[PATCH v6 22/27] kernel-shark: Make GLUT optional dependency

["Yordan Karadzhov (VMware)" <y.karadz@gmail.com>]

GLUT is not needed in order to build the KernelShark GUI. Currently
it is being used only by the plotting example, so it makes more sense
to removed it from the list of compulsory third party packages.
The patch optimizes the way the OpenGL and GLUT headers are included
and removes some duplicated code.

Signen-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
---
 build/deff.h.cmake   |  3 +++
 src/CMakeLists.txt   |  4 ++--
 src/libkshark-plot.c | 20 +++++++-------------
 src/libkshark-plot.h | 11 +++++++++++
 4 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/build/deff.h.cmake b/build/deff.h.cmake
index e398c0c..868ffec 100644
--- a/build/deff.h.cmake
+++ b/build/deff.h.cmake
@@ -23,6 +23,9 @@
 /** "pkexec" executable. */
 #cmakedefine DO_AS_ROOT "@DO_AS_ROOT@"
 
+/** GLUT has been found. */
+#cmakedefine GLUT_FOUND
+
 /** Semicolon-separated list of plugin names. */
 #define KS_BUILTIN_PLUGINS "@PLUGINS@"
 
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 3a07d82..cbd45ed 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -19,7 +19,7 @@ set_target_properties(kshark  PROPERTIES SUFFIX	".so.${KS_VERSION_STRING}")
 
 install(TARGETS kshark LIBRARY DESTINATION ${_LIBDIR}/${KS_APP_NAME})
 
-if (OPENGL_FOUND AND GLUT_FOUND)
+if (OPENGL_FOUND)
 
     message(STATUS "libkshark-plot")
     add_library(kshark-plot  SHARED  libkshark-plot.c)
@@ -33,7 +33,7 @@ if (OPENGL_FOUND AND GLUT_FOUND)
 
     install(TARGETS kshark-plot LIBRARY DESTINATION ${_LIBDIR}/${KS_APP_NAME})
 
-endif (OPENGL_FOUND AND GLUT_FOUND)
+endif (OPENGL_FOUND)
 
 if (Qt5Widgets_FOUND AND Qt5Network_FOUND)
 
diff --git a/src/libkshark-plot.c b/src/libkshark-plot.c
index 0c6b1a5..1c45f44 100644
--- a/src/libkshark-plot.c
+++ b/src/libkshark-plot.c
@@ -19,10 +19,6 @@
 #include <string.h>
 #include <stdio.h>
 
-// OpenGL
-#include <GL/freeglut.h>
-#include <GL/gl.h>
-
 // KernelShark
 #include "libkshark-plot.h"
 
@@ -37,6 +33,10 @@
 #define STBTT_STATIC
 #include "stb_truetype.h"
 
+#ifdef GLUT_FOUND
+
+#include <GL/freeglut.h>
+
 /**
  * @brief Create an empty scene for drawing.
  *
@@ -61,17 +61,11 @@ void ksplot_make_scene(int width, int height)
 	/* Open the screen window. */
 	glutCreateWindow("KernelShark Plot");
 
-	/*
-	 * Set the origin of the coordinate system to be the top left corner.
-	 * The "Y" coordinate is inverted.
-	 */
-	gluOrtho2D(0, width, height, 0);
-	glViewport(0, 0, width, height);
-
-	glMatrixMode(GL_PROJECTION);
-	glLoadIdentity();
+	ksplot_resize_opengl(width, height);
 }
 
+#endif // GLUT_FOUND
+
 /**
  * @brief Initialize OpenGL.
  *
diff --git a/src/libkshark-plot.h b/src/libkshark-plot.h
index 0edf5d5..063740d 100644
--- a/src/libkshark-plot.h
+++ b/src/libkshark-plot.h
@@ -15,6 +15,10 @@
 // C
 #include <stdbool.h>
 
+// OpenGL
+#include <GL/gl.h>
+#include <GL/glu.h>
+
 /*
  * STB TrueType (single-file public domain library)
  * https://github.com/nothings/stb
@@ -25,6 +29,9 @@
 extern "C" {
 #endif
 
+// KernelShark
+#include "KsCmakeDef.hpp"
+
 /** Structure defining a RGB color. */
 struct ksplot_color {
 	/** The Red component of the color. */
@@ -46,8 +53,12 @@ struct ksplot_point {
 	int y;
 };
 
+#ifdef GLUT_FOUND
+
 void ksplot_make_scene(int width, int height);
 
+#endif // GLUT_FOUND
+
 void ksplot_init_opengl(int dpr);
 
 void ksplot_resize_opengl(int width, int height);
-- 
2.25.1