[FFmpeg-devel] PATCH: gdigrab work for DPI in windows

[Matt Oliver]

On 5 October 2015 at 19:29, Matt Oliver <protogonoi at gmail.com> wrote:

> On 30 September 2015 at 02:48, wm4 <nfxjfg at googlemail.com> wrote:
>
>> On Wed, 23 Sep 2015 12:04:43 -0600
>> Roger Pack <rogerdpack2 at gmail.com> wrote:
>>
>> > From 6a972dda58bd5ab31524cd4e5326b4bcdeaeaa8c Mon Sep 17 00:00:00 2001
>> > From: rogerdpack <rogerpack2005 at gmail.com>
>> > Date: Wed, 23 Sep 2015 12:03:27 -0600
>> > Subject: [PATCH] gdigrab: grab right desktop size if DPI in use, based
>> on
>> >  patch from Alexander Brotzge
>> >
>> > Signed-off-by: rogerdpack <rogerpack2005 at gmail.com>
>> > ---
>> >  libavdevice/gdigrab.c | 44 +++++++++++++++++++++++++++++---------------
>> >  1 file changed, 29 insertions(+), 15 deletions(-)
>> >
>> > diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
>> > index 9a185d4..b0faf45 100644
>> > --- a/libavdevice/gdigrab.c
>> > +++ b/libavdevice/gdigrab.c
>> > @@ -235,6 +235,9 @@ gdigrab_read_header(AVFormatContext *s1)
>> >      AVStream   *st       = NULL;
>> >
>> >      int bpp;
>> > +    int vertres;
>> > +    int desktopvertres;
>> > +    float scale;
>> >      RECT virtual_rect;
>> >      RECT clip_rect;
>> >      BITMAP bmp;
>> > @@ -263,14 +266,34 @@ gdigrab_read_header(AVFormatContext *s1)
>> >          goto error;
>> >      }
>> >
>> > -    if (hwnd) {
>> > -        GetClientRect(hwnd, &virtual_rect);
>> > -    } else {
>> > +    /* This will get the device context for the selected window, or if
>> > +     * none, the primary screen */
>> > +    source_hdc = GetDC(hwnd);
>> > +    if (!source_hdc) {
>> > +        WIN32_API_ERROR("Couldn't get window device context");
>> > +        ret = AVERROR(EIO);
>> > +        goto error;
>> > +    }
>> > +    bpp = GetDeviceCaps(source_hdc, BITSPIXEL);
>> > +
>> > +    scale = 1.0;
>> > +    if (hwnd == NULL) {
>> > +      /* desktop -- get the right height and width for scaling DPI */
>> > +      vertres = GetDeviceCaps(source_hdc, VERTRES);
>> > +      desktopvertres = GetDeviceCaps(source_hdc, DESKTOPVERTRES);
>> > +      scale = (float) desktopvertres / (float) vertres;
>> > +    }
>>
>
> This seems a little redundant as scale is only being set when hwnd is null
> however in the below lines its then being used in the opposite conditional.
> Since this checks for hwnd essentially being non null then scale is always
> going to be the inital value of 1.
>
>
>> > +     if (hwnd) {
>> > +         GetClientRect(hwnd, &virtual_rect);
>> > +         virtual_rect.right = virtual_rect.right * scale;
>> > +         virtual_rect.bottom = virtual_rect.bottom * scale;
>> > +     } else {
>> >          virtual_rect.left = GetSystemMetrics(SM_XVIRTUALSCREEN);
>> >          virtual_rect.top = GetSystemMetrics(SM_YVIRTUALSCREEN);
>> > -        virtual_rect.right = virtual_rect.left +
>> GetSystemMetrics(SM_CXVIRTUALSCREEN);
>> > -        virtual_rect.bottom = virtual_rect.top +
>> GetSystemMetrics(SM_CYVIRTUALSCREEN);
>> > -    }
>> > +        virtual_rect.right = (virtual_rect.left +
>> GetSystemMetrics(SM_CXVIRTUALSCREEN)) * scale;
>> > +        virtual_rect.bottom = (virtual_rect.top +
>> GetSystemMetrics(SM_CYVIRTUALSCREEN)) * scale;
>> > +     }
>>
>
> This if else could be combined with the above if as scale is only a value
> different to 1 in the 'else' case. Also as wm4 said it would probably be
> better to keep the scale factors as ints.
>
>
>> >
>> >      /* If no width or height set, use full screen/window area */
>> >      if (!gdigrab->width || !gdigrab->height) {
>> > @@ -299,15 +322,6 @@ gdigrab_read_header(AVFormatContext *s1)
>> >              goto error;
>> >      }
>> >
>> > -    /* This will get the device context for the selected window, or if
>> > -     * none, the primary screen */
>> > -    source_hdc = GetDC(hwnd);
>> > -    if (!source_hdc) {
>> > -        WIN32_API_ERROR("Couldn't get window device context");
>> > -        ret = AVERROR(EIO);
>> > -        goto error;
>> > -    }
>> > -    bpp = GetDeviceCaps(source_hdc, BITSPIXEL);
>> >
>> >      if (name) {
>> >          av_log(s1, AV_LOG_INFO,
>
>
> However I think the basic dpi scaling technique is correct. However I
> would think it should be more along the lines of the modifications Ive
> attached.
>

Woops, allow me to try that again without windows messing up the patches
line endings.
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