
      DRAW "E2R30F2G2L30H2BR5P12,12" 'bottom horiz
  END SELECT
LOOP UNTIL num > 9

Explanation: The DRAW strings can be used more than once with different PSET positions to create more digits.

Using 32 bit or _RGB color STR$ values when using the DRAW C text statement


SCREEN _NEWIMAGE(800, 800, 12)
PRINT _ALPHA(10), _RED(10), _GREEN(10), _BLUE(10)

SLEEP

SCREEN _NEWIMAGE(800, 800, 32) 'comment out this line to use the non-32 bit screen mode 12
PRINT _ALPHA(10), _RED(10), _GREEN(10), _BLUE(10)

PSET (400, 400), 0 ' move to 320, 240... draw will start where pset leaves off
c = 14
DIM k AS _UNSIGNED LONG
k = _RGB(80, 255, 80)
FOR repeat = 1 TO 16
  FOR p = 0 TO 359
    c = c + 1: d = c / 14
    DRAW "c" + STR$(k) + " ta" + STR$(p) + " bu " + STR$(d) + "l7 u7 r7 d7 bd " + STR$(d)
  NEXT p
NEXT repeat

Explanation: DRAW strings will ignore spaces between letters and numbers so string trimming is not necessary.

See Also