Re: Aliased corner with rounded rectangle

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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