[PATCH v2] Cursor: 8 -> 1 bit alpha downsampling improvement

[PATCH v2] Cursor: 8 -> 1 bit alpha downsampling improvement

[Phil Dennis-Jordan]

Mouse cursors with 8 bit alpha were downsampled to 1-bit opacity maps by
turning alpha values of 255 into 1 and everything else into 0. This
means that mostly-opaque pixels ended up completely invisible.

This patch changes the behaviour so that only pixels with less than 50%
alpha (0-127) are treated as transparent when converted to 1-bit alpha.

This greatly improves the subjective appearance of anti-aliased mouse
cursors, such as those used by macOS, when using a front-end UI without
support for alpha-blended cursors, such as some VNC clients.

Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu>
---
 ui/cursor.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ui/cursor.c b/ui/cursor.c
index 29717b3ecb..dd3853320d 100644
--- a/ui/cursor.c
+++ b/ui/cursor.c
@@ -232,7 +232,7 @@ void cursor_get_mono_mask(QEMUCursor *c, int transparent, uint8_t *mask)
     for (y = 0; y < c->height; y++) {
         bit = 0x80;
         for (x = 0; x < c->width; x++, data++) {
-            if ((*data & 0xff000000) != 0xff000000) {
+            if ((*data & 0x80000000) == 0x0) { /* Alpha < 0x80 (128) */
                 if (transparent != 0) {
                     mask[x/8] |= bit;
                 }
-- 
2.39.3 (Apple Git-146)

Re: [PATCH v2] Cursor: 8 -> 1 bit alpha downsampling improvement

[Akihiko Odaki]

On 2024/06/24 19:10, Phil Dennis-Jordan wrote:
> Mouse cursors with 8 bit alpha were downsampled to 1-bit opacity maps by
> turning alpha values of 255 into 1 and everything else into 0. This
> means that mostly-opaque pixels ended up completely invisible.
> 
> This patch changes the behaviour so that only pixels with less than 50%
> alpha (0-127) are treated as transparent when converted to 1-bit alpha.
> 
> This greatly improves the subjective appearance of anti-aliased mouse
> cursors, such as those used by macOS, when using a front-end UI without
> support for alpha-blended cursors, such as some VNC clients.
> 
> Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu>

Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>

Re: [PATCH v2] Cursor: 8 -> 1 bit alpha downsampling improvement

[Marc-André Lureau]

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On Mon, Jun 24, 2024 at 2:11 PM Phil Dennis-Jordan <phil@philjordan.eu>
wrote:

> Mouse cursors with 8 bit alpha were downsampled to 1-bit opacity maps by
> turning alpha values of 255 into 1 and everything else into 0. This
> means that mostly-opaque pixels ended up completely invisible.
>
> This patch changes the behaviour so that only pixels with less than 50%
> alpha (0-127) are treated as transparent when converted to 1-bit alpha.
>
> This greatly improves the subjective appearance of anti-aliased mouse
> cursors, such as those used by macOS, when using a front-end UI without
> support for alpha-blended cursors, such as some VNC clients.
>
> Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu>
>

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>


> ---
>  ui/cursor.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/ui/cursor.c b/ui/cursor.c
> index 29717b3ecb..dd3853320d 100644
> --- a/ui/cursor.c
> +++ b/ui/cursor.c
> @@ -232,7 +232,7 @@ void cursor_get_mono_mask(QEMUCursor *c, int
> transparent, uint8_t *mask)
>      for (y = 0; y < c->height; y++) {
>          bit = 0x80;
>          for (x = 0; x < c->width; x++, data++) {
> -            if ((*data & 0xff000000) != 0xff000000) {
> +            if ((*data & 0x80000000) == 0x0) { /* Alpha < 0x80 (128) */
>                  if (transparent != 0) {
>                      mask[x/8] |= bit;
>                  }
> --
> 2.39.3 (Apple Git-146)
>
>
>

-- 
Marc-André Lureau

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Re: [PATCH v2] Cursor: 8 -> 1 bit alpha downsampling improvement

[Phil Dennis-Jordan]

