[cairo] win32 bug when using HFONT with appropriate size

[Fred Bca]

This topic is now covered by bug #94836

https://bugs.freedesktop.org/show_bug.cgi?id=94836

On Wed, Apr 6, 2016 at 10:13 AM, Fred Beca <fredbca21 at gmail.com> wrote:
> Thanks for the details. If I understand well then, the code has
> changed at some point, and the issue is the fact the logical scale
> factor is used when creating the scaled hfont, instead of being used
> in the WorldTransform.
>
> See scaled font creation here:
> static cairo_status_t
> _win32_scaled_font_get_scaled_hfont (cairo_win32_scaled_font_t *scaled_font,
>     HFONT *hfont_out)
> {
>     if (!scaled_font->scaled_hfont) {
> LOGFONTW logfont = scaled_font->logfont;
> logfont.lfHeight = -scaled_font->logical_size; ///< using the logicak
> size to create the font
>
> I guess this may also cause other problems if the font cannot be
> created with such a large scale.
>
> I will create a bug as suggested and will continue my investigations.
>
> On Wed, Apr 6, 2016 at 12:40 AM, Adrian Johnson <ajohnson at redneon.com> wrote:
>>
>> On 05/04/16 20:33, Fred Beca wrote:
>> > I have noticed a bug in the win32 font backend. When setting the font on
>> > a win32 surface with the code below and using the same size as the
>> > original HFONT for drawing, the resulting font size is extremely small
>> > (text is almost invisible).
>> >
>> > // assuming my_hfont was created with -12 for LOGFONT.lfHeight
>> > cairo_font_face_t*
>> > font_face=cairo_win32_font_face_create_for_hfont(my_hfont);
>> > cairo_set_font_face(ctx,font_face);
>> > cairo_set_font_size(ctx,12);
>> >
>> > The reason is that in _cairo_win32_font_face_scaled_font_create, the
>> > font matrix is checked against -font_face->logfont.lfHeight whereas if
>> > you look in _win32_scaled_font_get_scaled_hfont, the expected height
>> > should be multiplied by WIN32_FONT_LOGICAL_SCALE (scaled HFONT created
>> > by cairo uses logfont.lfHeight = -scaled_font->logical_size)
>> >
>> > This means that using anything else than 1 for WIN32_FONT_LOGICAL_SCALE
>> > as shown in the patch below will result in a downscaled font when using
>> > a HFONT that was created with the right size.
>> >
>> > However, if the check mentioned above is fixed, in order to have cairo
>> > use the original HFONT, it should be created with a much larger size
>> > (-WIN32_FONT_LOGICAL_SCALE*size). So this defeats the purpose of being
>> > able to mix native win32 fonts with cairo because of this scaling factor
>> > (mixing native and cairo code would require extra scaling everywhere).
>> >
>> > So here is my question: is the scaling applied with
>> > WIN32_FONT_LOGICAL_SCALE still useful? From what I have been able to
>> > experience so far, setting it to 1 makes no difference, even with very
>> > small fonts. And it seems this is actually used by many others.
>>
>> There were a couple of threads were the usefulness of
>> WIN32_FONT_LOGICAL_SCALE was discussed:
>>
>> https://lists.freedesktop.org/archives/cairo/2007-January/009288.html
>> https://lists.freedesktop.org/archives/cairo/2007-February/009661.html
>>
>> I don't think removing the logical scale is a good idea. We will need to
>> find a solution to make cairo_win32_font_face_create_for_hfont() work.
>>
>> I suggest creating a bug and linking it to the 1.16 tracker (bug 84197).
>> I'll look at it next time I am working on the windows backend.
>>
>> >
>> > Index: cairo-win32-private.h
>> > ===================================================================
>> > --- cairo-win32-private.h(cairo-1.14.6)
>> > +++ cairo-win32-private.h(working copy)
>> > @@ -51,7 +51,7 @@
>> >  #define SB_NONE 0
>> >  #endif
>> >
>> > -#define WIN32_FONT_LOGICAL_SCALE 32
>> > +#define ç 1
>> >
>> >  /* Surface DC flag values */
>> >  enum {
>> >
>> >
>> >
>>