Test GL_VERTEX_PROGRAM_TWO_SIDE and frag shader gl_FrontFacing features

diff --git a/progs/glsl/twoside.c b/progs/glsl/twoside.c
new file mode 100644 (file)
index 0000000..1db92b5
--- /dev/null
+++ b/progs/glsl/twoside.c
@@ -0,0 +1,348 @@
+/**
+ * Test two-sided lighting with shaders.
+ * Both GL_VERTEX_PROGRAM_TWO_SIDE and gl_FrontFacing can be tested
+ * (see keys below).
+ *
+ * Brian Paul
+ * 18 Dec 2007
+ */
+
+#include <assert.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+#include <GL/gl.h>
+#include <GL/glut.h>
+#include <GL/glext.h>
+#include "extfuncs.h"
+
+
+static const char *Prog = "twoside";
+static GLint WinWidth = 300, WinHeight = 300;
+static char *FragProgFile = NULL;
+static char *VertProgFile = NULL;
+static GLuint fragShader;
+static GLuint vertShader;
+static GLuint program;
+static GLint win = 0;
+static GLboolean anim = 0*GL_TRUE;
+static GLboolean DetermineInFragProg = GL_TRUE;
+static GLfloat Yrot = 0.0f;
+static GLint u_fragface;
+static GLenum FrontWinding = GL_CCW;
+static int prevTime = 0;
+
+
+static const GLfloat Red[4] = {1, 0, 0, 0};
+static const GLfloat Green[4] = {0, 1, 0, 0};
+
+
+static void
+Redisplay(void)
+{
+   float xmin = -1, xmax = 1, ymin = -1, ymax = 1;
+
+   glFrontFace(FrontWinding);
+
+   if (DetermineInFragProg) {
+      glUniform1i_func(u_fragface, 1);
+      glDisable(GL_VERTEX_PROGRAM_TWO_SIDE);
+   }
+   else {
+      glUniform1i_func(u_fragface, 0);
+      glEnable(GL_VERTEX_PROGRAM_TWO_SIDE);
+   }
+
+   glClear(GL_COLOR_BUFFER_BIT);
+
+   glPushMatrix();
+   glRotatef(Yrot, 0, 1, 0);
+
+   glBegin(GL_POLYGON);
+   glColor4fv(Red);
+   glSecondaryColor3fv_func(Green);
+   glVertex2f(xmin, ymin);
+   glVertex2f(xmax, ymin);
+   glVertex2f(xmax, ymax);
+   glVertex2f(xmin, ymax);
+   glEnd();
+
+   glPopMatrix();
+
+   glutSwapBuffers();
+}
+
+
+static void
+Idle(void)
+{
+   int curTime = glutGet(GLUT_ELAPSED_TIME);
+   int dt = curTime - prevTime;
+
+   if (prevTime == 0) {
+      prevTime = curTime;
+      return;
+   }
+   prevTime = curTime;
+
+   Yrot += dt * 0.1;
+   glutPostRedisplay();
+}
+
+
+static void
+Reshape(int width, int height)
+{
+   float ar = (float) width / height;
+   glViewport(0, 0, width, height);
+   glMatrixMode(GL_PROJECTION);
+   glLoadIdentity();
+   glFrustum(-ar, ar, -1, 1, 5, 15);
+   glMatrixMode(GL_MODELVIEW);
+   glLoadIdentity();
+   glTranslatef(0, 0, -10);
+}
+
+
+static void
+CleanUp(void)
+{
+   glDeleteShader_func(fragShader);
+   glDeleteShader_func(vertShader);
+   glDeleteProgram_func(program);
+   glutDestroyWindow(win);
+}
+
+
+static void
+Key(unsigned char key, int x, int y)
+{
+  (void) x;
+  (void) y;
+
+   switch(key) {
+   case ' ':
+   case 'a':
+      anim = !anim;
+      if (anim) {
+         prevTime = glutGet(GLUT_ELAPSED_TIME);
+         glutIdleFunc(Idle);
+      }
+      else
+         glutIdleFunc(NULL);
+      break;
+   case 'f':
+      printf("Using frag shader gl_FrontFacing\n");
+      DetermineInFragProg = GL_TRUE;
+      break;
+   case 'v':
+      printf("Using vert shader Two-sided lighting\n");
+      DetermineInFragProg = GL_FALSE;
