Multiple Graph Output

Question

//OpenGL functions, open a window and initialize
void display(void)
{
	glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
	glClear(GL_COLOR_BUFFER_BIT);
	glLoadIdentity();
	//issue the GL commands
	glTranslatef(-.3, 0., 0.);
	glRotated(45.,0., 1.,0.);
	glScalef(.5, .5, .5);
	glColor3f(0., 0., 0.);
	glBegin(GL_LINES);
	I = 0.;
	do
	{
		//draw the axes
	if (I==0)
		{
		glVertex3f(0., 0., 0.);
		glVertex3f(1., 0., 0.);
		glVertex3f(0., 0., 0.);
		glVertex3f(0., 1., 0.);
		glVertex3f(0., 0., 0.);
		glVertex3f(0., 0., 1.);
		glVertex3f(0., 0., 0.);
		}
	//draw the curve
		glVertex3f(PLOTX[I], PLOTY[I], PLOTZ[I]);
		glVertex3f(PLOTX[I + 1], PLOTY[I + 1], PLOTZ[I + 1]);
		++I;
	} while (I <= INOW);
	glEnd();
	glFlush();
Have the above sequence of commands in the "visual" function, using the OpenGL glutInit and execute commands. Strange
that the only output that I get is for the coordinate axes, not the curve data in the "do" loop? INOW=45 Sid Kraft

Answer 1

If the axes are rendering but the curve isn't, the OpenGL pipeline is probably working, so I'd start by checking the data rather than the drawing code.

A few things to verify:

• Make sure PLOTX, PLOTY, and PLOTZ actually contain valid values (not all zeros, NaN, or uninitialized).
• Check that INOW doesn't exceed the array bounds. Since you're accessing I + 1, the arrays need at least INOW + 2 elements.
• Print a few values of PLOTX[I], PLOTY[I], and PLOTZ[I] before calling glVertex3f() to confirm they're what you expect.
• Also verify the transformed coordinates are inside the visible viewing volume after glTranslatef(), glRotated(), and glScalef().

If you can share how PLOTX, PLOTY, PLOTZ, and INOW are initialized, it'll be much easier to pinpoint the issue.