Picture

From Xojo Documentation

Class (inherits from Object)

A Picture object contains a picture or an image.

Properties
Depth fa-lock-32.png HorizontalResolution RGBSurface fa-lock-32.png
Graphics fa-lock-32.png ImageCount fa-lock-32.png Type fa-lock-32.png
HasAlphaChannel fa-lock-32.png IndexedImage fa-lock-32.png VerticalResolution
Height fa-lock-32.png Objects Width fa-lock-32.png
Methods
ApplyMask CopyMask ToData
BestRepresentation CopyOSHandle
CopyColorChannels Save
Enumerations
Formats HandleType Types
Shared Methods
FromData IsImportFormatSupported OpenVector
IsExportFormatSupported Open
Constructors

Constructor(width as Integer, height as Integer)


Constructor(width as Integer, height as Integer, Depth as Integer)


Constructor(width as Integer, height as Integer, bitmaps() As Picture)


Notes

fa-info-circle-32.png
Console applications only support JPEG and PNG image types.

Image Sets and HiDPI

When adding Pictures to your projects, you create Image Sets which can contain the picture at various sizes for use with HiDPI displays.

Also refer to HiDPI Support for additional information.

Support for Transparency

Beginning with version 2011r4, Picture objects support alpha channels (transparency) directly, without the need for a mask.

Pictures with alpha channels are supported on macOS, Windows, Linux, console applications, and Web. On platforms without support for alpha channels, a PlatformNotSupported exception is raised when trying to create the Picture.

Support for the alpha channel is now built into the color functions: RGB, HSV, CMY, and &c. These functions have an optional fourth parameter that specifies the degree of transparency of the color. Here are the modified functions:

Function Parameters
RGB red as Integer
green as Integer
blue as Integer
alpha as Integer = 0
HSV hue as Double
saturation as Double
value as Double
alpha as Integer = 0
CMY cyan as Double
magenta as Double
yellow as Double
alpha as Integer = 0
&c RRGGBBAA, where the hex digits specify the amounts of red, green, blue, and transparency in the color. For the transparency parameter, 00 is opaque and FF is fully transparent.

In the Picture class, support for alpha channels means that the use of masks is no longer required. This streamlines the process and reduces memory support. To take advantage of this feature, you can create new Picture objects with alpha channel support and convert “old” picture objects to those with alpha channels.

Constructor

To create a Picture with an alpha channel, use the new constructor that omits the depth parameter:

Constructor(width As Integer, height As Integer)

When this constructor is used, the Picture instance defaults to transparent and can be returned to that state using Graphics.ClearRect().

A picture created without an alpha channel supplies the depth parameter:

Constructor(width As Integer, height As Integer, depth As Integer)

Updating "old" Pictures

Pictures loaded from disk, databases, project files, or Picture.FromData continue to return pictures with masks. This is required for legacy compatibility, but masked Pictures can be converted to a Picture with an alpha channel with the following code:

Function ConvertToAlphaPicture(input As Picture) As Picture
If input.hasAlphaChannel Then Return input

Var result As New Picture(input.Width, input.Height)
result.HorizontalResolution = input.HorizontalResolution
result.VerticalResolution = input.VerticalResolution
result.Graphics.DrawPicture(input, 0, 0)
Return result
End Function

New Properties and Methods

HasAlphaChannel Property

HasAlphaChannel As Boolean

This property indicates whether or not the Picture has an alpha channel. For Pictures using masks, this returns False.

CopyMask Method

CopyMask As Picture

When used on a picture with an alpha channel, this takes the image's alpha channel and creates the equivalent mask. If used on a picture with a mask, it simply returns a copy of the current mask. In neither case does it alter the original image and the copied mask is not updated when any drawing happens on the original Picture.

ApplyMask Method

ApplyMask(theMask As Picture)

When used on a Picture with an alpha channel, this overwrites the Picture's alpha channel with the mask data. When used on a picture with a mask, it overwrites the current mask with a copy of the mask passed in.

Other Alpha Channel Notes

Pixel and RGBSurface have been updated to properly support alpha channels by taking them into account when rendering them. Additionally, Pixel properly reports back alpha channel information, if available.

Pictures with alpha channels cannot also use masks. Trying to do so will raise an UnsupportedOperationException at runtime. Reading this value always returns Nil for pictures with alpha channels. For pictures without alpha channels, the mask functionality continues to work normally.

On Mac and Linux, Pictures are stored internally with their alpha channels premultiplied into the color channels. Since premultiplication is a lossy operation, the color you draw may not be exactly what you get out when inspecting it with an RGBSurface. For example, drawing a &cFF00EECC rectangle will result in a different color if read from that pixel using RGBSurface.

Plugin Support

The color type has changed from being XRGB to ARGB. If you previously put garbage into the first byte, this is going to cause problems now that the framework uses this to store the alpha component.

On macOS, a Picture with an alpha channel is represented internally as a premultiplied ARGB buffer wrapped by a CGBitmapContext. This buffer can be accessed the same way as for masked images: REALLockPictureDescription and then CGBitmapContextGetData.

On Windows, a Picture with an alpha channel is represented internally as a premultiplied 32-bit BGRA buffer. This buffer can be accessed the same way as for masked images: REALLockPictureDescription and the raw bytes are returned in the data field.

On Linux, a Picture with an alpha channel is represented internally as a 32-bit premultiplied ARGB buffer wrapped by a cairo_t. This buffer can be accessed the same way as for masked images: REALLockPictureDescription and then cairo_image_surface_get_data( cairo_get_target( cairo_t * ) ).

On console and web apps, a Picture with an alpha channel is represented internally as a 32-bit ARGB buffer wrapped by a gdImagePtr. Note: the ARGB buffer is NOT premultiplied, and the maximum alpha value is 127 instead of 255. This buffer can be accessed the same way as for masked images: REALLockPictureDescription with pictureGDPtr (this will give you the raw buffer with an 11 byte header).

Creating a Picture

A Picture object is created by adding a picture to the project, by calling the Picture constructor or the OpenVector method of a FolderItem object. When you use the New operator, you must use the constructor. If you use the New operator but run out of memory, an OutOfMemoryException error will be raised. If you specify a depth of zero, a picture with no pixel map at all is created, but with a preinitialized Objects property. Use this option for creating vector graphics pictures via the set of Object2D subclasses.

Here is an example on how to create a picture and handle the OutOfMemoryException exception:

// 2000 x 2000 Pixel works, but 20000 x 20000 Pixel will raise exception
Var width As Integer = 2000
Var height As Integer = 2000

// creates new picture
Var pic As New Picture(width, height)

// fill with red
pic.Graphics.DrawingColor = &cFF0000
pic.Graphics.FillRectangle(0, 0, 100, 100)

// and show picture in a window/canvas backdrop
Self.Backdrop = pic

Exception o As OutOfMemoryException
MsgBox("Picture dimensions too big." + EndOfLine + EndOfLine + Str(width * height * 4 / 1024 / 1024) + " MB")

Cross-Platform Formats

PNG, JPEG and BMP formats are cross-platform.

Unrecognized formats or formats not supported for the built target will result in an UnsupportedFormatException. The Message property of the exception will contain additional information about what went wrong.

JPEG Quality Constants

If you are using the JPEG format, then there is an optional parameter for the quality of the JPEG. You specify the quality using the following class constants.

Constant Value
QualityDefault 1
QualityHigh 80
QualityLow 25
QualityMaximum 100
QualityMedium 50
QualityMinimum 0

See Also

RGBSurface object; Graphics class.