+      break;
+   case 'r':
+      Yrot = 0;
+      anim = 0;
+      glutIdleFunc(NULL);
+      break;
+   case 's':
+      Yrot += 5;
+      break;
+   case 'w':
+      if (FrontWinding == GL_CCW) {
+         FrontWinding = GL_CW;
+         printf("FrontFace = GL_CW\n");
+      }
+      else {
+         FrontWinding = GL_CCW;
+         printf("FrontFace = GL_CCW\n");
+      }
+      break;
+   case 27:
+      CleanUp();
+      exit(0);
+      break;
+   }
+   glutPostRedisplay();
+}
+
+
+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 =
+      "uniform bool fragface; \n"
+      "void main() { \n"
+      "   if (!fragface || gl_FrontFacing) { \n"
+      "      gl_FragColor = gl_Color; \n"
+      "   } \n"
+      "   else { \n"
+      "      gl_FragColor = 0.8 * gl_SecondaryColor; \n"
+      "   } \n"
+      "} \n";
+   static const char *vertShaderText =
+      "uniform bool fragface; \n"
+      "void main() { \n"
+      "   gl_FrontColor = gl_Color; \n"
+      "   if (fragface) { \n"
+      "      // front/back chosen in frag prog \n"
+      "      gl_FrontSecondaryColor = gl_SecondaryColor; \n"
+      "   } \n"
+      "   else { \n"
+      "      // front/back chosen in prim setup \n"
+      "      gl_BackColor = gl_SecondaryColor; \n"
+      "   } \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);
+      exit(1);
+   }
+
+   GetExtensionFuncs();
+
+   fragShader = glCreateShader_func(GL_FRAGMENT_SHADER);
+   if (FragProgFile)
+      ReadShader(fragShader, FragProgFile);
+   else
+      LoadAndCompileShader(fragShader, fragShaderText);
+
+   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");
+   printf("Uniforms: %d\n", u_fragface);
+
+   /*assert(glGetError() == 0);*/
+
+   glClearColor(0.3f, 0.3f, 0.3f, 0.0f);
+
+   printf("GL_RENDERER = %s\n",(const char *) glGetString(GL_RENDERER));
+
+   assert(glIsProgram_func(program));
+   assert(glIsShader_func(fragShader));
+   assert(glIsShader_func(vertShader));
+}
+
+
+static void
+ParseOptions(int argc, char *argv[])
+{
+   int i;
+   for (i = 1; i < argc; i++) {
+      if (strcmp(argv[i], "-fs") == 0) {
+         FragProgFile = argv[i+1];
+      }
+      else if (strcmp(argv[i], "-vs") == 0) {
+         VertProgFile = argv[i+1];
+      }
+   }
+}
+
+
+static void
+Usage(void)
+{
+   printf("Keys:\n");
+   printf("   f - do front/back determination in fragment shader\n");
+   printf("   v - do front/back determination in vertex shader\n");
+   printf("   r - reset, show front\n");
+   printf("   a - toggle animation\n");
+   printf("   s - step rotation\n");
+   printf("   w - toggle CW, CCW front-face winding\n");
+}
+
+
+int
+main(int argc, char *argv[])
+{
+   glutInit(&argc, argv);
+   glutInitWindowPosition( 0, 0);
+   glutInitWindowSize(WinWidth, WinHeight);
+   glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
+   win = glutCreateWindow(argv[0]);
+   glutReshapeFunc(Reshape);
+   glutKeyboardFunc(Key);
+   glutDisplayFunc(Redisplay);
+   if (anim)
+      glutIdleFunc(Idle);
+   ParseOptions(argc, argv);
+   Init();
+   Usage();
+   glutMainLoop();
+   return 0;
+}