[Octave-bug-tracker] [bug #52413] Qt5 figures background first appears black or transparent

[Pantxo Diribarne]

URL:
  <http://savannah.gnu.org/bugs/?52413>

                 Summary: Qt5 figures background first appears black or
transparent
                 Project: GNU Octave
            Submitted by: pantxo
            Submitted on: Wed 15 Nov 2017 10:42:16 AM UTC
                Category: Plotting with OpenGL
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Regression
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: GNU/Linux

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Details:

The title says it all:


close all;
figure () 
## the figure has a transparent background
close all
plot (1:10)
## the figure has a black background until a paint event is forced by e.g.
switching window with Alt+Tab


I am using nouveau driver with an intel integrated graphics card on linux mint
17.3

I can get rid of this behavior using the following hack:


diff -r f3d754deb41d libinterp/corefcn/gl-render.cc
--- a/libinterp/corefcn/gl-render.cc    Wed Nov 08 16:34:23 2017 +0100
+++ b/libinterp/corefcn/gl-render.cc    Wed Nov 15 11:31:06 2017 +0100
@@ -829,7 +829,13 @@
 
     if (c.numel () >= 3)
       {
-        glClearColor (c(0), c(1), c(2), 1);
+        glClearColor (c(0), c(1), c(2), 1.0F);
+        // FIXME: hack to have the first glClear work even when nothing has
+        // been drawn.
+        glBegin (GL_LINES);
+          glVertex2d (-1.0, -1.0);
+          glVertex2d (1.0, -1.0);
+        glEnd ();
         glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);





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