BLoad

FreeBASIC

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BLoad

Loads arbitrary data from a file created with BSave, or a compatible BMP image file.

Syntax

Declare Function BLoad ( ByRef filename As Const String, ByVal dest As Any Ptr = 0, ByVal pal As Any Ptr = 0 ) As Long

Usage

result = BLoad( filename [, [ dest ] [, pal ] ] )

Parameters

filename

the name of the file to load the image from; can include a file path

dest

the memory location to load the image to, or null (0) to copy the image to the current graphics screen work page

pal

the memory location to load the palette to, or null (0) to change the current graphics screen palette, if it uses one

Return Value

Returns zero (0) if successful, or a non-zero error code to indicate a failure. (throws a runtime error)

Description

BLoad can be used to load image data or any other data from a file created with BSave, and store that data in an array or paste it to the screen. If dest is absent or null (0), the image data is pasted to the current graphics screen work page. Otherwise it is loaded as image data to the address given by dest.

BLoad can load 3 different types of files:

Old QB-like data files, saved with BSAVE from QB code, containing "raw" data preceded by a 7-byte header, beginning with &HFD;, up to 64 KiB in size
New FB-like data files, saved with BSave from FB code, containing "raw" data preceded by a 5-byte header, beginning with &HFE;. There is no 64 KiB limit with this format
BMP image files, supports a subset of valid ("Windows") .BMP files, beginning with "BM", saved from FB code with BSave, or created / saved in a compatible format using a graphics editor / converter.

QB-like data files and BMP files are converted to an FB-compatible image format when opened.

Image files with 8-bit per pixel resolution or lower contain a palette that describes the color values used in the images. If pal is not null (0), the palette is copied to memory starting at the address specified. Otherwise, if the current graphics screen uses a palette then its palette is changed to match that of the image file.

When using one of the 2 "non-BMP" file formats to save images, the image files must have been created with BSave in the same graphics screen mode as it is being loaded into. When using the BMP file format, this restriction doesn't apply.

When loading a BMP file using BLoad, the images must be true-color (15-, 16-, 24- or 32-bits per pixel) or palettized/indexed (8-bit or lower). The image data will be converted to the proper pixel format for the current color depth, except that true-color can't be reduced to a palettized image. BLoad doesn't support BMP files using RLE compression or other image file types (PNG, JPG, GIF, ...). BLoad will load alpha channel information, if available, from 32-bit BMP files with BITMAPV4HEADER or BITMAPV5HEADER file headers.

Runtime errors:
BLoad throws one of the following runtime errors:

(1) Illegal function call

dest was not specified or was null (0), and no graphics screen was set.
The Bitmap uses an unsupported BMP file compression type (BI_RLE4, BI_RLE8)
The Bitmap is true-color (16, 24, or 32 bits per pixel) and the current graphics screen uses a palette (8 bits per pixel or lower).

(2) File not found

The file filename could not be found.

(3) File I/O error

The file doesn't have any of the supported types
A general read error occurred.

Note: When you use BLoad to load a BMP file into an image buffer, the original dimensions of the image are not changed. If you want the image buffer to have the same dimensions as the BMP file, you have to find out the dimensions beforehand, and create an image of the right size yourself. See the example below for an example of how to do this.

Example

'Load a graphic to current work page Screen 18, 32 Cls BLoad "picture.bmp" Sleep

'Load a 48x48 bitmap into an image ScreenRes 320, 200, 32 Dim myImage As Any Ptr = ImageCreate( 48, 48 ) BLoad "picture.bmp", myImage Put (10,10), myImage ImageDestroy( myImage ) Sleep

ScreenRes 640, 480, 8 '' 8-bit palette graphics mode Dim pal(0 To 256-1) As Integer '' 32-bit integer array with room for 256 colors '' load bitmap to screen, put palette into pal() array BLoad "picture.bmp", , @pal(0) WindowTitle "Old palette" Sleep '' set new palette from pal() array Palette Using pal(0) WindowTitle "New palette" Sleep

'' A function that creates an image buffer with the same '' dimensions as a BMP image, and loads a file into it. Const NULL As Any Ptr = 0 Function bmp_load( ByRef filename As Const String ) As Any Ptr Dim As Long filenum, bmpwidth, bmpheight Dim As Any Ptr img '' open BMP file filenum = FreeFile() If Open( filename For Binary Access Read As #filenum ) <> 0 Then Return NULL '' retrieve BMP dimensions Get #filenum, 19, bmpwidth Get #filenum, 23, bmpheight Close #filenum '' create image with BMP dimensions img = ImageCreate( bmpwidth, Abs(bmpheight) ) If img = NULL Then Return NULL '' load BMP file into image buffer If BLoad( filename, img ) <> 0 Then ImageDestroy( img ): Return NULL Return img End Function Dim As Any Ptr img ScreenRes 640, 480, 32 img = bmp_load( "picture.bmp" ) If img = NULL Then Print "bmp_load failed" Else Put (10, 10), img ImageDestroy( img ) End If Sleep

Differences from QB

Support for loading BMP files is new to FreeBASIC.
Support for retrieving the palette from BMP files is new to FreeBASIC.
FreeBASIC uses a different file format from QBASIC internally, which doesn't have the 64 KiB limit, and is unsupported by QBASIC.