| Message ID | 20200226122054.366b9cda@table.localdomain |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] Arithmetic error in EDID generation fixed | expand |
On Wed, Feb 26, 2020 at 03:20:54PM +0300, Anton V. Boyarshinov wrote: > To calculate screen size in centimeters we should calculate: > pixels/dpi*2.54 > but not > pixels*dpi/2540 > > Using wrong formula we actually get 65 DPI and very small fonts. Added to vga patch queu. thanks, Gerd
Am 26.02.20 um 13:20 schrieb Anton V. Boyarshinov: > To calculate screen size in centimeters we should calculate: > pixels/dpi*2.54 > but not > pixels*dpi/2540 > > Using wrong formula we actually get 65 DPI and very small fonts. > > Signed-off-by: Anton V. Boyarshinov <boyarsh@altlinux.org> > --- > Changes from v1: get rid of casts > > hw/display/edid-generate.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/hw/display/edid-generate.c b/hw/display/edid-generate.c > index 75c945a948..e58472fde5 100644 > --- a/hw/display/edid-generate.c > +++ b/hw/display/edid-generate.c > @@ -360,8 +360,8 @@ void qemu_edid_generate(uint8_t *edid, size_t size, > edid[20] = 0xa5; > > /* screen size: undefined */ Gerd, is this comment still correct? > - edid[21] = info->prefx * info->dpi / 2540; > - edid[22] = info->prefy * info->dpi / 2540; > + edid[21] = info->prefx * 254 / 100 / info->dpi; > + edid[22] = info->prefy * 254 / 100 / info->dpi; The fix is good, but can be improved: According to the standard, the values are "rounded to the nearest centimeter". Currently they are not rounded, but truncated. So this would be a better approximation: edid[21] = (info->prefx * 254 / info->dpi + 50) / 100; ... Regards, Stefan
diff --git a/hw/display/edid-generate.c b/hw/display/edid-generate.c index 75c945a948..e58472fde5 100644 --- a/hw/display/edid-generate.c +++ b/hw/display/edid-generate.c @@ -360,8 +360,8 @@ void qemu_edid_generate(uint8_t *edid, size_t size, edid[20] = 0xa5; /* screen size: undefined */ - edid[21] = info->prefx * info->dpi / 2540; - edid[22] = info->prefy * info->dpi / 2540; + edid[21] = info->prefx * 254 / 100 / info->dpi; + edid[22] = info->prefy * 254 / 100 / info->dpi; /* display gamma: 2.2 */ edid[23] = 220 - 100;
To calculate screen size in centimeters we should calculate: pixels/dpi*2.54 but not pixels*dpi/2540 Using wrong formula we actually get 65 DPI and very small fonts. Signed-off-by: Anton V. Boyarshinov <boyarsh@altlinux.org> --- Changes from v1: get rid of casts hw/display/edid-generate.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)