Re: Aliased corner with rounded rectangle

Though I would not expect it to look as bad as described, you want the
first argument to be GL_ONE, not GL_SRC_ALPHA.


On Thu, Aug 9, 2018 at 6:07 AM, Lorenzo <[email protected]> wrote:

> Sorry, by i already have the BlendFunc method.
>
> I initialize my opengl system with this code:
>
> glViewport(0, 0, drm->rect()->w, drm->rect()->h);
> glDisable(GL_CULL_FACE);
> glEnable(GL_LESS);
> glEnable(GL_BLEND);
> glEnable(GL_TEXTURE_2D);
> glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
>
>
> Lorenzo.
>
> On 08/08/2018 08:00 PM, Bill Spitzak wrote:
>
> glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
>
> Sorry, I managed to cut & paste the one example I had that did not say
> "ALPHA"
>
> On Wed, Aug 8, 2018 at 10:59 AM, Bill Spitzak <[email protected]> wrote:
>
>> You have to change the OpenGL compositing to over the premultiplied
>> image. I think glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_COLOR) is what you need.
>>
>> On Wed, Aug 8, 2018 at 8:16 AM, Lorenzo <[email protected]> wrote:
>>
>>> Hi,
>>>
>>> i have a problem with the creation of a rounded rectangle with cairo.
>>>
>>> Environment info:
>>>
>>> cairo version: 1.14.8-1
>>>
>>> OS: linux
>>>
>>>
>>> A linux client creates a rounded rectangle with the following code:
>>>
>>>         let x = 0.0
>>>         let y = 0.0
>>>         let w = Double(size.w)
>>>         let h = Double(size.h)
>>>         let r = 20.0
>>>
>>>         logger.verbose("rounded rectangle x=\(x),y=\(y),w=\(w),h=\(h),r=
>>> \(r)")
>>>
>>>         cairo_move_to(context, x, y + r)
>>>         cairo_arc(context, x + r, y + r, r, Double.pi, -Double.pi / 2.0)
>>>         cairo_line_to(context, x + w - r, y)
>>>         cairo_arc(context, x + w - r, y + r, r, -Double.pi / 2.0, 0.0)
>>>         cairo_line_to(context, x + w, y + h - r)
>>>         cairo_arc(context, x + w - r, y + h - r, r, 0.0, Double.pi / 2.0)
>>>         cairo_line_to(context, x + r, y + h)
>>>         cairo_arc(context, x + r, y + h - r, r, Double.pi / 2.0,
>>> Double.pi)
>>>         cairo_close_path(context)
>>>
>>>
>>>         cairo_set_source_rgba(context, cl.red, cl.green, cl.blue,
>>> cl.alpha);
>>>         cairo_fill(context)
>>>
>>>
>>> After the surface fill  i have 2 different operations to be performed:
>>>
>>>     - write the png on the disk using "cairo_surface_write_to_png(surface,
>>> "testcairo.png")"
>>>
>>>     - display the png with opengl es 3.0 as a texture (done by copy the
>>> surface raw bytes with cairo_image_surface_get_data(surface)
>>>
>>>       in a shared memory used by the opengl server program)
>>>
>>>
>>> Save the image on disk is ok, the image is good.
>>>
>>> Display the image as a texture with opengl results in an ugly image:
>>> corners have some black pixels around them.
>>>
>>> Why this difference?
>>>
>>>
>>> I have done some checks:
>>>
>>> - data obtained with cairo_image_surface_get_data are the same that the
>>> graphics server loads from the shared memory (checked PixelxPixel) so the
>>> data transfer don't is the problem (checked also any signed/unsigned byte
>>> conversion)
>>>
>>> - loading the disk png as a texture instead of loading data from the
>>> shared memory results in a good image with no problems.
>>>
>>>
>>> My opinion is that the cairo_surface_write_to_png performs an
>>> antialiasing algorithm and accessing raw data bypass it taking the original
>>> image.
>>>
>>>
>>> Is my opinion correct? If yes, any advice to solve the problem?
>>>
>>>
>>> Regards,
>>>
>>> Lorenzo.
>>>
>>>
>>>
>>>
>>>
>>> --
>>> cairo mailing list
>>> [email protected]
>>> https://lists.cairographics.org/mailman/listinfo/cairo
>>
>>
>>
>
>

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