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    <p>Sorry, by i already have the BlendFunc method.</p>
    <p>I initialize my opengl system with this code:</p>
    <p>glViewport(0, 0, drm->rect()->w, drm->rect()->h);<br>
      glDisable(GL_CULL_FACE);<br>
      glEnable(GL_LESS);<br>
      glEnable(GL_BLEND);<br>
      glEnable(GL_TEXTURE_2D);<br>
      glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);</p>
    <p><br>
    </p>
    <p>Lorenzo.<br>
    </p>
    <br>
    <div class="moz-cite-prefix">On 08/08/2018 08:00 PM, Bill Spitzak
      wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:CAL-8oAggRSucr6krBQnLE7g4ZUe3aisdu7HwZW3M1-Fk1G5h1g@mail.gmail.com">
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        <div>glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);</div>
        <div><br>
        </div>
        <div>Sorry, I managed to cut & paste the one example I had
          that did not say "ALPHA"</div>
      </div>
      <div class="gmail_extra"><br>
        <div class="gmail_quote">On Wed, Aug 8, 2018 at 10:59 AM, Bill
          Spitzak <span dir="ltr"><<a
              href="mailto:spitzak@gmail.com" target="_blank"
              moz-do-not-send="true">spitzak@gmail.com</a>></span>
          wrote:<br>
          <blockquote class="gmail_quote" style="margin:0 0 0
            .8ex;border-left:1px #ccc solid;padding-left:1ex">
            <div dir="ltr">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.</div>
            <div class="HOEnZb">
              <div class="h5">
                <div class="gmail_extra"><br>
                  <div class="gmail_quote">On Wed, Aug 8, 2018 at 8:16
                    AM, Lorenzo <span dir="ltr"><<a
                        href="mailto:gatti88@libero.it" target="_blank"
                        moz-do-not-send="true">gatti88@libero.it</a>></span>
                    wrote:<br>
                    <blockquote class="gmail_quote" style="margin:0 0 0
                      .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi,<br>
                      <br>
                      i have a problem with the creation of a rounded
                      rectangle with cairo.<br>
                      <br>
                      Environment info:<br>
                      <br>
                      cairo version: 1.14.8-1<br>
                      <br>
                      OS: linux<br>
                      <br>
                      <br>
                      A linux client creates a rounded rectangle with
                      the following code:<br>
                      <br>
                              let x = 0.0<br>
                              let y = 0.0<br>
                              let w = Double(size.w)<br>
                              let h = Double(size.h)<br>
                              let r = 20.0<br>
                      <br>
                              logger.verbose("rounded rectangle
                      x=\(x),y=\(y),w=\(w),h=\(h),r=<wbr>\(r)")<br>
                      <br>
                              cairo_move_to(context, x, y + r)<br>
                              cairo_arc(context, x + r, y + r, r,
                      Double.pi, -Double.pi / 2.0)<br>
                              cairo_line_to(context, x + w - r, y)<br>
                              cairo_arc(context, x + w - r, y + r, r,
                      -Double.pi / 2.0, 0.0)<br>
                              cairo_line_to(context, x + w, y + h - r)<br>
                              cairo_arc(context, x + w - r, y + h - r,
                      r, 0.0, Double.pi / 2.0)<br>
                              cairo_line_to(context, x + r, y + h)<br>
                              cairo_arc(context, x + r, y + h - r, r,
                      Double.pi / 2.0, Double.pi)<br>
                              cairo_close_path(context)<br>
                      <br>
                      <br>
                              cairo_set_source_rgba(context, cl.red,
                      cl.green, cl.blue, cl.alpha);<br>
                              cairo_fill(context)<br>
                      <br>
                      <br>
                      After the surface fill  i have 2 different
                      operations to be performed:<br>
                      <br>
                          - write the png on the disk using
                      "cairo_surface_write_to_png(su<wbr>rface,
                      "testcairo.png")"<br>
                      <br>
                          - display the png with opengl es 3.0 as a
                      texture (done by copy the surface raw bytes with
                      cairo_image_surface_get_data(s<wbr>urface)<br>
                      <br>
                            in a shared memory used by the opengl server
                      program)<br>
                      <br>
                      <br>
                      Save the image on disk is ok, the image is good.<br>
                      <br>
                      Display the image as a texture with opengl results
                      in an ugly image: corners have some black pixels
                      around them.<br>
                      <br>
                      Why this difference?<br>
                      <br>
                      <br>
                      I have done some checks:<br>
                      <br>
                      - 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)<br>
                      <br>
                      - loading the disk png as a texture instead of
                      loading data from the shared memory results in a
                      good image with no problems.<br>
                      <br>
                      <br>
                      My opinion is that the cairo_surface_write_to_png
                      performs an antialiasing algorithm and accessing
                      raw data bypass it taking the original image.<br>
                      <br>
                      <br>
                      Is my opinion correct? If yes, any advice to solve
                      the problem?<br>
                      <br>
                      <br>
                      Regards,<br>
                      <br>
                      Lorenzo.<span class="m_-5063440743205944044HOEnZb"><font
                          color="#888888"><br>
                          <br>
                          <br>
                          <br>
                          <br>
                          <br>
                          -- <br>
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                            target="_blank" moz-do-not-send="true">cairo@cairographics.org</a><br>
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                            href="https://lists.cairographics.org/mailman/listinfo/cairo"
                            rel="noreferrer" target="_blank"
                            moz-do-not-send="true">https://lists.cairographics.or<wbr>g/mailman/listinfo/cairo</a></font></span></blockquote>
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