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Document Fl_Image_Surface::mask() with commented code example

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ManoloFLTK
2023-12-07 15:01:23 +01:00
parent ddf81baa65
commit d963dde3ef
2 changed files with 35 additions and 11 deletions
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documentation/src/masked_image.png
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src/Fl_Image_Surface.cxx
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@@ -217,19 +217,43 @@ void Fl_Image_Surface::rescale() {
drawing white areas on a black background there, and calling Fl_Image_Surface::image(). drawing white areas on a black background there, and calling Fl_Image_Surface::image().
\param mask A depth-3 image determining the drawable areas of the image surface. \param mask A depth-3 image determining the drawable areas of the image surface.
The \p mask object is not used after return from this member function. The \p mask object is not used after return from this member function.
\note The image surface must not be the current drawing surface when this function \note
gets called. The mask can have any size but is best when it has the size of the image surface. - The image surface must not be the current drawing surface when this function
A typical procedure is to use the image surface to draw first the mask (using white over black), gets called.
call Fl_Image_Surface::image() to obtain the mask, then draw the background, call - The mask can have any size but is best when it has the size of the image surface.
Fl_Image_Surface::mask(mask), draw the foreground, and finally get the resulting - It's possible to use several masks in succession on the same image surface provided
image from Fl_Image_Surface::image().
It's possible to use several masks in succession on the same image surface provided
member function Fl_Image_Surface::image() is called between successive calls to member function Fl_Image_Surface::image() is called between successive calls to
Fl_Image_Surface::mask(Fl_RGB_Image*). Fl_Image_Surface::mask(const Fl_RGB_Image*).
This diagram depicts operations involved in the construction of a masked image: Example of procedure to construct a masked image:
\image html masked_image.png "Construction of a masked image" \code
\image latex masked_image.png "Construction of a masked image" width=8cm int W = …, H = …; // width and height of the image under construction
Fl_Image_Surface *surf = new Fl_Image_Surface(W, H, 1);
// first, construct the mask
Fl_Surface_Device::push_current(surf);
fl_color(FL_BLACK); // draw a black background
fl_rectf(0, 0, W, H);
fl_color(FL_WHITE); // next, draw in white what the mask should not filter out
fl_pie(0, 0, W, H, 0, 360); // here, an ellipse with axes lengths WxH
Fl_RGB_Image *mask = surf->image(); // get the mask
// second, draw the image background
fl_color(FL_YELLOW); // here, draw a yellow background
fl_rectf(0, 0, W, H);
// third, apply the mask
Fl_Surface_Device::pop_current();
surf->mask(mask);
delete mask; // the mask image can be safely deleted at this point
Fl_Surface_Device::push_current(surf);
// fourth, draw the image foreground, part of which will be filtered out by the mask
surf->draw(widget, 0, 0); // here the foreground is a drawn widget
// fifth, get the final result, masked_image, as a depth-3 Fl_RGB_Image
Fl_RGB_Image *masked_image = surf->image();
// Only the part of the foreground, here a drawn widget, that has not been
// filtered out by the mask, here the white ellipse, is in masked_image;
// the background, here solid yellow, shows up in the remaining areas of masked_image.
Fl_Surface_Device::pop_current();
delete surf;
\endcode
\since 1.4.0 \since 1.4.0
*/ */