On Sun, Jul 31, 2011 at 01:38, Anton Khirnov <[email protected]> wrote:
>
> On Sun, 31 Jul 2011 00:27:46 +0800, Yu-Jie Lin <[email protected]> wrote:
>> +#define REGION_WIN_BORDER 3
>> +/**
>> + * Draw grabbing region window
>> + *
>> + * @param s x11_grab context
>> + */
>> +static void
>> +x11grab_draw_region_win(struct x11_grab *s)
>> +{
>> + Display *dpy = s->dpy;
>> + int screen;
>> + Window win = s->region_win;
>> + GC gc;
>> +
>> + screen = DefaultScreen(dpy);
>> + gc = XCreateGC(dpy, win, 0, 0);
>> + XSetForeground(dpy, gc, WhitePixel(dpy, screen));
>> + XSetBackground(dpy, gc, BlackPixel(dpy, screen));
>> + XSetLineAttributes(dpy, gc, 3, LineDoubleDash, 0, 0);
> ^
> Shouldn't this be REGION_WIN_BORDER?
It is.
>> + XDrawRectangle(dpy, win, gc,
>> + 1, 1,
>> + s->width + REGION_WIN_BORDER * 2 - 1 * 2 - 1,
> ^^^^^^^^^^^^^^^
> It's not very clear to me what are those for. Can you explain?
I should put a pair of parentheses:
XDrawRectangle(dpy, win, gc,
1, 1,
(s->width + REGION_WIN_BORDER * 2) - 1 * 2 - 1,
region_win's geometry's top-left and bottom-right points are
(0, 0), (width - 1, height -1),
where width and height are its window size, and
width = s->width + REGION_WIN_BORDER * 2
The rectangle should be drawn at (with line_width (i.e. REGION_WIN_BORDER) = 3)
(1, 1), ((width - 1) - 1, (height - 1) - 1),
The width of rectangle is
rect_width = width - 1 * 2
1 is the leftmost point, the other 1 is rightmost point.
The XDrawRectangle(..., x, y, w, h) draw a rectangle from top-left
point (x, y) to bottom-right point (x + w, y + h). So for the top line
of the rectangle, it is actually drawn with (x + w) - x + 1 = w + 1
pixels.
If we wants WIDTH pixels to be drawn, one pixel must be subtracted
from the desired amount of pixels, hence
rect_width_for_XDrawRectangle = width - 1 * 2 - 1
and it
= (s->width + REGION_WIN_BORDER * 2) - 1 * 2 - 1
Hope this clarifies.
>> /**
>> * Initialize the x11 grab device demuxer (public device demuxer API).
>> *
>> @@ -109,6 +175,7 @@ x11grab_read_header(AVFormatContext *s1,
>> AVFormatParameters *ap)
>> x11grab->draw_mouse = !strstr(offset, "nomouse");
>> *offset= 0;
>> }
>> + x11grab->region_win = 0;
>
> No need for this, private contexts are initialised to 0.
Thanks for the tip.
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