No image after rectf

OpenGL
1

The code works until The following code is inserted before the image code is run.

glColor3f (0.2, 0.2, 0.2);
glRectf(0.0f,0.00f, 120.0f, 60.0f);
glEnd();

All I get is the gray rectangle. If I comment out the above code all image code works fine.

What am I missing?

2

You are not supposed to have glEnd after glRect.
GlRect by definition is the following series of commands:
glBegin (gl_Polygon)
glVertex …
glVertex …
glVertex …
glVertex …
glEnd

3

I have the same results after removing the glEnd(). I found by accident that the

glColor3f (0.2, 0.2, 0.2);
glRectf(0.0f,0.00f, 120.0f, 60.0f);

is after the image code, everything is displayed correctly.
Why does it matter?

4

May be its in between a glBegin and glEnd already. Can’t say without seeing all the drawing code.

5

Somehow I missed that glRectf cannot be in between a glBegin and glEnd. I have not found an error yet. I will keep looking. I thought if such a condition existed I would get some kind of error. If there was any kind of error I thought I would notified somehow, compiler error or something. Do I have to look for errors?

6

It won’t be a compiler error but an OpenGL error. You have to call glGetError every frame. In fact in you keep calling that function continuously in a loop until it returns back no error. You might find it returns back invalid operation for such violations such as glRect between glBegin and glEnd.

7

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