fix(iv): iv shows constant brown and GL error messages on start-up. (A…

…cademySoftwareFoundation#4451)

This fixes a problem seen on RHEL 9.2 Linux when launching an image in
iv, eg:
  iv testsuite/texture-overscan/ref/out-exact.exr

The image displayed as a constant brown and the terminal showed:
  GL error create program 1281 - Invalid value
  GL error After attach vertex shader. 1281 - Invalid value

The fix is to initialize m_shader_program and m_vertex_shader in the
class constructor.


ERROR ANALYSIS:

The bug was introduced in 5fe4441 "feat(iv): OCIO color managed display
(AcademySoftwareFoundation#4031)".

Before that commit, create_shaders() initialized those members to 0
before they were used.

After that commit:

* uninitialized m_shader_program is passed to glDeleteProgram() (near
the top of create_shaders) ), causing the
"create program" warning (there isn't an print_error call after
glDeleteProgram so the error is reported as "create program").

* ununitialized m_vertex_shader is non-0 when checked by if
(!m_vertex_shader), causing the vertex shader not to be created and
causing the later call to glAttachShader() with uninitialized
m_vertex_shader to fail. That causes the second error message, and lack
of a vertex shader apparently causes the image to display as constant
brown.

Signed-off-by: David Adler <[email protected]>

src/iv/ivgl.cpp

@@ -47,6 +47,8 @@ IvGL::IvGL(QWidget* parent, ImageViewer& viewer)
     : QOpenGLWidget(parent)
     , m_viewer(viewer)
     , m_shaders_created(false)
+    , m_vertex_shader(0)
+    , m_shader_program(0)
     , m_tex_created(false)
     , m_zoom(1.0)
     , m_centerx(0)