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heefan

[SuperBible Code] Different result from the sample

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heefan    122
Hi all, I am new on OpenGL, and reading 'OpenGL Super Bible 4th' now. In the chapter 2 (Page 54), I run the sample code, but I got different result from the book. Actually I didn't get rectangle. The source code like this: #include "gltools.h" #include "math3d.h" void RenderScene(void) { // Clear the window with current clearing color glClear(GL_COLOR_BUFFER_BIT); // Set current drawing color to red // R G B glColor3f(1.0f, 0.0f, 0.0f); // Draw a filled rectangle with current color glRectf(-25.0f, 25.0f, 25.0f, -25.0f); // Flush drawing commands glFlush(); } /////////////////////////////////////////////////////////// // Set up the rendering state void SetupRC(void) { // Set clear color to blue glClearColor(0.0f, 0.0f, 1.0f, 1.0f); } /////////////////////////////////////////////////////////// // Called by GLUT library when the window has chanaged size void ChangeSize(GLsizei w, GLsizei h) { GLfloat aspectRatio; // Prevent a divide by zero if(h == 0) h = 1; // Set Viewport to window dimensions glViewport(0, 0, w, h); // Reset coordinate system glMatrixMode(GL_PROJECTION); glLoadIdentity(); CHAPTER 2 Using OpenGL 54LISTING 2.2 Continued // Establish clipping volume (left, right, bottom, top, near, far) aspectRatio = (GLfloat)w / (GLfloat)h; if (w <= h) glOrtho (-100.0, 100.0, -100 / aspectRatio, 100.0 / aspectRatio, 1.0, -1.0); else glOrtho (-100.0 * aspectRatio, 100.0 * aspectRatio, -100.0, 100.0, 1.0, -1.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); } /////////////////////////////////////////////////////////// // Main program entry point void main(void) int main(int argc, char* argv[]) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); glutCreateWindow(“GLRect”); glutDisplayFunc(RenderScene); glutReshapeFunc(ChangeSize); SetupRC(); glutMainLoop(); return 0; } The function of the program is to draw a rectangle. Is the code wrong?

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This is just a guess, but try throwing in the following at the beginning of your RenderScene function.

glLoadIdentity();
glTranslatef(0.0f, 0.0f, -0.5f);


If the rectangle is being drawn at 0 on the z axis and your camera's viewpoint is also at 0 on the z axis, you wont be able to see it. These two lines of code shift the draw position forward on the z axis.

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