POINT
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POINT in QBasic Legacy Graphic SCREEN Modes:
POINT in QB64 32 Bit Graphic _NEWIMAGE or _LOADIMAGE Modes:
Code by Ted Weissgerber
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The POINT function returns the pixel COLOR attribute at a specified graphics coordinate or the current graphic cursor position.
Syntax
- Graphic Color
- color_attribute% = POINT (column%, row%)
- Graphic cursor position
- pointer_coordinate% = POINT({0|1|2|3})
Parameters
Graphic Color syntax:
- The INTEGER column and row coordinates designate the pixel position color on the screen to read.
- The return value is an INTEGER palette attribute value or an _UNSIGNED LONG _RGBA 32 bit value in QB64.
Graphic cursor position syntax:
- The INTEGER position number can be 0 to 3 depending on the cursor position desired:
- If a WINDOW view port has not been established, the coordinate returned will be the SCREEN cursor pixel position.
- The return value is the current graphic cursor column or row pixel position on the SCREEN or WINDOW.
- Graphic cursor positions returned will be the last ones used in a graphic shape such as a CIRCLE center point.
Usage:
- Use _SOURCE first to set the image handle that POINT should read or QB64 will assume the current source image.
- _SOURCE 0 'sets POINT to read the current SCREEN image after reading a previous source image
- POINT cannot be used in SCREEN 0! Use the SCREEN function to point text character codes and colors in SCREEN 0.
- The INTEGER color attributes returned are limited by the number of colors in the legacy SCREEN mode used.
- Column and row INTEGER parameters denote the graphic pixel coordinate to read.
- In QB64 the offscreen or off image value returned is -1. Use IF POINT(x, y) <> -1 THEN...
- In QBasic the coordinates MUST be on the screen or an Illegal Function Call error will occur.
- Returns _UNSIGNED LONG 32 bit color values. Use _UNSIGNED values when you don't want negative values.
- _UNSIGNED LONG variables should be used when comparing POINT returns with _RGB or _RGB32 _ALPHA bit values
- Convert 32 bit color values to RGB intensities(0 to 255) using the _RED32, _GREEN32 and _BLUE32 functions.
- To convert color intensities to OUT &H3C9 color port palette intensity values divide the values of 0 to 255 by 4.
- Use the _PALETTECOLOR (function) to convert color port palette intensities in 32 bit modes.
Example 1: How _RGB 32 bit values return DOUBLE or _UNSIGNED LONG values in QB64.
DIM clr AS LONG 'DO NOT use LONG in older versions of QB64 (V .936 down) SCREEN _NEWIMAGE(640, 480, 32) CLS , _RGB(255, 255, 255) 'makes the background opaque white PRINT "POINT(100, 100) ="; POINT(100, 100) clr = POINT(100, 100) PRINT "Variable clr = "; clr IF clr = _RGB(255, 255, 255) THEN PRINT "Long OK" IF POINT(100, 100) = _RGB(255, 255, 255) THEN PRINT "_RGB OK" IF POINT(100, 100) = clr THEN PRINT "Type OK" 'will not print with a LONG variable type |
- Note: Change the DIM clr variable type to LONG to see how the last IF statement doesn't PRINT as shown in the output below:
POINT(100, 100) = 4294967295 Variable clr = -1 Long OK _RGB OK |
Example 2: Using a POINT mouse routine to get the 32 bit color values of the image.
SCREEN _NEWIMAGE(640, 480, 32) _TITLE "Mouse POINTer 32" 'LINE INPUT "Enter an image file: ", image$ 'use quotes around file names with spaces image$ = "QB64bee.png" 'any 24/32 bit image up to 320 X 240 with current _PUTIMAGE settings i& = _LOADIMAGE(image$, 32) IF i& >= -1 THEN BEEP: PRINT "Could NOT load image!": END w& = _WIDTH(i&): h& = _HEIGHT(i&) PRINT "Make background transparent?(Y\N)"; BG$ = UCASE$(INPUT$(1)) PRINT BG$ _DELAY 1 'CLS 'commented to keep background alpha 0 IF BG$ = "Y" THEN _CLEARCOLOR _RGB32(255, 255, 255), i& 'make white Background transparent _PUTIMAGE (320 - w&, 240 - h&)-((2 * w&) + (320 - w&), (2 * h&) + (240 - h&)), i&, 0 _FREEIMAGE i& _MOUSEMOVE 320, 240 'center mouse pointer on screen DO: _LIMIT 100 DO WHILE _MOUSEINPUT mx = _MOUSEX my = _MOUSEY c& = POINT(mx, my) r = _RED32(c&) g = _GREEN32(c&) b = _BLUE32(c&) a = _ALPHA32(c&) LOCATE 1, 1: PRINT mx; my, "R:"; r, "G:"; g, "B:"; b, "A:"; a; " " LOCATE 2, 2: PRINT "HTML Color: &H" + RIGHT$(HEX$(c&), 6) LOOP LOOP UNTIL INKEY$ > "" END |
- Explanation: Use the mouse pointer to get the background RGB of the image to make it transparent with _CLEARCOLOR.
Snippet: Creating an image mask to PUT an image over other colored backgrounds. See: GET and PUT Demo to run code.
FOR c = 0 TO 59 '60 X 60 area from 0 pixel
FOR r = 0 TO 59
IF POINT(c, r) = 0 THEN PSET (c, r), 15 ELSE PSET (c, r), 0
NEXT r
NEXT c
GET(0, 0)-(60, 60), Image(1500) ' save mask in an array(indexed above original image).
|
- Explanation: In the procedure all black areas(background) are changed to white for a PUT using AND over other colored objects. The other image colors are changed to black for a PUT of the original image using XOR. The array images can be BSAVEd for later use. QB64 can also PUT a full screen 12 image from an array directly into a BINARY file.
More Examples
See also
- _NEWIMAGE, _LOADIMAGE
- _MEMIMAGE, _MEMGET
- PSET, PRESET
- SCREEN, SCREEN (function)
- GET (graphics statement), PUT (graphics statement)
- Bitmaps, Creating Sprite Masks, Text Using Graphics