ImageInfo
Retrieves information about an image
Syntax
`
Declare Function ImageInfo ( ByVal image As Any Ptr, ByRef width As Integer = 0, ByRef height As Integer = 0, ByRef bypp As Integer = 0, ByRef pitch As Integer = 0, ByRef pixdata As Any Ptr = 0, ByRef size As Integer = 0 ) As Long
`
Usage
`
result = ImageInfo( image [, [width] [, [height] [, [bypp] [, [pitch] [, [pixdata] [, size]]]]]] )
`
Parameters
`image`
The address of the image.
`width`
Stores the width of the image, in pixels.
`height`
Stores the height of the image, in pixels.
`bypp`
Stores the bytes per pixel of the image - i.e. the size of a single pixel, in bytes.
`pitch`
Stores the pitch of the image - i.e. the size of each scanline (row), in bytes. Note that this may be more than just `width * bypp`, because the scanlines may be padded to allow them to be aligned better in memory.
`pixdata`
Stores the address of the start of the first scanline of the image.
`size`
Stores the size of the image in memory, in bytes.
Return Value
If `image` doesn't point to a valid image, one (`1`) is returned. Otherwise, `width`, `height`, `bypp`, `pitch`, `pixdata` and `size` are assigned appropriate values, and zero (`0`) is returned.
Description
`ImageInfo` provides various information about an image, such as its dimensions and color depth, but also provides you with the information you need to directly access all the pixel data in the pixel buffer.
It can also provide the size of the image in memory, which is useful for allocating memory to copy the existing image, or to write the image to a file.
The error code returned by `ImageInfo` can be checked using `Err` in the next line. The function version of `ImageInfo` returns directly the error code as a 32 bit `Long`.
Example
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'' pixelptr(): use imageinfo() to find the pointer to a pixel in the image
'' returns null on error or x,y out of bounds
Function pixelptr(ByVal img As Any Ptr, ByVal x As Integer, ByVal y As Integer) As Any Ptr
Dim As Integer w, h, bypp, pitch
Dim As Any Ptr pixdata
Dim As Integer success
success = (ImageInfo(img, w, h, bypp, pitch, pixdata) = 0)
If success Then
If x < 0 Or x >= w Then Return 0
If y < 0 Or y >= h Then Return 0
Return pixdata + y * pitch + x * bypp
Else
Return 0
End If
End Function
'' usage example:
'' 320*200 graphics screen, 8 bits per pixel
ScreenRes 320, 200, 8
Dim As Any Ptr ip '' image pointer
Dim As Byte Ptr pp '' pixel pointer (use byte for 8 bits per pixel)
ip = ImageCreate(32, 32) '' create an image (32*32, 8 bits per pixel)
If ip <> 0 Then
'' draw a pattern on the image
For y As Integer = 0 To 31
For x As Integer = y - 5 To y + 5 Step 5
'' find the pointer to pixel at x,y position
'' note: this is inefficient to do for every pixel!
pp = pixelptr(ip, x, y)
'' if success, plot a value at the pixel
If (pp <> 0) Then *pp = 15
Next x
Next y
'' put the image and draw a border around it
Put (10, 10), ip, PSet
Line (9, 9)-Step(33, 33), 4, b
'' destroy the image to reclaim memory
ImageDestroy ip
Else
Print "Error creating image!"
End If
Sleep
`
`
'' Create 32-bit graphics screen and image.
ScreenRes 320, 200, 32
Dim image As Any Ptr = ImageCreate( 64, 64 )
Dim pitch As Integer
Dim pixels As Any Ptr
'' Get enough information to iterate through the pixel data.
If 0 <> ImageInfo( image, ,,, pitch, pixels ) Then
Print "unable to retrieve image information."
Sleep
End
End If
'' Draw a pattern on the image by directly manipulating pixel memory.
For y As Integer = 0 To 63
Dim row As ULong Ptr = pixels + y * pitch
For x As Integer = 0 To 63
row[x] = RGB(x * 4, y * 4, (x Xor y) * 4)
Next x
Next y
'' Draw the image onto the screen.
Put (10, 10), image
ImageDestroy( image )
Sleep
`
Dialect Differences

- Not available in the -lang qb dialect unless referenced with the alias `__Imageinfo`.

Differences from QB

- New to FreeBASIC

See also

- `ImageCreate`
- `ImageDestroy`
- `ImageConvertRow`
- `Get (Graphics)`
- `Put (Graphics)`
- Internal pixel formats