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Add public function Fl_RGB_Image *fl_capture_window_part() 

In the context of HighDPI screens, the API of function fl_read_image()
is inadequate because a rectangle of size WxH drawing units
of a window may contain many more than W*H pixels.

Function fl_capture_window_part() returns an Fl_RGB_Image
object whose drawing size matches the size of the rectangle
and whose data size matches the, possibly larger, size in pixels
of the corresponding area of the mapped window.
This commit is contained in:
ManoloFLTK 2019-04-09 18:50:18 +02:00
parent 0ddf5e74a9
commit 8286e37b18
2 changed files with 20 additions and 0 deletions
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1
FL/fl_draw.H
View File

@ -794,6 +794,7 @@ inline void fl_draw_image_mono(Fl_Draw_Image_Cb cb, void* data, int X,int Y,int
inline char fl_can_do_alpha_blending() {return Fl_Graphics_Driver::default_driver().can_do_alpha_blending();}
FL_EXPORT uchar *fl_read_image(uchar *p,int X,int Y,int W,int H,int alpha=0);
FL_EXPORT Fl_RGB_Image *fl_capture_window_part(Fl_Window *win, int x, int y, int w, int h);
// pixmaps:
/**

19
src/fl_read_image.cxx
View File

@ -36,6 +36,8 @@
The \p alpha parameter controls whether an alpha channel is created
and the value that is placed in the alpha channel. If 0, no alpha
channel is generated.
\see fl_capture_window_part()
*/
uchar *fl_read_image(uchar *p, int X, int Y, int w, int h, int alpha) {
uchar *image_data = NULL;
@ -88,6 +90,23 @@ uchar *fl_read_image(uchar *p, int X, int Y, int w, int h, int alpha) {
return image_data;
}
/** Captures the content of a rectangular zone of a mapped window.
\param win a mapped Fl_Window (derived types including Fl_Gl_Window are also possible)
\param x,y,w,h window area to be captured. Intersecting sub-windows are captured too.
\return The captured pixels as an Fl_RGB_Image. The raw and
drawing sizes of the image can differ. Returns NULL when capture was not successful.
The image depth may differ between platforms.
\version 1.4
*/
Fl_RGB_Image *fl_capture_window_part(Fl_Window *win, int x, int y, int w, int h)
{
Fl_RGB_Image *rgb = NULL;
if (win->shown()) {
rgb = Fl_Screen_Driver::traverse_to_gl_subwindows(win, x, y, w, h, NULL);
if (rgb) rgb->scale(w, h, 0, 1);
}
return rgb;
}
//
// End of "$Id$".
//