Re: efficient drawing of complex data

[Owen Taylor <otaylor redhat com>]

On Thu, 2003-03-13 at 07:49, Markus Lausser wrote:
> Hello again.
>
> Problem: I have a GtkDrawingArea, the contents consists of rectangular
> areas which are painted pixel by pixel (cause i have to calculate the
> correct color for every single pixel). What is the fastet way to paint
> this?  Right now my solution is:
>
> 1. a rgb buffer for the rectangular areas, filling it pixel by pixel.
> 2. draw these areas in a GdkPixmap using gdk_draw_rgb_image(pixmap, ...)
> 3. finally showing this pixmap on screen using
>    gdk_draw_pixmap(drawingarea->window)
>
> Is it faster to paint every pixel directly in the GdkPixmap? What
> about the color allocation for every pixel?

No, this will be much slower. GdkRGB is the right approach.

> Is it faster to draw the areas directly on screen skipping the
> GdkPixmap (there might be thousands of rectangular areas).

If you are creating and destroying a GdkPixmap for each
small area, that might be a bit inefficient. A single big
pixmap won't slow things down significantly.

Note that with GTK+-2.x you might be using _two_ pixmaps if you 
aren't careful ... during the ::expose signal drawing to
drawingarea->window is redirected to an offscreen pixmap that 
is then copied to the screen at the end of the handler.

(See docs for gdk_window_begin_paint_region(), 
gtk_widget_set_double_buffered() for more information about
this topic.)

Regards,
                                         Owen