Replace duplicated code with new shaderutil.c functions
diff --git a/progs/glsl/twoside.c b/progs/glsl/twoside.c
index 1db92b5..77977be 100644
--- a/progs/glsl/twoside.c
+++ b/progs/glsl/twoside.c
@@ -16,9 +16,9 @@
 #include <GL/glut.h>
 #include <GL/glext.h>
 #include "extfuncs.h"
+#include "shaderutil.h"
 
 
-static const char *Prog = "twoside";
 static GLint WinWidth = 300, WinHeight = 300;
 static char *FragProgFile = NULL;
 static char *VertProgFile = NULL;
@@ -168,67 +168,6 @@
 
 
 static void
-LoadAndCompileShader(GLuint shader, const char *text)
-{
-   GLint stat;
-
-   glShaderSource_func(shader, 1, (const GLchar **) &text, NULL);
-
-   glCompileShader_func(shader);
-
-   glGetShaderiv_func(shader, GL_COMPILE_STATUS, &stat);
-   if (!stat) {
-      GLchar log[1000];
-      GLsizei len;
-      glGetShaderInfoLog_func(shader, 1000, &len, log);
-      fprintf(stderr, "%s: problem compiling shader:\n%s\n", Prog, log);
-      exit(1);
-   }
-}
-
-
-/**
- * Read a shader from a file.
- */
-static void
-ReadShader(GLuint shader, const char *filename)
-{
-   const int max = 100*1000;
-   int n;
-   char *buffer = (char*) malloc(max);
-   FILE *f = fopen(filename, "r");
-   if (!f) {
-      fprintf(stderr, "%s: Unable to open shader file %s\n", Prog, filename);
-      exit(1);
-   }
-
-   n = fread(buffer, 1, max, f);
-   printf("%s: read %d bytes from shader file %s\n", Prog, n, filename);
-   if (n > 0) {
-      buffer[n] = 0;
-      LoadAndCompileShader(shader, buffer);
-   }
-
-   fclose(f);
-   free(buffer);
-}
-
-
-static void
-CheckLink(GLuint prog)
-{
-   GLint stat;
-   glGetProgramiv_func(prog, GL_LINK_STATUS, &stat);
-   if (!stat) {
-      GLchar log[1000];
-      GLsizei len;
-      glGetProgramInfoLog_func(prog, 1000, &len, log);
-      fprintf(stderr, "Linker error:\n%s\n", log);
-   }
-}
-
-
-static void
 Init(void)
 {
    static const char *fragShaderText =
@@ -255,33 +194,16 @@
       "   } \n"
       "   gl_Position = ftransform(); \n"
       "} \n";
-   const char *version;
 
-   version = (const char *) glGetString(GL_VERSION);
-   if (version[0] != '2' || version[1] != '.') {
-      printf("This program requires OpenGL 2.x, found %s\n", version);
+   if (!ShadersSupported())
       exit(1);
-   }
 
    GetExtensionFuncs();
 
-   fragShader = glCreateShader_func(GL_FRAGMENT_SHADER);
-   if (FragProgFile)
-      ReadShader(fragShader, FragProgFile);
-   else
-      LoadAndCompileShader(fragShader, fragShaderText);
+   vertShader = CompileShaderText(GL_VERTEX_SHADER, vertShaderText);
+   fragShader = CompileShaderText(GL_FRAGMENT_SHADER, fragShaderText);
+   program = LinkShaders(vertShader, fragShader);
 
-   vertShader = glCreateShader_func(GL_VERTEX_SHADER);
-   if (VertProgFile)
-      ReadShader(vertShader, VertProgFile);
-   else
-      LoadAndCompileShader(vertShader, vertShaderText);
-
-   program = glCreateProgram_func();
-   glAttachShader_func(program, fragShader);
-   glAttachShader_func(program, vertShader);
-   glLinkProgram_func(program);
-   CheckLink(program);
    glUseProgram_func(program);
 
    u_fragface = glGetUniformLocation_func(program, "fragface");