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> Mouse cursors with 8 bit alpha were downsampled to 1-bit opacity maps by
>> turning alpha values of 255 into 1 and everything else into 0. This
>> means that mostly-opaque pixels ended up completely invisible.
>>
>> This patch changes the behaviour so that only pixels with less than 50%
>> alpha (0-127) are treated as transparent when converted to 1-bit alpha.
>>
>> This greatly improves the subjective appearance of anti-aliased mouse
>> cursors, such as those used by macOS, when using a front-end UI without
>> support for alpha-blended cursors, such as some VNC clients.
>>
>> Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu>
>>
>
> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
>

Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>


Thanks for the reviews folks! Is there anything I can do to move this
forward? Should I submit a v3 with the review tags included? The patch
continues to apply cleanly so it didn't seem necessary, but I admit I'm
still not 100% clear on whom I should badger (?) to get favourably received
patches actually pulled into staging/master.

https://patchew.org/QEMU/20240624101040.82726-1-phil@philjordan.eu/

Thanks!

Kind regards,
Phil

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Re: [PATCH v2] Cursor: 8 -> 1 bit alpha downsampling improvement

[Marc-André Lureau]

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Hi

On Wed, Jul 17, 2024 at 5:11 PM Phil Dennis-Jordan <phil@philjordan.eu>
wrote:

>
> Mouse cursors with 8 bit alpha were downsampled to 1-bit opacity maps by
>>> turning alpha values of 255 into 1 and everything else into 0. This
>>> means that mostly-opaque pixels ended up completely invisible.
>>>
>>> This patch changes the behaviour so that only pixels with less than 50%
>>> alpha (0-127) are treated as transparent when converted to 1-bit alpha.
>>>
>>> This greatly improves the subjective appearance of anti-aliased mouse
>>> cursors, such as those used by macOS, when using a front-end UI without
>>> support for alpha-blended cursors, such as some VNC clients.
>>>
>>> Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu>
>>>
>>
>> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
>>
>
> Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
>
>
> Thanks for the reviews folks! Is there anything I can do to move this
> forward? Should I submit a v3 with the review tags included? The patch
> continues to apply cleanly so it didn't seem necessary, but I admit I'm
> still not 100% clear on whom I should badger (?) to get favourably received
> patches actually pulled into staging/master.
>
> https://patchew.org/QEMU/20240624101040.82726-1-phil@philjordan.eu/
>
>
I'll include it in a UI-related PR.

thanks

-- 
Marc-André Lureau

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Re: [PATCH v2] Cursor: 8 -> 1 bit alpha downsampling improvement

[Phil Dennis-Jordan]

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On Wed, 17 Jul 2024 at 15:20, Marc-André Lureau <marcandre.lureau@gmail.com>
wrote:

> Hi
>
> On Wed, Jul 17, 2024 at 5:11 PM Phil Dennis-Jordan <phil@philjordan.eu>
> wrote:
>
>>
>> Mouse cursors with 8 bit alpha were downsampled to 1-bit opacity maps by
>>>> turning alpha values of 255 into 1 and everything else into 0. This
>>>> means that mostly-opaque pixels ended up completely invisible.
>>>>
>>>> This patch changes the behaviour so that only pixels with less than 50%
>>>> alpha (0-127) are treated as transparent when converted to 1-bit alpha.
>>>>
>>>> This greatly improves the subjective appearance of anti-aliased mouse
>>>> cursors, such as those used by macOS, when using a front-end UI without
>>>> support for alpha-blended cursors, such as some VNC clients.
>>>>
>>>> Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu>
>>>>
>>>
>>> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
>>>
>>
>> Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
>>
>>
>> Thanks for the reviews folks! Is there anything I can do to move this
>> forward? Should I submit a v3 with the review tags included? The patch
>> continues to apply cleanly so it didn't seem necessary, but I admit I'm
>> still not 100% clear on whom I should badger (?) to get favourably received
>> patches actually pulled into staging/master.
>>
>> https://patchew.org/QEMU/20240624101040.82726-1-phil@philjordan.eu/
>>
>>
> I'll include it in a UI-related PR.
>
> thanks
>

Thank you!

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