_MEMIMAGE - QB64 Wiki

_MEMIMAGE

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The _MEMIMAGE function returns a _MEM value referring to an image's memory using a designated image handle.


Syntax:

image_block = _MEMIMAGE[(image_handle)]


Parameters:

  • The image block _MEM type variable holds the read only .OFFSET, .SIZE, .TYPE and .ELEMENTSIZE.
  • The optional image handle requires no parameter or 0 if the image desired is the current _DESTination program screen image.


Usage:

  • Use the function to place images into memory access blocks for faster data access.
  • All values created by this function MUST be freed using _MEMFREE with a valid _MEM type variable.
  • Image handle values and the memory used must still be freed using _FREEIMAGE when no longer required.


Example 1: Darkening an image using memory with $CHECKING:OFF for greater speed. Use any 24 bit image file name on the second code line.

SCREEN _NEWIMAGE(1024, 768, 32) i& = _LOADIMAGE("turtle.jpg") '<<<<<<<<<<<<< use any 24 bit image file FOR n! = 1 TO 0.01 STEP -0.01 i2& = _COPYIMAGE(i&) DarkenImage i2&, n! _PUTIMAGE (0, 0), i2& _FREEIMAGE i2& _DISPLAY NEXT SUB DarkenImage (Image AS LONG, Value_From_0_To_1 AS SINGLE) IF Value_From_0_To_1 <= 0 OR Value_From_0_To_1 >= 1 OR _PIXELSIZE(Image) <> 4 THEN EXIT SUB DIM Buffer AS _MEM: Buffer = _MEMIMAGE(Image) 'Get a memory reference to our image DIM Frac_Value AS LONG: Frac_Value = Value_From_0_To_1 * 65536 'Used to avoid slow floating point calculations DIM O AS _OFFSET, O_Last AS _OFFSET O = Buffer.OFFSET 'We start at this offset O_Last = Buffer.OFFSET + _WIDTH(Image) * _HEIGHT(Image) * 4 'We stop when we get to this offset 'use on error free code ONLY! $CHECKING:OFF DO _MEMPUT Buffer, O, _MEMGET(Buffer, O, _UNSIGNED _BYTE) * Frac_Value \ 65536 AS _UNSIGNED _BYTE _MEMPUT Buffer, O + 1, _MEMGET(Buffer, O + 1, _UNSIGNED _BYTE) * Frac_Value \ 65536 AS _UNSIGNED _BYTE _MEMPUT Buffer, O + 2, _MEMGET(Buffer, O + 2, _UNSIGNED _BYTE) * Frac_Value \ 65536 AS _UNSIGNED _BYTE O = O + 4 LOOP UNTIL O = O_Last 'turn checking back on when done! $CHECKING:ON _MEMFREE Buffer END SUB

Code by Galleon
Explanation: The second value passed to DarkenImage is a value from 0.0 to 1.0 where 0.0 is full darkness and 1 is none.


Example 2: Reading information stored in an image with _MEMIMAGE to print ASC text characters to the screen.

SCREEN 13 _FULLSCREEN PSET (0, 0), ASC("H") PSET (1, 0), ASC("E") PSET (2, 0), ASC("L") PSET (3, 0), ASC("L") PSET (4, 0), ASC("O") PSET (5, 0), 32 PSET (6, 0), ASC("W") PSET (7, 0), ASC("O") PSET (8, 0), ASC("R") PSET (9, 0), ASC("L") PSET (10, 0), ASC("D") DIM m AS _MEM m = _MEMIMAGE x1$ = _MEMGET(m, m.OFFSET, STRING * 11) 'convert numbers to ASCII text characters _MEMFREE m 'free memory when done LOCATE 10, 1: PRINT LEN(x1$) 'prints 11 as byte length PRINT x1$ 'prints HELLO WORLD END

Notes: The colors in the upper left corner are the text data used. An image could hold a hidden text message this way.


See also:



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