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OpenGL 3d texture! HELP! S.O.S

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Hi! The program I wrote, should read the values of a volume ( the array “volumevalues” is an example of 1x1x3 volume) map it into 3 poligons, blend them, and put the result in an array. It should simulate a radiography.. I have a problem, the program compiles, and runs.. but after blend the 3 slices, in the array result there aren't color values, but only an alpha value ( that i'm not sure is right..). and maybe i must center the texel coordinates( if anyone can tell me..)Please Help! #include <cstdio> #include <cstdlib> using namespace std; // -------------------------------------------- // Include #include <gl\glew.h> #include <gl\glut.h> #include <gl\gl.h> #include <gl\glu.h> #include <windows.h> //trasform alpha from double to char and in the range 0-255 char DoubleToChar(double alpha){ return (char)(alpha*255.0); } int main(int argc, char **argv) { //Volume values: is a simple 1x1x3 poligon along z unsigned char VolumeValues[12]={1,0,0,1,2,0,0,0,3,0,0,0}; VolumeValues[3]=DoubleToChar(1.0); VolumeValues[7]=DoubleToChar(1.0/2.0); VolumeValues[11]=DoubleToChar(1.0/3.0); unsigned char result[12]; //array for the result // inizialize glut glutInit (&argc, argv); glutCreateWindow("radiographic simulation"); glewInit(); // create the texture GLuint tex; glGenTextures (1, &tex); glBindTexture(GL_TEXTURE_3D,tex); // target is a 3d texture // sets texture parameters glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_S, GL_CLAMP); glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_T, GL_CLAMP); /*void glTexImage3D (GLenum target,GLint level,GLint internalformat,GLsizei width,GLsizei height,GLsizei depth,GLint border,GLenum format,GLenum type,const GLvoid * pixels)*/ // allocate graphioc memory glTexImage3D(GL_TEXTURE_3D,0,GL_RGBA,1,1,3,0,GL_RGBA,GL_UNSIGNED_BYTE,VolumeValues); GLenum errCode; const GLubyte *errString; if ((errCode = glGetError()) != GL_NO_ERROR) { errString = gluErrorString(errCode); fprintf (stderr, "OpenGL Error: %s\n", errString); } /* void gluOrtho2D(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top); The clipping region is a rectangle with the lower-left corner at (left, bottom) and the upper-right corner at (right, top). void glViewport(GLint x, GLint y, GLsizei width, GLsizei height); Defines a pixel rectangle in the window into which the final image is mapped. The (x, y) parameter specifies the lower-left corner of the viewport, and width and height are the size of the viewport rectangle.*/ //viewport transform for 1:1 pixel=texel=data mapping glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluOrtho2D(0.0,1,0.0,1); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glViewport(0,0,1,1); glClear(GL_COLOR_BUFFER_BIT); glPushMatrix(); glEnable(GL_TEXTURE_3D); glEnable(GL_BLEND); glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA); float z= ((float)1)/3; float y =((float)2)/3; glBegin(GL_QUADS); glTexCoord3f(0.0,0.0,0.0); glVertex2f(0,0); glTexCoord3f(0.0,1.0,0.0); glVertex2f(0,1); glTexCoord3f(1.0,1.0,0.0); glVertex2f(1,1); glTexCoord3f(1.0,0.0,0.0); glVertex2f(1,0); glTexCoord3f(0.0,0.0,z); glVertex2f(0,0); glTexCoord3f(0.0,1.0,z); glVertex2f(0,1); glTexCoord3f(1.0,1.0,z); glVertex2f(1,1); glTexCoord3f(1.0,0.0,z); glVertex2f(1,0); glTexCoord3f(0.0,0.0,y); glVertex2f(0,0); glTexCoord3f(0.0,1.0,y); glVertex2f(0,1); glTexCoord3f(1.0,1.0,y); glVertex2f(1,1); glTexCoord3f(1.0,0.0,y); glVertex2f(1,0); glEnd(); glPopMatrix(); /*void glReadBuffer(GLenum mode): specifies a color buffer as the source for subsequent read and copy image commands*/ /*void glReadPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, GLvoid *pixels);*/ //reads data from the frame buffer and write them in the result glReadBuffer(GL_FRONT); glReadPixels(0,0,1,1,GL_RGBA,GL_BYTE,result); // print out results printf("Data before roundtrip:\n"); for (int i=0; i<12; i++) printf("%d\n",VolumeValues); printf("Data after roundtrip:\n"); for (int i=0; i<12; i++) printf("%d\n",result); getchar(); return 0; the output is: data before roundtrip: 1 0 0 255 2 0 0 127 3 0 0 85 data after roundtrip: 0 0 0 127 204 204 204 204 204 204 204 204

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