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Comments only: more extensive explanation of how virtual member functions of Fl_Graphics_Driver can support image drawing.

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git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@12835 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
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Manolo Gouy 2018-04-14 15:10:59 +00:00
parent bfac5462be
commit 82e70fae04
1 changed files with 26 additions and 14 deletions
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40
FL/Fl_Graphics_Driver.H
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@ -95,25 +95,37 @@ class FL_EXPORT Fl_Graphics_Driver {
friend FL_EXPORT void fl_delete_bitmask(Fl_Bitmask);
private:
/* ============== Implementation note about image drawing =========================
A graphics driver uses either its implementation of the draw_rgb(Fl_RGB_Image *,....)
or that of the draw_fixed(Fl_RGB_Image *,....) member functions to draw an RGB image.
Same thing with draw_bitmap(Fl_Bitmap *,....) or draw_fixed(Fl_Bitmap *,....).
Same thing with draw_pixmap(Fl_Pixmap *,....) or draw_fixed(Fl_Pixmap *,....).
- The driver uses draw_???() if it can directly map the image data,
A graphics driver can implement up to 6 virtual member functions to draw images:
virtual void draw_pixmap(Fl_Pixmap *pxm,int XP, int YP, int WP, int HP, int cx, int cy)
virtual void draw_bitmap(Fl_Bitmap *bm,int XP, int YP, int WP, int HP, int cx, int cy)
virtual void draw_rgb(Fl_RGB_Image *rgb,int XP, int YP, int WP, int HP, int cx, int cy)
and
virtual void draw_fixed(Fl_Pixmap *pxm,int XP, int YP, int WP, int HP, int cx, int cy)
virtual void draw_fixed(Fl_Bitmap *bm,int XP, int YP, int WP, int HP, int cx, int cy)
virtual void draw_fixed(Fl_RGB_Image *rgb,int XP, int YP, int WP, int HP, int cx, int cy)
- The 1st group of functions is used when the driver can directly map the image data,
sized at data_w() x data_h(), to the image drawing area, sized at w()*scale x h()*scale
where scale is the current GUI scale factor.
- If the driver does not support such scale-and-draw operation, it should use draw_fixed()
which is called by the library after the image has been internally resized to the adequate
drawing size and cached.
- The platform-independent Fl_Graphics_Driver class implements draw_???(image-class *,....)
that scales the image and calls the platform-specific implementation of
draw_fixed(image-class *,....) with the scaled, cached image.
- Some graphics drivers implement only draw_???() or draw_fixed() as in these examples:
- If the driver does not support such scale-and-draw operation, it should implement the
draw_fixed() function which is called by the library after the image has been internally
resized to the drawing size and cached.
- The platform-independent Fl_Graphics_Driver class implements the 1st group of functions.
Each resizes the image, caches it, and calls the platform-specific implementation of
draw_fixed(image-class *,....) with the cached image.
- Consider an image object, say from class Fl_RGB_Image. Fl_RGB_Image::draw()
calls the virtual member function draw_rgb(Fl_RGB_Image *,....). If Fl_XXX_Graphics_Driver
re-implements this function, this code runs and is expected to draw the image
adequately scaled to its drawing size. If Fl_XXX_Graphics_Driver does not re-implement
this function, Fl_Graphics_Driver::draw_rgb(Fl_RGB_Image *,....) runs. It internally
resizes the image, caches it, and calls Fl_XXX_Graphics_Driver::draw_fixed(Fl_RGB_Image *,....)
that draws the image from its cached form which already has the adequate size.
- Some drivers implement, for a given image class, only the function of the 1st group or
only draw_fixed() as in these examples:
- Fl_Quartz_Graphics_Driver implements only draw_rgb(Fl_RGB_Image *,....) because it
can perform the scale-and-draw operation whatever the RGB image and the required scaling.
- Fl_GDI_Graphics_Driver implements only draw_fixed(Fl_Pixmap *,....). The library
takes care of scaling and caching the Pixmap to the adequate drawing size.
- Some drivers implement both draw_???() and draw_fixed() :
takes care of resizing and caching the Pixmap to the adequate drawing size.
- Some drivers implement one function from both groups for a given image class :
- Fl_Xlib_Graphics_Driver implements both draw_rgb(Fl_RGB_Image *,....) and
draw_fixed(Fl_RGB_Image *,....) because scale-and-draw is possible only in the
presence of Xrender. In the absence of Xrender, the draw_rgb() implementation calls