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Add comments: "Implementation note about how Fl_Pixmap objects get printed under Windows"

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git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@12852 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
This commit is contained in:
Manolo Gouy 2018-04-18 15:36:45 +00:00
parent 15e3f4b2d2
commit 71d23d5574
1 changed files with 15 additions and 2 deletions
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17
src/drivers/GDI/Fl_GDI_Graphics_Driver_image.cxx
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@ -654,7 +654,21 @@ void Fl_GDI_Graphics_Driver::draw_fixed(Fl_Pixmap *pxm, int X, int Y, int W, int
unscale_clip(r2);
}
/* ===== Implementation note about how Fl_Pixmap objects get printed under Windows =====
Fl_Pixmap objects are printed with the print-specific Fl_GDI_Printer_Graphics_Driver
which uses the TransparentBlt() system function that can scale the image and treat one
of its colors as transparent.
Fl_GDI_Printer_Graphics_Driver::draw_pixmap(Fl_Pixmap *,...) sets need_pixmap_bg_color,
a static class variable, to 1 and recaches the image. This calls fl_convert_pixmap()
that checks the value of need_pixmap_bg_color. When this value is not 0, fl_convert_pixmap
runs in a way that memorizes the list of all colors in the pixmap, computes
a color absent from this list, uses it for the transparent pixels of the pixmap and puts
this color value in need_pixmap_bg_color. As a result, the transparent areas of the image
are correcty handled by the printing operation. Variable need_pixmap_bg_color is ultimately
reset to 0.
Fl_GDI_Graphics_Driver::make_unused_color_() which does the color computation mentionned
above is implemented in file src/fl_draw_pixmap.cxx
*/
void Fl_GDI_Printer_Graphics_Driver::draw_pixmap(Fl_Pixmap *pxm, int XP, int YP, int WP, int HP, int cx, int cy) {
int X, Y, W, H;
if (start_image(pxm, XP, YP, WP, HP, cx, cy, X, Y, W, H)) return;
@ -671,7 +685,6 @@ void Fl_GDI_Printer_Graphics_Driver::draw_pixmap(Fl_Pixmap *pxm, int XP, int YP,
float scaleH = pxm->data_h()/float(pxm->h());
fl_TransparentBlt(gc_, X, Y, W, H, new_gc, cx * scaleW, cy * scaleH, W * scaleW, H * scaleH,
need_pixmap_bg_color );
need_pixmap_bg_color = 0;
RestoreDC(new_gc,save);
DeleteDC(new_gc);
need_pixmap_bg_color = 0;