--- /dev/null
+/**
+ * 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;
+}
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