View Source wxMemoryDC (wx v2.4.2)
Functions for wxMemoryDC class
A memory device context provides a means to draw graphics onto a bitmap. When
drawing in to a mono-bitmap, using wxWHITE
, wxWHITE_PEN
and wxWHITE_BRUSH
will draw the background colour (i.e. 0) whereas all other colours will draw the
foreground colour (i.e. 1).
A bitmap must be selected into the new memory DC before it may be used for anything. Typical usage is as follows:
Note that the memory DC must be deleted (or the bitmap selected out of it) before a bitmap can be reselected into another memory DC.
And, before performing any other operations on the bitmap data, the bitmap must be selected out of the memory DC:
This happens automatically when wxMemoryDC
object goes out of scope.
This class is derived (and can use functions) from: wxDC
wxWidgets docs: wxMemoryDC
Summary
Functions
Destroys the object.
Constructs a new memory device context.
Constructs a new memory device context having the same characteristics as the given existing device context.
Works exactly like selectObjectAsSource/2
but this is the function you should
use when you select a bitmap because you want to modify it, e.g.
Selects the given bitmap into the device context, to use as the memory bitmap.
Types
-type wxMemoryDC() :: wx:wx_object().
Functions
-spec destroy(This :: wxMemoryDC()) -> ok.
Destroys the object.
-spec new() -> wxMemoryDC().
Constructs a new memory device context.
Use the wxDC:isOk/1
member to test whether the constructor was successful in
creating a usable device context. Don't forget to select a bitmap into the DC
before drawing on it.
-spec new(Dc) -> wxMemoryDC() when Dc :: wxDC:wxDC() | wxBitmap:wxBitmap().
Constructs a new memory device context having the same characteristics as the given existing device context.
This constructor creates a memory device context compatible
with dc
in
wxMSW, the argument is ignored in the other ports. If dc
is NULL, a device
context compatible with the screen is created, just as with the default
constructor.
-spec selectObject(This, Bitmap) -> ok when This :: wxMemoryDC(), Bitmap :: wxBitmap:wxBitmap().
Works exactly like selectObjectAsSource/2
but this is the function you should
use when you select a bitmap because you want to modify it, e.g.
drawing on this DC.
Using selectObjectAsSource/2
when modifying the bitmap may incur some problems
related to wxBitmap
being a reference counted object (see
overview_refcount).
Before using the updated bitmap data, make sure to select it out of context first either by selecting ?wxNullBitmap into the device context or destroying the device context entirely.
If the bitmap is already selected in this device context, nothing is done. If it is selected in another context, the function asserts and drawing on the bitmap won't work correctly.
See: wxDC:drawBitmap/4
-spec selectObjectAsSource(This, Bitmap) -> ok when This :: wxMemoryDC(), Bitmap :: wxBitmap:wxBitmap().
Selects the given bitmap into the device context, to use as the memory bitmap.
Selecting the bitmap into a memory DC allows you to draw into the DC (and
therefore the bitmap) and also to use wxDC:blit/6
to copy the bitmap to a
window. For this purpose, you may find wxDC:drawIcon/3
easier to use instead.
If the argument is ?wxNullBitmap (or some other uninitialised wxBitmap
) the
current bitmap is selected out of the device context, and the original bitmap
restored, allowing the current bitmap to be destroyed safely.