explicitly ask for opengl 2.1, also in shaders

glincludes.h

 #ifndef GLINCLUDES_H
 #define GLINCLUDES_H
 
-// GLew might not be needed on mac, or if a recent version of OpenGL is present
-#ifndef __APPLE__
-  #include <GL/glew.h>
-  #if (!defined GLEW_VERSION_1_5) || (!defined GL_VERSION_3_1)
-    #error GLEW 1.5.2 is required
-  #endif
-#endif
+// TODO: test on mac
 
 #define GL_GLEXT_PROTOTYPES 1
 #ifdef __APPLE__
   #include<OpenGL/gl.h>
   #include<OpenGL/glu.h>
   #include<Glut/glut.h>
-  #include<OpenGL/glext.h>
+  //#include<OpenGL/glext.h>
 #else
-  //#include <GL/gl.h>
-  //#include <GL/glu.h>
+  #include <GL/gl.h>
+  #include <GL/glu.h>
   #include <GL/glut.h>
   // is glext really needed?
   //#include <GL/glext.h>
 #endif
 
+// GLew might not be needed on mac, or if a recent version of OpenGL is present
+//#ifndef __APPLE__
+  #ifndef GL_VERSION_2_1
+    // OpenGL>=2.1 not found, try GLEW
+    #include <GL/glew.h>
+    #ifndef GLEW_VERSION_2_1
+      #error OpenGL 2.1 or GLEW is required
+    #endif
+  #endif
+//#endif
+
 #endif // GLINCLUDES_H

shaders/fragment_shader.frag

+#version 120
+
 uniform sampler2D diffuse_texture;
 varying vec2 texcoord0;
 varying vec4 K_color;

shaders/test_vertex_shader.vert

+#version 120
+
 varying vec2 texcoord0;
 vec4 pos;
 float u, v, x, y, z;
 varying float r, theta, s;
 float lambda, phi;
 float extent, scale, vis_mode, center_lambda, center_phi;
-varying float zbu,zbv,zblambda,zbr,zbR,zbalpha,zbrho;
+varying float zblambda,zbr,zbR,zbalpha,zbrho;
 
 void main(void){
 
@@ -80,13 +82,14 @@ void main(void){
     }
     else if (vis_mode==6.0) { // Zorin-Barr
         // perspective projection
-        zbu = x/(-z);
-        zbv = y/(-z);
+        u=x/(-z);
+        v=y/(-z);
         // Z-B transformation
+        // TODO: read zblambda and zbR from the interface
         zblambda=0.1;
         zbR=1.0;
-        zbalpha=atan(zbv,zbu);
-        zbr=sqrt(zbu*zbu+zbv*zbv);
+        zbalpha=atan(v,u);
+        zbr=sqrt(u*u+v*v);
         zbrho=(zblambda*zbr/zbR)+(1.0-zblambda)*(zbR*(sqrt(zbr*zbr+1.0)-1.0))/(zbr*(sqrt(zbR*zbR+1.0)-1.0));
         u=zbrho*cos(zbalpha);
         v=zbrho*sin(zbalpha);